Engine Miss - Intermittant - 1994 S500
 

I've got a 1994 S500 that recently developed an intermittant miss at idle and acceleration. I don't notice either way during cruising, but it may be missing then too.
Sometimes it will go 5-10 miles with out any signs of missing, and then it starts stumbling. Other times it starts missing from the get-go.
I'm not the original owner, so don't know when the plugs and plug wires may have last been changed, but the distributor caps and rotors were replaced about 10k miles ago.

Any ideas of where to start??
It's not bad enough for the check engine light to come on, but sure it will at some point.
Is there a fuel pump relay I can check??
How hard is it to replace (get to) the plugs??

Any thoughts would be appreciated.

Thanks

I just installed new plugs in my 1992 5OOSEL.easy,straightfarward job.You can do it,no sweat. Make sure to use anti-sieze on new plug threads.

I would check the wiring harness for deteriorating insulation. Its not as common on the 119 engine as the 104, but it does happen.

Brian

Any specific area or connectors on the harness I should be looking at??
Also, is there a relay for the fuel pump somewhere??
I woould like to rule that out as a problem if I can.

Thanks!!

Look at the wiring near the injector connector and the coolant temp sensor connector.

I'll get back to you on the fuel pump relay. (ever have a brain fart?) I guess thats what the books are for.

Brian

Got into it this morning, and went ahead and replaced the spark plugs since I'm taking it apart anyway.
The old plugs looked pretty decent (clean, with a light brown color), so I'm sure that wasn't an issue.
And it started and ran fine while I jockeyed cars around before I dug into it, and started up fine after the new plugs.

I will say that on the connectors to the fuel injectors, the wiring harness did have deteriorating insulation. It's cracked and brittle. No wires touching or anything, but it's not getting any better. I want to sell the car, but this is going to be a problem at some point soon.
And this problem DOES seem to show-up most when it wet outside, so there is a clue too......

Anyone know how expensive the fuel injector wiring harness IS for a 1994 S500??

Thanks for your help Brian, it's always good to have a clue as to where to look first...... :-)

Just a quick update.
It's been raining around here the past 2 days, and the S500 has been running like a champ through rain, puddles, etc.
Not one miss.
If it DOES start to misfire again, I know right where to look, and I may even re-wrap the wires myself, just to say I did.... :-)

Anyway, thanks to all that helped.

Barry