Well, I got a weird one for you guys. I am helping a buddy tune his LS motor. It is an LS3 block but we are using the early LS1 style PCM with a 1X cam position sensor and 24X crank trigger wheel. We are using Tuner Cat OBD II software for tuning and HP Tuners to data log. The car uses the original LS1 knock sensors.

The car starts and runs like a champ everywhere but WOT. As soon as you get to WOT the advance drops right to zero. This does NOT appear to be due to knock retard. We have turned off knock retard everywhere we can find it and HP Tuners does NOT report knock retard. It does show the timing going to zero and that's exactly how the car acts, like it has no timing. Goes flat as hell and stops pulling (we are testing on a chassis dyno with load applied to the rollers).

Any ideas?

Richard

 

Is it losing the signal from the crank sensor?

 

I don't know. How can I tell? Would it account for the weird timing?
Rich

 

That's what I think, too. It may be a slew rate problem or other bad signal.

 

It runs exactly the same with the cam sensor disconnected.

Rich

 

You mean it has "0" timing with the cam sensor disconnected?

 

No, the timing is fine (and it runs fine) until you hit ~35% TPS, then timing drops to zero and the motor goes flat as a pancake. Occurs regardless of gear, whether you creep up on it or slap the throttle, under light or heavy load. Exactly the same with or w/o the cam sensor. AFAIK, the only thing the cam sensor does is allow injector pulses to run sequentially. Without it, the first cyl to fire becomes #1. Cam position shouldn't affect the timing and does not apppear to. The motor is clearly firing on the correct cylinder, which is consistent with my understanding that the PCM is firing according to the crank position.

The TPS readings look fine, ~16% with the throttle closed and 100% with it wide open and smoothly increasing as you open it.

Rich

 

search through all the pids, the hp tuners scan tool does have knock retard


post up your tune,, tc obd2 or .hpt

 

Sounds like you need to run the crank relearn.

Chris

 

crank re-learn on these is only for misfire detection, it has no effect on how the engine runs