I have searched and searched for an answer to my problem, but I can't seem to find anyone with the same exact problem I have. My 1991 560SEL runs rough immediately after start up and sometimes takes a little bit longer than usual to start. The problem is usually worse once the engine is warm and has a miss on acceleration for about 30 seconds after starting, then it runs perfect. Idle is perfect and it even passed a California emissions test today with no trouble at all. It has a new fuel distributor, EHA valve, O2 sensor, spark plugs (the correct non-resistor ones), vacuum lines, and throttle switch. It also doesn't seem to have any vacuum leaks. I have also re-soldered the OVP relay, fuel pump relay, KLIMA relay, and idle control relay, yet this problem persists.

I'm concerned that perhaps I have an injector or two leaking after I turn off the engine. Is there a way to test this before I spend a load of money to replace them? I have also run a strong treatment of Techron through the system without much change. Thanks in advance.

__________________
1998 E320 Wagon

1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO

1992 500SL Parts Car

1991 420SEL Parts Car

I had something similar and a complete injector/sleeve/seal replacement solved the problem.

RayH

I would start by checking the fuel pressure with the car just starting. Running. And see what the fuel pressure is with the car off for about 30 minutes [check for "internal" fuel leak].

Note that Harbor Freight sells a fuel pressure testing gauge kit with a zillion adaptors - one of which will fit a Bosch KE-Jetronic fuel distributor. And at a reasonable price to boot!

I recently had a similar problem with my 190E 2.6.

M103 starting problem

Run the simple on-the-car fuel accumulator test that I describe. The fuel accumulator is often overlooked as a the cause of similar problems, and it may be the most common part to fail on CIS systems.

Duke

I noticed today after starting my car that one of the accessory belts squealed horribly when I revved the engine slightly after starting the car. I thought that was a bit strange as I had just replaced all of the belts. So, I started thinking that perhaps the air pump was locking up. So, I unplugged the clutch for it, so it could no longer engage. It fixed the start up squeal and the start up roughness. Or at least it would seem that way right now. I have only started the car a couple of times since doing this today, but it does seemed to have fixed it. The air pump must be seizing up and just lugging down the engine on start up.

I'll let you know if this has actually resolved my issue in the coming days. Thank you everyone for the quick replies.

__________________
1998 E320 Wagon

1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO

1992 500SL Parts Car

1991 420SEL Parts Car

I had been expecting this result. The rough start is gone when cold, but still there when the car is warmed up. Although, it still seems to be improved even at warm start up, but that might be my imagination because I don't think that the air pump runs after a warm start up.

I think that this problem is most likely the fuel injectors leaking. The fuel system seems to hold pressure just fine, since when I took the AFM and fuel distributor off to replace the throttle switch, fuel came out in a forceful spray when cracking the lines to the fuel distro. It had been sitting for many hours before I did the job and I think this rules out the accumulator, but it's not an entirely scientific test... I know.

I'm going to get a hold of one of those ultrasonic jewelry cleaners to clean the injectors. I've heard of people having fabulous results with this method and even if it doesn't fix this starting problem, it will probably improve the engine performance in all aspects... marginally.

__________________
1998 E320 Wagon

1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO

1992 500SL Parts Car

1991 420SEL Parts Car

with 161k on the odometer, cleaning will help it but the injectors are mechanically worn. the seats and tips can't seal when closed. kjet injectors are good for about 100k or o.

easy test-pull the injectors and the lines off the fuel dist. screw the injectors into the fuel dist.-same threads. dry them off, jump the fp relay and watch. bosch says damp is ok, drips are not. then open the air flow meter and watch the patterns. a cone shaped mist is ideal but you'll see streams and lack of consistency. only reason I like the alum fuel dists. iis because you can do it this way. good luck, chuck.

Thanks for the advice about putting the injectors into the fuel distributor. I'm pretty sure that these injectors have been replaced at least once in there life since they are brass and not the original silver color. At least, I was told that the originals were silver in color and that only the replacements are brass. Is this true?

If they are replacements, they shouldn't be too worn out yet... I really don't want to put out a load of money for what I would consider a slight inconvenience since if you give it a small amount of throttle on a warm start, then she fires right up with maybe a hiccup or two.

Anyway, I will take them out one of these days and put them on the fuel distro. to test them. Thanks again Porkface.

__________________
1998 E320 Wagon

1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO

1992 500SL Parts Car

1991 420SEL Parts Car