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Old 05-06-2019, 11:04 PM   #1
madgoatboy
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Exclamation 1985 Silverado with TPI Fuel Pressure Issues - Long post

I have a converted Silverado with TPI that is having intermittent fuel pressure issues. I can not get the pressure to stabilize near 43lbs. A little history:

Converted to TPI in 2005.
Engine and transmission rebuilt less than 6 months ago. New radiator, new switching valve, fuel selector switch, and fuel tank switching valve connector wire (not sure of the appropriate name ) -had the left tank pumping fuel into the right tank even until it poured out the side, new MAF sensor, distributor, ignition coil, etc.

Once I got the truck running, I ended up breaking down on the side of the road and unable to crank the truck. I was not getting 45 at the Schrader valve. Close to 25, so I replaced the pump. Had a loss of power again and it was determined that the tanks were rusty via a camera I ran in there.

So I replaced both tanks, sending units, fuel pump (yes again), all filters, all rubber line that I could get to. I left the metal lines in place and used a compressor to blow them out. I added a filter close to the switching valve to hopefully protect the pump just in case.

So when trying to start, I get a very loud whine from the fuel pump as if it's starving. The truck would not run on the left tank and only the right tank albeit badly. Fuel pressure is variable and will go up beyond 100psi and drop to 50 - back and forth. I changed the fuel pump again with the same results so I changed the fuel pressure regulator to an adjustable one today. I also removed the pre-pump high flow filter. The same thing happened but it did run for a few minutes longer on both tanks but had a variable idle. I reset the PCM, but this did not help.

Right now I'm not sure what to do next, I would really hate to have to drop the tanks. I did not run extra line from the tanks to the line and they were a PITA to put back. I have purchased another switching valve and selector switch just in case. I was told to check for line crimps, just not sure where this would occur as I did not remove any metal line and only replaced the rubber line with the exact same length of line and the tanks have three distinct size lines going to them.

If anyone has had this issue before or know what to try, the help will be appreciated?

I have attached two videos and hopefully, the admin will let you see them.

Fuel pump whine: https://youtu.be/4Q47OD3ELLw
Pressure jumping: https://youtu.be/yq-1wsDa-Sc
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Old 05-10-2019, 05:33 PM   #2
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

Okay, tried again to figure out the issue. I then noticed that I had a pool of fuel on the ground. Fuel seems to be coming from the pipe/connector underneath to the right the FPR (attached). This was definitely not there before and I know for a fact that I did not lean on it - I couldn't. Putting on the FBR was pretty straight forward. I'm not even sure where to go from here, I'm about to try to let a shop figure it out as I'm not even sure you can replace this tubing. Anyone have any ideas?
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Old 05-10-2019, 07:46 PM   #3
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

My guess was going to be a fuel leak somewhere, that obviously confirms it. If that line is cracked, which is a bit unusual, Ebay is full of TPI fuel rails.
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Old 05-10-2019, 07:50 PM   #4
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Quote:
Originally Posted by Bloodhound View Post
My guess was going to be a fuel leak somewhere, that obviously confirms it. If that line is cracked, which is a bit unusual, Ebay is full of TPI fuel rails.
Thanks. It wasnít initially leaking just had a weird pressure issue. Only after the Adjustment Fpr did this happen. After about 5 min of running. Iíll see if I can find a rail
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Old 05-17-2019, 12:01 AM   #5
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

Quote:
Originally Posted by Bloodhound View Post
My guess was going to be a fuel leak somewhere, that obviously confirms it. If that line is cracked, which is a bit unusual, eBay is full of TPI fuel rails.
Well, the leak was coming from the new adjustable pressure regulator. Resolved it by tightening it some more (my fault) for not double checking. Fuel pressure did the same thing after resolving it.

I did notice something semi-weird. I unplugged the throttle position sensor and the truck ran for a lot longer before the pressure suddenly dropped. It would sort of hover around 50 - the needle was not stable but would stay there at least before going back off the rails and then to 30. It would still die if I went to the left tank. I have a combination of problems I think and hopefully, the shop can fix it. I'm out of time.
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Old 06-22-2019, 10:40 AM   #6
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

Well..I fixed the leak issue and sent it to a shop because I don't have much more time to work on it. Turns out there was a compressed vacuum line going to the plenum (looked normal on the exterior). That resolved the pressures going up and down. Next issue is to figure out the problem with the left tank.
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Old 06-22-2019, 06:07 PM   #7
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

Was it a regular rubber vacuum line or a pretty dress up vacuum line?
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Old 06-22-2019, 06:14 PM   #8
madgoatboy
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

Quote:
Originally Posted by cadillac_al View Post
Was it a regular rubber vacuum line or a pretty dress up vacuum line?
It was a regular one. It could've been crimped when I replaced the fuel pressure regulator. I didn't completely remove the plenum when i did it, just lifted it enough to the side so I could get to the regulator. I don't know. I removed all decorated ones a while ago to help with troubleshooting.
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Old 06-23-2019, 04:38 PM   #9
AussieinNC
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Re: 1985 Silverado with TPI Fuel Pressure Issues - Long post

Make sure the tank changeover valve is not clogged with debris....I have personally seen a totally clogged port in a valve so bad that I could not clear it out.....

If you have to, totally isolate the left tank...and get the truck working correctly on the right tank...dont try and do too many changes at one time....

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Old 06-23-2019, 06:38 PM   #10
madgoatboy
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Originally Posted by AussieinNC View Post
Make sure the tank changeover valve is not clogged with debris....I have personally seen a totally clogged port in a valve so bad that I could not clear it out.....

If you have to, totally isolate the left tank...and get the truck working correctly on the right tank...dont try and do too many changes at one time....

Thanks Iíve already purchased another just in case.
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