Hey guys... I am posting this up for a friend who is having issues with his 84 vette. I am heading out to look at it in about an hour.. Not even sure where to start.

This is what has been done over the last week and a half.
New fuel pump - the reason why they startd working on it

After the install.... He is telling me it rained that night, and the following issues started the next day.. Perhaps a short somewhere?

Started car and it would die.

They replaced ECM/ chip - started car and still dies.

Replaced TPS switch and set to corret voltage - start car and dies.

They tested the fuel pressure - once the pedal is pressed, the pressure falls to around 3-4 psi and car dies. They disconnected the fuel return line, plugged it.. car runs fine.

Thats about all i know guys... Can someone please give me a place to start with this? My friend is doing this work on a car for a man who has terminal cancer - it was the guys dream to own a vette... This is standing in the way of enjoying it. I appreciate any kind of feedback!!

Thanx!!

 

Sounds like the fuel pressure regulator in the rear throttle body. What pressure does it have with the return line plugged?

 

The fuel system is very simple.

tank -> fuel pump -> filter -> front TB -> rear TB with regulator -> tank

The fuel pump creates a fuel FLOW.

The regulator works like a valve restricting the flow back to the tank and that builds the pressure between the pump and regulator.

Where do you measure pressure?
Do you have the front and rear TB mixed somehow?

 

just got back from messing with car... I removed the rear tb and stuck it on my car to test... My car ran perfectly fine with his rear tb... I tested the pressure on the car and its around 4.. the fuel hardly spits out of injectors... I test the pressure before TB #1 and i had 12psi... I unfortunately had to get to work so was unable to remove and test that one. Is there something in tb 1 that would block up the pressure?

ideas/ comments?

Thank you!

 

Currently the pressure is being measured between tb 1 and 2.. pulled the hard line and made a make shift one to measure the pressure... If we block the return line, pressure will build slightly.. 7psi.. car will run a bit.. but very poorly..

 

On which car...both?
Theoretically, it shouldn't matter where you measure the pressure as long as it is between the pump and the regulator. Between the TBs is the most common point. The fuel pressure spec is 9# to 13#. I'm not sure what the max for the pump is, but it is WAAAAAY above that. The regulator should hold the pressure to spec. Blocking the return line should cause the pressure to sky rocket. There is nothing in the front TB that will fail and block the fuel passage, but that doesn't mean it couldn't become blocked by some foreign material.

I once had a similarly perplexing problem. There was a leak in the hose, inside of the tank, leading from the pump to the metering unit flange. It wouldn't cost anything to take a look.

RACE ON!!!

 

Ok guys... Turns out.. My initial diagnosis turned out to be the problem. When i approached the car for the first time i immediately realized that the hard fuel lines were routed incorrectly. Judging by the way each pipe was bent, i could tell it was forced into the position. This led me to believe that perhaps the line was bent/ kinked up somewhere. Well after talking to the owner a bit, he informed me the AC comp. was replaced with a R134 unit - so this is probably why it was moved to begin with? That we dont know.. Anyway, the line now hangs by the inner frame rail beneath the car. About three weeks ago (when the car started acting up) The guy ran over some kind of animal and did minor damage to the passenger side footwell.. In the process the object hit the hard line that was not positioned correctly and caused a serious kink. This kink dropped the fuel pressure to 5-7psi.. It is not messuring a contant for some reason.

Total freak thing.. There have been 5 mechanics working on this car trying to figure it out.. Replaced ecm, tps, chip, fuel pump twice, regulator, and got nothing. Needless to say, the car should be finished tomorrow and returned to the current owner.. Thanks for the insight guys! It is greatly appreciated...

 

Excellent!

 

CFI-EFI, are you sure the stock 84 pump puts out way more than that? I know the 85 and up TPI pumps do, but I thought the 84 pump put out somewhere around 15lbs??? Not trying to prove you wrong - honestly curious and want to know. You give some really great advice on this forum!



quicksilver458, I'm glad the fuel problem is fixed.

I remember with mine, it went to a shop three times to fix it before they finally told me they thought it was an ECM problem. Thats when I told them to stop working on it and went and got it myself. Turned out they said they had put two pumps in it (the first one being defective) I don't know if they did or not. I have doubts they ever put a second pump in. I hooked a fuel gauge in front of the filter with enough line for a friend to hold it outside the passenger window and went for a spin... It would run a constant 9lbs, then, all of a sudden, drop to like 2-3lbs and finally quit. Sometimes it would hold the 2-3lbs for awhile, sometimes not. Everytime, I could here the pump running after the car quit, so I knew it should have been pumping. Capping the return line, I would pull a constant 13lbs off of the pump (thus, my question to CFI-EFI) but with the regulator, it was only 9lbs.

Long story short, I diagniosed a bad pump, pulled it and put in an 85 Carter pump from NAPA. It's been runnig great ever since. I never tested the pressure with teh return plugged on the new pump, but it does put out a constant 10lbs now - under load or not, where my old pump would drop to 5-6lbs under load. It's got the regulator pegged My next missin is to modify the factory regulator to make it adjustable and bump up system pressure to about 12lbs...

That was when I learned never to take my car to a shop anymore. A hard lesson, but one I think we all come to learn after awhile...

And that also reminds me to thank everyone on this forum. This forum is full of the most helpful enthusiasts that I have come across anywhere and I'm grateful that I found it.

 

I have never totally blocked the return line to check the maximum pressure of my pump. I HAVE run the 1/4 mile with the pressure set at 17#. My everyday fuel pressure is set at 14#. I cut the steel fuel line between the TBs and installed a tee fitting with Schrader valve. Now I can easily check my fuel pressure, any time I want, just like the "big boys" with TPI.

RACE ON!!!

 

Sweet! I was thinking of doing that. Will it clear the stock air cleaner assembly? It was a pain rigging brass T's and whatnot to splice on to my filter to check pressure... then i had to put a new length of hose on when i was done and check for leaks.

That would be a bad place for a fuel leak... so close to the exhaust pipe and all...

 

And out of sight, too.

The tee clears everything. It is 45° inverted flare at each end and tapped for 1/8" NPT in the middle. I slide the 45° inverted flare nuts onto the fuel line tubing and double flared the tubing. The fuel line connections at the tee are the same as at the TBs.

RACE ON!!!

 

i like the idea of putting the valve in there.. I would love to be able to monitor mine from time to time.. Have been toying with the idea of upgrading to the 85 fuel pump as well... 177k miles on my current pump... Im sure its about time..

 

I keep preaching that there is nothing to be gained with an '85 pump over a properly operating '84 pump. Like every other component on your car, test it before you condemn it. I hooked up a pressure gauge with a little bit of hose, and ran the hose under one of the windshield wipers to keep the gauge in view. Then I made a blast down the 1/4 mile, over winding every gear to put the greatest demand possible on the fuel pump. Even at 6200 rpms in second gear, the gauge needle never quivered. If the old pump does the job... If it ain't broke, don't fix it.

Now IF you do need a new pump, a later pump is a good idea.

RACE ON!!!