Thread: Fuel Pressure ?????

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Originally Posted by R Pope

Dare I suggest hooking up the stock pump???

It's always the simplest things that get overlooked! That does sound like a good idea, I don't think I ever tried the stock mechanical on it.

Thank you all for all of your input. I'm sure you know how frustrating it can get to be so close yet so far.

Still got problems. I tried moving the electric pump back as close to the tank as possible, tried the stock mechanical, tried the stock mechanical and electrical at the same time and even talked to the preacher, but he wouldn't do the exorcism. Always get the same result- works fine with 6-7 lb until it heats up then slowly drops down to nothing. I've felt all the lines by hand and figured if I can touch them, they can't be too hot. Is it still possible the lines in the engine compartment are still too hot? Will a bigger line work? I'm getting a little ticked off about this.

One simple test would be to temporarily hook a full peice of rubber line from pump to carb. Doesn't have to be pretty for now, it's only temporary. This will answer the question of existing lines under the hood or any other hard lines running down the frame. Have you had a chance to run a volt meter at the pump connections while this thing acts up?

I think you're gonna have to drop the tank. There must be a chunk of crud floating around in there, or the sock filter is plugging.

Originally Posted by R Pope

I think you're gonna have to drop the tank. There must be a chunk of crud floating around in there, or the sock filter is plugging.

I thought about waiting till it acts up then using a 5 gallon canister to draw out of instead of the tank, but haven't tried it yet. I'll ckeck the voltage, but I already did the temp hose thing.

My bad....I overlooked your post on the 24th. My thought at this time would have to follow along the lines of bad pump or junk in the tank. Proceed with voltage check first please.

One time I had a guy come in that had a problem where the car would die unexpectantly. After it died, the thing would restart and run OK until some random time when it died. It would idle forever. Turns out he had a shop rag in the tank that wandered around and eventually covered the sock. When the pump stopped, the rag wandered away and the car restarted....I dont think that yours is that problem since it appears to be predictable.

Do you still have a regulator in the return line? What is it...is it specifically made for this application in the return line? Something is fishy here...something that appears to heat up and affect the performance of a component....regulators can heat up, pumps can heat up, fuel lines can heat up.....by the way, has the tank internal lines been changed....as in the return line modified or is it GM stock?

mike in tucson

Originally Posted by robot

One time I had a guy come in that had a problem where the car would die unexpectantly. After it died, the thing would restart and run OK until some random time when it died. It would idle forever. Turns out he had a shop rag in the tank that wandered around and eventually covered the sock. When the pump stopped, the rag wandered away and the car restarted....I dont think that yours is that problem since it appears to be predictable.

Do you still have a regulator in the return line? What is it...is it specifically made for this application in the return line? Something is fishy here...something that appears to heat up and affect the performance of a component....regulators can heat up, pumps can heat up, fuel lines can heat up.....by the way, has the tank internal lines been changed....as in the return line modified or is it GM stock?

mike in tucson

I've tried it with and without the return line. Matter of fact I put the return line in after having these problems hoping for a fix. When I plumbed in the mechanical pump a few days ago I 86'ed the regulator and return line all together. It originally did not have a return. I had the tank custom made when I started this project by a reputable tank maker, but who knows, something may be in there. Something is definitely fishy. I've talked to the tech guys at HOLLEY, who usually do a real good job, and it's got them miffed too.

By all means use the process of elimination. If you can run it off a 5 gal. jug,do so,then you know it's tank related. I had one give me problems years ago,somebody switched the sender,and used rtv and the cork gasket and then ran in the 10/32 screws.the little strings of rtv swell in gas. When I finally got them out they were3/4" dia and 3" long. Hank

OK, Ive tried everything I can think of and still haven't figured out what the deal is. I'm back to thinking my origanal though which is that it is just getting too hot in the engine compartment. Is that possible? I have a 396 that is .060 over and have never had any kuck keeping it to run cool. Is it because the cylinders are too thin and creating more heat then I can get rid of. I thought the fuel pressure was leading to the engine running hot but now I'm leaning toward the engine running hot effecting the fuel pressure. Any other ideas?

Originally Posted by wrenchaholic

OK, Ive tried everything I can think of and still haven't figured out what the deal is. I'm back to thinking my origanal though which is that it is just getting too hot in the engine compartment. Is that possible? I have a 396 that is .060 over and have never had any kuck keeping it to run cool. Is it because the cylinders are too thin and creating more heat then I can get rid of. I thought the fuel pressure was leading to the engine running hot but now I'm leaning toward the engine running hot effecting the fuel pressure. Any other ideas?

Is the fuel tank properly vented?

Don In Austin

To my way of thinking your problem has to be in the pump. They have two check valves,inlet and outlet,with the outlet maintaining backpressure all the way up to the carb. The only other thing that I can think of would be a fuel hose collapsing internally blocking the line. If you keep the fuel line away from engine and exhaust heat then vapor lock shouldn't be a problem. Hank

I'll take a few pics tonight when I get home from work and post them.

The tank is ventilated and I even ran the fuel out of a 5 gal. container after I started it and the pressure dropped. When I did this I could feel hardly any suction from the end of the hose through the mechanical pump.

Except for a few small peices of rubber hose at the filter, tank and where I temped in the mechanical pump its all 3/8 hard line.

I've used 2 different electric pumps and 1 mechanical so I didn't think it was the pump. However, I ran out of fuel once on the way to the river in this vehicle and pumped fuel from the boat to use. Since then I had to replace the fiberglass tanks in the boat because the resin was breaking down and doing all kinds of bad things. 2 of the pumps I've been trying have been subjected to this bad gas so could that create the same problem. The one in the boat still works fine.

SUCCESS!!!!!!!! Well, kind of. I bought another new mechanical fuel pump, 5' of 3/8 hose and a new hard tube. I went from the carb to the fuel pump in 3/8 hard steel line and from the fuel pump straight to a 5 gallon container. I started it up and in about 20 minutes the pressure dropped to 0. Then I took the pressure gauge and carb fuel feed line off and capped it. Finally I started the truck with the remaining fuel in the bowls to read the pressure and it was at 7lbs. For good measure I reinstalled the fuel line to the carb and started it and it was still at 0. SO. This tells me it's the carb. Through the site glass I can see the floats are adjusted right, but is there some way the needle/ seat are staying open? The first thing I'm gonna do is rebuild it. then if I still have a problem, HOLLEY is getting a call. I've had nothing but problems with this thing since I bought it. They might get a call anyway for the rebuild kit.

Bypass the pump with a foot or so of rubber line and then use an air hose to to blow out the line from the carb back through into the tank. Use common sense with amount and duration of air pressure back into tank so yuo do not cause a problem here )short blasts of air). This is to blow off a sock filter in the pick up side if present and prove no obstructions. Cap on tank must be off and be aware of gas fumes and dangers.
Hook system back up and rig a volt meter up to wiring at the pump. Watch voltage as it starts up and has pressure to point of losing pressure. If voltage remains constant it is a bad pump that may be failing from a internal heat related fault but faulty regardless. A new pump is cheaper than all your time and old pump is 5 yrs old anyway. Also easy to check flow rate or gallons per min of old pump, time how long it takes to fill a 1 quart can at carb inlet and do the math on output from time to fill 1 qt. good luck .... be safe