Diesiel question

Old Roy · Mar 25, 2011

Ok not a tractor , but an 84 Mercedes sedan 5 Cyl

at idle the engine misses badly as to shake (kinda as bad as a flywheel out of balance) the car after start up but if you open throttle it seems to smooth out let it to idle it will run like it should for maybe 15 seconds then will run rough again.

In the past it has been run on homemade fuel, I don't believe that to be a problem because the guy that had it ran the same mixture in his tractors. with no problem.

Can just part of the pump be going bad?
Filters have been changed twice in two tanks of fuel,---only on suspicion that that may have been the problem same results.

Have tried to replace injectors off a known good engine.

Bob · Mar 25, 2011

"In the past it has been run on homemade fuel, I don't believe that to be a problem because the guy that had it ran the same mixture in his tractors. with no problem."

(LOL!!!!!)

WARNING!!!!! DO NOT proceed unless you understand the dangers of getting high-pressure fuel injected into your skin and know how NOT to have that happen while "cracking" the lines loose!!!!!!

First thing would be to loosen each injector line one at a time and see which has no effect @ idle, identifying the "missing" cylinder.

Then, pull that injector and have it checked or swap two injectors and see if the miss changes places along with the injectors.

If that's not the problem, since this is an in-line pump, the pumping unit associated with the missing cylinder could be bad or simply out of adjustment.

ANOTHER possibility would be low compression on the affected cylinder due to piston/ring sealing issues, valve problems, or even a bad headgasket.

Old Roy · Mar 25, 2011

You just reminded me of the shots we got in the service. guy ahead of me moved bled like a son of a gun. didn't like it when my turn came. but I live through it -- LOL

I figured he solved that idea though when he took injectors out of another engine he has sitting.
he bought another car just for that engine. he was going to put it in a skidsteer. abd decided to try process of elimination

Mike (WA) · Mar 25, 2011

I had a '68 Mercedes 200 diesel, and believe it or not, the injector pump had a vacuum line to it. I never did understand what the relationship between vacuum and the pump was, but it developed symptoms like yours, and turned out to be a cracked (metal) vacuum line. Patched it up and it ran good as new. Which was about 65 MPH, flat out.

Old Roy · Mar 25, 2011

Thanks Mike ! I believe he said his had vacuum lines running to places he didn't understand. he did have it running good for a couple days - then started acting up again just may be something moved enough to seal off a leak.

I am totally diesel dumb I quit working on gas jobs when all the electronics took over. I liked it when your tool box contain a screwdriver, a half and 9/16 wrench a piece of bailing wire and if real fancy a pair of vice grips.

k6zrx · Mar 25, 2011

Is air getting into the system? I have had it happen, runs OK at speed, but won"t idle or dies.

I drive one all the time, good cars. Mine is a turbo.

Josh

Old Roy · Mar 25, 2011

This one is a turbo as well PO did change the air intake cleaner system to the cone shaped (big airflow style.)

I was thinking something bordering what you say with me (not understanding how the fuel pump works)

If it had separate pistons for each line as it looks like it may have maybe one not producing the correct pressure needed ?

guido · Mar 25, 2011

Hello Old Roy,
Is the idle the same as when the engine had no miss or vibration?
If not, I would do what bob said, and se if it is just one injector that is bad.
Swapping injectors between a good firing and missfiring cylinder, is one way verify the bad one.
Guido.

Old Roy · Mar 25, 2011

yes the idle speed was never tampered with. car does have over 200.000 on it but to some peoples suggestions that is no major concern the one he had been driving he bought as a junker for the engine. with 325.000 miles on it .The PO left him drive it home on his plate-- Needed floor boards under drivers seat-- He liked it so well he fixed it up - ran it for all last year for an investment of 600.00 and he found this nicer one. Body almost perfect.
in the process of trying to find this problem he did take out the injectors on the one he was running as it no longer will pass Pa state inspection.

Rather than go completely through the process of elimination I decide to ask here Plus I don't know how much different the engines may be with 2 years difference in the models one and 82 the other 84

Old Roy · Mar 25, 2011

all good sensible info to at least look at.
Will keep you informed .

Diesiel question

Old Roy

Well-known Member

Bob

Well-known Member

Old Roy

Well-known Member

Mike (WA)

Well-known Member

Old Roy

Well-known Member

k6zrx

Member

Old Roy

Well-known Member

guido

Well-known Member

Old Roy

Well-known Member

Old Roy

Well-known Member

Similar threads