Guys,

I could use your help in diagnosing my spark plugs. I just changed them after a 100,000 mile interval and all 8 appear to be carbon fouled (black sooty deposit). The car was running fine and is used mostly for highway trips, with only occasional city driving. Last year I was having problems with running rich caused by clogged fuel injectors which I cleaned and everything has been running fine for the last year.

When I just changed the plugs, I was surpirsed to see them carbon fouled. I am using Bosch +4 plugs as speced by Bosch. From my mods listed below, I don't see anything that should cause this. Should I just try a hotter plug? Any suggestions to check? I just put a new set in but I am now thinking I should have tried a different plug. The last time I changed these plugs, I did not have the carbon fouling so I don't think it is the plug's fault.

Do you think there could be an undiagnosed problem with the engine? Not burning any oil and everything runs great.

Ideas?

Thanks,

Jeff

 

100 g on plugs is quite a bit, but not too unusual. I'd switch to NGK 55s. Plats or irradiums if you want them to last a long time, otherwise I'd just get some inexpensive TR55s coppers gapped at 0.50 should do fine. I have not heard many positive things about those Bosches. JMHO

 

You have 298,000 miles on that engine and tranny??

 

bosch platinum +4's are gimmicky pieces of crap if you ask me sure you've got multiple spark paths but who cares what you want is one concentrated spark! there is absolutely no reason to have more than one path for the spark to travel

 

302,000 miles now. All original and never been rebuilt. Everything still runs like new also.

I have seen others recommend the NGK plugs but I have had no performance problems with the Bosch plugs. When I changed them at 200,000, they were clean. Around 280,000 miles I was having hesitation problems and I found it was running rich due to clogged injectors. Once I cleaned them, the car has been running fine.

Could the sooty deposit be left over from that issue or should the 20,000 miles since I changed them have cleaned the plugs by now?

Thanks,

Jeff

 

How can a clooged injector cause it to be RICH??

 

thats what i was thinking marshall, clogged injectors would cause there to be less fuel not more in the mixture, normally it would run lean. Whens the last time the o2's have been changed because they could be causing a mixture that is off somewhat

 

Maybe he meant clogged open i.e. leaky injector???

 

Guys,

The injector tips were dirty so I was not getting good atomization. The O2 sensor detected this as a lean condition and compensated by making the LTERM counts in DataMaster go into the 130s (i.e. red). That is what I meant by running rich.

I cleaned the tips and all has been good for about the last year but now when I replce the plugs, they show signs of carbon fouling (black sooty deposit). I have put about 20K miles on those plugs since the injector problem.

Could the soot be left over from that prior problem or do you think there is something else going on?

Remember the car is running fine (both before and after new plugs). I am just trying to head off another problem that might not be affecting performance yet. Any ideas?

Jeff

 

If you left them in there for 100k miles and the car was running fine but the plugs had some carbon soot on them I really wouldn't worry. Regardless, some pictures of the plugs would help.

 

Is this the highest mileage car on the site?

302k on the original, not rebuilt engine and A4 tranny?!

 

I'll see if I can borrow a digital camera. Here is a link to a website with plugs that look like mine. Here is the link:

http://www.spark-plugs.co.uk/pages/t.../diagnosis.htm

My plugs all looked like the one labeld as dry fouled (2nd picture from the top) on this page.

Jeff

 

I haven't ever met anybody with even close to the miles I have on my car. When I go to car meets, I open my hood and when guys look, they don't see what is so special, then I tell them the miles and everybody is amazed at the shape of the car. I have a good picture of it I'll try to put in my signature. Other than some stone chips on the front bumper, it look like new.

Jeff