Ready to give up!!! PLEASE HELP!!!!
Ready to give up!!! PLEASE HELP!!!! Ok so heres my dilemna. I am having a problem that seems to be common yet noone has fixed it or gotten a response on how to fix it. I start my car up, cold it runs fine, crisp throttle response, shifts and all. FP reads 43 at idle with vac on. Now when it goes into closed loop (when O2s start to read) is when my problem starts. If i step on the gas it sputters trying to kickdown and has a hesitation. I checked FP with the car idling and when it does the sputter the pressure drops. It also drops when you rev it up. It has a brand new fuel pump on it. My injectors seem fine no leaks. Coil and ICM are perfect (tested). Anyone able to diagnose this and give me some pointers?
A little info on the car. 94 formula has impy head gaskets, 503 cam, 1.6rrs, mid lengths, hooker catback, intake (cone filter on end of stock bellow), NGK tr55 plugs, new wires.
Now one thing I have been thinking is the KM. it still has the stock tune and stock KM. if I upgrade to the LT4 KM will it maybe help this? I am also thinking opti. But I am not getting an SES light at all for the opti. Would it be beneficial just to start with a new cap and rotor?
Please help guys. I have missed every chance to take it to the track because of this. An i didn't put time and money in to get nowhere with it.
A little info on the car. 94 formula has impy head gaskets, 503 cam, 1.6rrs, mid lengths, hooker catback, intake (cone filter on end of stock bellow), NGK tr55 plugs, new wires.
Now one thing I have been thinking is the KM. it still has the stock tune and stock KM. if I upgrade to the LT4 KM will it maybe help this? I am also thinking opti. But I am not getting an SES light at all for the opti. Would it be beneficial just to start with a new cap and rotor?
Please help guys. I have missed every chance to take it to the track because of this. An i didn't put time and money in to get nowhere with it.
O2's. Have you checked them? What's their condition? Old, new, crazy readings? Fuel pressure. What's the deal on your pressure regulator? Old, new, stock, what? Where are you checking pressure? At the rail? Is there any way you can check pressure before the regulator? How is the new pump wired up? Is the voltage dropping during the pressure drops?
haven't checked the voltage. The FPR is the stock one. I am checking the FP at the schrader valve. O2s are good. I unplugged them to keep it in open loop and it does the same thing.
Alrighty then. I might turn my attention to the FPR as I don't really know a good way to check fuel pressure before the reg on stock lines anyway. Also voltage on the pump. May be a wiring problem or if voltage is good, might be a bad pump outta the box. Racetronix kits have provisions for keeping voltage up on the pump.
Originally Posted by dhdenney
Is the voltage dropping during the pressure drops?
LT4 KM and a tune for all mods done would really help.
Is it running rich at all?
You have long tubes?? Your O2's are further away than the stock location so they are not getting the same temp as they would have before. Get your tuner to correct the temp settings.
Trending Topics
Originally Posted by sleeperMULLET
good question, I was thinking the same thing. really the only thing to make fuel pressure drop at idle is a bad pump or a voltage problem, whether it be high resistance or battery/alternator problem.
LT4 KM and a tune for all mods done would really help.
Is it running rich at all?
LT4 KM and a tune for all mods done would really help.
Is it running rich at all?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote
10 Reasons the LS7 Is GM's Most Extreme Naturally Aspirated V8 Engine Ever
Verdad Gallardo there was no wiring to do when I installed the pump. It was an OEM replacement pump. It isn't dropping at idle it is dropping when revved.
The headers are mids not long tubes.
It seems to be running kind of lean IMO. I am going to have it tuned this weekend and install the LT4 KM before so.
The headers are mids not long tubes.
It seems to be running kind of lean IMO. I am going to have it tuned this weekend and install the LT4 KM before so.
I would check the fuel pressure regulator. that and I had a similar problem with my lt1. it turned out to be the little flex tube inside the fuel tank connecting the pump to the outside of the tank. which was weird. it had some type of crack or hole in it... just a thought
One thing, if your opti fails it won't necessarily trip your SES light. I had a opti fail, no SES light, even if you gave it some gas and it obviously wasn't running right. My car was running strong, and then it sputtered a little, then it got worse over the next minute. I limped it back to where I was parking it. Idle would be just barely off, but then when you gave it gas it would sputter and go up in the rpms very unsmoothly, then usually a fireball of unburnt fuel.
Replaced the opti and it started and ran just fine.
This isn't the typical blame it on the opti thing, I just gotta put it out there for people that my car ran just fine and the next minute ran like garbage, no SES light even though it was a opti failure. If you don't know if the opti has ever been changed take a look at it. Def. don't waste your time with just a cap and rotor, you get down that far might as well replace the whole thing. I did this, just cap and rotor, 6 months later I pulled it all back apart to replace my original stock opti that failed after 130k or so. Probably would have crapped out sooner than 6 months, but I went to Japan and lent a friend the car, he barely drove it. As soon as I got back and started running it the way a LT1 should it couldn't hack my abuse I guess.
Replaced the opti and it started and ran just fine.
This isn't the typical blame it on the opti thing, I just gotta put it out there for people that my car ran just fine and the next minute ran like garbage, no SES light even though it was a opti failure. If you don't know if the opti has ever been changed take a look at it. Def. don't waste your time with just a cap and rotor, you get down that far might as well replace the whole thing. I did this, just cap and rotor, 6 months later I pulled it all back apart to replace my original stock opti that failed after 130k or so. Probably would have crapped out sooner than 6 months, but I went to Japan and lent a friend the car, he barely drove it. As soon as I got back and started running it the way a LT1 should it couldn't hack my abuse I guess.
I have seen those line crack and sucked air into the fuel lines. Wouldnt hurt to double check. If you are going to keep the car, make you a trap door so you can get to the tank without pulling it. Not sure if you have done so already