Engine break up under boost?!?!?
 

Okay to start, Ive searched and tried the suggested fixes and it still does it.

Here's the issue. Recently the car started sputtering bad under full boost pulls (26-28 psi on a white rabbit). I threw in new plugs gapped at .024 (bpr7es) and it would be fine for 2- 3 pulls then get worse. Tried another set gapped at .020. Same issue. Took the coils and wires off another evo that pulls great. Car pulled great for 3-4 pulls then got progressively worse. I put the old wires and coils back in with new plugs and once again, ran fine for 2 pulls. I grabbed some high gauge wire and make direct grounds from the batter to the head and intake manifold where the firewall ground hooks to. I honestly think I made it worse because it doesnt break up a few times under a full pull, its 100% of the time under boost now.

Logs show AFR's falling quickly to 11.5-6:1 before the issue even starts every time, but has sudden spikes to about 12:1 when it happens so I know its leaning the cylinders out slighty. I check the connections at the injectors and they seem tight.

Coolant temps at 199.4, intake temps at 90. Never really climbs from there. Injectors are FIC 1150's with maybe 3k miles. Car has run great up until about 2 weeks ago.

Edit: Heres some things Ive tried and the problem continues
Compression test: 155-155-160-158
Helicoiled two coil pack holes that were stripped
Tried the coils/wires off another evo that pulls great
Tried the MAF off same evo
Tried the ECU from the same evo
Switched to a non-tephra ROM
New cam angle sensor (different issue but still has been changed)

When the problem first existed was when I switched ROMs. I immedietally switched back and it was okay. Then the car started having the same issue on the first ROM. I switched back to the Tephra v7 and nothing different. Then I would swap plugs with different gaps. Would work fine for a few pulls then back to bad. Now its bad all the time. Everything above I have changed one at a time, test drove and no difference.

Boost leak test.

Those lean spikes you're seeing are likely the misfires. Unburned mixture shows up as a lean pulse. How old are your coils?

Why would it be lean? When you misfire its unburnt air/fuel, the o2 sensor ONLY reads oxygen (hence the name oxygen sensor :updown:) not fuel so it will be reading more oxygen than normal = richer...Someone correct me if I'm wrong

And when mine was misfiring since one plug was at .060 and the rest were .030 the afr's were off the scale rich

I havent done a boost leak test yet but when the car does make normal pulls its holding right where I have it set.

Im assuming those spikes are the misfires as well. Thats why I checked my injector connections. Heard of it happening to someone else. It doesnt go full lean, just a few spikes then back to 11.5:1 all during the same pull. There's never any knock counts.

Ill try a boost leak test in a day or two just to see if there's an issue but Im convinces its an ignition issue or sensor related to the ignition.

I could be way off base here but...

If you have a boost leak going on, the turbo might be able to cope with it for a few pulls, but when it starts to heat up to insane levels I'm sure its efficiency goes down or at least it makes it more difficult for your intercooler to cope. That could be why you're seeing solid performance and then a fall off?

check for vacuum leaks with popped off vacuum lines, if all checks out well, check your fuel injector seals make sure none are cracked. and if those are all ok, check for a boost leak.

it shows as a lean spot because all the air that was in that cylinder during the misfire is still air, rather than exhaust. It's full oxygen content is intact, so it reads lean. The fact that your misfire showed rich was probably due to the ecu overfeuling the other three cylinders to reach stoich. You'll only see the lean spike at higher engine speeds because the exhaust has less time to mix with the other exhaust pulses.

Thanks for the tips. Ill look into those soon. Currently swapping a clutch on another evo so nothing is happening to this particular car for a few days.

what fuel?

have you done a cyl leak down test?

does the engine use water?

It has done it on both pump 93 and e85. Didnt seem to make a difference as far as the breaking up.

Have not done a leak down test. I did a compression test. 155 accross the board so I figured the leakdown wouldnt show any leakage with that good of compression.

The engine does not use any water. Basically when its not under boost it drives great. Just a few weeks ago it would boost great, then the problem as progressed worse. I would say that when I added the extra grounds it was the worst ever. That was also right after another set of fresh plugs gapped at .020. I can't believe a better ground would make it worse though.

Intermittent misfires are a *****. The dealer I just picked my car up from spent a week trying to diagnose a cylinder 4 misfire, and it turns out the ECU was corrupted. They did plugs, wires, coils, cam and crank sensors, etc, and finally swapped the ecu.

I would also recommend a leak down test, just for peace of mind.

Im seriously about to take the ecu out of my other evo and throw it in just to eliminate a possible cause. Rare but ive seen it happen on other cars.

leak downs reveal where a potential leak might be.

for instance, lets say a guide or guides are leaking oil, that oil will help retain compression, but in an engine that was free of oil , the compression would be lower, thus giving you a different answer.

when post dyno'ing race engines prior to going to the track, we would leak down all cylinders & note where & the % of leakdown.

so did this misfire happen after a differnt flash was put into the ecu? trying a different ecu will help eliminate that aspect & is easy to swap / flash.

GL

So I just did a boost leak test. Interesting results. I hear air hissing out of the exhaust with only 5 psi of boost... t/b closed. Looks like my shaft seals are shot. Would that cause a bad break up under full boost or just the inability to hit full boost?

Whats weird is shaft play is very minimal and theres no signs of oil leaking into the exhaust. I just swapped downpipes 2 days ago.