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Gumby
06-10-2013, 04:13 PM
So recently my roommate bought a 99.5 lazer red a4 with a ko4 running a pc-16 file, but it had bent valves.

I helped him swap heads with a good awm head I had off my car. I transferred his cams, and cam chain tensioner over from his aeb head, and dropped it on his 058 block. Compression came back 120 130 150 150 after the swap.

Now after priming the engine it tries to start, but won't actually fire. It isn't throwing any codes, but the tach isn't reading anything when cranking the engine. I replaced the crank position sensor thinking that may be the issue, but it still won't register on the cluster. I checked through vag-com and it's showing 240rpm when cranking. All four cylinders have spark, and fuel. I've kind of ran out of ideas, what else should I check?

Seerlah
06-10-2013, 04:18 PM
That 120psi cylinder is way too low. Going to go out on a limb here and say you probably contacted valves on the replacement head. It could be the piston rings, but that head is going to have to come back off most likely. And when it does, get it pressure tested.

Gumby
06-10-2013, 04:21 PM
That 120psi cylinder is way too low. Going to go out on a limb here and say you probably contacted valves on the replacement head.

Wouldn't valve contact result in zero compression? I didn't lap the valves or anything because I didn't have a valve spring compressor. The new head had about 130k on it.

Seerlah
06-10-2013, 04:44 PM
I would think so too. But regardless, that 120psi is too low. The wear limit is 108.75psi and 10psi above that is basically calling that cylinder a goner. I say find a pick and pull, get an AEB head for like $50, have a machine shop pressure test/clean it, then throw it in after a deck. Costly thing to do, but might be what you need to do. This is what I would do.

When I bent valves, I picked up a used head from nynoah, had to swap over cams, CCT, and other parts, had the machine shop pressure test it, had it decked, slapped it in, and that was that.

hanzy
06-10-2013, 04:50 PM
Wouldn't valve contact result in zero compression? I didn't lap the valves or anything because I didn't have a valve spring compressor. The new head had about 130k on it.


Not always. Sometimes you get a slightly bent valve(s) that are still sealing somewhat, but are still leaking down.

Seerlah I don't think that those numbers are low enough to cause a no start condition.

I just had a B5 AEB Passat in the shop with(approx) 90, 175, 150, 175 that started and ran fine. A bit of an extended crank on a cold start, but that's it.

Do you have injector pulse?

If you have spark, fuel, and injector pulse you should start.

How was the comp check done?

*Seerlah is right that the numbers are low and are going to be a problem, I just don't feel that they are low enough to cause a no start condition.

walky_talky20
06-10-2013, 05:09 PM
Check CTS reading in VCDS, make sure it's showing ambient. Might be flooded - clear the cylinders and install fresh copper plugs.

Cluster won't normally react during cranking, as far as I have ever seen. RPM in VCDS and presence of spark means your crank sensor is good.

Gumby
06-10-2013, 05:29 PM
The cts is brand new. The car had a cracked rear coolant flange when he got it so I replace everything when I was in there. I verified thought vag-com that I do have injector pulse. The car has brand new plugs, and tsi coil packs with 034 adapter harnesses.

I just pulled all four coil packs out to check spark again, and it doesn't have spark on cylinder 1. I swapped coils, and adapter harnesses around without any change. I guess it's shorted out somewhere in the engine harness itself.