Contour Enthusiasts Group Archives Forums Modifications Duratec Maintenance Just changed my plugs and wires..

...and I did it all by myself!

Ok, it isn't that hard and I didn't have any doubts I could do it.

Anyway, I know quite a bit can be learned about the engine's performance by "reading" the old plugs. Well, as soon as an admin approves the pics I just uploaded to my profile, I'll post them here to get some feedback.

But, as a summary, all 6 plugs looked basically the same. They had been in the car for 67k miles or so. The plugs were put in at the SVT dealer where I bought the car and had it serviced. They used the Motorcraft platinum 32F plugs and it still had the stock wires (car has 162k+ miles). I just put in the Autolite double platinums with Magnecor wires.

Here were the primary features of the old plugs:
- They were dry. no oily build up
- The side electrode appeared grayish-white in color, but no obvious build-up of any kind
- The center electrodes all looked good, with a point, not flat into the porcelain or worn down.
- I have some brown coloration on the porcelain above the threads on all 6 plugs.
- The passages in the header where the spark plugs go were all clean (at least on cylinders 4-6 where I could look into them. The boots on the wires for all 6 appeared normal.

Basically, what I gather from the Haynes manual I have, I am running a little hot or a little lean (I have occasionally had a CEL for too lean, but not for quite a while), but my plugs don't look near as bad at the picture example in the book. I don't have the brown to grayish tan color the manual says would be good/normal plug wear on the electrodes themselves, but the rest of it looks that way.

Am I reading this right or am I way off?

The next question is, what if anything do I need to do to improve the engine performance based on the plugs?

Thanks.

Your plug description sounds lean to me, defintely lean for a stock tune on a stock motor, if thats in fact what you have. However, lots of highway cruising can give you those dry, hot lean burn looking plugs. Whenever I'd pull plugs on my Pontiac they looked lean, but under WOT I was plenty rich, I had the scan tools to verify this, it was just running hot and lean on the highway, as any modern car does for maximum fuel economy. WOT stock tuning is pretty far on the rich side, I know the SVT is supposed to be hella rich... for whats thats worth. If you're throwing lean codes, you've defintely got something going on. It'll be easier when the pictures are up to actually see them. Could be a lotta stuff, low fuel pressure, air entering after the MAF sensor, etc. The fact that they are all basically even eliminates a bad fuel injector or an air leak into a specific cylinder. A scan tool is a must for these situations. I'd run around a bit on the new plugs and pull one or two and see how they look.

Something else you could consider trying is a plug chop. Its something done for tuning a/f ratios on motorcross bikes. You put in a new plug (in you're case just one fresh one would be ok if you say they are all coming out the same, six would really be a pain) and make a WOT pass to the redline and cut the ignition, close the throttle, and step on the clutch, all at the same time. The idea is to get an idea of you're a/f ratio under WOT, and by starting with a fresh plug and cutting it off with letting it idle or slow cruise around, you can really see what things look like. I've never tried this with a car, but the concept is the same. Usually, its easier to just get a scan gauge of some kind and at least get a rough idea based on the narrowband o2 readings.

Lets see those pictures!

I also will reserve judgement until I can see the pictures, but I suspect that the plugs are normal from the description.

The technique of reading plugs as you have described is also called "cut clean". It was beneficial in days long past, but isn't near as helpful as other tools today in determining air/fuel mixture. You can get a much more accurate picture with a scan tool while driving.

To properly do a "cut clean" required room on a race track to run at heavy throttle for a while before hitting wide open throttle, holding wide open throttle for as long as safe, and then shutting off as you have described. The idea to have no other factors involved to dirty the plugs.

I only did the "cut clean" technique a few times. I soon found other ways to give me the information I needed, at least close enough, to make my evaluations with that I felt were safer for a street rodder. When I could, I used an exhaust gas analizer. When not available, I would use atrificial enrichment (feeding metered propane). If you felt a boost in power by adding propane you were too lean. If you didn't feel a boost, you may be OK or could be too rich. I would richen up the jets (or other measures) until I was barely able to feel the increase. Anyway, as primitive as is was, it worked for me. I would have loved to been able to read a scanner instead.

Ok, here they are... (and don't tell anyone that my profile isn't approved yet... )





As for the comments about highway miles, yes I drove a LOT of extended periods on the highway going to and from car stereo shows on these plugs. Not as much in the last 12-18 months (only put on 12k miles in the past year when I was averaging closer to 20k before that).

The look fine. I wouldn't be too concerned with that. Like Big Jim and I have said, a scan tool would be useful in checking out your WOT a/f situation. I'd be wary if you were seeing lean codes every now and then. The Aeroforce Interceptor OBDII scan gauge should be done a in a few weeks, that'd be a perfect tool for you!

I agree, those plugs look absolutely normal for the miles.

Thank you both for the feedback.