Another Fuel Pump Replacement?!

[Bryon]

I replaced my mech. fuel pump shortly after buying my 89 GW this past February. It seemed that parked slightly down hill with a half tank of gas was preventing the fuel from getting to the carb? Any way, I replaced the pump and it worked.

This past weekend I replaced my fuel tank skid plate and all the hoses. When trying to start her up afterward I tried cranking her a couple times before priming with a little carb cleaner straight down the barrel while cranking. This caused her to fire a few times before sputtering our. This continued u til the battery was dead.

I am going to replace the fuel pump tomorrow because I can’t think of any other problem. I checked for fuel at the filter and it dribbled out when I disconnected the return line and also when I disconnected the sending line into the filter, but there was no fuel in the line between the filter and carb. There was no leaked fuel and the drips from the filter were not enough to have drained the whole line. So it seems that the pump didn’t have the pressure to push the fuel all the way up to the carb.

My biggest concern is when I install a surge tank under the hood that uses the stock lines and mech. pump (RobbMc) is that the main tank slosh will cause the mech. pump to burn out because of sloshing under half a tank.

Has anybody else gone through so many pumps so quickly?

[RamJetFSJ]

Have you tried just priming the lines with fuel? Pumps don’t pump air very well. If it worked before the stuff you did, it probably is ok, and just needs some fluid in the lines to get it going.

[kansasboy001]

Here's some info on the mechanical pumps. There are really only 3 different ones http://www.ifsja.org/forums/vb/showthread.php?t=184794.

On my jeep I kept having fuel pump problems, come to find out I had a nasty vapor lock problem between the pump and tank. I replaced everything and it wouldn't go away even with external electric pumps. Eventually put an in tank pump in from a 1995 blazer and a bypass regulator before the carb and it's been fine ever since.

If you don't want to do in tank Stewart warner sells some electric pumps made by Walbro that the semi truck guys use that can dry lift over 3 feet and would probably push through any vapor lock issue.

[acct21]

Lots of possibilities. While not impossible that you have had two bad fuel pumps, it seems leas likely. You could have a stuck float in the carb, which is not allowing fuel into the bowl. You could have an obstruction at the pickup in the tank. Not absolutely certain to be the fuel pump.

Should try taking a length of 5/16” fuel hose and run a small tank of fuel directly down to the mechanical pump. Take the bowl cover off the carb and check the float/needle to make sure it is letting in fuel.

[acct21]

And don’t worry about fuel slosh with the mechanical pump. It will tolerate a momentary loss of suction just fine. That’s what the fuel in the carb bowl allowed for — as long as you still have fuel in the tank, the mechanical pump will immediately re-prime and keep going.

[acct21]

RobbMc also makes an AMC mechanical pump here in the USA. Expensive, but no doubt a quality part.

[kansasboy001]

RobbMc also makes an AMC mechanical pump here in the USA. Expensive, but no doubt a quality part.

That pump is only for the pre 1976 timing cover with the pump mounting 180 degrees off from the later ones

[letank]

which brand of E pump? what is the set up w the surge tank... may be too much pressure or restriction in the system

[acct21]

RobbMc also makes an AMC mechanical pump here in the USA. Expensive, but no doubt a quality part.

That pump is only for the pre 1976 timing cover with the pump mounting 180 degrees off from the later ones

But I don't think the timing cover or the cam eccentric changed -- just the pump orientation. The early pumps should install and function fine on a later motor (and later pumps on early motors), they'll just look "upside down" from stock. Need to account for the lines/fittings, but the pump itself should work on all 2nd/3rd gen V8s.

**Edited to add**

Confirmed with Robb at RobbMc -- the AMC 2nd/3rd generation pumps will only mount the way they were designed -- but run off the exact same mounting point and cam eccentric. So the early pumps (like the RobbMC) will hang diaphragm down, while the later pumps "point up." As long as you can account for the new location of the lines (probably OK, since You can mount hose barbs and rubber lines to the inlet and outlet on the pump if you aren't comfortable relocating/re-making the hard line that goes up to the carb on the later 360s), that pump should work fine on later GW/J trucks.

[Bryon]

Thank you for all of the advice!
When I disconnected the hoses from the fuel pump I heard a strong sucking whoosh. The line had been pinched at the tank when i bolted it in place. I dropped the tank an inch and relieved the pinched hose through the hatch under the rear seat and redirected it.

I emailed RobbMc and he told me to get an Airtex 6505 and be sure it’s not a chinese knock-off for the mech. fuel pump.

Now I have to wait for that bonus to get the surge tank!