half throttle, car goes lean instantly...

[DynamicGN]

So I slowly get on the peddle watching the a/f and knock numbers, everything is fine as boost starts rising and a/f numbers are in the mid 800's, but instead of it leaning out to high 700's and staying there as I step on it more, a/f drops suddenly to 710 then over 10 points knock, this is right after half throttle. If I don't let off fast enough the car goes "pop pop"... What can make fuel pressure drop so suddenly? Am I out of injector? I have adjusted the regulator to add more fuel, but the same thing happens...No malfunction codes and scanmaster readings are normal at idle.

 

[LOST.w/o.HRP]

This is a guess, but could it be something simple like a dirty or clogged fuel filter? Good luck.

 

[turbofabricator]

What does your fuel pressure gauge say when it starts acting up? If you do not have one, you really need one. But it sounds like a fuel delivery issue to me.

 

[grocerygetter]

my car did the same thing right after I got it and installed the 340. The rubber line on the top of the 340 split...so it would build enogh fuel psi for idle and light driving but then lean out real bad at 50% + throttle.

 

[onefastcar]

Same issue here runs great but leans out when i get on it part throttle, changed fuel filter guess i need to drop the tank and look at it also checked my fuel lines they look good and regulator is good and had the injectors flowed and checked good approx. 3 mos ago, so i'm in the same boat.

 

[Jerryl]

Same issue here runs great but leans out when i get on it part throttle, changed fuel filter guess i need to drop the tank and look at it also checked my fuel lines they look good and regulator is good and had the injectors flowed and checked good approx. 3 mos ago, so i'm in the same boat.

What boost is this at and is the alky turned up enough?

Edit:
What about MAF dropout, TPS condition?
Did this just start all of a sudden, or after some change and/or upgrade?

 

[DynamicGN]

The alky is turned up all the way, brand new pump...it starts doing this around the same time the alky kicks in at 12 psi, maybe a lil sooner...after it spools, the boost flys up so I am not too sure...I know I need a FP guage so we can get a better picture, I'll order one ASAP. Fuel filter is less than a eyar old and I barely drive the car, but I will check everything as much as I can. TPS at idle is at .42 volts...Not sure what you mean by MAF drop out... I have been chasing this problem for a while, I used to be that my wastegate was stuck so I couldnt get more than 10 pounds, then I changed it and got RJC's adjustable one as well. After that, car seems like it wants to fly, but I just cant get on it due to this.

 

[DynamicGN]

also, the car sat for a good 4-5 months with 3/4 tank gas...I never drained it, I just ran it out. Could the injectors be clogged due to possibly bad gas? Should I put some additive in the tank?

 

[Top Speed]

Checking A/F with the stock "narrow band" sensor is futile at best. Get a wideband and really see what is going on. What boost are you running?

 

[DynamicGN]

22 psi with the alcohol, but I never even get to half of that before it starts knocking. The funny thing is I can step on it slowly, watching the numbers, and then out of nowhere at around half throttle right when the boost really wants to rise, it goes lean.

 

[84BuickGNYorkPA]

If you end up dropping your tank, be sure to check out your wiring inside the tank, I found that a ground wire came off my pump

Chuck

 

[Blazer406]

So I slowly get on the peddle watching the a/f and knock numbers, everything is fine as boost starts rising and a/f numbers are in the mid 800's, but instead of it leaning out to high 700's and staying there as I step on it more, a/f drops suddenly to 710 then over 10 points knock, this is right after half throttle. If I don't let off fast enough the car goes "pop pop"... What can make fuel pressure drop so suddenly? Am I out of injector? I have adjusted the regulator to add more fuel, but the same thing happens...No malfunction codes and scanmaster readings are normal at idle.

If you set your boost where no alky is needed and turn alky kit off all together..... does it still pop like that at part throttle?

 

[DynamicGN]

Alright, I lowered boost to 15 pounds, a/f numbers stay a little too rich at around 830 at half throttle, i dont know if the boost reaches 15 psi yet, but it starts popping and knocking 13 points...So basically I have no idea whats going on here, I thought it was leaning out and that was causing the knock, but I guess it's something else...any ideas...Also, I put a new alternator and wiring on last week... but before that the car just sat for awhile.

 

[TurboBob]

what chip? What are your translator settings?

 

[DynamicGN]

dont know, Cal custom burned it for the 50's and alky....lol it was tuned perfectly when I got it back from him a couple years ago ...anyway, the translator settings are at 5 and 5...10% lean at idle...10% rich at WOT

 

[wordy1]

This sounds exactly the same as whats happening to my 1985 Monte Carlo with a 4.3L TBI, could I also have an injector problem? No codes at all either. It "feels" like an accelerator pump, but obviously it cannot be .

The mixture comes back when I floor it, but it leans out at mid-throttle and I have to flutter the pedal to keep it running. Fuel pressure is good, good spark, checked timing, TPS, EGR, etc. I even replaced the computer with a known good unit, same problem.

It runs fine at highway speeds and at WOT, idles fine too.. It is a little hard to start sometimes (ironically when its warmer out), but idles fine once its started. Just falls flat on its face at mid-throttle and wants to die, this cannot be good for things, and could be causing other problems.

Is there any scan tool software that will work with my OBD cable for my laptop to give me better readings? All it came with is WINALDL and it doesn't do much except read for error codes and "general" things, but it does give reasonably accurate O2 readings, enough to know that the car is leaning out considerably at mid-throttle. Something similiar to Direct Scan would help nail whats wrong.. but cannot find anything.

Otherwise, how do I check the injectors on this car? They are VERY expensive and I'd rather not buy them unless I knew for sure that this is the problem.

Also, once I get the car running good again, (Lord willing I will), is there a company or chip-burner amoung us that can burn me a chip for me? No one seems to know where I can have it upgraded at, not even the guys at the S-10 forums with the same computer.

I know this post is not totally related, but the symptoms are, and I thought I'd ask, Thanks guys...

 

[Ron Coleman]

i had this problem andchased for months!

i would check the fuel pump sock....mine was dirty and collapsed:

good luck

 

[TurboBuRick]

Alright, I lowered boost to 15 pounds, a/f numbers stay a little too rich at around 830 at half throttle, i dont know if the boost reaches 15 psi yet, but it starts popping and knocking 13 points...So basically I have no idea whats going on here, I thought it was leaning out and that was causing the knock, but I guess it's something else...any ideas...Also, I put a new alternator and wiring on last week... but before that the car just sat for awhile.

These typs of problems can drive you crazy. Do you have a analog vac/boost gauge? Does the needle start bouncing during the condition?

 

[TurboBuRick]

This sounds exactly the same as whats happening to my 1985 Monte Carlo with a 4.3L TBI, could I also have an injector problem? No codes at all either. It "feels" like an accelerator pump, but obviously it cannot be .

Sound like something has a dead spot tps/maf?

 

[onefastcar]

What boost is this at and is the alky turned up enough?

Edit:
What about MAF dropout, TPS condition?
Did this just start all of a sudden, or after some change and/or upgrade?

This was after complete rebuild on engine (rebuild due to blown HG due to ttops leaking on ecm connector causing corrosion on injector pins leaning car out) Haven't really looked at MAF readings, TPS is set as per gnttype but haven't revisited this possibility of a dead spot on it i will and happens at approx. 10 psi of boost. Talked to John Spina about my connectors and he says that when the corrosion is done on connectors that you just need to replace and understand his thoughts its just my soldering skills stink and with the amount of wire its gonna be a PIA to do anyhow if i even had great soldering skills but want to drop the tank this weekend and investigate that possibility.