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Old 10-09-2006, 06:17 PM   #1
CG77VETTE
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Default Bad Fuel Pump Symptoms?

I haven't had a chance to check the FP but I started experiencing something wierd over the weekend on my '86 L98. I have been trying to resolve a stalling issue and by process of elimination per the FSM, narrowed my problem down to a bad IAC. I replaced it and all was well, so I thought. On Saturday, I filled up the tank and the stalling started all over again. No codes set, just stalls when decellerating from highway speed. All of my other diagnostic work was begun when the tank was 3/4 full and by the time I was done troubleshooting, I only had about 1/4 tank. Can the fuel level in the tank cause a faulty fuel pump to act differently at different levels? It doesn't seem probable but hey, you never know. Thanks for any help or light you can shed on this topic.
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Old 10-09-2006, 06:22 PM   #2
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It shouldn't, as it is submersed at the bottom of the tank. Can you hear it running, and when was the last time you changed your fuel filter? You will need to put a pressure gage on it, and check it. Also, the lines are usually long enough on the gauges that you could tape it to the windshield, and go for a ride to see if there are any fluctuations.
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Old 10-09-2006, 08:30 PM   #3
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Quote:
Originally Posted by CG77VETTE
I haven't had a chance to check the FP but I started experiencing something wierd over the weekend on my '86 L98. I have been trying to resolve a stalling issue and by process of elimination per the FSM, narrowed my problem down to a bad IAC. I replaced it and all was well, so I thought. On Saturday, I filled up the tank and the stalling started all over again. No codes set, just stalls when decellerating from highway speed. All of my other diagnostic work was begun when the tank was 3/4 full and by the time I was done troubleshooting, I only had about 1/4 tank. Can the fuel level in the tank cause a faulty fuel pump to act differently at different levels? It doesn't seem probable but hey, you never know. Thanks for any help or light you can shed on this topic.
..i had some related problems with my 88 and found that the fuel guage was screwed up and thusly, i fixed it...however, if you are positive your fuel level is way up there then, it could be a multitude of problems.

...i eventually traced my stalling/dying problem to 1 of 4 things after the car dying out on me on the interstate and in parking lots, etc... .i replaced the coil, the electronic spark controll module near the heater box at fender, the ignition module and the pick up coil in the distributor....

...i wish i could narrow it down better for you but, i replaced the coil first and still had the problem...then, it was the electronic spark controll module, and then it was the ignition module and pick up coil at the same time.

.. i know this is a bit of a ramble but, it was between the last two and the problem quit. i will assume that your pump is good as well as pressure..........
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Old 10-09-2006, 08:47 PM   #4
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Fuel level can make a difference to a failing pump. More fuel in the tank keeps the pump cooler. When the pump started failing in my vette it would stumble and hesitate after a hard corner with any less than 1/2 a tank. A little later it would actually die while driving and not restart until after the pump cooled down (4-6 minutes on average). As the tank got lower, the pump shut off more often. Barely got it home that time. I'd check the pressure while driving if you can. I hooked a gauge into the line that my friend held from the passenger window and I made some hard acceleration passes in second and third. Pressure shouldn't drop more than .5 psi or so.
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Old 10-09-2006, 08:52 PM   #5
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Quote:
Originally Posted by JLeatherman
Fuel level can make a difference to a failing pump. More fuel in the tank keeps the pump cooler. When the pump started failing in my vette it would stumble and hesitate after a hard corner with any less than 1/2 a tank. A little later it would actually die while driving and not restart until after the pump cooled down (4-6 minutes on average). As the tank got lower, the pump shut off more often. Barely got it home that time. I'd check the pressure while driving if you can. I hooked a gauge into the line that my friend held from the passenger window and I made some hard acceleration passes in second and third. Pressure shouldn't drop more than .5 psi or so.
....i think he said that he had plenty of fuel and it was still stalling....when my pump started going bad, it was actually intermittant.....when i took it out it to bench check it, barely ran at all..that too could be his problem and i missed addressing it when i read his post...
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Old 10-09-2006, 08:55 PM   #6
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Thanks for all the help guys, I'll check FP at idle and while driving and post results.
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Old 10-09-2006, 09:29 PM   #7
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when my fuel pump went out the car wouldnt start at all... dead on the road. i had to get it home with a tow truck 100 $'s later, i changed the fuel pump, which thankfully was very easy. nice thing about corvette c-4's, you dont need to drop the tank to change the pump!! hesitation is also a symptom of a failing pump, when and if you change it the fuel pump it's also a good thing to change the fuel filter , so that you will be off to a fresh start!
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Old 10-10-2006, 07:09 AM   #8
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Usually, fuel pump start showing failure when the demad is high. But sometimes not the case. Besides using a fuel pressure guage attached the windshiled trick, you can run a hot wire from the positive side battery to terminal G of the ALDL. This should run the pump until the wire is removed. This is just a test and you should be able to hear the pump. Also check the connector above the tank for shrunk insolation and check the connection and check the voltage at the connector. If the pump is good, anything resitricting flow can cause the stalling among other things. Clogged strainer, sock, lines or line connection, fuel filter, or faulty FPR.
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Old 10-10-2006, 07:36 AM   #9
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Quote:
Originally Posted by CG77VETTE
I haven't had a chance to check the FP but I started experiencing something wierd over the weekend on my '86 L98. I have been trying to resolve a stalling issue and by process of elimination per the FSM, narrowed my problem down to a bad IAC. I replaced it and all was well, so I thought. On Saturday, I filled up the tank and the stalling started all over again. No codes set, just stalls when decellerating from highway speed. All of my other diagnostic work was begun when the tank was 3/4 full and by the time I was done troubleshooting, I only had about 1/4 tank. Can the fuel level in the tank cause a faulty fuel pump to act differently at different levels? It doesn't seem probable but hey, you never know. Thanks for any help or light you can shed on this topic.
Don't forget to check all your injectors too. It's easy and it doesn't take long at all.
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Old 10-10-2006, 07:36 PM   #10
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Quote:
Originally Posted by RRT vette
Usually, fuel pump start showing failure when the demad is high. But sometimes not the case. Besides using a fuel pressure guage attached the windshiled trick, you can run a hot wire from the positive side battery to terminal G of the ALDL. This should run the pump until the wire is removed. This is just a test and you should be able to hear the pump. Also check the connector above the tank for shrunk insolation and check the connection and check the voltage at the connector. If the pump is good, anything resitricting flow can cause the stalling among other things. Clogged strainer, sock, lines or line connection, fuel filter, or faulty FPR.
......been there!.....
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Old 10-14-2006, 07:54 PM   #11
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Here's a follow up to my stalling problem. I checked FP today and got 37 psi with key on and stayed at 38 psi with engine running. I replaced the fuel filter in case something is lodged in it causing the stalling and took her out for a spin. Ran strong for about 10 minutes then when coasting to a stop from a heavy acceleration, the engine died. I mean no juice at all dead. No lights at all, no chimes, nothing. It was like I took out the battery.

I jiggled the battery cables and checked for a loose connection but the cables were tight. Also, a month ago I replaced both the terminal bolts so they are clean and tight. There was one smaller wire coming off the positive cable that has what looks like a fused connector that was abnormally bent so I straightened it out. I'm not sure if jiggling the cables or straightening the smaller wire did it, but I had juice again and was able to start the engine and get her home. It was like I disconnected the battery, all the radio stations were reset and the a/c was on auto etc. etc.

Could this be the root of my stalling problem all along. This is also the first time I lost total power and was unable to start the engine. With all the previous stalls, I was able to start the engine right up. What do you guys think could be causing this problem? I'm thinking a bad ground or the cables themselves might be bad. Heck, they've been in the car for over 20 years. Thanks for any suggestions or advice you may have regarding this problem and enjoy the rest of your weekend.
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Old 10-14-2006, 09:00 PM   #12
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Quote:
Originally Posted by CG77VETTE
Here's a follow up to my stalling problem. I checked FP today and got 37 psi with key on and stayed at 38 psi with engine running. I replaced the fuel filter in case something is lodged in it causing the stalling and took her out for a spin. Ran strong for about 10 minutes then when coasting to a stop from a heavy acceleration, the engine died. I mean no juice at all dead. No lights at all, no chimes, nothing. It was like I took out the battery.

I jiggled the battery cables and checked for a loose connection but the cables were tight. Also, a month ago I replaced both the terminal bolts so they are clean and tight. There was one smaller wire coming off the positive cable that has what looks like a fused connector that was abnormally bent so I straightened it out. I'm not sure if jiggling the cables or straightening the smaller wire did it, but I had juice again and was able to start the engine and get her home. It was like I disconnected the battery, all the radio stations were reset and the a/c was on auto etc. etc.

Could this be the root of my stalling problem all along. This is also the first time I lost total power and was unable to start the engine. With all the previous stalls, I was able to start the engine right up. What do you guys think could be causing this problem? I'm thinking a bad ground or the cables themselves might be bad. Heck, they've been in the car for over 20 years. Thanks for any suggestions or advice you may have regarding this problem and enjoy the rest of your weekend.
.........now we seem to be getting somewhere!........i am not sure if the cables themselves are bad and if they are "bright and shiny" at the battery, probably not......i would now be checking the fusible links to see if they are blown or in someway have a broken wire under the insulation......i do not have a helms in front of me at this time but, i believe that a fusible link may be in line to the fuse box and if that is defective in some way (as above) it will shut you down......now before the critics get hold of that statement, i/we are aware the the link is a fuse and when it blows, it blows. i am suggesting a bad frayed or broken connection under the insulation...is there not a "junction block" of sorts right behind your battery?...is so, start snooping around there!...

Last edited by Da Mail Man; 10-15-2006 at 01:32 PM.
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Old 10-15-2006, 12:33 PM   #13
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Problem Solved First of all, I'd like to say Thank You to all the Forum members who assisted me in solving this problem. Here's what it was. I left my door open so the lights would stay on so I could see if anything happened as I jiggled various wires. There is a junction block right behind the battery (Da Mail Man comes through again) with six or seven red wires bolted to it. When I initially inspected this junction, it seemed tight and rather clean. I jiggled one of the wires attached to the junction block and the lights went out. Out came the battery to give me better access to the junction and I proceeded to remove and inspect each of the wires.

There was a significant amount of gunk between the connectors. I cleaned each connector with solvent and then hit both sides of each connector with my Dremel sanding wheel. I also cleaned up the junction block and reattached all the wires nice and tight and sprayed dielectric grease over the entire connection. Took her out for a nice test drive and all is well. No stalling at all of any kind I guess this will now be on my list of regular maintenance items. Thanks again to all and have a Great Weekend!
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Old 10-15-2006, 01:32 PM   #14
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....COOOOLLL!.....spike that football!... .end zone dance!.... ..glad ya made out!

**ps, get that grease off of there now!..there is a better way to do this..pm me!

Last edited by Da Mail Man; 10-15-2006 at 01:44 PM.
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Old 10-15-2006, 01:32 PM
 
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