Possible fuel delivery problem

JasonMiller94SC

Registered User
I think my girlfrinds 94 SC is having a fuel delivery problem. Sometimes when you start the car it runs very rough and even stalls out. If you give it a little gas for about 30 seconds and then let off it runs fine. This does not happen every time you start the car and it doesn't seem to matter if the car is already warmed up or not. When this happens you can smell gas inside the car for a few seconds.
It also has a problem when driving and you floor it it just seems to stop pulling past 4000 rpms and takes forever to get to 5000 and shift. If you back off of the pedal slightly it seems to pickup.
Last time she had it at the track I swaped in a new set of plugs and pulled one out after a couple of runs and it did not look brown at all but the groud tip had a slight rainbow color to it. Too lean right?

I'm wondering if maybe the fuel pressure regulator is going bad or if it's the pump? The car does have over 150k on it so I'm sure a new pump wouldn't hurt.

So far I've tried swapping MAFs to see if that was the problem and got no change. The car will hold fuel pressure over night and I changed the fuel filter just to make sure that was no plugged up.

If I get a new pump what should I put in it? Would the 190lph be enough? She's already told me that she dosen't want to make a "monster" like I have and she drives the car everyday. I don't think the car is gonna receive too many more mods that it already has.
Full exhaust with hi flow cats
CAI
75mm TB
10% overdrive
Shift kit
Jerry W tune
 
Doesn't sound like a fuel pump issue...sounds more like dirty MAF or bad o2 sensors. If cleaning the MAF doesn't help, I'd try disconnecting the negative battery cable for about 10 minutes to clear adaptive, then see if it starts and runs better.

David
 
I've had 3 differnet MAF's on the car. Cleaned the stock one, pulled the battery off. Didn't help.
Borrowed another stock maf. Same deal.
Borrowed an aftermarket MAF that was programed for a 94/95 SC and the car seemed to run a little better at first but its doing the same thing again.

Car isn't throwing any codes. Is there a way to test the O2's?
 
Yes, you can test the O2's by hooking up a voltmeter to the signal wire and ground. (You need to use either an an analog or a digital voltmeter - I forget which, but I think it's analog so you can see the needle swing.) Then you induce momentary rich and lean conditions on each bank and check that the sensor responds quickly and correctly. (Rich = 0.9 volts, lean = 0.1 volts. Or if I got that backwards, then oops - but the sensor won't read backwards, so you will be able to deduce which is which anyway.) You can induce those conditions by using propane or something to make it rich and pulling off a vacuum hose to make it lean.
 
Yes, you can test the O2's by hooking up a voltmeter to the signal wire and ground. (You need to use either an an analog or a digital voltmeter - I forget which, but I think it's analog so you can see the needle swing.) Then you induce momentary rich and lean conditions on each bank and check that the sensor responds quickly and correctly. (Rich = 0.9 volts, lean = 0.1 volts. Or if I got that backwards, then oops - but the sensor won't read backwards, so you will be able to deduce which is which anyway.) You can induce those conditions by using propane or something to make it rich and pulling off a vacuum hose to make it lean.

You don't need to do the propane thing etc. When you start the car the O2 sensor should show almost 1 volt because the car will be rich. Let the car warm up for a bit and once it goes closed loop, you should see the voltage start swinging back and forth from 0.1 to 0.9 quite rapidly.

If all is well that is.

Frit
 
Maybe I'll just put in a new set of O2s. I dont' know if they have ever been changed and the car has 150k+miles on it.

So no one thinks this is a fuel problem?

I noticed today when we drove it that it started fine when the car was cold but a couple of time when we started it after it was already warmed it is would idle very rough and almost stall.
 
I'm pretty sure that is a fuel problem, just not sure that it is a fuel pump problem. Incorrect AFR is the primary cause of idle problems like you are describing. Solving them is somewhat more difficult. It would help to see fuel trims and spark timing during periods of rough idle.

As for the high rpm stuff that is almost entirely a result of the 10% pulley. The EEC is likely pulling so much timing that the motor will barely run at those rpms. With a 10% pulley on a 94 peak power will occur around 4000-4200rpm due to high ACT and knock retard.
 
The 10% may have made things worst I suppose but the car had the same problem with the stoock pully on it.

Not sure if it helps much or not but there is also a 8" fan behind the intercooler.

I suppose I could test out the knock retard the next time we go to the track by puting some 104 race gas in it and see what happens.

Thanks everyone for the input. Hearing all of this is great! :)
 
The 10% may have made things worst I suppose but the car had the same problem with the stoock pully on it.

Not sure if it helps much or not but there is also a 8" fan behind the intercooler.

I suppose I could test out the knock retard the next time we go to the track by puting some 104 race gas in it and see what happens.

Thanks everyone for the input. Hearing all of this is great! :)

I doubt that the two symptoms are related (idle and 4000+rpm power) but before going too far down that road there are two ailments that are common on the 94's and should be looked at before chasing too many gremlins. 1) balancer. It is worth your time to remove the retaining bolt and see if the balancer is broken. Many 94's break their balancers but continue to run (albeit poorly). 2) Catalytic converters. If the balancer is shot it is common for the car to suffer ignition retard which in turn causes the converters to overheat and melt down. The resulting restriction causes all sorts of other problems. I suggest eliminating those possibilities.

With a stock IC and 10% pulley (on a 94/5 SC) you can pretty much be assured that you are experiencing full knock retard (-10 deg) and with a stock IC over 4000rpm you can expect at least another 4 if not 6 or 8 deg ACT retard. Taken from a base ign timing of 18 deg that means you could be trying to make power with 0-6 deg advance at 4000+ rpm. That just doesn't work. You need to find a way to balance things so that you see at least 16deg net to make power. If lots of ice and some race fuel fix that problem then you know. ;)
 
This sounds ALOT like what my car is doing.. Alot of times when you do get it running it stalls and dies when you go to back it up. Always get the fuel smell etc... The fuel pressure is good and does go up with boost BUT you hit 4000rpm or so and it misses or cuts out eraticly... somtimes it does somtimes it doesent..
 
The cats on her car are about 3 weeks old.
We had a full exhaust put on the car from the manifold back with hi flow cats and it seemed to run slightly better after that was done for a bit.

I can try putting the stock blower pully back on and see what happens.

I have taken all of the belts off of the car are tried to move the crank pully and I see no wobble. I had been thinking about replacing the ballancer just because it has 150k on it. I suppose a new ballancer and O2 senosor's couldn't hurt it any.

Not sure if would help any but I replaced the stock plugs with some autolite 103s and gaped them to about .045 to see if that would help any. No change.
 
Since you have a 94 like mine, try swapping the EEC relay with the one next to it. The EEC makes the ground for the fuel pump relay located in the IRCM.

Ed
 
I have taken all of the belts off of the car are tried to move the crank pully and I see no wobble. I had been thinking about replacing the ballancer just because it has 150k on it.

You have to take the retaining bolt off as well. Many times the balancer will simply fall off in 2 pieces when you remove the bolt.
 
Hi,

the owner of the car here :)

This problem with the top end has been going on pretty much since I have owned the car.

As jason has previously posted:

Removed Air Silencer
75mm Throttle body
K&N 9" Cone Filter
MAF Programmed for 94SC
3" Intake tube
Full Exhaust Hi-flo Cats, no mufflers, straight pipes
Jerry Tune w/ 300hp Jmod, Trac-loc w/373s
Raised Blower top
10% Overdrive Pulley
8" Intercooler Fan (Stock Intercooler)
Pusher Fan Modded for continuous run option

Now there are TWO distinct problems with this car:
ONE: INTERMITENTLY the worst word in the technical dictionary it will on starting stumble and stall. With numerous tries it will catch and start, and you will smell gas. Now originally when I FIRST noticed this problem a year or so ago I was sitting on a hill in a driveway with less then 1/4 tank of gas, the low fuel and check gauges was on, I passed it off as, well get gas stupid. Then it did it again sometime later in a flat parking lot with 1/4 tank. It has been gradually getting worse on different levels of gas in the car. It will do it with a completely full tank of gas fresh from the pump. I have noticed but am not 100% sure that it seems to do it more on the 2nd and on starts for the day, that the intial start-up for that day seems to be more likely to be ok.

With this issue we have:
Seafoamed ...actually NOTHING came out the tailpipes of this car????
Ran BGK44 thru it ... no change with the problem
Changed the fuel filter...no change
Numerous Troubleshooting items below as well such as plugs/wires, cleaning MAF, cone filter, etc.

Now TWO:
Over the past year and a half with this problem which started as a miss and losing power at the top end at the track we have tried:

The ETs for the car all in all suck it started at 16.0 and have come down to 15.2 thru all of the bolt ons and with this problem continuing.

New plugs and wires..no change to the problem
Intercooler fan..no change
Modified the main pusher fan with a switch to run it continuously at the track
Replaced the cam sensor (threw a code at one point)...fixed the code
Replaced the blower belt...no change
Put the stock pulley back on...no change same with all three pulleys
Pulled the chip..no change
New 75mm throttle body...no change
Cleaned the stock MAF...no change
Cleaned the K&N...no change
Changed the stock MAF for another Stock MAF...no change
Added a New MAF programmed for a 94SC...it seemed to run perfect at the track one day.....then we added a new intake tube to fit it and aggrivated the problem.
Returned the stock MAF, Intake tube, K&N Cone.....problem remained, not as intense.
Changed the Plugs (103s) and wires, returned the new MAF and intake tube...tested it at the track...the car ran EXACTLY the same with both setups.
Pulled the plugs and the ground was rainbow looking and not brown.

After trying it with both MAF/Intake tube setups we left it with the new MAF/Intake setup. The car runs the same as before. You would never know it has a problem unless you punch it and it hits 4200rpms then it flatlines until it crawls to 5000rpms and slams you into the backseat.

We have a set of o2 sensors in the backseat we plan to put in it next. Though to me the symptoms aren't there. My LX acted alot differently when its o2's went. I actually got codes from it (Air to Fuel and bank 2 running lean) and it ran irractically ALL the time.

EDIT:
Here is a pic of the o2 Sensors that came out of the car: The one thats burned off is from the drivers's side. Although both problems we have been having with the car remain, the gas mileage has gone up :cool:

Picked up the balancer today......

DSC03718a.jpg



Thank you everyone for listening and ALL of your imput :cool:

>>k<<
 
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After changing the o2 sensors, you should probably dissconnect the battery for about 10 minutes to clear adaptive. Then drive it for a while and report back.

David
 
The battery was disconnected before we started taking the sensors out and reconnected after they were put in. I'd say the battery was disconnected for at least 30 min if not an hour.

The car is still running the same except the gas milage went up a bit. :D

I'm wondering if maybe the ballancer needs replaced. That would affect the timming if the ballencer was starting to wobble at high rpms wouldn't it?
 
Very possible, put the front up on jack stands and watch the pulley, balancer, etc from below...unsafe but it works with a timing light.
 
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