sputtering past 5psi please help!!! long

SCboost

Registered User
my car for a bit would only sputter on a tank with like less than a 1/4 left. and it would do it around a corner under full boost. and i would back out of it. but then it would not do it for a long time. and it has slowly crept up to where it is now. now i can't boost anywhere close to 5psi. turning or not. empty or full gas tank. does this sound like a fuel pump? injectors? plugs? computer (doubt it but maybe), could it be something like the maf? i just have my stock one and a k&N. but no problems with it and i've had it for like 3 months so far. i just got my exhaust done and was worried about running lean. i have 2.25 downtubes, high flow cats, and then 3" to my borla xr-1 and all hte way back. so it flows very well. NO restrictions in it. could i be running lean? i don't hear any detonating. it just like...dies and comes back to life. someone help me. any ideas? ask away if you ahve any ideas and i'll give more info if needed. thanks again guys. you're always a great help.
 
The fact that this was occuring originally with a quarter tank of gas and now occurs most of the time implies the gradual failure of a device which would be affected by the quantity of fuel within the tank, in this case the fuel pump. I believe it starts to make an audible noise when it is going, mainly during crusing and perhaps startup. This, and the fuel filter, are the first things I would check..
 
If your engine can't get RPM's up, or hold vacuum, you won't generate much boost. Are you able to get good speed? If you stand under the hood with the engine running and snap the throttle, do you see the bypass valve snap closed?

If so, and you still have low boost, you'll have to look for a leak somewhere.

This is likely a seperate problem from your issue with fuel.
 
Plugs and wires

Have you ever changed the plugs and wires? If not take a look at the wires if they say 1990 on them they have never been changed. Do not use Bosch Platinums.

Jeff
 
Could be your fuel pump reservoir broke loose from the tank. It's inside the tank and the fuel pump sits down inside of it. It's purpose is to hold gas for the fuel pump on quick acceleration/hard cornering with a low tank. This happened to me on my 95 SC. On quick take offs with a quater tank of gas or so it would just die and come right back to life as soon as the car lost momentum. If I had half a tank or more it wouldn't do it. Took me awhile before I figured it out. Bought a new tank and no more problem. Just a thought. :D
 
i had the EXACT same problem with my bird as well during the winter about a year and a half ago. it was too cold to do anything so i just lived with it and yes it gradually became worst. first of all , not exactly sure what my problem was, but my plug wires were BAD and so was my fuel filter so i did a mild tune up which included the following:
1.replaced fuel filter(nasty brown sludge came out of the old one)
2. replaced plugs and plug wires; put in motocraft plugs and magnacore wires.-> one of my plug wires was cracking and we figured that it was grounding on one of the headers and that's what was causing the car to cut out like that.
3. replaced air filter.
after that my car ran like a million bucks
good luck
josh
 
if i try to gradually boost to 5psi its fine. i can even boost hard to 5psi and its fine. anything above that in any gear it sputters. i used to hear a light noise when i came to a stop light from my fuel pump. i know my car and it didnt' sound right. my friends could never hear it but its not their car so they aren't used to it. ya know. i will put in new plugs and wires soon anyway. but im curious if i should ask for a fuel pump for my birthday. i was hoping for gears but...i think it's not gonig to happen now. but maybe who knows. im not going to put in gears and not fix this first. i have normal vac. car runs perfect aside from boosting aboe 5psi. any way to check my fuel pump. its original i know i should replace it anyhow. if i want to run 38# injectors i should go with a 255lph pump right? thanks again. later. steve.
 
i think asking for a fuel pump is a very good idea. imo i dont think you should worry about adding 38'ers just yet though.
 
alright. update. 1st gear...cant' boost past 1psi. 2nd gear...3 psi. 3rd gear...about 5psi. 4th gear 2psi. and 5th gear...1psi. i checekd for noise in my fuel pump by listening to it with my gas cap off. no noise. its quiet and peaceful in htere. hehe. my car pushes 40psi of fuel pressure at idle. i will change my plugs tomorrow i hope. and wires. but we will see. i also noticed a pretty big supercharger leak. right at hte snout. so that doens't make me to happy either. oh well. any more ideas shoot them at me guys. thanks. steve.
 
Boost is a function of sealing, and vacuum. The bypass valve must close firmly for boost to build. Then the tubes after the SC must all be sealed properly for the boost to build.

Spark plugs don't affect boost building.
 
The problem is described as sputtering at 5psi, it’s not that he can’t get any higher. He is probably lifting the throttle as soon as it starts sputtering. When my plugs and wires were on their way out that is what would happen. I went so far as to floor it and just held it to the floor the engine would barley accelerate. If I downshifted the boost would go up to about 7psi but the engine ran so badly that the rpm’s wouldn’t come up very fast and I would back out of it because I was afraid of damaging it. I had about 5 different mechanics that I know look at it and only one of them told me it was plug or wire problem. I kept saying it runs fine at idle or if I don’t get on it, about this time I found this board and read through about 2 pages when I came across someone with the exact problem. They had done just as I and checked codes asked and I couldn’t believe that plugs and wires would cause this. As I drove the car it progressively got worse. It happened at 0 then at 10in/hg so I decided to change the plugs and wires. It took me 4 hours and $75 for plugs and wires (I just about croaked). But after that it was all good.

Jeff
 
Sorry, his description threw me off.

I'm not sure what sputtering is. I guess he should start with pulling a few plugs and inspecting them. See what they look like and check their gap. Should be able to tell if he is running lean enough to cause the problems he reports.
 
J57ltr said:
The problem is described as sputtering at 5psi, it’s not that he can’t get any higher. He is probably lifting the throttle as soon as it starts sputtering. When my plugs and wires were on their way out that is what would happen. I went so far as to floor it and just held it to the floor the engine would barley accelerate. If I downshifted the boost would go up to about 7psi but the engine ran so badly that the rpm’s wouldn’t come up very fast and I would back out of it because I was afraid of damaging it. I had about 5 different mechanics that I know look at it and only one of them told me it was plug or wire problem. I kept saying it runs fine at idle or if I don’t get on it, about this time I found this board and read through about 2 pages when I came across someone with the exact problem. They had done just as I and checked codes asked and I couldn’t believe that plugs and wires would cause this. As I drove the car it progressively got worse. It happened at 0 then at 10in/hg so I decided to change the plugs and wires. It took me 4 hours and $75 for plugs and wires (I just about croaked). But after that it was all good.

Jeff
hump.gif


minus the mechanics and add more money for plugs+wires that's what i did.
 
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