more tbi trouble

[chevyuser74]

here's the issue my truck stumbles/slightly backfires out exhaust at moderate throttle when its cold, giving it or driving easy doesnt bother it. i can also get it to do it when its hot, but not very consistent or often at all. happens when its cold though. used to do it when it was hot too, but replaced the tps sensor and pretty much took care of it when it was hot. what are your guys thoughts? this is all what i know its not
fuel pressure/volume
computer or computer grounds
cap and rotor
plugs
wires
valves are adjusted properly
timing set to 0 with brown wire disconnected.
temp sensor reads good
map sensor reads good
distributor/module in distributor
no vacuum leaks
tps sensor
looked at more crap but cant think of all right now, this has been on the back burner for a couple weeks now.
i developed this problem after going after more power so i rebuilt my engine so i pulled it and replaced pretty much everything and had a custom chip burned and they said all the data seems to be standard for what i did. it only does this for the first five minutes of driving but it is annoying, and it bothers me that i cant figure it out, one thing ive learned custom work/custom problems. any q's just ask. all responses appreciated.

 

[bigblock72]

I'll bet the chip needs to be richened in the transitional (acceleration enrichment) settings. This is common with non-stock combinations especially when aftermarket intake manifolds are used.

Try bumping the base timing up 2-3 degrees and see if that helps. Sometimes a little more timing will cover lean spots.

 

[chevyuser74]

the first chip i got actually dumped too much fuel down, fouled the plugs a bit, second chip seemed to take care of that problem, as far as timing goes, i moved as far 10 degrees forward no difference in my problem(although my gut feeling all along is it has something to do with the timing) is there a way to test the electronic spark control module, besides just replacing it. http://www.autozone.com/autozone/ca...Spark+Control+Module&searchText=spark+control

 

[chevyuser74]

i also feel it cant be the oxy sensor, as when its cold its in open loop no taking that into account, i also sealed up my exhuast leaks, needed to be done anyways.

i also thought it was a fuel issue with the chips but brian says it looks good in that respect and nobody really seams to have a complaint with his work.

 

[chevyuser74]

what really kills me is when i figure it out, i know it will be probably something simple, and i overlooked it cause its my own vehicle. if this was somebody elses i probably could figure it out easy.

 

[bigblock72]

Has it always had this problem since the engine was put back in?

I still think a minor tweak in the acceleration enrichment tables will fix the problem.

 

[chevyuser74]

didnt occur right away but almost, first i broke in the cam, drove it home the next day( bout 8 miles) parked it. next day started doing it. i came to that opinion about the fuel too, mainly because i pretty much eliminated everything else in the system. but i sent him a bunch of data logs, most were when it was acting up. and apparently it looked ok, not that i really can read the logs myself that good.

 

[bigblock72]

I'm sure the main fuel map is fine which is about all the data log is going to show anyway.

Just e-mail Brian and tell him it has a hesitation and ask him if he'll add a little to the acceleration enrichment tables.

The AE tables basicly act like an accelerator pump, there are two different tables. One is based off of the TPS and the other is MAP based.

 

[dyeager535]

Is idle ok?

I notice on my setup, which I haven't properly tuned, since I changed heads, added headers, etc., that when cold, idle isn't rock steady. It won't die and doesn't misfire, but it will hunt for RPM a bit, and might allow me to kill the engine if I don't keep the RPM's up when I put it in gear (manual).

I'm figuring it's all on the "open loop" side, as the fueling requirements have changed over stock. I agree, that's more than likely what your issue is. Have you tried other chips, maybe the stock one, to see if the problem gets better or worse, confirming the problem is tune?

 

[chevyuser74]

idles up and down sometimes, smooth others