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Username Post: 87 IROC Fuel pump Woes        (Topic#368112)
Posts: 2

Reg: 04-07-22
04-07-22 08:31 PM - Post#2839450    

It's my first post but I looked around to see if I saw a similar problem. I have a 1987 Iroc with original 5.7 block in it. Its a 383 displacement now with late model heads. Its carbureted and i used the cavity in the block that was covered from the factory for the mechanical fuel pump. I have a Holley high volume pump with a stock length milodon fuel pump rod. Ill skip alot of this nightmare to say it will sometimes after 15-20 minutes die and not have fuel pressure. I have measured fuel pump rod 5.75" I checked to make sure fuel pump lobe is pushing rod. I did not mic it but it seems like about 1/2" of travel. Specs i found call for .375".
Its not the lines or tank because it will do it connected to a gas can at fuel pump. Its not overheating it runs 180 degrees. When it does it you can take line off going to carb and no fuel coming out while cranking. After things cool down it had been restarting. The holley pump was a couple years old so I purchased a new one last week. It did same thing except after it died the second time from running it never restarted. You can put your finger on fuel pump while cranking no suction. I did manually work the pump and it pulls vacuum while out of car.
I am ready to scrap the whole thing and setup an electrical fuel system but I kind of want to solve the mystery.
One last detail is the pump in tank was removed and a hose put in its place. That had no effect when i was hooked the pump straight to a gas can.
Any wisdom would be appreciated.

Edited by Motorheadtom on 04-08-22 03:31 AM. Reason for edit: No reason given.


Valued Contributor
Posts: 2555

Loc: Lake George, NY
Reg: 11-11-15
04-08-22 05:42 AM - Post#2839467    
    In response to Motorheadtom

Seems like you haven't missed anything. I have seen this issue a few times on BB Mopar engines that had steel roller cams and had the wrong fp push rod,they wore about 3/16" at the lobe end, same symptoms. They make a special push rod that is compatible with the steel cam. Maybe there are different length pushrods for different applications, roller to non roller engines, or FI to non FI?

Edited by Shepherd on 04-08-22 05:44 AM. Reason for edit: No reason given.

Senior Member
Posts: 551

Loc: CA
Reg: 07-18-00
04-08-22 11:58 AM - Post#2839485    
    In response to Motorheadtom

Some carbureted 3rd Gens (LG4) ran both an in-tank and mechanical fuel pump; I was told because of vapor lock issues.

You're running the existing hard fuel lines, yes? The routing under the hood is close to the exhaust system.

There are proper venting issues that are required too.

Go here, search, ask:

1987 IROC-Z 5.0L
1992 Lumina Euro 3.1L
2003 GMC Safari

Posts: 2

Reg: 04-07-22
04-09-22 03:01 AM - Post#2839517    
    In response to paulo57509

I understand they had tank/line issues but this happens even when it has a hose attached a dropped in a gas can. I am leaning towards it havingto be a cam lobe issue because the rod measures the correct factory length. This has a steel roller cam from Comp Cams. I Am going to measure arm distance on holey pump to a delco today for grins. After that its electric system with a return line.
Anyone have recommendations for in tank pump for factory hanger? I assume I could use factory line to feed carb but install a bigger return line. Ive seen a couple psot about this.

Super Senior Member
Posts: 6003

Loc: paradise
Reg: 09-05-03
04-17-22 11:03 AM - Post#2839923    
    In response to Motorheadtom

i would pull the pump and plate. hold the pushrod against the cam and crank it. that should tell you if there is enough lobe on the cam. i am not a fan of electric pumps. if you mount one on the body or frame it may be very loud. i would use a piece of rubber like a conveyor belt to isolate the buzzing noise. an intank pump may require tank mods. i would search hard for a drop in pump. i would also recomend using oil pressure to cut out the electric pump for saftey reasons.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


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