Have you considered that Jerry may be right on the fuel pressure, but you have other problems that are masked by low pressure.

I have no idea about these engines. Please don't take this the wrong way. I'm sure you know what you are doing. But your problem remains. You must have overlooked something.

A sticking fuel injector is the first thing that comes to mind. Perhaps your ECM is bad or the wrong one for this engine. Just trying to give you some ideas.

Good Luck.

I don't think fuel pressure is the answer here. The stalling seems to have ceased. Maybe it just needed to run for sometime to figure its self out. Although I must admit this engine with all the goodys just doen't seem to run as well as the old worn out 3.4. I mean really worn out like 3qts of oil a week wornout. Thanks for the idea's I'll keep looking futher.

The ECM does need to get some miles on it to 'learn' the new engine. And maybe this motor is still tight and will 'loosen' up after 500-1000 miles or so. Your other worn-out 3.4 would have had very loose tolerences and likely pretty low internal friction as a result.

My 3.4 was also doing some of that stalling and it's pretty much settled out after re-adjusting the idle air and TPS voltage. I still need to get my 2-1/2" exhaust put on to get the motor uncorked, it's strangled like crazy past 4500!

Keep us posted on how it's running.........ed

I just stumbled across this post while searching on VSS posts.I saw what Jerry posted about fuel pressure being 16-18 PSI for the 3.4 engine.Wouldn't that be a little high as the stock TBI runs from 9-13 PSI?I am running at 12 PSI constant as I have a pressure guage mounted under the hood , and another in the cab of the truck so I can watch my pressure due to an issue I had before with intermittant stalling , which turned out to be my fuel pump as I used a non EFI pump which couldn't handle the pressure and keep it constant.After swapping out the pump to an EFI pump , I had no more issues and the truck runs great with lots of power , being able to hit 107 MPH on the dyno , and I think it could have gone higher but the trans went into overdrive instead of staying in 3rd for the run.

Is there anyone else running a 3.4 with higher pressures?If so did you just modify the TBI to give a little more pressure or did you add a standalone regulator?I know the pump I have can handle up to 35 PSI constant with no problems , but its the TBI and regulator that cut it down to just under 13 PSI.I'm just curious on this as if the higher PSI would give me a little more performance, it might be worth looking into.The question is would the ECM handle the difference ok or would it complain and start throwing out different codes and problems.

If I'm not mistaken the writeup at the Planet was referring to jacking up the fuel pressure that high if you were using stock 2.8 injectors????

Original post in this thread indicates TBI mods, so I'm assuming either a modified GM 4.3 TBI or a Holley Big-Bore was used, either case you probably wouldn't need to increase fuel pressure much (if any) beyond the normal regulated range since those TBI's are running higher-flow injectors than stock 2.8 items.

I'd expect that if one were to crank in a ton of excess fuel pressure the ECM will be able to limit it to some degree, by chopping injector pulses. But it would run terribly rich in Cold Loop.

Quite an old post to resurrect, wonder if the problem ever sorted itself out, eh??????

HEY DAVE , ED IS RIGHT ON THIS , WE WERE USING THE 2.8 INJECTORS AND HAD TO GO UP TO JUST UNDER 18 PSI TO GET IT TO STRAIGHTEN OUT AND NOT HAVE S TUMBLE, ON TAKE OFF AND IT WOULD HAVE A LEAN SURGE AT LITE THROTTLE CRUISE , THE LARGER INJ WOULD I AM SURE REQUIRE DROPPING THE PRESSURE BACK DOWN..I MUS HAVE HAD THAT REG OFF AND APART A HALF DOZEN TIMES , SHOULD HAVE WENT AHEAD AND BOUGHT THE LARGER INJ , JERRY

Ok , thanks Jerry.I have the 4.3 injectors so I should be good then running at 12 PSI.The only thing I didn't do is bump the timing.I think I am at the stock timing of 10 degrees, not the 13-14 like a lot of people are running.This engine with the way I have it setup is not the easiest to adjust the timing on with the electric fan and shroud in there.