upon driving i have to barely ease into the gas... if i give too much throttle there will be a loud "POP" or ping from the engine along with its almost violent hesitation. something is obviously wrong here...

what causes this hesitation then detonation? is it a lack of fuel or too much fuel? or is it a spark issue?

could the computer have a play in this as well, what if the thermostat is changed from stock?

i think i should check the fuel pressure and timing. which should be done first? the fuel pressure, or timing?

i just need a basic idea of where i should start looking... this is a horrible problem and i **** my pants everytime it detonates.

Its a GMPP crate vortec 350, 454TB w/55lb inj, 17PSI, and a bit advanced on the timing.

i also have the 68lb cop car injectors with a custom chip as well, and it had the same issue only not nearly as bad. so i tried going back to the old 55lb and previous custom chip, the only thing which has changed is the 454TB instead of the old 350TB. the 55lb injectors flow less... so maybe i should try jacking the fuel pressure way up to compensate?

Any and all advice is welcome thanks for your help!

 

The detonation is probably due to too much timing in certain spots with maybe too little fuel, along with the lack of egr if you dont have it hooked up. The tbi timing tables look like the swiss alps so when you advacne the base timing there will be spikes in certain places that can cause detonation. The hesitation is the ecm pulling timing out for a few seconds since it sees alot of knock counts, especially if you can hear audable detonation. If you havnt already done so hook up winaldl so you can see where the detonation is and where the engine might be lean. You may also be going lean due to too little pump shot. Either way you should address it as soon as possible. Severe detonation can crack piston rings, crater pistons, etc. so its not good for the motor.

 

I'd venture to guess that your engine is doing a lean backfire out the intake. Isn't the GM vortec 350 a 330 HP motor? You need a bit more injector then 55's at 17 psi. That and a 2" 2bbl TBI is going to open a lot of bore with little throttle change.

Put the 68's in and run the fuel pressure at 24 psi. This will be enough fuel for 326 HP at 85% DC with a .5 BSFC. This in itself will increase the acceleration enrich and probably eliminate the lean backfire. If not then change the AE in the bin.

RBob.

 

RBob brings up a good point. Is it a 'Pop' sound like a firecracker would make or is it a metallic ping sound. Detonation can be pretty loud if its severe but it sounds alot different then a backfire through the tbi. To me it sounded like a gun went off when i had a backfire out the tbi while I was working on the engine.

 

That is exactly what is happening! Its a backfire through the TBI.

So its running lean in spots... not rich as i thought.

I'll try bumping the fuel pressure to 24PSI as you said, even though CFMtech who made my chip said 13-14PSI.

I changed the spark plugs for good measure (damn headers were in the way of each one!) the only difference in the plugs was the gap of the spark at the end... i didn't know i should have made the gap match the old plugs.. (its almost twice the gap) it still runs better than it did, but i should probably pull them out again and gap em' right.

I haven't the tools to do programming myself yet, so i'm going about this through fuel pressure and timing adjustments.

I've had many backfires like this... my stupid *** had to keep driving to work/school because i had no choice. hopefully my engine with only 20k isn't already damaged.

 

Ack, this isn't any good. You really need to get the equipment to do PROMs yourself. Once you bump up the fuel pressure you will need to adjust the BPC and re-align the VE table.

Otherwise the engine will be too rich all over. When I responded to your post I figured that you were having a minor problem and needed a bump.

If the general VE table is OK then leave the FP alone until you can burn PROMs. Too rich all over and it'll wash the oil off the bores and wear the motor quickly.

RBob.

 

It won't work.
You can't cure software problems like this, with hardware bandaiding, CORRECTLY. You can get kinda, sorta, results at best.

The point at which your engine makes best VE is going to be a different rpm then the stocker, the only way to shift the tables around to account for that is with shifting the tables around, and that takes tuning the prom.

At this stage it's just a matter of how much damage you do before getting things right. You can't do any good running an engine that far out of tune.

 

I still have 2 tries to get the programming right through CFMtech.

If i can save myself the cost of buying the equipment, it would be nice.

Yet, I need the cable/software to obtain the information needed to see whats going on? I doubt they'll be able to get it right within 2 tries... (seeing as you need your own equipment to burn/reburn many times)

Please referr me to a good post about the equipment i need...
Place to buy cable at decent price, software to download, etc.

Sorry to waste your time with silly noobie questions, but at this point nobody will get this engine running right except for me. As someone put it, the mechanics say "i wouldn't touch that thing with a 10 foot pole"... hehe

I sure do appreciate the help, and i'll surely need more of it when it comes down to the programming. Just wish i could turn back time and have known what i was getting into before the motor swap. GM parts dude: "oh yeah, that motor will drop in there fine with no problem." i think they owe me a new motor!

 

https://www.thirdgen.org/newdesign/tech/promintro.shtml

RBob.