[ou1954]

Yup. The injectors and the coils are the only things that obviously have to work harder at higher RPMs. The coils may heat up a bit but probably can't self repair in the short time between shutdown and restart. The plugs are apparently ruled out and it seems to me that items not linked to the two specific cylinders have to be ruled out.

Now what would be interesting is to see if a GRADUAL increase in RPM might indicate two distinct failures. It's unlikely that two injectors in separate banks would decide to fail at the same time and RPM.

 

[RESTO SL]

Update?

 

[DBCoooper]

Sorry, all. Life has kept me busy for the past couple of weeks- no progress. The car runs fantastic until I hit almost redline so I have driven it a bit here and there while the weather allows. This car will see little to no action once the rains set in for the next 8 months except for the occasional start/warm-up to keep seals and gaskets pliable.

I still need to get a scanner that does live stream. I'll post back when I know what the issue is so we can close the loop for others with similar problems.

When I removed the MAF to clean it a couple of weeks ago I notice the MAF slide very easily in and out of the seal it sits in. I also noticed the seal (Mercedes 112 159 00 80) between the intake elbow and throttle body aka mass air sensor bracket and between the MAF and the bracket ( Mercedes 112 159 01 80) were somewhat brittle. These could cause a leak downstream of the MAF which of course can cause all sorts of fueling problems. I have replaced these but have not had a chance to drive the car since then. Since they were a bit brittle it was needed regardless of the result.

All other tubes and hoses under the hood as they relate to intake/EGR etc. seem fresh and pliable with no cracks.

 

[mikes129]

This car will see little to no action once the rains set in for the next 8 months except for the occasional start/warm-up to keep seals and gaskets pliable

These cars are fine in the rain! Hardtop on, it's like being in a fixed roof car. The soft-top if in good condition keeps the car dry inside (mine does at least). I would still try to drive it a little... And cycle the soft-top roof action.

 

[DBCoooper]

I actually had time to take the car for a short spin and was able to catch some freeze frame data after I tripped the CEL. Doesn't really tell much that I can see except fuel trim isn't too far out of whack.
Does anyone see anything I'm not with the limited data? What this tells me is at the time the data was stored the engine was under 93% load, short and long term fuel trims weren't out of tolerance, Engine was at 5600 revs and the car was moving at 70 mph. MAP looks OK...

Fuel Sys 1	NA
Fuel Sys 2	NA
Calc Load%	92.9​
ECT F	177​
STFT B1 %	0​
LTFT B1 %	9.3​
STFT B2 %	0​
LTFT B2 %	7​
MAP (inHg)	26.8​
Eng RPM	5600​
Veh Spd	70​

I know it doesn't tell much...still need live data.

 

[Photodude]

Engine was at 5600 revs and the car was moving at 70 mph. MAP looks OK...

Just to be clear, MAP (manifold absolute pressure) at 26.8 inHG (900 mBar) means there is very little manifold vacuum, at that moment in time. Pretty meaningless value though, in the freeze frame context, as engine vacuum fluctuates depending on RPM, load etc.

Did you test fuel pressure? Especially at high RPM?

Given your symptoms, I would want to see how the fuel pump performs, in general, but especially at higher volume demands… before moving on to test MAF sensor.

 

[DBCoooper]

Fuel pressure was checked and was about 54 psi at idle, very little change at high RPM but this was with no load. A WOT snap test was performed which showed about a 3 psi drop for a brief moment, then back to 54- again with no load.
My comment about MAP was based on the car being at WOT at the time so little vacuum would be expected. Ambient conditions weren't recorded either so yes, very little meaning at this point. By "OK" I meant "expected".

Any input on how to do a fuel pressure test with load? Can that data be pulled from OBD? I just received a new scanner (Autel 519) so can now do live data.

 

[DBCoooper]

During testing, I noticed that the car starts to act like it's hitting a rev. limiter while in park at 4200 RPM. It sounds like a severe miss but does not trip the CEL. Is this normal? I'm not familiar enough with the system to know. With load, the car pulls well past 4200 rpm with gusto.

On edit: There is apparently a no load rev. limiter on the M113

It's raining so I'm not driving the car for the driving portion of the MAF test. It has you drive the car at 40 mph then floor it. Yes, I know rain won't melt it...
Further testing with live data and using the test that was provided on post #10. As discussed, no-load fuel pressure tests are within limits. LTFT is right around zero according to the new scanner which is within limits. MAF sensor at idle is .6 lbs per minute.

 

[Photodude]

Fuel pressure was checked and was about 54 psi at idle, very little change at high RPM but this was with no load. A WOT snap test was performed which showed about a 3 psi drop for a brief moment, then back to 54- again with no load.

Your test values are marginal at best. 54 psi at idle, that’s bare minimum, if it drops below that when you rev it up, even briefly, that would be concern. The pump may struggle to deliver when demand is at its peak. You could test delivery rate at the fuel line, if my memory serves me well, it should be 1 liter in less than 35 seconds.

With these fuel pressure values though, I would be concerned how much longer the fuel pump will last. Regardless of the symptoms you are experiencing.

And yes, there is rev limiter with gear selector in P/N.

 

[DBCoooper]

Yeah, good point. I was reading another post that had different values for acceptable but now that I look at the troubleshooting guide that you provided I see that it is on the very low end of the requirements. Is there a brand of fuel pump that is preferred? I learned the hard way with the spark plug wires that some that "fit" may not be the best, so I'll try to stay with whoever provided Mercedes with the original part.

In this case is the pump provided by Pierburg?

 

[sushipaste]

Yeah, good point. I was reading another post that had different values for acceptable but now that I look at the troubleshooting guide that you provided I see that it is on the very low end of the requirements. Is there a brand of fuel pump that is preferred? I learned the hard way with the spark plug wires that some that "fit" may not be the best, so I'll try to stay with whoever provided Mercedes with the original part.

In this case is the pump provided by Pierburg?

Yup pierburg is the way to go

 

[5literrag]

Your test values are marginal at best. 54 psi at idle, that’s bare minimum, if it drops below that when you rev it up, even briefly, that would be concern. The pump may struggle to deliver when demand is at its peak. You could test delivery rate at the fuel line, if my memory serves me well, it should be 1 liter in less than 35 seconds.

With these fuel pressure values though, I would be concerned how much longer the fuel pump will last. Regardless of the symptoms you are experiencing.

And yes, there is rev limiter with gear selector in P/N.

I had questioned the same thing in post # 67. Its a long way around, but I think its entirely reasonable to think the original equipment pump might be the fault here.

 

[DBCoooper]

OK so MAF test is interesting. The troubleshooting guide Photodude provided said to drive the car at 40 mph and go to WOT. The MAF reading should go right up to 480 Kg/H or 133 G/S or 17.6 Lb/Min.

My reading went to .54 lb/sec. on the first run and .52 lb/sec. on a second run a few minutes later.

If I convert that to Lb/Min. by multiplying by 60 I get 32.4 Lb/min. for the first run and 31.2 Lb/min for the second run.

The troubleshooting guide doesn't say the 17.6 is a minimum.

Thoughts? And a new pump will be on it's way soon.

 

[Photodude]

This troubleshooting guide is based on Mercedes DAS. WOT drive test is really meant to be done on a Dyno. Nevertheless, when you floor the accelerator at 40 mph and you air mass goes to 480 kg/h or above… your MAF is likely OK. Assuming 2000 rpm and idle readings are also within range. Ideally you’d want to check corresponding Voltage range during each test, not sure your scanner would have that option though, SDS certainly does.

MAF sensor going bad/ dirty will usually under report air flow volume. However, idle speed readings can also be negatively influenced by vacuum leaks. That’s why you test it under different parameters to be sure.

 

[DBCoooper]

Thanks. Am I reading the above correctly that with the transmission in 3rd, at 4000 rpm my mass air reading should be between 480-580 kg/h? Battery voltage must be above 10V.

Interestingly, the new scanner only finds a misfire on cylinder 5 now. Just the one code. Previously my old Innova would show 3- 0300, 0303 and 0305.

Fuel pump is still in the running as the issue. Just need to do some more testing.

 

[Photodude]

Am I reading the above correctly that with the transmission in 3rd, at 4000 rpm my mass air reading should be between 480-580 kg/h?

Yes

 

[DBCoooper]

As said, these tests are for use with a dyno so pretty hard to get a WOT reading in 3rd gear. With the gear selector in 3, as soon as I go to WOT the trans downshifts to 2. At 4000 rpm which in 2nd gear translates to 50 mph the MAF reads 718 kg/h. It's certainly not that the MAF is reading light. 3rd gear at WOT is faster than I want to be driving around here. I'll need to hit the freeway for that, which isn't happening today.

Only the one code keeps setting now, which is P0305.

 

[DBCoooper]

New fuel pump went in yesterday. Fuel pressure is now at 59 psi at idle. Misfire condition still exists with all three codes (0300, 0303, and 0305) still showing. I believe the previous code scan showing only the 0305 code was a fluke.

 

[5literrag]

New fuel pump went in yesterday. Fuel pressure is now at 59 psi at idle. Misfire condition still exists with all three codes (0300, 0303, and 0305) still showing. I believe the previous code scan showing only the 0305 code was a fluke.

Does yours have a cam sensor? Might be another wear item to give some thought to.

 

[Photodude]

You could, possibly, have couple of injectors spraying less than perfect pattern. If misfire only happens at WOT… you have to think what is practical way to test this. SDS actuation test (at idle) may, or may not pick this up… so unless they are really bad, this kind of test may be inconclusive. Testing injectors spray pattern requires removal and proper equipment… you’d need to send them somewhere to be tested.

I would suggest running couple of fuel tanks with Techron (or equivalent) fuel system treatment… and see what happens. These injectors should not be failing at 73,000 miles but, if somebody (PO) only used cheapest gas they could find, you never know.