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Hey guys, a little more than a month ago I posted about a problem I am having with my 96SS. I did not get it fixed before I left for tour but I am back at it now and still need some help. Heres the details....

Fuel Pump intermittently cuts off/on
Replaced Sending Unit, Fuel Pump, and Fuel Filter, still same issue.
Fuel pressure is steady at 40psi
Connected the bypass connector next to the fuse box under the hood to + power and it does make the Fuel Pump run continuously.
Metered the Relay, has 12V
Metered the Fuel Pump connector black and grey wires and got 12V.
Car will start and run for a little bit after several times of it intermittently priming itself, so I know the engine will actually run.
I am at a loss here. Anyone have any suggestions on where to check next? It really seems like its a loose connector that is barely making connection somewhere.

Thanks in advance for any help guys.
 

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Matt, just a thought

Do you have a oil pressure gauge?..or has the "oil" light ever flickered?

IIRC when the OP sender senses 5 or less PSI it cuts fuel. The sensor could be bad if this is the case...or your have major issues with internal motor...but you would likely also be hearing a knock.

Then there is always the WTF happened because my car has been sitting and now something is not right.

is the 40 psi of FP with vacuum hooked to FPR? if without vacuum than 40 is low. Typically FP is 45-48 without vacuum and 36-40 with at idle with it increasing some as you increase rpm

I also have toured for decades and after being gone for several weeks or months a perfectly running car when I parked it is no longer happy about something. Frustrating
 

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Discussion Starter #3
Yes, this is a WTF happened because my car sat for a month. Then sat for another month after I started fixing this because i had to leave again.

The PSI is a steady 40 with the vacuum line plugged in. When I unplug the vacuum line it goes to 60PSI when its priming then settles back at 40PSI.

Never had any oil light come on at all.
 

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...
Fuel Pump intermittently cuts off/on
Replaced Sending Unit, Fuel Pump, and Fuel Filter, still same issue.
....

Thanks in advance for any help guys.

May be out there, but could it be you're misreading the symptom? Unless you're reading that current to the pump is actually breaking, then the so-called cutting off could be electrical. As in IC, ICM or opti (or its harness). On another note, I was out of the country an extended period and my black car was not acting at all right when I returned. I had good luck after - disconnecting batt a long time, and just doing a bunch of adjustments to make sure they were on. IAC, TPS, cleaned the EGR valve, sprayed the MAF, etc. It decided to run well again but I don't know what did it. It could have even been the double shot of Techron! lol



Now for the bad news. That new pump may have a non-steller connection with the harness. My new pump and harness and sender did. I got to drop the tank and redo the whole thing a second time just a couple weeks after the new parts.
 

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Have you tried bypassing the VATS, or programming it out?
 

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Discussion Starter #6
I have not tried anything with the VATS. Its really acting like theres a connection thats loose and just barely making enough connection to come on and turn off again. This one sucks.

Hey, besides the ground right next to the battery and the grounds in the trunk on the angle pieces next to the trunk hinges, are there any other grounds I could/should check?
 

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Discussion Starter #7
We can add Fuel Pressure Regulator to the list. Swapped that out this morning and no change unfortunately.
 

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Discussion Starter #9
Nope, new sending unit, new fuel pump, same result.
 

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Try swapping the fuel pump relay with another relay? I had a buddy (not on the forums) just spend $$$$ on a new fuel pump and sending unit while on a trip only to have the same issue when he got home and discovered that the relay was going bad.
 

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f6john, Yah, I also caught no mention of harness both above and in the original post. It's rather important to replace as all the rest while you're already in there. Airtex is favored as it has larger gauge wiring v. oem.


MattM, you got a head-scratcher fersur. Really getting interested in what the culprit turns out being.
 

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Discussion Starter #13
Yep, sorry, I didnt list that. Did swap the relay.
 

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Discussion Starter #14
Update to my intermittent fuel pump issue...

After replacing fuel sending unit, fuel pump, fuel filter, fuel pressure regulator, fuel pump relay, I am still chasing down this electrical issue.

I can get it to run every so ofter for about 5 seconds

When it does not start I do not have spark

I unplugged and replugged every connector under the hood I could find and still no change

I have an appointment at a local shop Wednesday but would love to solve this before that happens. Anyone have any ideas/suggestions?
 

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Yep, sorry, I didnt list that. Did swap the relay.

Not the relay. The harness. It's just some wires and connectors. IDRecall now, but if it comes with the pump as an assembly then you're covered. --> But <-- as mentioned the Airtex harness is an oft-mentioned purchase to answer oem notoriously deficient gauge (thin enough to provide repeat pictures on here of the insulation burnt completely off).
 

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No spark - BINGO. You have an ignition problem not a fuel problem if it holds 40 psi.
Start by replacing the coil and ignition module (ICM) as they are easiest.
If problem persists, replace the distributor (opti).

Nab
 

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Discussion Starter #17
ANNNNDDDDD......It was the Opti!

Thanks for all the help everyone, shes back on the road!
 

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I have not tried anything with the VATS. Its really acting like theres a connection thats loose and just barely making enough connection to come on and turn off again. This one sucks.

Hey, besides the ground right next to the battery and the grounds in the trunk on the angle pieces next to the trunk hinges, are there any other grounds I could/should check?
There's a connector on the left side of the trunk. Behind the carpeting, towards the top of the trunk. This connector feeds the brake lights, power to the fuel pump, and also the fuel level to the gauge cluster.

IDK why, but at some point my car would shut off if I stepped on the brakes, and the fuel level was always pegged at full. I unplugged that connector and cleaned all the contacts and it never happened again.
 

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And how did you come to find that as the problem? That would be key info for those of us still trying to get our cars running without replacing a bunch of parts. I had my ICM tested as bad but a new ICM and new coil was not the answer.
 
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