[ebatl]

Hey Guys,
I hate that my first post here is such a complex one - I've been lurking around this site for a long time but I've got myself in a mess and I'm hoping someone can help so thanks in advance for any insights....

I recently picked up a very nice, original 73 280sel 4.5 but like so many of these cars it had been sitting for a while.

I've been methodically sorting through lots of issues. It still runs like crap. When I first started digging into it I found that the fuel return was blocked and it was running 90psi in the rail, obviously running rich. It also had massive intake leaks which were counteracting the extra fuel and it was actually running pretty decent, albeit very rich. Long story short - I've fixed the fuel pressure and vacuum leak issues. Its running lean - it runs OK if I bump fuel pressure to about 60-70psi by crimping the return line. I've been through the tests on all sensors, adjusted tps, all new ignition components and checked timing. Pulled/ cleaned / tested injector trigger points. Could running at 3 times the standard fuel pressure have damaged the injectors? My gut tells me yes but I want to hear it from someone else before dropping 700 bucks on a new set. I have confirmed that they are all firing - however they are shooting a straight stream, not a nice atomized cone that I would expect. Any other thoughts? I've swapped ECU's as well and its runs about the same... Will not even idle at 30-40 PSI in the rail unless I disconnect temp sensor 1 which should make it richer...

Fuel pressure regulator is new, fuel pressure seems to be correct now at about 30psi, MPS tests good (holds vacuum at 10 hg and the resistance readings are correct across the pins).
TS1 (coolant) 1.541 k Ohm at 77F
TS2 (ambient) .372 k ohm at 59F
TPS tests correctly at closed setting and fires 20 times as expected when actuated.

Thanks for any help!!
Nick

 

[agillot]

first , set ign timing at 5 deg bef tdc at idle . unplug the trottle valve switch , now , you can adjust the fuel mix at the pressure sensor at the fire wall , remove the black plastic cap , you will see a allen screw , with engine hot , running , unscrew that screw slowly , a little at a time , the engine should pick up speed and smoothness .the use of a co tester here would be nice . try that .

 

[agillot]

make sure that the air filter temp sensor is connected when you do that . coolant temp sensor at 70 f is 2 to 3000 ohms . at 180 f , 200 to 400 ohms . air temp sensor at 70 f is 200 to 400 ohm . the injectors have a screen in the inlet , make sure they are not plugged , use carb cleaner with a straw to flush .

 

[Grubeguy]

I disagree with the changing of the pressure sensor adjustment - the air-fuel ratio adjustment is on the ECU, not the fire wall. Setting the idle is with the idle adjustment screw, on the front of the engine - tough to miss, and it has a spring under it to keep tension.

Run a general search in the forum for fuel spray patterns - if you have a straight stream and not a nice atomized mist, I'd go with the notion that the injectors are bad... But I thought those same ones were used on other cars using Bosch injection systems, and could take higher pressures (don't quote me on that because I could be misremembering something).

Before you do much else, I'd recommend getting into the online resources portion of the forum - there are a bunch of tech procedures and info articles I posted about adjusting, verifying, etc etc.

Out of curiosity, are you running an electronic/aftermarket ignition system, like Crane or Pertronix? Moving to one made a bunch of my own issues disappear...

Something you might consider, is finding a shop in your area with a gas analyzer. In no time flat, that will tell you whether your air fuel ratio is set correctly, and whether your manifold air pressure sensor (on the firewall) is set properly. You fiddle with the map for speeds above 3000 rpm, if memory serves. There's a procedure uploaded for that also.

 

[agillot]

the main fuel mixture is adjusted at the pressure sensor , the idle mix at the knob on brain , PERIOD .

 

[3.5 Tony]

Get your injectors rebuilt

If you are concerned you can get them rebuilt. It is usually $15-$20 each-much less than new ones. they clean them, replace the screens/caps, ect and flow them. Do a search-you will find several places.

 

[agillot]

the only time i replace them , is when the plastic to metal leaks , or electrical not working .cleaning the screen at time will fix a lean issue at some cylinders , usually caused by paper from a overdue filter [ decades old ]. the spray patern is not a issue there , since the injectors shoot in a vacuum , the gas will vaporize easily .

 

[adler]

The injectors are the same as those used a Datsun 24O Z . Same Bosch. D system under licence then. Prices quite reasonable at Datsun.

 

[Grubeguy]

the main fuel mixture is adjusted at the pressure sensor , the idle mix at the knob on brain , PERIOD .

The issue at hand is the thing running like crap while at rest. To adjust the idle and how the car runs at idle, the fuel/air mixture is adjusted at the ECU.

See http://www.benzworld.org/forums/vintage-mercedes-benz/1185674-online-resources-4.html for a number of tech articles on the matter, and the attached, first page, section H.

Idle speed is adjusted by the idle air screw.

You WILL effect the idle speed by fiddling with the ECU knob, but as a result of misadjusting the air/fuel mixture. Doing so will compound other issues and contribute to poor engine performance at idle.

Once the running-at-idle is sorted out, and you see how the car runs while under normal operation, adjusting the pressure sensor will effect how the car runs. There are testing steps, also located in http://www.benzworld.org/forums/vintage-mercedes-benz/1185674-online-resources-4.html, but they require the use of a specialty Bosch test set that I've yet to find on eBay, etc.

The pressure sensor can be adjusted using an exhaust gas analyzer (the procedure and gas values are also put up online). You're more likely to find the analyzer at the DMV or repair shops that specialize in older cars. The pressure sensor is not too awfully finicky, and can be "ballparked" with trial, error and more trial. Misadjusting the thing will cause you to run lean or rich at operating speeds, and will have a marked effect on gas mileage.

 

[ebatl]

Thanks, all, for the input. Eight new fuel injectors later and some additional minor tweaking and it starts, idles and runs beautifully.

 

[adler]

Thanks for the update.
Was it the injectors that were causing the running faults ?
Ad.

 

[ebatl]

Yes. Here is the full sequence of problems/resolutions.

Hard to start, missing at idle and running very rich at idle. Idle screw and adjustment on ecu had no effect. Ran okay off idle, but still seemed a little rich (observed black smoke out of tailpipe).

Checked fuel pressure and it was pegged at 90 psi. Discovered blocked return line from regulator. With pressure at 30 psi car would not run at all. Cranked pressure up to 50-60 psi and it ran, poorly, as through it were starving for fuel.

Sprayed ether around intake and discovered several vacuum leaks (the seals between the upper and lower intake were badly cracked).

Pulled the intake and replaced the seals and gaskets. Still wouldn't run without forcing it to run rich (disconnecting temp sensors and cranking up fuel pressure).

Tested injectors -- flow rate and spray pattern was suspect. Perhaps the ravages of time and high pressure damaged them? $700 later (thanks worldpac same day delivery) and it was running like a top. So there were several issues to unravel, but new injectors were, indeed, the final piece.