I just recently picked up a 1985 380SE W126 116.963. I am a benz tech but only work on the late model mercedes and have never messed around with any of the older ones. This 380se will start, idles very rough, any application of the throttle will cause it to die.

When I first started the diagnosis, I sprayed a little starting fluid into it and it revs up just fine. I traced the fuel pressure as far up as the first vacuum fuel pressure regulator and it seemed to have decent pressure. I removed the first regulator and applied vacuum to it and it does not seem to react but I do not know if that is an accurate test for that part. Can anyone tell me how to accurately test the fuel pressure regulators and if there are any other common problems that I should look into as well?

Thanks

Josh

Update: Fuel pressure regulator seems to be ok and fuel pressure seems to be ok. With the fuel pressure ok, what other causes of this problem can anyone think of?

I assume that the engine is warmed up. The first thing I would look is the fuel distributor. If you can get ahold of some of the old cis gauges you can test system pressure with the pump running. Does the pressure stay up when you open the throttle or does it dive? A rare problem would be a clogged fuel filter. That is a longshot though. The fuel distributors are tempermental. You can pull one injector and manipulate the air plate to see if you are getting an increase in volume. Check to see that the plate moves freely. You have to remove the big boot to do this. Don't pull it any direction other than up.

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Presume you checked the OVPR ?
They usually are out of spec on C/O%.
Try running it to warm...check the O2 reading with O2 diconnected ...should read around 0.200vdc to 0.750vdc on a DVM.

Then you can trim the C/O% to about 0.500vdc or just lower.
If you open the air flap as you open throttle does it rev okay?


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Hey guys, thanks for the diag. tips.....got the idle and acceleration problem fixed BUT....now I have a brand new problem:

The engine runs good and smooth and revs up well, but when you put the vehicle into drive and press the accelerator, the car will hardly move and takes a long time to get up to speed and shift. When it does shift, it shifts very hard. I have already adjusted the cable to the max both ways and it has not changed the problem. The transmission fluid is clean and full but I do not know when the transmission filter and fluid was last serviced. Do you guys think that could be the problem or are there other causes for the transmission shifting and the slow acceleration?

Thanks again

Vacuum system problem perhaps. Based on the change in transmission shifts now there as well. I believe there are vacuum feeds to the fuel body/idle tube area. If a line blew off with a backfire for example . Or you accidentally damaged one or disconnected one when in the area working What did you find was your original problem? Where were you working? I do not know anything about the 3.5 litre engine basically other than there are vacuum circuits in the fuel supply system I believe. If you cannot find it easily you might have to employ a shop manual and a mity vac type device. Could be something else of course but the hard transmission shifts change at the same time is a strong indicator.

I have checked all vacuum lines around the engine bay and can find none of them are damaged, broken, or disconnected. Are there any others that would affect the transmission anywhere else? Also, when adjusting the idle on the car, it dramtically changes the throttle response and transmission shifting....any idea why?

Is the Economy gauge all the way to the left at idle?

How are you adjusting the idle?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

yes it is, then it moves almost all the way to the right under any acceleration

Sounds like its not getting enough fuel. Did you check system and control pressures? Check all electronic connections, including the ECU behind the passenger kick panel.

The 1-2 shift is usually hard, more so with a bigger throttle opening. Check the condition of the vacuum hose down at the transmission modulator.

__________________
1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

fuel pressure seems to be good, engine runs and revs great while in neutral or park. It seems like the transmission is in 3rd gear when you accelerate from a stop, you have to push all the way down on the pedal for at least 5 seconds before the trans will kickdown and pick up any acceleration. Once the vehicle is up to speed and you press the accelerator, you get almost nothing for 5 or 6 seconds before it begins to gain speed.

If it starts in 3rd, I don't think there is any external adjustment to fix that. Does it upshift to 4th? Can you move the shifter to low to force it down?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

yes, it does shift and accelerate better when shifting manually, but it still doesn't seem to accelerate anywhere near what it should as compared to some other 380se i have driven. I am wondering if there might be some clogged passage ways in the valve body or a dirty trans filter