Error in my tune-$100 to find it for someone

[LS1_Dragster]

Why would the temps be a factor then? I guess its coincedental....

[5.7ute]

Why would the temps be a factor then? I guess its coincedental....

I have noticed with higher octane pump fuels here a tendency for the pump to cavitate with temperature. My 044 pump screams like a kid at the candy store once ambients get up to around 30deg C.
I do not believe this to be the issue here though.

[LS1_Dragster]

I do not believe this to be the issue here though.

I dont think so either, I would assume the AFR would be out the roof, Gotta be spark...... Even though we dont see the spark being changed by the computer.

[LS1_Dragster]

Any chance it's mechanical such as valve float? Broken spring(s)?

[jetblast]

i know you said the cam sensor was changed, but that is the circuit i would be checking to make sure the pcm is getting a clean signal, that would include the connector pins at the sensor and pcm and any other connectors in between . i would get a scope in the hole and do a visual ck. of the teeth. the sprocket on the ck shaft is or should be spot welded on or else it can brake loose or so i heard. i would also try another pcm. it sure seems as though the pcm is not able to fire the plugs on time and thats why you are backfiring. did you actually change the engine protection timing to 22 or even 18 to see if it fallows? that certainly would not mean much except that the pcm is comanding eng. protection mode for perhaps the lack of a good timing signal.

[LS1_Dragster]

jetblast - he actually uploaded my custom OS and tune so to me that eliminated any issues with the tune.

I believe he's changed out the computer too.

If it was a sensor or loose teeth etc. then why does it run good up to a certain RPM? And why does temp play a part?

I cant wait for the answer, this would of driven me nuts if it was mine!

Lee

[67SS509]

Too late, it has driven me nuts...going to check in at Vallyview Nut House tomorrow.

I have checked the reluctor wheel (reluctor wheel is spot welded) and cam gear with a Snapon boroscope. Sensor gaps are on factory specs. Spaced them till they throwed a code so they must be working right.

Made some changes on the fuel system yesterday. Aeromotive is satisfied now that the fuel is not a problem but it is still doing the same thing.

I have went back to old school reasoning. If someone brought an old big block Chevelle to me with the same symtoms I would would be looking at the ignition system. I'm going to make something so I can check it with a timing light and then an osciliscope. I feel what's happening is occuring in the cylinder.....peak at the wrong time or weak...just have no idea what can be causing it.

[LS1_Dragster]

On my LS1 I just put the #1 to TDC and marked a line on the balancer. Not very accurate but it does let me check it.

BTW, can you rev it to 6000 while stationary? I myself hate doing that but maybe if you mark your balancer and just rev it to 6K maybe you'll be able to see if the timing freaks out. This is why I suggested a dyno, it can be done safely and under load.

[jetblast]

i really think he should log a wot run from 3.5krpm to 6krpm, with ect temps at 130,160, and the highest temp that his thermostat is rated at respectively. also, i would like to see mph along with the rest of the inj. data. and finally i would change the b5913 to different timing values to see if the pcm actually follows and comands as the rpm rises from column to column. well if he excluded the pcm, then the connectors for that circuit have to be ckd., he said th idc continues to climb and so a clear indication that the pcm is not cutting out the injectors. really seems to me that the timing signal is breaking up, it's possible that ect temps are a factor, but won't know for sure until he logs clear identical rpm excursions under different temps. as you know materials expand as temperature encreases, so that's one potential but highly unlikely cause, also as temperature rises electrical circuits are not as efficient. maybe if he swaps the harness with a known good one to exclude that as the culprit.

[LS1_Dragster]

jetblast - I agree on making a cold run, I mentioned this several pages back but I'm not sure what it will really tell us now.

Also, his timing has changed, it's now using my timing!!! It was originally locked at 24 and now it's 27 at WOT and 35 at idle.

No MPH, he's running a glide.

I cant figure out what would cause the timing to not follow the commanded timing, but a timing light and a few zings to 6K should tell us if the timing is the culprit.

I would also look at the following:

1) valve springs
2) crossed wiring to the injectors
3) low voltage to the coil packs - there are 2 12v feeds, these same feeds run the injectors, I would make sure the wire and fuse feeding them are the correct sizes. A volt meter with memory should let you know. Just hook up the volt meter and do a run and see what the voltage does. I guess you could even run a wire to the cab and have a passenger watch the volt meter, but this has to be wired directly into the coil pack 12v feed. Hell for that matter you could run a temporary 12v line and tie directly into the coil packs and also do the same with a ground, just splice it right in, this would take care of any ground or power issues!

Just throwing wild ideas out....