LS2 Engine won't rev up
Thread Starter
Teching In
Joined: May 2011
Posts: 5
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From: South Florida
LS2 Engine won't rev up I am looking for help on a puzzling problem. We installed an LS2 from a 2005 GTO which came with factory harness & ECU. Since this car is a dedicated race car, we had Howell In Michigan do a custom wiring harness and reprogramed the stock ECU. The engine was rebuilt by Total Engine concepts in West Palm Beach & ran on the Dyno with the computer & harness. Once the engine was installed, it started & ran great cold.
When we took the car to the track it ran well for 3 laps and then lost power. We let the engine cool, checked fuel pressure was ok. and a local tuner checked for codes, etc. We took the car out again same thing. Lost power when warm.
Took the car to a local tuner who put the car on a Dyno, troubleshoot wiring, coils, etc. Replace fuel injectors with larger ones, etc.
Took the car to the track. Same thing. Soon as engine warms up it wont rev over 3000 RPM.
Back to the shop. Took the car to a different tuner. He checked & reprogramed ECU. We re-routed the fuel lines to keep cool, replaced the MAF, TPS, Crank, Coolant , O2 sensors, wrapped the headers, replaced coils, changed spark plugs, etc. We again checked fuel pressure, checked & replaced fuel pumps in fuel cell, replaced fuel pressure regulator. Checked fuel cell vent. Changed ignition wires. Still the same thing. The engine starts right up, idles normally, and seems ok when cold.
I guess next to to send the ECU out to be checked or swap one?
When we took the car to the track it ran well for 3 laps and then lost power. We let the engine cool, checked fuel pressure was ok. and a local tuner checked for codes, etc. We took the car out again same thing. Lost power when warm.
Took the car to a local tuner who put the car on a Dyno, troubleshoot wiring, coils, etc. Replace fuel injectors with larger ones, etc.
Took the car to the track. Same thing. Soon as engine warms up it wont rev over 3000 RPM.
Back to the shop. Took the car to a different tuner. He checked & reprogramed ECU. We re-routed the fuel lines to keep cool, replaced the MAF, TPS, Crank, Coolant , O2 sensors, wrapped the headers, replaced coils, changed spark plugs, etc. We again checked fuel pressure, checked & replaced fuel pumps in fuel cell, replaced fuel pressure regulator. Checked fuel cell vent. Changed ignition wires. Still the same thing. The engine starts right up, idles normally, and seems ok when cold.
I guess next to to send the ECU out to be checked or swap one?
Why are you throwing parts at it without any real diagnosis of a faulty part or system? You need someone who knows how to diagnose with a scanner. It's not rocket science, its air, fuel and spark. Do you have any data logs of it acting up? You might describe the car the power train is in and what kind of laps.
Thread Starter
Teching In
Joined: May 2011
Posts: 5
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From: South Florida
Scanners & Parts I have taken the car to two shops, Both had scanners. The parts were changed either at those shops or upon their failure, in desperation by me.
Obviously it is not quite as simple as you make it sound, because we have all those elements.
It appears the cars ECU which is in a tube frame race car with fuel cell, 4 speed Tex racing trans, etc, is pulling back the timing as it thinks the engine is in trouble. What we can't figure out is why. I have replaced & added grounds, triple checked all the connections, charged & replaced the battery. So I guess the ECU swap is next?
Obviously it is not quite as simple as you make it sound, because we have all those elements.
It appears the cars ECU which is in a tube frame race car with fuel cell, 4 speed Tex racing trans, etc, is pulling back the timing as it thinks the engine is in trouble. What we can't figure out is why. I have replaced & added grounds, triple checked all the connections, charged & replaced the battery. So I guess the ECU swap is next?
TECH Fanatic
Joined: Aug 2005
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Do you run a solid roller cam in this?
You should datalog the engine as this happens. May be the engine is picking up a false knock and timing is dropping. Just a guess. I remember at one time solid rollers would do this time to time.
Just my opinion, i wouldnt throw and ecm at it yet. You need to datalog whats going on when the engine gets warmed up. Probably not the answer you want, but, its where you should look first.
The engine is pulling timing for a reason, for all you know there could be a parameter that is set wrong. Or, hopefully not, there may be a knock when the engine is warm and thats why its pulling timing. Is the knock sensor code shut off? What program is being used for tuning?
You should datalog the engine as this happens. May be the engine is picking up a false knock and timing is dropping. Just a guess. I remember at one time solid rollers would do this time to time.
Just my opinion, i wouldnt throw and ecm at it yet. You need to datalog whats going on when the engine gets warmed up. Probably not the answer you want, but, its where you should look first.
The engine is pulling timing for a reason, for all you know there could be a parameter that is set wrong. Or, hopefully not, there may be a knock when the engine is warm and thats why its pulling timing. Is the knock sensor code shut off? What program is being used for tuning?
Obviously the shops with the scanners you went to don't know how to diagnose with one. With what you've spent on parts that didn't fix it you could have bought HP Tuners and have the ability to show people that do know how to diagnose with one data logs of the problem and the tune file in the PCM. And yes it really is that simple.
Thread Starter
Teching In
Joined: May 2011
Posts: 5
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From: South Florida
Hp Tuner was used at both shops. I am sure you are correct about the data logging though I am not familiar with data logging and do not wish to purchase the equipment. I hope someone can recommend a shop in Florida that has the diagnostic capabilities.
In today's EFI world, whether with OEM controllers or aftermarket, racing and data logging go hand in hand. I don't see how anyone can seriously engage in competitive racing (which it sounds like you are doing) without the ability to tune and data log a race car. Is the shop tuner going to go to the race track with you every time you race?
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My $.02 Suggest you f/u on the data logging suggestion. [Hire one of the tuners to go with you??]
Sounds like this is either a off road car, or a modified stock racer. Beating and banging can/will set off the knok sensors.
[Won't help w/ the life span on a MAF, either.]
Sounds like this is either a off road car, or a modified stock racer. Beating and banging can/will set off the knok sensors.
[Won't help w/ the life span on a MAF, either.]
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On The Tree
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From: Braking Point, Turn In, Apex, Exit - Repeat
Did they get any codes back when they scanned the PCM? If so which ones?
I have seen track cars go into limp mode for multiple reasons. If they replaced all of those sensors is it possible that the 5V reference is corrupted either by a short to ground or short to power?
I had to track one of those down - not fun - but an easy way to do it is to disconnect all of the individual sensors one by one, then back probe the individual wires at the ECM one by one. I checked for continuity between the wiring and the ground first and got lucky. We had a wire that was shorting to ground and corrupting the 5V reference. May be possible there is something funky going on in the wiring harness.
The second thing I've seen are issues with the car going into limp mode due to the throttle by wire - they needed to tune in a larger variance between the two throttle position sensor values.
Just some things I've seen in the past with track cars.
I have seen track cars go into limp mode for multiple reasons. If they replaced all of those sensors is it possible that the 5V reference is corrupted either by a short to ground or short to power?
I had to track one of those down - not fun - but an easy way to do it is to disconnect all of the individual sensors one by one, then back probe the individual wires at the ECM one by one. I checked for continuity between the wiring and the ground first and got lucky. We had a wire that was shorting to ground and corrupting the 5V reference. May be possible there is something funky going on in the wiring harness.
The second thing I've seen are issues with the car going into limp mode due to the throttle by wire - they needed to tune in a larger variance between the two throttle position sensor values.
Just some things I've seen in the past with track cars.
TECH Senior Member
Joined: Apr 2002
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From: So.Cal.
You will need to find someone with an oscilloscope to capture waveforms of ignition secondary (various cylinder #), injector trigger circuit (various cylinder #), CKP and CMP sensors, when the problem happens (running on the dyno).
Thread Starter
Teching In
Joined: May 2011
Posts: 5
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From: South Florida
All good ideas. I spoke with Jeremy Formato in Tampa area. He suggested we swap out the ECU and then bring the car to his shop for him to diagnose & re- tune. If not in the old ECU, the problem is probably voltage or grounds somewhere. I did re-ground the car and added a ground as well. I will keep you posted on what he finds.
Thanks, Dell
Thanks, Dell