I have been having problems with dropping fuel pressure the last few weeks. The car will go from running normal (about 60psi fuel pressure, 14's a/f) to ZERO on the fuel pressure gauge and completely lean on A/F gauge, and the car will begin to decelerate. All of a sudden, fuel pressure will return and the car will run fine again... for a while, until this happens again.

The car has had a new fuel filter a few months ago, new fuel pump last week (after the first issues with this started happening), checked the boost-a-pump for the supercharger, and still having this loss or pressure issue.

Here are all codes pulled

P0135 HC
P0155 HC
C1222H
C1233HC
C1283H
C1295H
B2583H
U1064H

Anyone have any ideas??

 

Check this out concerning the first couple of codes and see if the minfuse is OK.
I'll try to look more into the others tommorrow but you might want to run this past Bill Curlee as he is pretty good with C5's.

Carlos

 

Can you temporarily disconnect the boost-a-pump and drive around carefully (without getting into boost) to see if that is the problem?

 

Great idea, actually if you can run a wire from the BAP outlet to a volt meter while driving and have some see the volts and see if they are dropping. The BAP has two connections a two wire that goes to vacumm or boost switch that closes to signal make sure that is working properly or simply bypass that switch closed. The other is the reostat adjustment for the amount of voltage increase, make sure that one is bypassed and both connections as well as the wires into and out of the BAP main to fuel pump are making good contact. I soldered mine in to the #10 fuel pump hotwire.

 

i already bypassed the boost a pump and there was still no power coming from the front of the car to the pump, at all.

the first time it totally quit, i replaced the pump, disconnected the boost a pump, switched the relay, checked the fuse, and still got no power at all. i removed the fuse cover from the fuse center in the passenger floor board to see if there was anything fuel related in there. of course there's not, so i put the cover back on and the car had pressure again.

the car quit again a few days ago. it once again wasn't getting power. i checked all the same stuff and cleaned/checked 3 of the grounds that are known to be issues. still no power. i pulled the cover off the inside fuse panel and she had power again. my guess is there's a loose connection under the dash somewhere and the cover is just letting it regain contact. i haven't had a chance to see what fuel pump related wires/connectors are in there.

also worth noting is that about a month ago, the car started running quite a bit richer than normal. the a/f was bouncing around like crazy during normal driving, and under boost or a heavy load, it would completely go lean. i figured it was the boost a pump, so i checked everything there and it was fine. next thought was o2 sensors. replaced those and it was fine. then the fuel pump quit, so i thought maybe the issues were just pump related. replaced the pump and still have issues. she's gotten pretty moody this spring.

 

alright, round 3. the car died again last night. wouldn't get any pressure at all.

while waiting on a tow truck, a fellow c5 owner and I tried to diagnose it. checked all the fuses and stuff again. tried messing with the fuse panel inside the car again, but it didn't work this time. tried bypassing the fuel pump relay with no luck. put the relay back in and jumped the wires for the hobbs switch for the boost a pump. it started getting pressure again.

called off the tow truck and sent my wife on her way. she got a few miles down the road and it died again. you could turn the key, it would get pressure, start it, still have pressure, start driving and it would just die. you could keep doing this, but obviously not getting very far.

i noticed the hazards weren't flashing normal. the 3rd brake light was flashing in opposite sequence of the brake lights. the headlights also wouldn't go down. i get to thinking the alternator is shot, not giving enough juice for the ECM and BCM to function properly and it was the cause.

pulled the battery, charged it, put it back in the car, started right up, but died shortly after again. while running, it would get 13-13.5V on the voltmeter. i decided to limp it home since we were so close. i put on the hazards and the fuel pressure was fluctuating with the hazards, but it got me home. if i turned the hazards off, the pressure would completely go away.

i do some diagnosing in the garage. i can bypass the fuel pressure relay and get 12.4V at the connector on the fuel hat (but the fuel pump isn't supplying fuel). with the relay in, it gets 0V. with it bypassed and the hazards on, it bounces between 0 and 12V (and you can hear the pump pushing fuel every time it alternates). with the relay in, it bounces between 0 and negative 12 volts.

 

Call me pm sent

 

Eric, hopefully Bill C. will help you get squared away. In the meantime here is some food for thought, make sure your grounds are all good and don't always assume a wire does not have an internal break inside. In my low mileage Z06 I found the ground battery wire last year had some resistance. I only found this by disconnecting both ends of the ground then testing the ends because redundant grounds can lie sometimes. Also had an issue with the battery and replaced it with an Optima because I had heard of C5's having gremlins due to less then ideal battery condition. The battery would charge up and start the car but was found to be bad through a load test.
I did have a bad wiper switch stalk but that was probably left over problem from a previous accident. The car also had issues with turn signals not working right all the time but after the ground and battery replacement the problems seem to go away.
I don't know enough about the VATS to be of help, but it sounds like a bad ground, broken connection. I saw in the cars description, its supercharged, does it have a fuel pump hotwire? I know when I installed my FP hotwire kit Racetronix puts in a redudant ground for the fuel pump in the back. The pulsing of the pump with the flashers sounds like it could be trying to find a ground through other sources.
You might also check the boost switch connections but you said you tried bypassing it completely. My Z06 is NA so I just bypassed the vacuum switch and use the reostat for my purposes.
Sorry about the rambling of ideas. I know these problems can be buggers until the issue turns into a simple solution! ........
Please keep us updated on the diagnosis and hopefully quick solution!

Carlos

 

yeah, i'm hoping bill can get us squared away too. the car currently has an optima in it due to a previous bad battery. the fuel pump wiring is stock but it has a kenne bell boost a pump installed. i'm thinking the issue is one of 3 things at this point, bad alternator/charging system issue, bad bcm, or some sort of ground issue.

i've gone through some of the ground, but haven't metered anything to check resistance. i have a friend who may be lending me a bcm to try, but not sure when i'll be able to get it from him. i'm just at a loss with the weird randomness that's been happening.

 

You better be talking about the car!!!

 

Heres the schematic that you need to solve this issue:



You have THREE MAJOR things to check!

GROUND G-105

Ground G-401

The 12 VDC supply voltage for the relay from the IGNITION SWITCH ..HOT IN ON & START

Use a DC Volt meter and read the voltage on fuse #13 Fuel Pump to ground. The ignition key will need to be ON! That fuse voltage should read exactly what battery voltage reads. If its load (fuel pump running),, see what it reads. Shouldn't change!!

The ground G-105 and 401 need to be removed, cleaned and reinstalled! Eliminate them from the equation!

Provide me the results of your test!

Bill

 

well it looks as though the fuel pump issue is fixed. still not sure what's up with the a/f being all over the place, but i'm sure that's not related.

ended up being the ground behind the driver's side rear tire. it was broke and holding on by one strand. it had continuity so that's what threw me off. turns out it just had an insane amount of resistance and it was causing a ton of problem. i cut out the broken section, put a new ground ring on it, and it fired right up. the hazards now function correctly, and it seems to be good to go. i think it was making intermittent contact while driving and made things a pain to diagnose.

i appreciate all the help guys!

 

Excellent, glad you got it worked out!
If memory serves correctly the Racetronix fuel pump hotwire has a redundant ground for the relay and fuel pump. There are guys that make up their own hot wire with #10 wire and a relay but for the $70.00 for C5 kit IMHO its a worthwhile upgrade to insure all the fuel gets to the engine. The installation is easy, setting up the BAP in that wheel well and running the hotwire through the rocker panel was quick and easy!

Carlos

 

Im glad you got the car running again. Good info in here that I'm giong to try since mine is now doing the same thing. BAP with supercharger. Car started then shut off with no fuel pressure.