lt1 beast

i have a new 383, it starts for a few seconds then dies. Im thinking it may not have enough fuel pressure. it has a stock tb until i have more money for a 54 or 58mm tb. It also has 32lb injectors. could it also be the tb is to small?

96capricemgr

No chance it is the TB all that will do is restict topend power.

Has it been retuned for the mods?

lt1 beast

yes i have a pcm tune form PCM For Less for all the mods i have done.

96capricemgr

Do you have another car you could drop that pcm into to verify it is working right? Even if the other car is completely different setup dropping it in and running for say 15 seconds to confirm the pcm is booting properly would do no harm, or if you have a stock unmolested pcm to drop in your car for the same sort of test. PCMs can lockup when flashed and the car will act like you describe.

Ported MAF is a bad thing not likely to cause this though.

lt1 beast

i dont have another pcm or car with an lt1 motor unfortunitly but i doubt its the pcm, i will try to get another pcm if i cannot solve the problem as it is a probable cause. The PCM came from PCM For Less, ive heard good things from them could it be possible that they gave me a bad tune?

lt1 beast

i forgot to mention that im using the stock fuel pump on with 32lb injectors the stock injectors are 24lb. could it be that i need a stronger fuel pump such as a bbk 255Lph or grantinelli 255Lph

96capricemgr

Again that would be a topend problem not an idle one.

All the 255lph intank pumps are Walbros of some sort with the possible exception of the TRE which is likely a chinese Walbro knockoff. Since all the 255LPH pumps are the same basic manufacturer you pick based on fitment not name(granatelli makes garbage anyway) and Racetropnix has the version that fits the best, recommend the wiring upgrade at the same time. This is not the problem though unless the stocker outright died during the swap which is unlikely.

Try unplugging the MAF once, the pcm and the MAF are the only things I have ever had cause something like this. though the MAF will usually set a code at which point the car will start and ignore it.

Injuneer

Why do you think it may not have enough fuel pressure? Did you measure the fuel pressure, to verify you have 40psi after the pump primes? Does that pressure hold up after the engine starts? Have you scanned it for codes?

lt1 beast

i got a scanner today and im going to check fuel pressure maybe it is just a sensor. ill post later on tonight with the results. thank you to everyone for your help. ill post the fix when its done.

lt1 beast

i found out that my fuel pressure sits at 40 when the key is at the on position and 38-35 when the motor is on. the motor still stalls after 2-3 seconds and dies if i step on the gas. i also found out that the iac sensor only opens up 1-2mm if the key is on the on position. I am getting new tps and iac sensors tommorrow do you think this will solve the problem? i also checked all my grounds

Injuneer

How many IAC counts does the scanner show for the brief period when the engine is idling?

Have you checked the intake elbow to make sure its not torn, or folded under at the bottom of the throttle body? Did you try starting it with the MAF sensor disconnected?

I wouldn't start throwing money at rpelacement parts until you get some sort of idea what the problem is.

lt1 beast

i get the sensors for basically nothing so i think 30 bucks for 3 sensors is worth it

Injuneer

Ok.....

lt1 beast

injuneer that was not meant to be snappy or nasty. i just mean that would help eliminate some possibilities.

6089wally

Does the car seem like its running like it is supposed to during the 3 secs. I had that same problem after a mail tune and found out I didnt get the same pcm back and the anti-theft kept shutting it down. It hadnt been disabled on that pcm. Had to send it back to get that fixed. We figured it out after checking the injectors with a volt meter. They would quit pulsing after a few seconds every time but then would start right back up. Worth a try.