Dr Poofist

iTrader: (1)

I've got an LS1 with a problem: Under full throttle it POPS loudly (BRAAAMP--PA-PA-pa) and completely looses power over around 5200rpm. It then continues to pop sporadically until I turn the engine off and pull over. Wait 30 seconds and it starts right back up and runs fine. It sounds like all the racket is coming from the engine bay, I don't hear it out the mufflers much I think.

I'm scared to try to replicate the problem under part throttle just in case it is a lean fuel issue, but I don't hear it detonating.

Motor specs:

Stock bottom end refreshed 400kms ago (new rings and bearings etc)
Stock top end with unknown mileage (seller said 80,000kms)
LS6 intake
Harness, cam and ecu from Painless. They no longer offer this kit and are no help. The ecu has a tune done by a third party for them for the included cam. They cannot provide info as to rev limit, fuel curve, cam profile, etc...


Any ideas? Valve float? broken valve spring? bad tune running way rich? What should I eliminate first?


Thanks,
Dylan

LT1559

iTrader: (5)

I just posted a similar problem like 30 min ago lol

99wssixm6

iTrader: (3)

I had this once and it was water in my o2 sensor connector causing my short term fuel trims to lean way way out.

Dr Poofist

iTrader: (1)

Doubt that's the issue the car hasn't seen rain.

383 lt1

lQUOTE=Dr Poofist;17422963]I've got an LS1 with a problem: Under full throttle it POPS loudly (BRAAAMP--PA-PA-pa) and completely looses power over around 5200rpm. It then continues to pop sporadically until I turn the engine off and pull over. Wait 30 seconds and it starts right back up and runs fine. It sounds like all the racket is coming from the engine bay, I don't hear it out the mufflers much I think.

I'm scared to try to replicate the problem under part throttle just in case it is a lean fuel issue, but I don't hear it detonating.

Motor specs:

Stock bottom end refreshed 400kms ago (new rings and bearings etc)
Stock top end with unknown mileage (seller said 80,000kms)
LS6 intake
Harness, cam and ecu from Painless. They no longer offer this kit and are no help. The ecu has a tune done by a third party for them for the included cam. They cannot provide info as to rev limit, fuel curve, cam profile, etc...


Any ideas? Valve float? broken valve spring? bad tune running way rich? What should I eliminate first?

Sounds like your knock sensors are picking up a noise and thinking its detonating and pulling back the timing. I had this same problem onmy lt1 when i swapped to the 1.6 rockers. Ran strong up until 5000 rpm and started to break up really bad.
The lt4 knock sensors fixed that deal. Thanks,
Dylan[/QUOTE]

ryridesmotox

Do you have any engine codes lighting up your dash?

I had an issue exactly like this once... Dirty MAF sensor. The way they work is that an electric current runs through a little wire and the airflow over the wire allows your computer to calculate airflow. If is dirty the reading will be screwed up especially in the upper rpm range.

99Bluz28

iTrader: (35)

You need to scan for codes first.

Dr Poofist

iTrader: (1)

My Painless MEFI ECU is throwing a "TPS (out of range)" code. Seems weird.


Would false knock be causing the motor to pull so much timing it pops and stalls?

Dr Poofist

iTrader: (1)

Just repeated this problem under part throttle while at a stop. Slowly reved it up and at about around 5600 it POPPED loudly and quit. Let off the gas and it just died with a backfire when it went past 1000rpms.

Plugs are new, injectors are not. It holds ~50psi fuel pressure.

Dr Poofist

iTrader: (1)

Should have mentioned the MAF is deleted, motor runs off the MAP sensor.

ryridesmotox

Oh ok. I figured since it was tuned most people run a speed density. Also in your posts you mentioned a Throttle Position Sensor code. Like knock sensors a tps will go bad. Its inevitable really, electronics don't like a lot of heat. Just the way it goes...

http://www.rockauto.com/catalog/more...400&cc=1353170

Dr Poofist

iTrader: (1)

Here's something I didn't mention:

The tune was done with the stock intake, I have the LS6 intake. Could that be throwing my ecu for a loop?

I don't think that's the issue as the car backfires alot when this happens which means either (1) too much fuel or no spark is causing fuel to enter the exhaust or (2) valve float is letting fuel enter the exhaust and intake on the compression stroke.

Is my reasoning above correct? I don't want to spend a bunch of money on sensors I might not have to replace.

ryridesmotox

Well when they put the intake on they could have messed up the tps wiring harness. If the computer says the sensor is bad its because its not getting proper feedback from it. That occurs with a messed up wire or a messed up sensor.

Oh also is the LS6 intake done properly? Its a little different than an LS1.

Dr Poofist

iTrader: (1)

It's done properly I did it myself.

Steve83ta

Were the valve springs matched to the cam? It sounds a lot like valve float. The ls1 to the LS6 manifold will NOT cause that issue. If your running speed density that TPS HAS to work properly While running in sped density the computer uses a combination of the map sensor readings and tps to gather load on the engine for fuel control.

Dr Poofist

iTrader: (1)

Valve springs are stock but the issue happens so suddenly across the board I feel float is low on the list of possibilities.

I will check my TPS tonight with my multi-meter.

I've had someone else suggest it could be a bad crank position sensor.

ryridesmotox

I forget the code number but the crank position sensor has a code that will come up. I had it in my last car and can't remember off hand what it was. It would come up when you pull the codes.

Steve83ta

If yoiu have access to a fuel pressure gauge with a long hose, for some reason you might not be getting engough fuel to the engine, cracked plastic line in the tank.. The fuel rail needs to maintain 60 psi all the way up to redline that has to be checked to.. Espicailly if after you shut it off and the fuel system reprims the problem go away.

Dr Poofist

iTrader: (1)

Fuel pressure is above 55psi all the way from idle to the problem. Fuel pump and lines are new.

I've verified the ecu is getting 13.8 volts from the ignition relay.

I've verified the TPS works correctly.

No codes are being thrown now.

If it's not raining tonight I'll swap out the crank sensor, if that doesn't help I'm at a loss. The closest MEFI support for me is a 14hr drive. I might just say **** it and swap the ecu out for a MS unit.

99Bluz28

iTrader: (35)

I know if the Camshaft Position Sensor is bad or bad connection it'll cause similar problems, I'd take a look at it.