Author Topic: Hey All, have fuel flow but no fuel pressure issue...  (Read 179 times)

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Offline Chrisssssssss

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Hey All, have fuel flow but no fuel pressure issue...
« on: October 09 2020, 08:54:29 PM »
Hey everyone...

Finally got the 86 back on the road again and was driving beautifully however when I went to park it the other day, put the car into reverse...died ...and hasn't started since. Checked for fuel pressure at the rail and nothing. There is fuel flow and i hear my fuel pump going when I jumper the grey wire in the engine bay... but there is no pressure. I have an accufab FPR and it seems to be ok. I took it apart and looked at it and the diaphragm is fine. I even replaced it with a Bosch unit I had lying around which was not from a GN but some other car (Mercedes or BMW I think i recall but it fit exactly) and it seemed to not make a difference. Still no pressure. Replaced the fuel filter still same. So my thoughts now is to drop the tank and see if the fuel pump is somehow leaking back into the tank. Is this possible? Is there anything else I should check before doing that? I recall there being a walbro pump (not sure which one but it is about 10 yrs old) installed. I hear it whirring away In the tank but if the fuel pump to the gas line hose or whatever has some sort of breach I think this would be the result. The car is on the street parked so i will be doing it there. I used the pump as is to drain the tank into gas cans, but if i put my thumb over the connected tube I can stop the flow like nothing. No pressure. Fuel pump is hot wired also.  Thoughts? Thx in advance...

Chris
86 GN

Offline Steve Wood

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #1 on: October 09 2020, 09:24:43 PM »
Sounds like the hose between the pump and the pick up on the bottom of the tank is cracked to me.

It is also possible that an old pump has just died and will no longer make any pressure.
Steve Wood

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Offline Steve Wood

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #2 on: October 09 2020, 10:49:19 PM »
BTW, not all fuel injection hose can be used in the gas tank.  Only hose marked  SAE 30R10 can be submersed.  I recall a lot of people sold fuel pumps and included regular fuel injection hose with them some years ago.  It soon cracks and leaks.

 SAE 30R10 costs a lot more per foot than regular fuel injection hose.
Steve Wood

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A lot of broken parts does not make you a racer; it makes you a slow learner.

Offline Chrisssssssss

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #3 on: October 10 2020, 05:34:31 AM »
Well well... ^^winner winner chicken dinner^^

Dropped the tank, and low and behold the fuel line was a big cracked out pile of goo... disintegrated and was mushy. You were exactly right. This is kinda what i thought it would be but not as severe as it was. Looks like I will be grabbing me some SAE 30R10  when I get a chance. I have on hand some SAE 30R7 but i am assuming that it will end up doing the same thing as what i already got?

Also the hose was just a very short straight piece going from the pump to the outlet feeder tube... I have seen in other examples tbat the hose should take a sort of roller coaster style loop to the tube.  Should I leave it straight and short or do a loop de loop to the outlet tube? Just curious.

Thanks for the tip.

Offline Steve Wood

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #4 on: October 10 2020, 09:30:21 AM »
yes, the R7 will come apart.  The outside of the hose is not fuel resistant.

I have never seen one with a loop in it.  I assume that is an attempt to muffle the noise from the pump a little.  I have always used and seen a short piece of the same hose as used to go to the pick up.

We always drill out the restriction in the tube as well or ream it--whatever  Talking about the  neck down restriction in the tube in the hanger.
Steve Wood

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A lot of broken parts does not make you a racer; it makes you a slow learner.

Offline earlbrown

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #5 on: October 10 2020, 03:13:53 PM »
30R7 will blow apart before it has a chance to turn to goo.

That's carb fuel line (and not even the 'good' stuff for carbs).  Not rated for FI pressure, not rated for boosted FI pressure, and damn sure not rated for submersion.
'87 GN - 4.2L SFI Turbocharged innercooled V6 - Chrome valve covers - supra pump - 14" K&N - 52mm throttlebody - rocker shaft supports -  1/2 intake spacer - TB coolant bypass - 3" ATR exhaust tip - Alum intake pipe - NOS timing cover - chip - relocated charcoal canister - CR42's - stock

Offline Chrisssssssss

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #6 on: October 10 2020, 06:55:41 PM »
Okokok... finally found me some SAE 30R10 and omg the price! Cost me $40 for a foot! Well at least I won't have this problem again. Thanks for the tip becuase at the first and second auto parts store they were selling me the other stuff and said it is what they always sell and never heard of any problems with it. Gonna bring them a piece of this stuff and show them whats up. I dont want to be stranded in the middle of bf nowhere. Now to reinstall the pump and tank...

Offline Steve Wood

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #7 on: October 10 2020, 07:10:02 PM »
Damn!  Gone way up.  $20 a foot at Napa and $30 on amazon
Steve Wood

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A lot of broken parts does not make you a racer; it makes you a slow learner.

Offline nocooler

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #8 on: October 10 2020, 07:16:23 PM »
A lot of stuff has moved the convoluted plastic/ptfe tubing for the submersed fuel line. 
IhaveaV8

Offline earlbrown

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #9 on: October 10 2020, 09:52:22 PM »
....and when that cracks, I replace it with 30R10 and FI hose clamps....
'87 GN - 4.2L SFI Turbocharged innercooled V6 - Chrome valve covers - supra pump - 14" K&N - 52mm throttlebody - rocker shaft supports -  1/2 intake spacer - TB coolant bypass - 3" ATR exhaust tip - Alum intake pipe - NOS timing cover - chip - relocated charcoal canister - CR42's - stock

Offline Chrisssssssss

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Re: Hey All, have fuel flow but no fuel pressure issue...
« Reply #10 on: October 11 2020, 03:08:12 AM »
Sooooo... I got fuel pressure out the yin yang... however car still won't start. I think i lost spark. Going to create a new topic for that problem. Coincidental I think that it happened at the same time. I think my ignition pack or ecm may be fried. When I was removing the FPR during troubleshootin g, I accidentally touched the ratchet to the alternator battery terminal and shorted something fierce.