I would like to introduce myself first. My name is Tom Sarno and I am a contributor to the C3 board and came to the C5 board for help. I wanted everyone to know I am not Googler that just found this board, posted a question and plan on disappearing with posting the outcome. I hate when members take the time to trouble shoot and suggest fixes and never find out if it worked. The outcome helps others that search threads for info.

Now the question that is not 100% Corvette related, but I know someone here might be able to help. I am working on a GTA car that is running an LS3 motor controlled by what I was told was a 2000 LS1 computer. The new motor went in a few days ago and fired right up but had a hard time holding an idle. On the track it felt like it had a 3500rpm set on the rev limiter.

The scan tool showed the desired idle was set to 965rpm and the max engine speed to be 7000rpms.

One thought that went through my mind, is there a valet mode this might have gone into? There is no knock sensor which was my second guess. The scanner showed PO336. A new crank sensor and the code went away but still rpms limited to 3500 by what feels like a soft touch rev limiter.

We have EFI live but the lic agreements were used on other cars. Is the a better program for diagnostics/programing that does not cost as much to use?

Any help would be appreciated.

Tom

 

Update...New computer was over nighted and installed. EXACT same symptoms. car will not idle without accelerator manipulation and breaks up at 3500rpms. No codes set. Three crank position sensors were tried and there was no difference.

Is there a 'safe' mode that keeps the computer from not allowing more the 3500rpms due to a sensor going out of limits.

I will keep everyone posted.

 

EFILive is a great scanner, scan the PIDs for spark advance, adaptive spark scalar (ADSPARK), Bank 1 O2 Sensor 1, Bank 2 O2 Sensor 1, and Long Term Fuel Trim for both banks. Take it up to 3500 at part throttle and report back w/ findings.

Also...how was the LS1 PCM tuned for your LS3's needs? At a minimum the fuel injector maps have to be rebuilt for the LS3's injectors, the cylinder displacement needs to be changed, and the VE table is probably wrong. And then there's the MAF table...are you running an LS1 MAF sensor or an LS3 one?

The LS1 PCM uses the MAF up to 4,000RPM but after that it's calculating fuel delivery directly from the VE table...so if that table is miscalibrated the engine will be very unhappy.

 

Crainholio,

Thanks for the response. I am not sure how the tune was set up on the LS1 ECM, that part I am still trying to learn, but it is common in road racing. The reason an LS1 ECM is used is because you can not run an electric throttle body.

It is using a 24 tooth reluctor wheel so my guess it is using all LS1 sensors. There will not be any adaptive aspark scalar info since there is no knock sensor (it was removed through the set up tune)

It seems like it is in 'engine protection mode' if there is such a thing on these ECM;s. Would you know if there is a limp home mode on either the LS! or LS3? I am starting to think these ECM's are a bastardized combination of both computers

I will keep you posted.

Tom

PS, My C3 started to run rough so I cleaned the points with emery paper and it is good as new. I love the simple life!!!

 

The scalar is still there, so scan it and verify it reads 100.

edit: unless the PCM has been loaded w/ a custom OS that doesn't have it.


In order for reduced power mode (limp home) to be active there has to be an error code set...P0300 for example will dump it into reduced power mode after prolonged input.

Scan the PIDs listed previously and post findings.

 

I will list as soon as they are sent to me. The car is over two hours awy from me at the moment.

Would an over heat condition cause Reduced Power Mode and what happens in RPM. If the temp sensor is reading an erroneous high temp condition will it set a code?

Thanks again.
Tom

 

I think it's fixed. The guys that actually have their hands on the car reported as soon as they plugged the car in it was obvious that there was a miss calibration between the tachometer in the car and the actual rpm reported by the laptop via EFI Live. It is possible that the motor was actually hitting the rev limiter at 6800rpms when the tach was showing 3500rpms.

The second problem was that the throttle stop was accidentally relocated only allowing 3/4 accelerator travel which made it feel like the RPM's were not climbing fast enough. This was compounded by the steeper gears that were installed at the same time the motor was.

The ECM was not at fault, and that was why there were no codes. The problem was just a host of stupid problems.

I will post the final out come after we actually get some track time to confirm it is fixed.

Thanks
Tom

 

A matchbook is the best tool to keep in the glove box for points ignitions...in a pinch you can use the striker emery to clean the points, and the cardboard cover to gap them! That got me home a time or two.

 

The LS1 PCM outputs a 4cyl tach signal from the factory, but most of the tuning packages can modify the multiplier to output a V8 tach signal.

 

If you are using a LS1 computer that had a cable throttle and the LS3 has a " drive by wire" you have to change that settng in the ECM in "platforms" Is your TPS working ?

 

Cranholio,

You are correct about the tach needing to be set to four cylinder. It turns out that the LS1 ECU tach out pin #10 on the red connector is showing one bank of four coils. Once we calibrated it for 4 cylinder it read the same as the laptop and limited at 6800RPM's.

The throttle position sensor is the next thing to look at. The car does not have O2 sensors and is set up to just run off the MAP and MAF. Under quick throttle release the engine takes a second or two to find idle. We drilled a hole in the throttle body plate and this helped a little

I will keep you posted.

Thanks
Tom

 

Car is running well thanks for the help the car is 08 in the video http://youtu.be/-mxw03AYGyA