All symptoms suggest plug wires
TPI Fuel pressure
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,802
Likes: 1,714
From: Summerville SC
TPI Fuel pressure
I have a newly rebuilt '86 TPI with Maf. It has been put into a '78 C3 so this set up is all new. Pretty much stock engine with appropriate ECU and matched set Bosch injectors from Fuel Injection Connection 22lb @ 43.5 PSI. I have an In tank new AC Delco fuel pump for '86. Timing was set at 6 degrees with wire disconnected. Computer is not throwing any codes. Engine fires up but runs rough. Also has a backfire at about 2500rpm. I have a new Holley 512-501 adjustable pressure regulator but cannot get the pressure to go higher than 40 with the engine off ( or vacuum disconnected)or 32 with the engine running and vacuum hooked up. The system will hold good pressure for about an hour after it is shut down and then gradually bleeds off. I cannot find anything that could be causing this other than a bad fuel pump. Have read lots about bad NEW parts and wanted to know if anyone has any other ideas before I start throwing parts at this thing. Thanks.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,802
Likes: 1,714
From: Summerville SC
When I was accumulating the engine parts, there was no regulator. I ended up getting a fuel rail with an adjustable regulator on it. When the time came to assemble things I realized that the adjustment bolt in the top of the regulator was really difficult to use while the plenum was on the car. So I came across the holley which has a **** on it, which is easier to adjust while the car is running. And the prices I was finding for an OEM regulator were no cheaper than the holley. I have tried 2 different fuel pressure gauges and get the same numbers, so I am leaning towards the fuel pump.
Intermediate
Joined: Jan 2010
Posts: 47
Likes: 10
From: Dania Beach, Florida
I have a newly rebuilt '86 TPI with Maf. It has been put into a '78 C3 so this set up is all new. Pretty much stock engine with appropriate ECU and matched set Bosch injectors from Fuel Injection Connection 22lb @ 43.5 PSI. I have an In tank new AC Delco fuel pump for '86. Timing was set at 6 degrees with wire disconnected. Computer is not throwing any codes. Engine fires up but runs rough. Also has a backfire at about 2500rpm. I have a new Holley 512-501 adjustable pressure regulator but cannot get the pressure to go higher than 40 with the engine off ( or vacuum disconnected)or 32 with the engine running and vacuum hooked up. The system will hold good pressure for about an hour after it is shut down and then gradually bleeds off. I cannot find anything that could be causing this other than a bad fuel pump. Have read lots about bad NEW parts and wanted to know if anyone has any other ideas before I start throwing parts at this thing. Thanks.
GOOD LUCK I have a 90 6SP and I just when thru the whole car runs great now.
Ray
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
IIRC, stock pressure is about 43. Maybe you could get a stock regulator since there might be an issue and you don't really need an adjustable. So key on and engine off you get 40? You say it doesn't bleed down quickly so maybe crimp off the return line and let it prime and see what it really hits?
Drifting
Joined: Feb 2008
Posts: 1,537
Likes: 177
From: NE Ohio
2024 C4 of the Year Finalist - Unmodified
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,802
Likes: 1,714
From: Summerville SC
Not sure how the plug wires would keep my fuel pressure from going up? I will double check but I am thinking Mr. Raya 123 is onto something. Having a hard time getting a good idle, and the car is sucking up gas. A lot. Thought I had a couple of gallons in it the other day while trying to figure this out and couldn't get it to start. OOPS, no gas, should have been a few gallons in it. The injectors were newly rebuilds, but sat on my shelf for almost a year while I got things going. Don't really want to pull it all apart ( fuel pump would have been easier) but the injectors make sense. Will look at wires first, but as I said, they would not effect fuel pressure. Any more ideas, let me know. And thanks to all of you for the input.
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Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,802
Likes: 1,714
From: Summerville SC
Fuel INjection Connection, and that is the path I am going down right now. It might be something else, like the pump, but I have read enough about letting injectors sit is not good for them. Lucky for me I am not relying on the car to get to work tomorrow! Long term project and I guess I will pull the injectors out while I am working on somwthng else.
Drifting
Joined: Jun 2018
Posts: 1,678
Likes: 229
From: Michigan
Could be a lot of things, but I have mentioned this here before so I want to make sure you know... some have issues with those. New parts never means verified good parts. Other suggestions in this thread should be followed up on as well, but do question the injectors.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,802
Likes: 1,714
From: Summerville SC
The regulator is screwed down all the way, which is the direction it needs to go to raise the pressure. I believe. I will follow up on the simple things like wires etc. Have double checked timing, tps voltage etc and they would be the cause of running rough but not sure how that would keep the pressure low. Which leads me back to the injectors. I am not assuming they are good, since they are new and they were sitting for some time so there is a good chance that they got gummed up sitting on the shelf. Plan is to take them out next week, see if there is anything obvious going on before getting another set. Thanks for the input.
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
Forget everything and lets try this. Turn the key on and do not crank. What pressure do you see?
Does it bleed down quickly?
If it doesn't, your regulator might be ok.
If it does, wait for a few minutes and repeat the test. This time, crimp off the return line and see what happens
Does it bleed down quickly?
If it doesn't, your regulator might be ok.
If it does, wait for a few minutes and repeat the test. This time, crimp off the return line and see what happens
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,802
Likes: 1,714
From: Summerville SC
TO close up this thread, I ended up removing my injectors and after sending an email to Fuel INjector Connection and explaining my issue, and the fact that they had been sitting on a shelf for over a year, and I offered to pay whatever it would cost to either clean them up again, or buy a new set. I immediately got an email back from them telling me to return them and once they arrived another set would immediately be sent to me. The day after my old ones arrived at tehir shop, another set was shipped out and arrived 2 days later,, at NO COST to me. I put them in the car today and fired it up. My fuel pressure problem is solved. I cannot say enough good things about this company and their customer service. If you are in need of either new or rebuilt injectors, check them out. Thanks to all who were involved in this thread.
Last edited by kanvasman; Apr 21, 2019 at 04:59 PM.