Low Fuel Pressure!
Thread Starter
Heel & Toe
Joined: Dec 2010
Posts: 19
Likes: 0
From: Kingwood TX
Low Fuel Pressure!
I have been trying to diagnose my low fuel pressure issue on my C5 for a couple of weeks now and have not had any luck. The car will only put out about 50 psi at idle and goes down to 38 at WOT. At first I thought it was the pump (it had a stock pump in it), so I replaced the pump with a Walbro 255. Same exact problem with fuel pressure. I also replaced the fuel filter. I noticed that when I removed vacuum from the fuel pressure regulator (98 model), the pressure spike to 57 at idle but still went to 38 at WOT. I replaced the regulator just to be sure that wasn't it. No change. I checked all fuses, relays, etc. and everything shows to have 12v and the pump seems to be grounded good (checked at pump). I pulled the pump just to make sure nothing came loose and everything looked fine. The car is only charging about 13.2 -13.5 when warmed up. When cold it shows around 13.8 - 14.0. I am not 100% sure of how the charging system works on these cars but I have not had a problem with the battery and even had the charging system tested on the car and it checked out fine. I know I am missing something, but I cannot figure out what to do next. Any and all help is appreciated. Thanks!
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
What's the voltage at the pump cover with the car running? That's important to know. I like to run 10ga fused wire from the back of the alternator down the rocker to the back, add a relay, use the gray pump hot wire to trigger the relay and then run the relay output to the pump. This will bring the voltage up quite a bit. The second thing that I like to do is remove one of the 7mm bolts and add a ground from that to the frame after sanding the frame to shiny metal and using a star washer. You might be able to pinch off the return line somewhere and make a quick WOT pass to see if the pressure stays up. If it does, you know your regulator is a POS. That's really the last component remaining that I think could be causing the problem.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Check the actual voltage at the ump with the engine running ---and if you can somehow under a load---
There are 2 products that address voltage losses on the fuel delivery system on a LS which can result in low fuel pressure----
Don't know for sure if 38 #'s at WOT is enough -- I would be more concerned if the engine is in fact leaning down at 38--as you can adjust the PE table to compensate
One is the "Hotwire Kit"
the other is the "Boost a Pump kit "
here are the links::
http://www.kennebell.net/KBWebsite/A...boostapump.htm
http://www.casperselectronics.com/st...x=0&search.y=0
There are 2 products that address voltage losses on the fuel delivery system on a LS which can result in low fuel pressure----
Don't know for sure if 38 #'s at WOT is enough -- I would be more concerned if the engine is in fact leaning down at 38--as you can adjust the PE table to compensate
One is the "Hotwire Kit"
the other is the "Boost a Pump kit "
here are the links::
http://www.kennebell.net/KBWebsite/A...boostapump.htm
http://www.casperselectronics.com/st...x=0&search.y=0
Last edited by tblu92; Dec 13, 2012 at 01:13 PM.
Thread Starter
Heel & Toe
Joined: Dec 2010
Posts: 19
Likes: 0
From: Kingwood TX
I have a hotwire kit I will try. I will first check voltage and put an extra ground at the pump. Thanks for tje help guys. I will check back in tomorrow and let you know what I find.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Your fuel pump power comes from your IGNITION SWITCH. Its the Hot in RUN & START buss.. The electrical contacts inside the ignition switch gets burnt and can not supply the correct voltage and current to the pump. When the DEMAND of the pump increases, without proper power, the pump performance falls off.
Check out this post for the details on what happens and how to fix it;
- C5 ignition Switch repair - http://forums.corvetteforum.com/c5-t...ch-repair.html
Check out this post for the details on what happens and how to fix it;
- C5 ignition Switch repair - http://forums.corvetteforum.com/c5-t...ch-repair.html
Thread Starter
Heel & Toe
Joined: Dec 2010
Posts: 19
Likes: 0
From: Kingwood TX
Bill,
Thanks for the insight. I will pull the igntion switch when I get home from work in the morning and take a look at it. Hopefully this solves the problem so I can get back to enjoying the car again. Its been a headache to say the least. Thanks again!
Thanks for the insight. I will pull the igntion switch when I get home from work in the morning and take a look at it. Hopefully this solves the problem so I can get back to enjoying the car again. Its been a headache to say the least. Thanks again!
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
Your fuel pump power comes from your IGNITION SWITCH. Its the Hot in RUN & START buss.. The electrical contacts inside the ignition switch gets burnt and can not supply the correct voltage and current to the pump. When the DEMAND of the pump increases, without proper power, the pump performance falls off.
While you're investigating this and before you ground the fuel pump hat, measure the voltage between the hat and a clean chassis ground point with the pump engaged. If there's any voltage showing on your meter, that's a voltage drop on the ground circuit and the suggestion on the additional ground will eliminate that voltage drop.
Thread Starter
Heel & Toe
Joined: Dec 2010
Posts: 19
Likes: 0
From: Kingwood TX
I had a few minutes to work on my car today. I put a volt meter on the car and drove it to make sure I did not have a charging system issue. The voltmeter showed 13.8 volts even at WOT.
At least the charging system seems to be working properly. I was curious about the ignition switch and it did not seem like it was that difficult to take out, which it was not. I took the switch out and took it apart, and as Bill showed in his pictures on the other thread, the contacts were burnt inside the ignition switch. I installed a new switch thinking I had found the problem, but that did not alleviate my fuel pressure problem. The fuel pressure still reads around 50 pounds at idle and drops of to around 38 at wide open throttle. I did not have a way to lift my car up and check the grounds at the pump. I will try and get to that this weekend sometime. Thanks again for all of your help. Unfortunately its back to the drawing board for me.
At least the charging system seems to be working properly. I was curious about the ignition switch and it did not seem like it was that difficult to take out, which it was not. I took the switch out and took it apart, and as Bill showed in his pictures on the other thread, the contacts were burnt inside the ignition switch. I installed a new switch thinking I had found the problem, but that did not alleviate my fuel pressure problem. The fuel pressure still reads around 50 pounds at idle and drops of to around 38 at wide open throttle. I did not have a way to lift my car up and check the grounds at the pump. I will try and get to that this weekend sometime. Thanks again for all of your help. Unfortunately its back to the drawing board for me.
Last edited by torch_red_98; Dec 14, 2012 at 05:13 PM.
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Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Before you go pulling your ignition switch, you mentioned that you have a hotwire kit already. And it's installed? If the answer is yes then your voltage comes from the back of the alternator (if it's a Racetronix and installed properly) and no longer from the ignition switch. The factory relay only triggers the relay in the hotwire kit.
While you're investigating this and before you ground the fuel pump hat, measure the voltage between the hat and a clean chassis ground point with the pump engaged. If there's any voltage showing on your meter, that's a voltage drop on the ground circuit and the suggestion on the additional ground will eliminate that voltage drop.
While you're investigating this and before you ground the fuel pump hat, measure the voltage between the hat and a clean chassis ground point with the pump engaged. If there's any voltage showing on your meter, that's a voltage drop on the ground circuit and the suggestion on the additional ground will eliminate that voltage drop.
BLOWNBLUEZ06,,,,,,,,,,,,, Great recommendation on checking the GROUNDS!
BC
Thread Starter
Heel & Toe
Joined: Dec 2010
Posts: 19
Likes: 0
From: Kingwood TX
I checked the ground at the fuel pump hat and did not have any voltage showing on the meter. I checked the voltage at the pump with the engine running and had 13.8 volts (thats with hotwire kit installed) at the pump. Im thinking it may not be an electrical issue if I am not getting any voltage drop at the pump and have a full 13.8 at the electrical connector on the pump. I guess it's possible I have a bad pump, or maybe a fuel injector is stuck open. I would think if the injector is stuck open the car would run poorly correct? Is there any way to check and see if an injector is stuck open?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
You can check a ground using a volt meter BUT,,, you have to use it in series with the circuit. If you put the volt meter in series with pin D wire and Pin D on the pump connector, you should see battery voltage.
Disconnect pin D on the fuel pump and using an OHM Meter, read pin D ( The wire) to a known good bare metal chassis ground. You should have zero ohms or very close to that value.
If you read Terminal D to ground with a volt meter, you should see zero volts,,,, Zero volts,, the ground is good!
If you see voltage, the ground is compromised. The more voltage you see, the worse the ground is. Full Battery voltage and the ground is OPEN/broken.
BC
Disconnect pin D on the fuel pump and using an OHM Meter, read pin D ( The wire) to a known good bare metal chassis ground. You should have zero ohms or very close to that value.
If you read Terminal D to ground with a volt meter, you should see zero volts,,,, Zero volts,, the ground is good!
If you see voltage, the ground is compromised. The more voltage you see, the worse the ground is. Full Battery voltage and the ground is OPEN/broken.
BC
Last edited by Bill Curlee; Dec 15, 2012 at 04:39 PM.