So I have this really crazy problem. Back in the spring / early summer of '07 I had my car (2006 Evo IX GSR) modded with a AMS TBE, AMS MBC, Buschur LICP, AEM Intake, Walbro and was making 298WHP / 278TQ on a Mustang Dyno. I added some Cosworth Mivec (272's) Cams to the mix, went back for a re-tune and we were only able to get my car to make 302WHP. At the time of the cam install there were 20,000 miles on the clock. We were seeing a ton of knock and the car just didn't want to make power. The car was tuned so there was no knock, but it was only making 296WHP / 288TQ on a mustang dyno at this point.

Up until November my car was running fine, it was just down on power, then all the sudden P0300. Now my car has been misfiring while I am starting from a stop sign if it isn't fully warmed up, and it also has the occiasional misfire when I am at partial thorrtle on the freeway.

Anyways, a week after the re-tune with cams I went to another local shop for a second opinion. They did a compression test and Cylinder #1 came back with 90PSI while 2-4 were 245-250 (Spec Evo IX Compression). We then did a leak-down test and #1 was at 45-50% leak-down at 45psi, and cylinders 2-4 gave 0-5% leak-down at 45psi. I didn't get to see them do this test in person, so I went back to the orginal shop who tuned me and watched them do the compression and leak-down tests in person. Same results came up again. We did a wet test on #1 and it came back with spec compression, so we assumed that something was wrong with the rings on #1.

Last week I took it back to the shop to pull out the cams and flash it back to stock, but I decided to give it one more shot at finding and fixing the problem. Now here are all the things the shop has tried to fix it. I've spent a few days down at the shop helping out so I know they're not just taking me for a ride.

Thus far the head has been pulled, piston rings have been replaced on #1, Cosworth Head Gasket, and ARP Head Studs replacing OEM parts. The leak-down test is still showing 45-50% at 45psi for #1 while #'s2-4 are showing 0-5%. We pulled the head again, pulled out the valves around #1 and brought it all to a machine shop. The machine shop confirmed the valves were not bent. Valve seats were also inspected as well as the piston, and no problems were evident. They also grinded the valves and reseated them. We brought it all back to the shop, bolted the head back on, still seeing a ton of leakdown on #1.

After a weird crazy idea, the shop owner loosened up a couple head studs around #1 and all the sudden 0% leak down. (He wanted to see how much loosening it would take before air started leaking out from the head gasket.) Yeah this is great and all, but I am not going to drive my car around at 22-24psi with head studs at less then spec torque requirements. Anyways, we figure that the head has to be warped. We pulled the head again, sent it out to a machine shop and they say that the head is perfectly fine using their straight edge. A dye test was also done to check for any possible cracks. None were found. The machine shop said that it may be the block, but we're looking for a few other options before dropping the transmission and pulling the block.

Right now the shop owner thinks that something is messed up with the way the head bolts onto the block. It really doesn't make sense how loosening the head studs around #1 would bring the leak-down from 45-50% to within tolerance, but I saw for myself how loosening the bolts a little bit eliminated the leak-down.

Anyone have any sort of advice?

 

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Could be that cylinder 1 is slightly out of round while the head is torqued down. It would explain the problem. The only way to fix that would be to bore .020 over using a torque plate and replace the pistons.

-Paul