86 560SEL engine miss - fuel distributor? - PeachParts Mercedes-Benz Forum

rsmartin · #1 11-25-2010, 11:25 AM

been having problem with rough idle and now has a regular miss. vacuum guage indicated slightly low vacuum so i've been over vacuum lines like Sherlock Holmes and replaced obvious ones

took it to indy who did smoke test for vacuum leaks. he determined that fuel injector seals were leaking so replaced all those and now says no vacuum leaks. as for the miss he says it's #8 cylinder and that i have low fuel pressure. he switched injector to different cylinder with no change in miss and no problem with the other cylinder missing with the original #8 injector says did compression test and leak down test with no problems noted. also says very hot spark. i run fuel cleaner through every couple months.

so fuel distributor maybe he says?

car has 92K. as far as i know wires, distributor, rotor never changed in 24 years. i'll do that first.

anyone else have some thoughts.

Cal Learner · #2 11-25-2010, 12:29 PM

If you have any reason to believe that the ignition components are original, you should certainly replace them first before launching into more expensive repairs/replacements (fuel distributor, for example). Your indy should have at least checked their condition (are the plugs sooty? is there arcing from the wires? etc.). When you replace the plugs, the conventional wisdom is that you should only use copper core non-resistor plugs.

jhodg5ck · #3 11-25-2010, 12:45 PM

Swap the lines on the fuel distro, ie, put # 7 fuel line to # 8 hole on distro. If misfire follows the "hole" they you know it's the distro

If ignition parts have never been done I feel as though your indy is kinda wasting your $$..it's time to freshen those up. Plugs are worn by about 15-20K, cap and rotor is spent by 50-60K @ best!

Jonathan

rsmartin · #4 11-25-2010, 03:50 PM

i changed plugs last year, don't remember mileage. but the old plugs were fine as best i could tell. no wet or sooty ones. i did buy non-resistor plugs.. don't remember brand but i think they were NGK.

rsmartin · #5 01-09-2011, 05:32 PM

Quote:

Originally Posted by jhodg5ck

Swap the lines on the fuel distro, ie, put # 7 fuel line to # 8 hole on distro. If misfire follows the "hole" they you know it's the distro

If ignition parts have never been done I feel as though your indy is kinda wasting your $$..it's time to freshen those up. Plugs are worn by about 15-20K, cap and rotor is spent by 50-60K @ best!

Jonathan

The fuel distributor isn't timed?? I'm kinda ignorant about how it works so sorry if that's a dumb question.

I asked my indy who has a real good business servicing german cars about putting on new electrical stuff.. He said it wouldn't hurt but it won't fix the problem. He said they tested the electrical stuff exhaustively and have determined that there is low fuel pressure on the #8 cylinder. they switched the #8 injector to another cylinder just to check but the #8 cylinder continued to miss and was low on fuel pressure.

i didn't ask him to switch the fuel distributor lines yet. kinda wanted to ask about the timing issue first.

jhodg5ck · #6 01-12-2011, 03:01 PM

Nope, not timed @ all...any cylinder can be hooked up to any port on the fuel distro. Continuous Injection System

Jonathan

rsmartin · #7 01-12-2011, 09:44 PM

so more curiousity... how does the injector know when to inject the fuel?

Cal Learner · #8 01-13-2011, 09:34 AM

There's no "knowing" about it--the injectors continuously inject fuel. As Jonathan said, they're not timed. The Bosch Continuous Injection System is a basically mechanical system that sprays continuously while the engine is running. Later fuel injection systems became electronic, and they are timed to specific cylinders.

rsmartin · #9 01-18-2011, 07:25 PM

curious to know what goes wrong in a fuel distributor? since it's not timed i assume all the ports are at the same pressure? so why would just one cylinder be affected?

i've run a number of bottles of fuel system cleaner through over the few years i've owned the car. it was a very low mileage car when i bought it so sat alot for it's first 23 years.

maybe i need to run a can of seafoam through somehow to get a high concentration through the fuel distributor?

any ideas or do i just go for the replacement. my mechanic insists the miss problem is low fuel pressure to #8 cylinder.

jhodg5ck · #10 01-18-2011, 07:32 PM

have you swapped lines around yet?

rsmartin · #11 01-18-2011, 08:30 PM

sorry, no.

i'm gonna have to find another guy i guess because he doesn't seem to want to do it. if i swap the lines is there any way i can tell? or does one need some high tech machine?

maybe i'll bring it to you. i'm in Chattanooga, so not that far.

jhodg5ck · #12 01-18-2011, 08:48 PM

I'd be more then happy to assist, I know your car reasonaly well @ this point.

That said, you a 12 and 14mm open end wrench and you could do the swapping on your own.

First verify it IS cylinder number 8 by cracking open the fuel line @ the fuel distro while the car is running, if it is 8 that is missing, doing so will NOT change the idle.

Crack open a few other lines to test similar and replicateable change in idle.

From there (this will require some bending) swap around two fuel lines and repeat.

If you give it a go and have real time questions, give a ring 404 850 1357.

Jonathan

rsmartin · #13 07-23-2011, 04:33 PM

cracked open #8 and at least half the others enough to leak gas one by one and none of them being cracked seemed to change how the engine idled, at least to me

Quote:

Originally Posted by jhodg5ck

I'd be more then happy to assist, I know your car reasonaly well @ this point.

That said, you a 12 and 14mm open end wrench and you could do the swapping on your own.

First verify it IS cylinder number 8 by cracking open the fuel line @ the fuel distro while the car is running, if it is 8 that is missing, doing so will NOT change the idle.

Crack open a few other lines to test similar and replicateable change in idle.

From there (this will require some bending) swap around two fuel lines and repeat.

If you give it a go and have real time questions, give a ring 404 850 1357.

Jonathan

jhodg5ck · #14 07-23-2011, 05:52 PM

just re-read, cracking none of the lines did nothing to the idle?????

That's about impossible. There should be One line that will make for no change, while the others should all cause an additional misfire/missed beat in the idle.

Make a few rounds w/ the wrench, there should absolutely be a change with the lines that are not feeding a mis-firing cylinder.

jonathan

rsmartin · #15 07-23-2011, 11:14 PM

Quote:

Originally Posted by jhodg5ck

just re-read, cracking none of the lines did nothing to the idle?????

That's about impossible. There should be One line that will make for no change, while the others should all cause an additional misfire/missed beat in the idle.

Make a few rounds w/ the wrench, there should absolutely be a change with the lines that are not feeding a mis-firing cylinder.

jonathan

i did it again. when i crack each line other than #8 the idle slows down a little. #8 doesn't seem to change anything.

so i think i understand what you meant. i was looking for something really pronounced like a dead cylinder when i did it before.

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