kap

My f20c threw a misfire code for cyl 1 and 4.

Comp tests:
1- 190
2- 200
3- 200
4- 140

Leak down: all under 5% leak under 100psi.

My engine has 110k mi. I drive my car pretty hard at the track: I hit the rev limiter occasionally, I overrev once in a while (4th to 3rd to 2nd off a long straight going into a tight turn).

I took it to the shop (not going to say where, but he's a real smart guy) and he told me that my cyl walls may have damage.

1. What are my options? Buy a new short block (My head is fine)? Bore the cyl walls? I want to get things done the right way, but at the same time I don't want to go broke fixing my car.

2. What causes this? When I took it to the shop before (7-8 months ago), they did work on my head, and told me that my cyl walls were fine when my head was pulled off. I put on about 8k mi in those 7-8 mo, and 3 track days. I'm just surprised that within 7-8 months, my cyl walls have issues, since they were said to be in good condition 7-8mo back.

3. What wiuld you do? This is my DD and it drives fine for DD duties, but I plan on going to the track 2-4 times a year (its very addiciting).

Ps. I check my oil every gas fill up, and I make sure it's within range at all times.

freq

abused AP-1 with the old oil banjo bolts?

kap

It's an 03, banjo bolts are not an issue I believe.

postman

Use a different leakdown/compression tester and recheck. The 2 tools have a direct correlation and something is not correct in your results somewhere.

MR.T

X2. Did you happen to make a home-made leak down tester?

kap

I took it to a pretty reputable shop. I'm pretty confident that they did the tests properly. Although you never know...

Just out of curiosity, what makes you think the results may be wrong? It made sense to me that at tdc the comp test was weak, but the leakdown was strong with the piston at the bottom of the cycle. Were it the valves or rings, leak down would have been bad too. Please correct me if I'm misinformed, I'm here to learn.

MM3Kwolik

Compression test is done by cranking the (warm) engine over with the throttle plate open. Leakdown test is done with each cylinder at TDC (also warm). You can have poor compression and good leak down as the rings may be sealing at the top of the stroke but not as well during the stroke due to excessively scuffed cylinder walls. If you trust the mechanic you went to, then I'd have no reason to doubt his findings. Another thing to do, if he has one, is to use a borescope and visually inspect each cylinder through the spark plug hole with each piston at BDC.

MR.T

Yeah, that makes sense to me now. I guess if you loose air through the bottom of the stroke there's less air to compress at the top, resulting in the lower comp numbers.

MM3Kwolik

Precisely.

Soviet

OP, saw that you have been online recently. Ever get this resolved?