mercedes 420 sel fuel distributor

[LarryWard]

Put this question on mercedeslist and got some helpful tidbits but maybe some TDRs have some input on the problem. Namely a miss that now seems to involve 5 cyl and barely runs on the 3. It is a '87 420 v8 with 183k and did sit around a bit before given to me. Ran pretty good in beginning. Put in new plugs and seemed to improve some and did get up and go. Later it passed calif smog and very next day started up with a miss and occasional driving it seemed to get worse. Experienced friend mechanic said the fuel distributor diaphargms(thin rubber) with disuse are known to crack and fail. We eleminated ignition as problem but all of the new plugs even the ones that were on cylinders that were carrying the load, all were totally heavily black sooted. Another set of new plugs did nothing to eleminate the missing. It is obviously overfueling.



Found a source for rebuilts in Florida w. shping nearly $400 which is cheap compared to new or other rebuilts. Wondering what range of years of this engine interchanges adapt if I were to find one at PicNPull, etc.

 

[JoshPeters]

Take and while the engine is running at idle, crack the lines at the fuel distributor head and tap on the head with your wrench. Do this to each line and you'll be supprised the crap that will come out.

I'd be more apt to believe that an injector failed than the fuel head. MOST of the fuel heads I've seen fail don't give one cylinder trouble, it's all of them.

JP

 

[Dieselnut59]

Do a compression test on it. You will need a diesel compression tester. It will test through the glow plug holes.

Also, it may be starving for fuel because of a restricted fuel line, screen or failing transfer pump.

 

[LarryWard]

Thanks for idea but this is a 420 SEL v-8 gasoline fueled engine with sooted spark plugs, etc, etc as you may detect in my post. Perhaps your post was inadvertantly misplaced and intended for a different discussion topic.

 

[JoshPeters]

Does it have a "cam tick" at idle? Those engines were known to eat Camshafts as well.

JP

 

[OKish]

Does it have a "cam tick" at idle? Those engines were known to eat Camshafts as well.



JP

i 100% agree, i have rarely seen problems with the bosch mechanical injection. im betting on a wiped out lobe or a bad plug wire.

 

[LarryWard]

No it has no idle cam tick. I have verified fire at end of each plug wire. Apparently we have overfueling on 5 cylinder to such an extent that they will not fire, but 3 will fire and enable engine to start every time quickly but then barely idles due to only 3 cylinders doing the work. All plug, two different set of new ones, the last being NGK are totally sooted bad. It will rev up but slowly and will even go under its own power but very reluctantly.



Tomorrow, I plan to do the suggestion of Josh to crack each connection at fuel head to release any potential debris.

 

[LarryWard]

Today I took Josh"s suggestion and cracked open each fuel line individually, tapped on fuel head. And it cleared up wonderfully all but I think one. But it did have a few, very few small perhaps 1/64 specks. Next I will drive it a little, pull the new plugs to check for soot, verify which cylinder is not firing. Then what? Remove an injector? What do I look for or what tests are there?



Between rain forcast for tomorrow I will identify which one is missing, but I want to thank you for suggestion. Who knows it still may be the fuel distributor doing bad for just one. I am surprised no one on mercedeslist suggested that procedure. Larry

 

[JoshPeters]

I spent 5. 5 years as a Benz tech. There are quite a few little tricks that people don't know, or talk about.



Since it cleared up quite a bit, I'd do 2 things. Drive it a bit harder than normal, blow the carbon out so to speak. The other would be, if you still have a bad cylinder, since the injectors are easy to get to, I'd swap that injector with a good one. You may find the miss moves. If it does, then you know you have a piece of debris in that injector.



JP