fuel pump issues

[NATO4x4]

I have a PITA request to bother people with. I need pics of the passenger side of an 86 trooper head and of the fuel pump push rod. My trooper started to cut out at higher speeds and rpms. A few months ago it got the point that it would not crank. I replaced the fuel pump, cleaned the tank, changed the fuel filter, checked all lines, and still no fuel flow. With the fuel pump off, where the rod contacts the arm of the pump, the head looks chewed up like some metal was floating around in there.

Has anyone had trouble with push rods or fuel pumps?

My rod has a groove cut in it at the bottom that makes me think something is missing.

Anyone on the east coast have a head or junk engine laying around? I might need to buy some parts.

Help would be greatly appreciated. Its been taking up my garage for 3 months.

[800XL]

I'll see if I can get you a picture from my junker head. From memory though I recall the pump end of the push rod being pretty much flat, cam end too for that matter. I recall the head casting being a little rough around there, but chewed up sounds like more than normal.

[NATO4x4]

Thanks so much for your help.

My push rod is flat at the pump end it just has a groove cut around the circumfrence about 1/16" up from the bottom. I was wondering if there was some kind of cap that came off then got ground to pieces.

Do you know if there is a way to remove the rod without removing the cam?
Should it just slide out the fuel pump opening?

[800XL]

Sorry I have not gotten a pic of my dead head for you. I do recall there was nothing on the end of the shaft, just a flat end. The groove also sounds familiar. The shaft has to come out the top. There is a keeper ring around it at the top to keep it from falling out the bottom. It might be possible to get that ring off and drop it out through the fuel pump hole, but I don't know. I know pulling the cam, timing belt, and etc is a tough job, but that is the only way I know for sure to get that rod out.

Sounds to me like you must have a block in the line somewhere, seems unlikely that the rod could get boogered up enough to not activate the pump enough to get you some gas. Blow some air through the line from the filter back to the tank, and pull the line at the check valve just before the pump and blow back to the filter. It would at least eliminate that as a possibility, and it is way easier than yanking the cam/belts/etc.

Since doing headwork and replacing the fuel pump on my 86 I've been having serious oil burning issues. I'm beginning to wonder if the new pump could be sucking oil into the fuel system. Previously the old pump just dripped some oil from the breather hose, but now I have no leaks, just eats a quart of oil in 100 miles. So have I had issues with the fuel pump? Yeah, I am about to bypass it and toss an electric pump on there.

[NATO4x4]

No rush on the pics. Thanks for your help in the meantime. I have blown through all the lines from the check valve back. Seems to be clear all the way to the tank. With everything hooked up as it should be and my wife turning over the engine I can see fuel in the filter pulling forward then running back. There is some pull forward but not enough to keep the gas going.

Do the check valves need to be replaced? Is there a way to test it. Napa could not locate one. I don,t even know of any local isuzu dealers.

What do you know about electric pumps?

[800XL]

On the electric pump, here is what I've come up with. You need to source power from a relay triggered by something with power when cranking, and when the motor is running. The idea being if you get in an accident the power cuts off to the pump and keeps it from feeding a fire under the hood.

Next you'd need some kind of return line plumbed in. On a previous rig I found a filter at Autozone that had large inlet/outlets like the main line and then a small return port that was pretty close to the size of the return line.

Electric pumps tend to be better at pushing fuel than pulling it, so it would be optimal to place it back closer to the tank. Mechanical pumps apparently tend to be better at pulling fuel from a distance but suck at pushing it very far. I was thinking it would work ok as a test under the hood, but if you really want the best setup it should go further back.

As for specs, I think 3-6 PSI would be about right.

It almost sounds like you have a clog near the carb, or the needle valve in the carb isn't opening. Hard telling though.

[Rude_Dog]

Electric pumps tend to be better at pushing fuel than pulling it, so it would be optimal to place it back closer to the tank. Mechanical pumps apparently tend to be better at pulling fuel from a distance but suck at pushing it very far...It almost sounds like you have a clog near the carb, or the needle valve in the carb isn't opening. Hard telling though.

Most pumps, electrical and mechanical, are better at pushing fuel than sucking fuel. I imagine the reason mechanical pumps aren't in the back by the tank, is the mechanical linkage nightmare required to operate them would never hold up. That is, mechanical pumps are near the engine because that is where they get their power. Electrical pumps have the option of working anywhere wires will reach, and having the pump near or in the tank is best.

Nato4x4, what's the actual problem you're having? Engine won't start? If so, how are you sure the fuel pump is to blame? When you try to start it, if you trickle a small amount of gas down the carb throat (first trickle, then try to start. Don't do both at the same time), does the engine at least sputter or run for a second or two and then die out again? If not, fuel supply may not be your problem.

If your carb's float chamber is correctly full, you will not see any fuel going by through the filter (when cranking or just idling). It will likely appear just as you describe (fuel pumped up to some pressure, then bled backward to satisfy an internal regulator in the pump). You would only see continuous fuel flowing if the carb's float chamber were empty, and it would only continuously flow until the chamber is full.

To see if the pump will work as advertised, you could try disconnecting the fuel line on the carb side of the pump (point the lose line into a mason jar or milk jug or some such) and get wifey to crank the engine over. If you get fuel this way, it's unlikely that the pump, pushrod, etc. is bad.

If you don't get fuel this way, unbolt the pump from the engine, but leave it connected to fuel lines. Operate the pump manually as above. If it doesn't move gas to the milk jug, and you're sure there is no blockage between the tank and the pump, the pump is bad.

Completely disconnect the pump and, while holding it in your hands, operate the pump manually while covering the suction port with your finger. You should be able to feel it build a vacuum if your finger is sealed over the port. And, if you release the inlet and cover the outlet of the pump with your finger, you should feel it pushing air past your finger when you operate it manually. You can test our next one right at the auto parts store this way.

Once you know you've got a good pump, how do you know if your carb's actually got fuel in it? Most carbs have an accelerator pump. If you operate the throttle while looking down the venturi, you can usually see a little sqirt of fuel on each stroke of the throttle. If you see the squirt, it's a reasonable indicator that there's enough fuel in the carb's float chamber to get you running. If not, you might have to take a peek inside the carb and see if the float chamber is full of fuel.

If it turns out that your carb's had fuel in it and has been working correctly for quite some time, there's a good chance your spark plugs are fouled with wet fuel. Once you fix why the engine won't start, the plugs may not spark if they're wet with fuel. It wouldn't hurt to pull them and let them dry off, or stick in some new ones.

Good luck!

[800XL]

RD: Yeah I was just relaying what I had heard about mech vs elec pumps in general. I ran an electric on an old Jeep CJ with a V6, pump sitting loose on the intake, and it did fine. Most rigs I've seen with an electric pump (other than in tank style) have it sitting below the level of the tank but very close to it on the frame rail somewhere.

You make an excellent point (points actually) about really troubleshooting out this problem. The more I think on it, the more it sounds like the pump is working fine and there is some other problem. There is a fuel return line though, so I would think that it should flow some fuel through the filter even with a full carb bowl. It would just pass it back to the tank via the return. My gut says it is a fuel problem, but some things need to be eliminated by testing. If you verify good fuel flow comes out at the line going into the carb, that would eliminate the pump and all the lines back to the tank.

A dribble of fuel down the carb throat is an great first test. If that does not get it to fire, there has to be something other than just fuel going on.

[Rude_Dog]

There is a fuel return line though, so I would think that it should flow some fuel through the filter even with a full carb bowl. It would just pass it back to the tank via the return. Fuel return line? From the pump? from an intermediate regulator of some sort? Or, is it from the carb? If it's from the carb, it's probably a vent/flood receiver. That is, if any pressure builds in the float chamber, or if the float fails, the return gives excess fuel and fumes somewhere to go that is more safe, environmentally correct and well...legislated. If the return line comes from the carb and is an actual fuel return line from a regulator internal to the carb, then I'm out of my element. I've never seen a carb with a pressure regulator in addition to or instead of float/needle setup. If the return line comes from a regulator which is plumbed in between the pump and carb, then yes, there should be no belch-back. You should see only forward swishing.

How 'bout it, Nato4x4? Let's get this thing runnin'! :bounce:

[800XL]

There is a return line on the pump. In total the pump has one inlet from the tank, one outlet to the carb, one smaller return, and one breather tube connection. Four tubes. That is unless my memory is shot, it is late and I haven't seen my fuel pump for a few months.

[Rude_Dog]

There is a return line on the pump. In total the pump has one inlet from the tank, one outlet to the carb, one smaller return, and one breather tube connection. Four tubes. That is unless my memory is shot, it is late and I haven't seen my fuel pump for a few months.That works, then. If his filter is between the pump and the carb, and his carb is full of fuel, then he might see the back and forth swishing that nato4x4 mentioned. Speaking of nato4x4, I imagine he's found/corrected his engine problems. His last post to this thread was on the 29th.

[NATO4x4]

Sorry for the lack of replys, work, house projects, 5 week old baby, bla bla.

One thing to mentoin is I have a 32/36 weber and that was my first thought. Cleaned it and it runs fine if I pour gas into it.

I was thinking there was a problem in my tank so I hooked one of those cheap plastic siphon pumps to the tank and gas pumped out. With both new and old fuel pumps hooked right to the tank and being pumped by hand I can't get consistent fuel flow. That might have to do with the return lines on the pump or it might need a check valve in line to keep moving the fuel forward.

My filter is back at the tank. The fuel system goes tank, filter, check valve?, fuel pump, carb.

The sequence of the problem was at first decreased power at highway speeds and cutting out while accelerating. I started taking longer and longer to crank. Starting fluid would get it going and it would run rough. It started lacking power at slower speeds like 1st to 2nd. Finally it refused to start. Cleaned carb, tank, filter, pump. No fuel pumping into carb.

I tried to locate a check valve today and the parts guy said I would have to point at it in a book. Go figure. When I get a few hours to piss away Ill go get one and try that. Im about to switch to LP, to hell with pumps.

[Rude_Dog]

My filter is back at the tank. The fuel system goes tank, filter, check valve?, fuel pump, carb.

I tried to locate a check valve today and the parts guy said I would have to point at it in a book. Go figure. When I get a few hours to piss away Ill go get one and try that. Im about to switch to LP, to hell with pumps.

and

With everything hooked up as it should be and my wife turning over the engine I can see fuel in the filter pulling forward then running back. There is some pull forward but not enough to keep the gas going.


OK, now, I'd say if the "check valve?" is a check valve, then it is easily what the problem is. However, before replacing it, you will want to first rule out a leak in the line somewhere between the filter and the pump. If there's an opening between the filter and the pump, on every stroke of the pump, a gulp of air will leak in. The pump would create a quick surge of vacuum which would cause an initial forward rush of fuel, but as air leaks in, the loss of vacuum would let the fuel run backward toward the tank again before the next stroke of the pump can build on the forward motion of the last stroke. This would be especially true under the non-starting conditions it's in right now. That is, carb bowl empty and the pump's not pumping very fast because of cranking speed.

If you had a mighty-vac or some such hand vacuum pump, you could disconnect and stopper the fuel filter inlet, then connect the vacuum pump to the hose that connects to the inlet of the pump. If you can't pump up a vacuum that last more than just a few seconds, then you've got an air-leak-in somewhere on that line.

[NATO4x4]

Ill go back through all the lines as soon as I can. The vacum pump sounds like a good idea.

Are there any good oem parts stores online or mail order that yall are familiar with. I need someone with enough intelligence to look up a part based on a description.

[800XL]

I had an old used 32/36 on my LUV that was doing pretty much the same thing. There is a filter screen in the carb inlet that was caked with gunk on mine. There is a brass nut looking thing on the bottom of the inlet part of the carb, unscrew that and the screen should drop out.

Other than that, it sounds like you are well on your way to tracking it down.

The check valve, I kind of assumed that is what it is. I need to dig out my factory service book and check my memory for sure. I'll go do that and let you know.

[NATO4x4]

If you have a minute to check your fsm I would greatly appreciate it. I have been calling it a check valve, but im not really sure thats what it is. Its in line right before the pump. Looks like a filter. One line in and one out directly across from one another. I can easily blow through it in both directions and I can see a little light shining through looking into the tubes. Once we figure out what it is I think it will be easier to diagnose.

[800XL]

The fsm doesn't mention a thing about it anywhere that I could find. Plenty about the pump, filter, and carb but nothing about that little doodad. I can't think of anything else that would be put in that position. It doesn't make sense for it to be a filter as it is bolted down and tough to remove. I figured with the pump so far from the tank it was a check valve to help keep the pump primed.

[NATO4x4]

Makes sense. Ill check with Isuzu next friday and let you know.