96 Blue Maro

So 2 days after getting my tranny back from t56 rebuilds i find out that i have a burnt valve. I dont know why i ever bought this piece because the guy before me dogged the hell out of it. Im a college guy, broke, and really dont know what to do. If i get the valve fixed i will worry about it happening again. I am thinking of just saving for a crate ls1... as crazy and as expensive as that sounds. So for those of you that have been here before give me some ideas. Im not too familiar on what to do with internal stuff or good prices or anything else like that. Thanks.

Grimes

iTrader: (3)

If all that's wrong is the burnt valve, and you don't want to keep the stock head, why not just get either another stock head, or get a cheap aftermarket head?

crainholio

iTrader: (2)

Burned valves are typically caused by chronic fuel:air mixture problems, which are rare in a closed-loop computer managed fueling system like the LS1. It's unlikely this would happen without the SES light being on for quite a while.

So...how do you know for sure it's a burned valve? Leakdown test and stethoscope is about the only way I know of to diagnose compression loss to the source, did you do this or some other diagnostic procedure?

96 Blue Maro

Well the car doesnt have cats and i dont think it has ever been tuned for it either so im sure that messes up the air/fuel ratio. The guy wants to do the compression test along with all the other but he told me he was 95% sure it was a burned valve. Hes pretty good so i figured he most likely got it right. Basically the car is burning alot of gas, it smells very rich out of the exhaust pipes, and its "bumping" like it has bad plugs. You guys got any other ideas. Also have a bad O2 in that same side exhaust manifold if that matters, thanks.

WS6nJAX

iTrader: (207)

the problem may just be the bad 02.

crainholio

iTrader: (2)

If your guy can diagnose a burned valve without even a compression test, I'm in awe of his mad skillz. Go ahead w/ the compression test if he's not charging too much $$, but be prepared for it to be inconclusive.

Then, I'd get someone who knows EFI to hook up a scanner and check out the computer's operation. O2 sensor readings, LTFT variation between banks, stored error codes are my favorites.

I helped a guy w/ a freshly "tuned" LS1 that wouldn't make power and idled super rough/gassy, turned out the shop had cut one of his O2 sensor wires to force it to run open loop. Soon as he repaired it and put the stock firmware back into flash, the thing woke up and started behaving.

96 Blue Maro

He hooked it up to the handheld thing and went through all these steps and went through and did whatever he did on each cylinder. I dont know what readings he looked at but he said the 5 cylinder wasnt right and he figured it would be a burnt valve but he would need to do all of the tests to figure it out. Like i said, its just very rich, burning lots of gas, and it gets to bumping and missing under load. I hope its just an O2 but i wouldnt have a clue. Im kinda wondering if i should take it somewhere else now.

crainholio

iTrader: (2)

Like I said, the compression test is good data to have so if his price is reasonable I'd do it. Make sure he gives you the actual compression reading for each cylinder, not just "OK" or "bad."

When an engine fails the compression test, I do a TDC leakdown test at 100psi on the affected cylinder(s). You can hear the air escaping either into the oil pan (bad rings/piston), or the intake (bad intake valve), or the exhaust manifold (bad exhaust valve). Much more conclusive than a compression test, where you can't tell where compression is being lost. No sense pulling the head on an engine w/ a holed piston or ripped ringland, for example.

Get the compression data for all 8 cyls and report back. Again, I'll be really surprised if he finds a problem but it's a good diagnostic step. If the compression is good (all cyls within 10% is a good baseline) then ask what his next proposed step is and report back.

96 Blue Maro

Ok man thanks. Im not familiar with this stuff so what is a fair price for a compression test? And if all is good with the compression, what would be the usual next step?

crainholio

iTrader: (2)

Figure about 1.5 to 2 hours of labor at whatever his hourly rate is. LS1 plug holes are a bear to get to in the back.

If the compression is good, it's time to get busy w/ the laptop or whatever scanner (not a code reader, an actual diagnostic scanner) and find out how the engine's burning.

Verify it's going into closed loop at operating temp, check for major variation in LTFTs between the two banks, verify you're getting at least 85% adaptive spark scalar, check for stored codes.

If it's really snotty w/ fuel at the exhaust, one of these will usually tell the story.

I've had my LS1 develop a persistent misfire and an error code related to injector bank voltage (P201?) that turned out to be a damaged spark plug wire...the ign coils on each bank are fed voltage by the same circuit that feeds the injectors on that bank, so the electrical transient showed up on the OBD-2 injector monitoring side. Lots of head-scratching involved on that one, I only found the bad plug wire because I was removing them to read the spark plugs.

06TDI

iTrader: (45)

Well, you seem to possibly have multiple issues. You really need to see what the car is telling you. Obviously you have the SES light on for the no cats/no tune condition. You really need to atleast have the rear sensors turned off or install Sims. You really need to see what codes your car is throwing. I doubt aswell that it is a burnt valve. Get the codes read and post up what they are. At this point, it's all guessing about to many things it could be.