Status update:

I replaced my O2 sensor and performed adaptations. This ought to remove it out of the list of possible contributors to my issue.

I've pondered quite a bit how the logic/circuitry could cause what I believe is an over-shoot in signalling to de-fuel. All signals to the fueling are essentially for de-fueling and any lapse in signalling would, I therefore figure, run counter to de-fueling. IF the MOSFET for the Y74 or Y94 were to fail OPEN or struggle to conduct electricity (I believe it's opening a gate to ground) then the signalling would be LESS which means MORE fueling. However, IF the MOSFET struggles toward a SHORTED condition (heat is always the suspect) then the signalling to the Y74 and or Y94 would tend to be increased beyond what should otherwise be expected to occur. In the case of a misbehaving MOSFET the computer could not be expected to identify any problem other than the results and "results" are only seen from that reported by the pressure sensor. A sudden request to drop fueling as happens when hitting "coasting mode" would cause the circuitry for the Y74 and Y94 to become quite active and at this point it could be expected to become a lot warmer.

It is possible that the circuitry (includes wiring) for the pressure sensor has issues. Here it would be something needing to support a higher voltage reading than the sensor is actually reporting: higher voltage means higher pressure. Perhaps a hint of shorting is the only way I'd think this possible. In this case heat could also be a driver.

I got my new oscilloscope but am thinking that data logging will have to come first. I am fairly confident that I know how to repeat this problem and that once I capture it in data I can then use the oscilloscope to understand WHY it's happening.

I first need to take an asprin. This stuff is making my head hurt!

 

I assume that the HPFP needs to have fuel flowing through it while it's turning, as that's what lubricates it. The Y94 controls the quantity of fuel going into the HPFP. Shutting off injectors completely will cause the quantity injected to go to zero. The pump still requires fuel flow for lubrication, so the quantity control valve can't go all the way to zero. It will still flow minimum fuel through the pump to keep it lubricated. Without something else happening, this will cause rail pressure to spike.

That something else is the Y74.
IIRC from earlier in this thread, the Y74 is open when de-energized (a normally open or NO function) and closed when energized. That way when the driver stops the engine or the system loses electrical power, Y74 opens to "safe" the system by dumping whatever pressure may remain in the fuel rail. If the ground-side driver failed with a short, Y74 would stay closed and pressure would spike. If the driver failed open circuit, Y74 would never close and there would never be any fuel pressure.

When Y74 is commanded open for coast mode, it is DE-energized and there's no current flowing through the driver.
I haven't watched live data on my car, but I don't think simply being off the throttle puts mine into coast mode.
My observation:
1. Set cruise control
2. Accelerate above set speed
3. Cancel cruise control
4. Lift foot off pedal
5. Resume cruise control (still above set speed)

In step 4, the car will decelerate. For step 5, I feel the car decelerate harder when I resume cruise and it's trying to slow down to the set speed. So when I have my foot off the pedal and the car is slowing on its own, it's still getting a little fuel. When I resume cruise and that system is trying to get the car down to the set speed as fast as possible, it cuts fuel off completely.

This is similar to DFCO (deceleration fuel cut off) in gasoline engines. Above a threshold RPM, gasoline EFI systems will shut fuel off completely at closed throttle. There's generally a 1-2 second delay, so the driver can feel a subtle surge when the system makes the state transition. That was before pop tunes became popular, though.

Does that jive with your observations?

 

I feel the car decelerate harder when I resume cruise

That's because the car uses the brakes to slow down. It's been a standard option on MB for so long that the option code no longer appears in the datasheet. Not a function of engine.

While deaccelerating, above a set rpm threshold the ECU will cut off fuel injector and open Y74 by means of PWM to maintain pressure in the rails.

In diesel, the fuel cutoff happens above 1500. In gasoline, it is 1200.

 

I'm going totally by MB's own documentation.

Coasting mode:

Y74 function:

It is my understanding/interpretation that the Y74 requires increased power (voltage/PWM?) to open up for spilling fuel. I think that the spring is set to hold a certain amount of pressure on its own and will mechanically open at a point in which there is excess pressure and the ECU is unable to command the Y74 to dump fuel/pressure I'll admit that I'm still not all that clear on all of this: but what the ECU wants to happen is clearly laid out in the operating modes ("Coast mode" is one and is shown in the first pic I posted).

I haven't limited my research to just the om648 nor MB, I've looked at other CR diesels (most which have CP3 pumps as things tend to be pretty close) and even gasser CRs (the theories are applicable across the board).

 

I'm going totally by MB's own documentation.

Y74 function:
View attachment 2863554

It is my understanding/interpretation that the Y74 requires increased power (voltage/PWM?) to open up for spilling fuel. I think that the spring is set to hold a certain amount of pressure on its own and will mechanically open at a point in which there is excess pressure and the ECU is unable to command the Y74 to dump fuel/pressure I'll admit that I'm still not all that clear on all of this: but what the ECU wants to happen is clearly laid out in the operating modes ("Coast mode" is one and is shown in the first pic I posted).

I haven't limited my research to just the om648 nor MB, I've looked at other CR diesels (most which have CP3 pumps as things tend to be pretty close) and even gasser CRs (the theories are applicable across the board).

Well... something is wrong with this diagram, because it shows magnetic force and spring force in the same direction for both valve states.

 

No, adaptive cruise control maintains the speed relative to the vehicle in front of you.

Regular cruise control can and does use the brakes to slow the car down. How else do you think the car maintains the speed on downhills?

Every single MB with regular cruise control since W202/W210 has used the brakes in some fashion to maintain speed.

 

Do you have use of brakes with cruise in documentation someplace?
Not sure about the first gen adaptive cruise, but second gen adaptive cruise definitely used brakes if the car in front slowed.

For gasoline cars, the engine braking from pumping losses due to manifold vacuum is plenty to slow the car on downhills. Diesels don't have manifold vacuum, so they have less engine braking, but still have enough due to internal engine friction (mostly from the piston rings).

 

More research turns up that temperature sensors can be a contributor/culprit. In general, and MB in specific, ECUs are programmed to drop rail pressure in relation to high fuel temperatures. A BIG problem I've found with people trying to track down these kinds of problems is that they tend to operate on the premise that a particular sensor is either working 100% or not at all. Further, and I've been struggling with this as well, one has to try to understand how bad data -bad sensor readings (not a failed sensor, which nearly any ECU is going to be able to discern)- could essentially trick the ECU into doing something that it shouldn't be doing; in my case, dumping more fuel pressure than it should. A spurious reduced resistance here would indicate higher fuel temps and result in a command to drop fuel pressure; perhaps when the sensor is running hotter it has a bit of an internal short?

I had had fuel temperatures on my list of data to capture/monitor but I now believe that it could be even more important than I'd thought it was/could be.

Also in the fuel temperature equation is the fuel heater. I've read where fuel heaters have stuck ON and that's producing hotter fuel. From what I understand the heater isn't monitored by the ECU. I have this on my list to check.

Fuel return blockages can also jack up fuel temperatures but I'd expect that I'd see problems in other driving scenarios.

I am still trying to analyze whether the accelerator pedal could send the wrong signals. The pedal is clearly also in play here and is, so far when the CEL trips, always when it is NOT depressed (when I've let off). I cannot think of how any bad behavior here could result in these low rail pressure errors.

 

Temperature, yes. Grid heater, no, since it's timed and controlled by glow plug to my understanding.

Accelerator pedal has dual sensors for verification, and chances of both of them going bad at the same time and failing at the same rate is very low.

 

It's the fuel heater, the one in the fuel filter that I was referring to. There's a ton of same era Duramax guys running into P0087 codes and it seems as though fuel temperatures have been noted as being responsible for a lot of such errors- the solution, however, seems nearly impossible to nail down (one guy does some tuning work to tune around the issue).

I can't seem to come up with a way to convict the accelerator pedal. Keep in mind that in each sensor/controller there's the associated wiring. While the pedal might be fine it could be the wiring (odd resistive addition/subtraction happening). The pedal that's in this car is the original. I will note, and one reason why I have a bit of a concern with it, is that the car had kickdown issues (and going into limp mode) when I got it, with it's original drivetrain (which I have replaced- engine wiring harness included).

 

If it had kickdown issue with original drivetrain and no more kickdown with new drivetrain, the issue is not with the APP.

APP on this car utilizes two 5v reference sensors that are reverse polarity. Meaning one sensor starts at 4.5v and goes down, other sensor starts at 0.5v and goes up. At any moment you should be able to add the values from both sensors and they should add up to 5v.

Very simple and very easy to verify. Also not all sensors fail equally or at the same rate, so if APPS1 fails, it will start even lower at, say 3.5v instead of 4.5v. Adding both sensor values comes up with 4v at idle, which will trigger codes. Or It starts reading higher, or whathave you.

Point is, I dont think this is your problem. If you dont have kickdown issue NOW, it is NOT the APP.

 

Correct, no kickdown issues at all: I was quite happy that this was the case- I swapped out the transmission (even though the original one had less miles) with fingers crossed that the issue would end with it. This car runs and does everything exceptionally well except for this odd/nasty fueling hiccup.

 

I doubt filter heater can warm flowing fuel so high it would cause problems.

Yes, fuel temp and coolant temp both will reduce injected fuel. Remember at least one case where faulty fuel temp sensor prevented starting. But both these values you see live data. Plus boost temp.

 

Do these coolant temperature sensors have two circuits, one for gauge and one for ECU? My VW TDIs do; when they go bad they typically do so on the gauge side, causing gauge readings to go wonky; ECU will see proper readings.

I'm pretty sure that I'd read of someone with a Duramax encountering issues due to their fuel heater being stuck ON.

 

Do these coolant temperature sensors have two circuits, one for gauge and one for ECU?

Single circuit, two wires. Instrument cluster does not have any direct connection. Seven wires. Ground, circuit 30, circuit 15R, CAN-B x2, CAN-C x2.

 

OK, thanks. The assumption, then, is that if the readout on the cluster looks OK (and, well, the gauge on the cluster isn't wonky) then the actual engine temperature is OK. My VWs don't really use canbus so that's likely why the two circuits.

 

Here's an interesting observation (that's self-damning, maybe, but in the interest of full disclosure...). I pulled my ECU to send off for cloning (have a spare*) and It SEEMED as though the wire connector might not have been locked in fully (the plastic slide piece not fully pushed in). I'm wanting to say that the connector kind of pulls down at the wire bundle end as you engage the lock. It's toward this end that the Y74 pins are- #4 (POS) and #52 (GND). Perhaps a chance there was a less than perfect seating of these pins? The pins for the Y94 and rail pressure sensor are more toward the middle of the connector (less affected by any rocking?) and perhaps a little more secure. I should track down what pins are used for the injectors as my issue pops up when the ECU is shutting off fueling (coasting mode): IF the injectors aren't being fully shut off as is expected, due to a connection issue (common ground for all injectors?), then such unexpected/unaccounted-for fuel use is going to contribute to dropped fuel rail pressure.

* The part number on the spare ECU (newer- from a 2006) is different in which case I've got an inquiry into whether it will even work.

 

Adding another point of reference to my previous post, the injector wires/pins are also located on the bundle end and could also be subject to less-than-ideal connections. This said, logic suggests that this cannot be a source of my problem as any reduction in connectivity for any of these connections for these fueling components would tend to favor less reduction in fuel pressure. Injectors would see less voltage [activity] and would use less fuel and therefore not add to a reduction in fuel rail pressures. For the Y94 and Y74 less voltage [activity] would also tend to bias toward more pressure than less.

Hoping today to check wire resistance. Not thinking I'll find anything wrong here but need to eliminate any doubts. ECUs sent out for cloning.

 

Measured wiring resistance for Y94, Y74, pressure sensor, fuel temperature sensor and injectors and didn't see any problems here. Minimum was about .3 ohms and max .8 ohms.

 

A kind-of update... I had my ECU cloned so I now have a different ECU to test out: it is noted that there was no signs of physical issues and simple tests/checks (of suspected/involved circuits] seem to indicate that it was OK. BUT... before I swap ECUs I was wanting to log data to see exactly what is going on such that if/when swapping I'll know what to do to verify that it is or isn't the ECU. I've spent time trying to figure out how to do logging in Star's Vediamo but have come up empty: it's almost like it's verbotten to share information on MB diagnostic tools; frustrating. I'm really wanting to do this in order to SHARE information; this is my "free" time and energy. I shelled out money to subscribe to MHH Auto to get some help but have gotten a simple pointer that I have not gotten to work and the help appears to have dried up.

OK, so rantings aside, I am wondering whether there couldn't be some sort of incompatibility between the 2005 ECU and the 2006 engine. The part numbers on the ECUs are different. I had the 2006 ECU cloned from the 2005 [which I had previously had tuned]. If it were software issues [MB changes between the years] then swapping the ECUs would likely still introduce the same software issues.

 

I thought EGR was different between 05 and 06. I've heard (haven't verified in EPC) if you go to the dealer and buy an 05 ECU, you have to replace the EGR, too. Which tells me you're buying an 06 ECU and making it compatible by replacing EGR with 06 unit.

 

My tune has this all addressed (vis a vis EGR; I installed an intake w/o swirl flaps so that part of tune* was necessary). I see no direct differences between the hardware of the two engines (as they were before swapping): recall that I had an identical car [now fully parted out] only it was a 2006. This doesn't, however, go to reason that MB couldn't have made software changes.

*Issue pre-dated tune.

Worst case I may just end up taking it to a tuner and having them bump up the time interval value on monitoring duration of pressure drop. I know that lots of folks out in the earlier(?) Duramax years had/have low pressure issues that seem only able to be corrected by tweaking with mapping tables: likely GM didn't allow enough variance to deal with aging stuff. Not my first choice but I'm holding it out as an option*.

*Engineers are concerned with starving the fuel pumps in which case they are very cautious about allowing low fuel pressures to persist. As I'm experiencing this issue on the LOW end, actually NO FUEL demand, I think it would be safe to be more tolerant. Nearly all such errors that I have seen people encounter are a lack of fueling under high demand; go figure that I have to have something that is acting different!

 

Latest update.

Had an outing racking up about 150 miles or so a week ago and encountered no errors. Today, however, after about 410 more miles I got an P2017 and P2047. This time the engine didn't shut down, it went into limp mode. Both codes point to the Y94. I have been logging data and today was no different in which case I captured data when this happened. I'll try to cover how I interpret the data...

Was running at around 1,900 rpm on the highway and had been running with a steady 20% pedal request. Fuel and coolant temperatures held steady throughout this in which case i can state with a high degree of confidence that they have no bearing on this issue (there was a very slight possibility). Fuel rail pressure was holding pretty steady at around 584 bar: I saw it higher a bit before but this is roughly the status-quo target. I'll now lay out the recorded timeline showing key changes (assume all unstated/not-listed items holding fairly steady)... (timeline in seconds following a restart of logging following a stop for lunch)

814.734s Pressure sensor -> 1950 mV Rail Pressure _> 584 bar Y94 -> 37% Y74* -> 26% RPMs -> 1,909 <<< STEADY AND STABLE STATE just before any real changes in data

814.812s Pressure sensor -> 904 mV <<< Nothing commanded to drop pressure yet reading has plummeted

815.250s Rail pressure -> 107 bar RPMs -> 1,758 <<< First reporting in bar showing problem and with RPMs declining a bit

815.328s Y94 -> 30% <<< ECM has commanded a reduction from 37%, why?

815.958s RPMs -> 1,713 <<< Might be decrease in speed and in overrrun (already in limp mode?)

816.125s Y74* -> 20% <<< ECM trying to reduce leakage from Y74 so it clearly realizes the ship is sinking (but why not drop/close further?)

816.250s Rail Pressure -> 77 bar <<< Pretty close to LPFP pressures; engine just in overrun mode

816.328s Y94 -> 37%

816.484 Pedal request -> 37% <<< This is the point where I'd realized a problem and I was checking for response (none to be had)

827.812s Pressure sensor -> 1525 mV Rail pressure 15 bar Y94 -> 25% Y74* -> 18% Pedal request -> 0% RPMs -> 759 <<< Coasted to side of road and almost stopped

828.125s RPMs -> 701 <<< Now at an idle on the side of the roadway

828.250s Rail pressure -> 404 bar <<< No changes in anything other than the pressure is now up

* I am assuming that the object item "Sollwert Tastverhaltnis fur Druckregekventil" is the pressure regulator valve, the Y74.

Not clear the exact moment the ECM went into limp mode: 814.812 or 815.250 second mark? I felt it happen and reacted within about 1 second but got no response from the pedal.

Once at the side of the road and at idle the rail pressure built back up w/o any ECM commanded changes to the Y94 and Y74. This would suggest that under overrun (rolling and with no pedal request) the ECM was actually fueling the injectors at the rate associated with the RPMs?

Odd was that the ECM commanded the Y94 to reduce from 37% to 30% at/by the 815.328 second mark. Clearly the low rail pressure of 107 bar at that point does not call out for a decrease in fueling to the HPFP. IF the HPFP and or the LPFP were somehow struggling I'd think that the ECM would look to increase the Y94's fuel flow. The error codes indicate that the ECM's logic figures the Y94 is the source of the problem. Again, this is a new Y94. If it were the Y94 circuit that wouldn't explain why the ECM cut back on fueling (unless it was officially in limp mode at that point?).

I don't know of anything else I can monitor that would expose the real source of the problem. I suppose the only next step is to swap in my spare ECM. I really hate throwing parts at problems.

 

Well this 'my mind graph' is bit tough to follow but... You might try to see how much injection ECU is commanding mm3/hub^ (Rail pressure under 150 bar should cut out injection?). Also how much boost pressure ECU is asking and what is actual reading. It is just giving a hint does engine need more or less fuel... of course if pressure sensora are playing up; why not monitor intake/boost/exhaust back pressures...

 

Really appreciate you looking to torture yourself here [many thanks for the inputs]

I think that monitoring the mm3/hub^ won't get me anything as changes here would be based on rail pressures (and or pedal request) and the ECM adjusts via Y94 and Y74 and there is no change in those two components (as well as pedal request) leading up to and just after the mV sensor drop.

Regarding boost, yes, this circuit could also be the source. I'll look to add MAP sensor monitoring: IF it shows it's dropping boost pressure before the rail pressure mV drops THEN that will point toward the boost logic/circuitry. Given that there's no change in pedal request (no change in RPM) I'd think that the actual physical boost components are fine and that anything here would be originating from the ECM circuitry, an ECM problem. Anything I need to add will require trasnlating German, sigh...

Here are some snapshots of just before and then just after the fuel rail pressure sensor mV drop readings (followed just after this the bar reading shows the collapse- I'm assuming it's a delay in processing, that at the moment of the mV drop that the actual bar would also be equivalent).

Just before (all seemingly steady, data shows this):

Here's the pressure sensor mV drop (again, note that the Y74, Y94 and pedal request hold steady during this time- the Y94 is the first to drop right at the same time that the actual bar pressure drops):

With no issues with any of the boost or fueling components it seems that the issue is that the ECM is unable to adjust because the circuitry is flaking out.

This capture shot, just after the ECM reports the drop in rail pressure in bar, shows a HUGE deviation, which I'd think is what it wants vs what it's getting. 523 bar is the maximum upper limit on deviation in which case this is the bottom dropping out: I don't think the limp mode values would have things out of whack like this in which case this has to be before the ECM actually locks into limp mode. Perhaps the fuel rail pressure sensor circuitry is collapsing and is what sets it all off: could be that the actual pressure hasn't actually plunged it's just that that's how the ECM's circuitry is deciphering and then it panics and goes into limp mode. The voltage data never falls out of range in which case the sensor is good as far as the ECM figures.

 

Quick update...

I swapped in my spare ECM. Only about 25 miles put on as of yet but I think that I notice something worthy of reporting on...

Upon first start I see the GP light and then it goes out. NO CEL! I'd been having a CEL for the #1 GP; clear it and it would consistently pop on every time I started the car [with the original ECM]. That #1 GP had ohm'd OK. I just kind of put this as something else I'd have to deal with later; frustrating because since commissioning the car I'd had to swap the GP controller and the #5 GP and then yet another GP issue! [NOTE: I'm pretty sure the ground wire for the GP, the one that goes on top of the intake manifold, is good because I was aware of a bad ground causing lots of issues with the GP system and made sure this was installed properly.]

Just a couple days ago I was talking with my truck mechanic about the latest on this fueling issue. I told him that I suspected the rail pressure circuit and he said that if it shared the 5v source with something else then it could be something else pulling down the voltage. I said that nothing else, no component, was testing as problematic, that only complaint was pointing at the Y94 and that since the Y94 tests good that it has to be the pressure sensor circuit, the pressure sensor is reporting an incorrect reading because the circuit has an issue (collapsing mosfet?); the problem has to lie within the ECM. I told him that I had a spare ECM and he just looked at me and said: Install it. Later after talking to him I thought about my GP issues and wondering if that circuit is in the mix (and it's appearing as that's the case).

I have thoughts about buying a circuit diagram for the ECM. Just curious, but not sure if $108 [USD] is worth it: likely the only time I'd ever look at it would be just to check this 5v thing. If someone knows whether the 5v source is shared by both the GP and fuel pressure sensor circuits (and anything else) I'd like to hear about it.

 

Another day in my low-rail-pressure-errors diary... ["replacement ECM" and some reflection on the hiccup with the original ECM]

Started the car and got a CEL. #1 GP. So much for hoping I could take out two birds with one stone (ECM swap). Now appears that GPs aren't likely involved with the topic at hand.

Put on about 75 miles w/o incident: ECM/engine that is- I had to cut things short because I picked up a screw in one of my tires and didn't want to find out whether it would hold air or not for any longer than getting myself home. I reviewed the data that I managed to log and everything looks good (comports with how things ran). I added a bunch of objects for logging that I thought could be MAF and boost related and nothing stands out with these.

I revisited the data I logged with the original ECM, from the log of the captured event. I wanted to see how stable the rail pressure sensor's mV data was. It all looked good except for the "event." The suddenness of the drop stands out like a sore thumb. What I also realized is that the ECM's computed rail pressure after the "event' is flat-out non-sensical. Rail pressures managed to drop to a low of 15 bar which I believe would be too low for the engine to run* but yet the engine WAS running, though likely in overrun mode (rpm dropping because I was slowing down and pulling over- rpms roughly 900 at this point- injectors firing continued to lower the fuel pressure more?). I'll note that fuel temperatures rose slightly, I'd think they'd be dropping due to lower pressure- there appears to be a contradiction. And within 1/8th of a second, and with no changes to the Y94, Y74 or pedal request (still zero) the ECM reports pressure at 464 bar (the mV had just bumped up to 1524 mV at the 15 bar point). I cannot see how, without any changes to fuel trim, that the pressure can go from 15 bar to 464 bar in 1/8th of a second. It is almost as though the circuit had cooled and snapped back to life/stability. Either the ECM is trashing the data from the sensor or the ECM is sending lower voltage to the sensor and that is dropping the value of the returned data (lower return voltage in with same pressure results in a lower voltage back in the data stream); I don't think this is happening within the wiring harness as the occurances of these events is so infrequent, in which case I'm leaning toward this being the ECM (until proven otherwise).

* I looked at a lot of log data and nowhere can I find pressures dropping this low other than with this event. And no way would limp mode look to drive pressures this low.

If I am correct in my hypothesis then this issue should be eliminated with this replacement ECM. First need to get my "screwed" tire repaired before putting on more test miles.

 

UPDATE

I was hopeful, until today... Managed about 1,025 miles [post ECM swap] before I got another low rail pressure error- P2017. This latest incident occurred as I was coming off the freeway, all the way off the accelerator, and coming to a stop; I cycled the key and the engine would crank but not start- cycled a couple of times and then went to plug in my diag tool to clear the code and in a slight panic due to the traffic light turning green I cycled the key again and this time the engine fired.

P2017 is related to the Y94 (Quantity Control Valve). To refresh, I've already replaced this valve: OEM; first thing I replaced when first encountering these errors. I'll note that this is the second time that the car has struggled to restart; such behavior is a common symptom of a bad Y94.

ALL errors have occurred with minimal or no driver fuel request.

I am totally stumped at this point. The frustration is that it is so intermittent. This starting issue lines up with typical/known problems with a bad Y94.

Though I've checked resistance on the Y94 circuit and found it to be OK [and DAS tests come up OK] that this does not rule out an issue with it, I suppose. The odds of there being an issue with BOTH ECMs seems rather remote. Either the HPFP has something quirky going on (how? DAS HPFP test are fine) or it's the wiring/wire harness itself. The HPFP and the wiring harness are the only things left that are original to the engine I swapped in: keep in mind that the donor car came with a spare wiring harness and fuel rail- I could not get any info on why (the engine had been replaced and it's possible that these were just spare bits from the swap but I have no statement pointing either way).

I'm running out of ideas and patience. I can only think of trying to bypass the Y94 wiring: how to do isn't clear- messing with the connector pins and such isn't something I'm confident in/with.

 

SOLVED?

Have encountered two more incidents but this second/last/latest one has surfaced, I'm hoping, the source of the issue. I'd had a couple incidents in which the car had to crank a couple of times in order to restart. This time, however, the car would NOT restart. Foxwell showed essentially no rail pressure. Fumbled around a bit but finally came to the conclusion that I wasn't getting fuel delivery from the tank (I was over 3/4 full): felt no pressure in the supply line at the input to the fuel filter. No start. No tools. Tow time...

Back at home, wallet lighter (from the tow), and with my tools (and parts) I commenced to track this down.

Verified fuse and relay (rear SAM) were both good.

Opened up the left/driver's side access cover to the fuel tank and unplugged the wiring connector and this is what I found:

The rightmost slot is supposed to be the ground wire. It was there but pushed way back, the barbs on the wire end were curled. Someone was clearly here before. I could not salvage the wire end and ended up splicing in a good wire (from my parts- wiring harness from parts car).

I'd been data-logging when this latest incident occurred. It showed the same profile of a previous event I'd recorded. Pressure drop at the rail pressure sensor was instantly slammed down (dropping 1v in about .08 sec). In my mind this was a circuit-related issue. I was right but wasn't looking in the right place: and who would expect something like this? The in-tank fuel pump would work perfectly well 99.999% of the time, incredibly infrequent. I realize that one of the first diagnostic steps is to verify fuel pressure and flow from the tank; this, however, would never have shown up as an issue as the pump is fine and there's no blockage or other such issue. Apparently enough heating up of the connector (ambient temps as well) and that ground connection would drop out: but only today did it decide that it wasn't going to get back in the game.

I'll report back after a while with what I now expect to be a final wrap-up of this thread.

 

Congrats on finding... something!

Crimping on a new contact would not have been difficult, but would have required you to order both a new contact and open barrel crimp tools... sounds like you were faster getting it on the road this way.

 

Thanks, Will. Yeah, would have preferred that solution. My splice job works and I dressed it all up and no one (except us folks here ) would ever know or be able to tell.