PPI Results-Big Question

[astark]

Well the PPI came back on my 87 Carrera. Mechanic states:
Compression between 160-180, Leakdown 3-4% on all cylinders BUT ONE!

I didn’t catch the compression on the “bad cylinder,” but leakdown 50-60%. Mechanic says that a piece of carbon may have come off the spark-plug and is preventing the valve from seating completely. He wants to repeat the compression/leakdown tomorrow. Says the car runs strong.

Does this sound right to you???

I am hesitant, but want to know if I should be?? Is it possible that the mechanic can replace the spark plug, run the car a while and the re-test will come back fine???

Thanks,
Alan Stark

[imcarthur]

Alan

I have walked from 2 cars in the last 3 weeks for the same reason. I've read & searched & asked. I would like the answer too, but I suspect it will be fuzzy.

Both mechanics involved suggested that the car just hasn't been run enough & carbon has built up. With a good thrashing, the valve will reseat.

Can it?

Ian

[pwd72s]

If possible, I'd suggest running it hard for a while, with a good carbon cleaning additive in the gas, then retest. If that one cylinder remains bad? I'd walk on buying the car. Rebuilds, even just top end ones, aren't cheap...

[Rot 911]

What the mechanic says is possible. Could also be a bad valve adjustment or a burnt valve. I would run the car then retest.

[Por_sha911]

Every bad motor "just needs a good tune-up and it will run like new..."
If its not carbon, you just bought an extra $5-10k worth of repairs. How big a gambler are you? Don't let your emotion and desire to have a car cloud good judgement.
IMO: buy a bottle of techtron and ask the owner to drive it till empty and you'll have the test done again -or- walk away.

[imcarthur]

Just to complicate things, Alan's car & one of mine were 1000 miles away & we're relying on a good mechanic & a PO to do all of this . . .

[astark]

Thanks Guys, So What I'm Hearing:

If the cylinder re-tests OK, then don't worry-be happy and drive the car home.

More than 10% variation in compression and/or more than 5-6% leakdown (other cylinders 2/3%) WALK.

Ian--we've never met, but I feel as though I know you! We have been in the market for a p-car and both have had disapointments. Sounds like you (and I) are willing to walk until the right car/right price comes along.

Thanks for all the input, keep it comin

Alan

[imcarthur]

Good luck, Alan.

I hope it works out - you'd look good in that car & the drive home would be fun. But, walk if you have to . . .

Ian

Oh yeah, and while you're in Florida do you mind having a look at a car for me . . .

[jyl]

Might have the owner pay for a valve adjustment too. I had seemingly bad leakdown numbers on my PPI (15%-ish), the mechanic did a valve adjustment and re-tested, leakdown was much better (<3%-ish).

[fintstone]

Only buy if discounted enough to pay for the risk unless you get better results on test.

[Jdub]

Prior to retest, have mech. adjust valves on the bad cylinder only. Drive it hard, then retest. That's the cheapest way to get to the bottom of this.

John

[chrisp]

Step 1: Toss a bottle of Techron in the tank and drive the tank empty (so you get the cleaning benefits of a full bottle of Techron).

Then do the retest.

The valve adjust sounds like a viable option but I would consider that step 2 if step one doesn't work..

[Westy]

Old Cadillacs (500 CI's) used to build up a lot of carbon, and it would eventually break off. I heard one with this problem and I swore a rod had snapped. Scary but harmless. Threw a can of Carbon Blaster in there and BAM!! it was all gone. I just can't imagine a piece of carbon sitting in the valve seat area. All the air and cycling of the cylinder would (should) pass it through the motor. Hmmmmm JMO

Brian

[teamgomez]

Had same with engine out- tapped hissing valve with plastic hammer and the carbon dislodged, valve seated 4.0 and engine fine. I believe best practice is to leave plugs in until you get to that cylinder so any carbon doesn't fall during removal and get a chance to lodge itself in the valve seat. In my case I think it was intake garbage that came off when I removed the intake runners.

[Westy]

I stand corrected. Gee, there's a surprise. I just read an excerpt from Wayne's book, and he clearly discusses the carbon on the valve and how it can flake, then sit in the valve seat causing lack of closure. I think it's in chapter 18. Oh well..............