TPI fuel pressure
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,841
Likes: 1,754
From: Summerville SC
TPI fuel pressure
Need some ideas. I have a 1986 L98 newly rebuilt and almost stock engine, in a C3. I am having fuel issues. It started with some leaky rebuilt Bosch3 injectors. It would not hold pressure and leaked down right away. I Finally decided to just put a NEW SET in of the Bosch 3 exact fit from FIC and it holds pressure for a long time. Maybe dropping a few psi over 2 or 3 hours. Good. When I hit the ignition, pressure builds up to 38 psi and holds it. But when I start the car ( it is difficult to do probably because of low pressure) the highest I can get the pressure is 30 PSI. I have a stock AC Delco pump ( less than 3 hours on it) going into a 10 micron RobbMc filter gong a the Holley 502-501 adjustable regulator then the new 22lb injectors. Would I be correct in assuming the new pump is bad, internal leak maybe? Any ideas for replacements for an in tank pump? Thx.
Le Mans Master
Joined: Jan 2001
Posts: 6,753
Likes: 1,393
Do you have an adjustable fuel pressure regulator?
This below is supposedly for 85-91 corvettes:
https://www.summitracing.com/parts/j...te?prefilter=1
This below is supposedly for 85-91 corvettes:
https://www.summitracing.com/parts/j...te?prefilter=1
Last edited by carriljc; Aug 2, 2020 at 05:34 PM.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,841
Likes: 1,754
From: Summerville SC
Yes I do. Holley https://www.jegs.com/i/Holley/510/512-501/10002/-1 I know it says for a 5.0 TPI but the pressure goes to 65PSI which is plenty for my needs. I had tried another one, but it was a pain to adjust that little screw. This one has a big dial on top, making it pretty easy to use. But something is not right. And the consensus is look at the regulator first ( I also have this posted on the C4 tech forum). I almost wish it was the pump because that will be easier to change out than the regulator, with removing the upper plenum etc. Thx.
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Le Mans Master
Joined: Jan 2001
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Good move. That is a fantastic adjustment k n o b. I like it.
I find it odd that the fuel pressure regulator cannot raise pressure above 38 psig. I would clean the filters and give it another test. Is your vacuum hose to the FPR in good shape?
I find it odd that the fuel pressure regulator cannot raise pressure above 38 psig. I would clean the filters and give it another test. Is your vacuum hose to the FPR in good shape?
Last edited by carriljc; Aug 3, 2020 at 10:54 AM.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
I have had an L98 on my '72 for some 22 years......and some years ago switched to LT1 induction, with HEI up top in back, because sparks and water don't mix, said mommy nature......but I noticed the engine had some issues, and so finally went for 24 lbs injectors.....a bit better but no go....found the pressure was only 30 some odd maybe 36 if I adjusted it up.....finally put in a longer screw in the regulator cap.....43.5 at idle, and thing runs fine.....L98 engine and cam with 1.6 roller rockers.....
Instructor
Joined: Nov 2019
Posts: 221
Likes: 71
From: Kalispell, MT
If your injectors aren't plugged and your fuel lines are clear, I can only imagine that it is the fuel pump. Did you back blow the lines when you installed the pump? Is the fuel tank clean? 43.5 is the recommended pressure at the regulator if you injectors are sized correctly. I read many discouraging reviews about so called "factory" fuel pumps, including Delco's, because they are all now made off-shore. I choose a Walbro for that reason. Both FIC and South Bay, where I bought my injectors, should be able to give you some additional advice and testing procedures.
Last edited by C3TPI; Aug 4, 2020 at 11:15 AM.
Le Mans Master
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Thread Starter
Safety Car
Joined: Dec 2012
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From: Summerville SC
Actually not very PINCHABLE, steel, braided and nylon. Fuel tank is new but that doesn't mean something didn't get into it. I will pull the filter. It has a reuseable media that can get blown out if needed. But as C3TPI mentioned, I have heard lots of issues with the offshore pumps that want you to think they are made in USA. I am looking at a Quantum 255 pump, made in USA with lifetime warranty. That's after I check everything else out. And Mrvette I agree with the OEM fpr not putting out 43 psi. My understanding was it was only good for 38-40 MAX. ANd I have a call out to FIC for some more thoughts. Will let you know how this turns out. 
Thanks to all.
Thanks to all.
Melting Slicks
Joined: Jun 2016
Posts: 2,979
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From: Woodinville WA
Where did you add the regulator?
(Should be on the OUTLET side of the fuel rails, not before the inlet.)
Should be Pump -> Filter -> in to Rail -> Crossover -> out of rail -> in to Regulator -> Return to tank.
There's lots of Chinese fake Walbro pumps, but I don't know about chinese AC Delco knockoffs...
Adam
(Should be on the OUTLET side of the fuel rails, not before the inlet.)
Should be Pump -> Filter -> in to Rail -> Crossover -> out of rail -> in to Regulator -> Return to tank.
There's lots of Chinese fake Walbro pumps, but I don't know about chinese AC Delco knockoffs...
Adam
Thread Starter
Safety Car
Joined: Dec 2012
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From: Summerville SC
On my TPI there is only one place for the regulator, the housing is built into the rail itself. Fool proof for people like me! And my set up is the same sequence you described. As for the Delco pump,I have seen a lot of NEW stuff not work. I just had the air conditioning guy here at the house 2 weeks ago, compressor wasn't working. They figured things out and I needed a new fan on top of the unit. Great.Old one was 10 years old. Started right up. In an hour it shut off. This went on all day and there were 2 guys looking at everything possible that could cause the compressor to shut off. Finally at 9 o'clock at night the boss came by with another NEW fan. Put it in and it hasn't shut down since. He was going to give his guys a lesson on "just because it's new doesn't mean it's not bad". SO that is the road I am going on with the pump. But I will follow a few of the suggestions I have gotten off these boards before I throw the pump out.