I noticed that 3 of the used plugs in my 4.5 are white from running lean while 3 are black with soot, one was just right and one was wet with gas. The car runs rough but has good power so I was wondering what is causing the mxture to be so uneven. What are the likely causes? The problem appeared fairly suddenly, since the last time I changed the plugs about 3000 miles ago. I had driven the car about 10 miles after storing it for the winter when I pulled the plugs. Could old gas do this? I did use a gas stabilizer.

The leading cause of uneven mixure on a D-Jet is dying or dirty injectors, followed by bad or dirty trigger points. Next in line is vac leaks.

I'd run a bottle of RedLine injector cleaner through it before getting too excited, since gasoline residue can make the injectors stick -- if one doesn't open properly, that cylinder will run lean, if it doesn't close properly, that cylinder will run rich.

The seals between the upper and lower intake manifold halves also can leak -- this will cause the cylinders where the leaks are (there are eight seals) to run lean, and if you then adjust the mixture at the tailpipe, the others can be rich.

Bad trigger points will cause the injectors to not open, usually, often intermittantly. Cylinders will be affected in pairs, don't remember which ones at the moment, but can look it up. Usually won't cause white insulators, but hey.

And don't forget to check the condition of plug wires and points -- iffy wires can cause rich running symptoms from misfire, completely unrelated to mixture.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks Peter, I would like to know which injectors are activated in turn by each trigger point cause the bad mixture would follow that pattern if the trigger points are the main problem, correct?

Bill:

Injector pairs are:

1&5
4&8
3&6
2&7.

I don't know which trigger point first what set, though.

Don't forget that vac leaks at the injector seals will cause lean running on that cylinder, too!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks again Peter, very helpful. I've come to the conclusion that the rich/lean pattern is random and probably the result of sticky injectors or vac leaks not dirty trigger points. I've got a can of techron in there now. BTW is there any diagnostic significance to adjacent cylinders running rich or lean cause 2 and 3 are too rich while 6 and 7 are too lean?

Yeah, makes me think of manifold leaks, either at the head or the rings between the two sections. Could also be a bad idle air hose, the funny "y" shaped one.

My guess is a vac leak, unless you have a ground problem with some of the injectors -- they all ground to the firewall behind the battery, probably a good idea to check that -- if some ground OK and other's don't, the ones with a bad ground will tend to open improperly, causeing a lean condition.

With a little luck, the Techron will clean things up and fix it.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!