Still trying to diagnose an erratic positive fuel trims. Next step will be making sure that the lean condition i have is caused by less fuel delivered or weak spark not a vacuum leak. I pulled spark plugs today and took a picture. I would appreciate any insights on the status of all four cylinders.

Thank you!

image 1

  • That looks like oil deposits to me, but it could be due to fuel additives too. Have you run a compression check? It could be overheating as well, which would be consistent with an overly lean mixture. Can you take pictures from a better angle, showing more of the top of the plugs? – GdD Dec 15 '20 at 19:36

The end with the spark gap is primary importance . What are you burning ? I have not seen that much crud since the leaded gasoline days. This much fouling would be typical of leaded fuel , not a worst case. At that time the deposits were very complex ; some combination of lead oxy sulfate with bromine. No significant difference between cylinders. You might try platinum plugs , although I never used platinum with leaded gasoline. Another thing that has changed along with lead removal is significant reduction of sulfur. So, I have no clue other than it looks like leaded gas fouling.

  • Hi blacksmith37. I bought the car 4 months ago and not sure what was the original owner using. Now i use Chevron only. Thanks! – Flamenco77 Dec 15 '20 at 19:59
  • New plugs has to help.. In the lead days you needed to change plugs at 15 to 20,000 miles. Lube oils can have zinc, barium ,calcium , maybe other stuff but it would need to be burning oil to foul plugs. I have changed 2 sets of platinum plugs in cars with 100,000 miles and they looked so good I hated to throw them away. Before I retired it would have been interesting to find out what the deposits were ( off the books). – blacksmith37 Dec 15 '20 at 21:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.