Engine Fuel Flow Stumper!

[N9VIW]

Guys, I gotta take a break from beating my head against this Jeep, I got a headache and an AMC logo stamped across my forehead...

1982 CJ7 , swapped-in '93 242 with the Gronk MC2100 carb conversion and HEI, T-176 , Dana 300 , 2.73 in stock axles. 20-gal poly tank.

It was my daily driver for the last 6 years, first with the stock AMC 258 i6 / 4.2l and then with this donor 242. I've been driving on the 242 since April, and not a lick of trouble until a month or so ago when it started acting like it was running out of gas occasionally. Now it seems I get less and less further from the house every time I test-drive it; I'm waiting for the day when I won't even be able to get out the driveway.

So far I've replaced the fuel pickup sock, fuel pickup, all rubber lines to the tank including the breathers, all steel lines to and from the tank. Because the 242 has no mechanical pump provision, I have a Carter vane-style electric pump mounted to the frame near the engine. New pump. New filters, both the inline filter I put before the pump (when I was diagnosing a similar issue that wound up being rusty steel lines) as well as the stock dual-outlet filter at the carb. All rubber lines to the filters, the pump, the carb, and the return line to the steel return to the tank. Rebuilt the carb, new needle and seat, and the float floats and does not sink. New air filter with clean prefilter.

It started one day when I got almost to work and it started giving me guff. After work I made it to the local station and filled up, and no problems for weeks.

Next time I was on my way to work and got maybe halfway there. Pulled off at a station and filled up, no problems to work or home again.

Next DAY I made it to the next town over, and it started again, with a full tank! Coaxed it home, and it died on the way. I pulled over and looked it over, couldn't see anything wrong, but the steel line I had from the pump to the carb (at the time) seemed hot. Vapor lock? Got it started again and got it home and took the wife's Tracker to work.

I replaced the steel line from pump to carb with rubber, and took it to work the next day. I made it maybe 5 miles when it started running out! Raced home, coasting and goosing it all the way, took the Tracker again.

I drained the tank, dropped it, cleaned it, blew the lines out, replaced the pickup sock, replaced the inline filters again, rebuilt the carb, and put it all back together with fresh gas.

Took it to my neighbor's house a mile away for a test run, and it died in his driveway. And again a half mile from there, and repeatedly thereafter, every few hundred feet. On one stop I opened the carb with my Leatherman, and the bowl was indeed low, darn near empty. No leaks.

I was able to make it home by pinching off the return hose to force all fuel to the carb, but several times I almost flooded it out and had to rev it up to clear the carb.

When I got home, with the engine off, I ran the fuel pump and noted that, with the return line pinched, the pump would not overwhelm the float needle- it didn't overflow, it just stopped flowing. When I removed the zip tie I'd used to clamp the return line, it started flowing again.

I want to get back in the saddle again, not only because I LOVE our Jeep and I HATE my wife's Tracker, but so she'll have something to drive in my absence.

I'm at an absolute loss- can anyone help?!

Nick

 

[TSB8C]

Fuel pump? No gas in carb bowl after cleaned out tank, new filters, rebuilt carb, insufficient pressure when return line pinched off - seems pump isn't providing sufficient fuel/pressure.

 

[N9VIW]

The thing is, I've been running on the same electric fuel pump since april, and that one was almost 7 years old. I replaced it with the new one, thinking the old one was the problem, and it did not make a difference. I suppose it's possible I got a bad one out of the box, but I would be hard-pressed to prove it since, when it is running open and unobstructed, it flows like crazy.

Does anyone have a suggestion for a good inline fuel pump to use?

 

[N9VIW]

Following a friend's suggestion, I tied the ground lead from the pump directly back to the battery negative post. I replaced the 1/4" rubber lines between the frame line, the inline fuel filter, and the pump with 3/8. (That is a little oversized, but they didn't have 5/16".) I also replaced the 1/4" return rubber line with 3/16", hoping that it would provide more resistance and ensure I wasn't flowing too much back to the tank. Oh, and the filter is definitely oriented with the return port at 12:00.

I took it for a test run and made it about 2 miles. When it died, the inline filter was full. I got it restarted, I backed into a spot off the side of the road and thought, "I've never replaced the HEI module in this distributor since I bought it used 6-1/2 years ago." I had a spare in the console, so I swapped that out. Incidentally, the distributor base was hot to the touch; who thought *that* was a good place to put a heat-generating electrical component?!

Back together, I got it started and continued on. It died a half mile or so later. I checked and still saw fuel in the inline filter. I switched on the ignition and made sure I gave it enough time in case it had to refill the carb, then restarted the Jeep and busted a quick u-turn to head home.

I babied it and idled it all the way home; it died a mile down the road back, then again about a mile later. Even letting the fuel pump run with the engine off, it took a long time to get it restarted. I got it another 100 yards and it died again.

Now I was on the frontage in front of my farm, so I popped the hood and took the top off the carb. The inline filter is still full, but that carb bowl is STONE COLD EMPTY. I switched on the ignition and watched the fuel flow; it dribbled in with no great force, gradually but not with any enthusiasm. At one point, with the float bowl still half-empty, flow STOPPED, but the pump was still running!

I pinched off the return line, and the flow started with a vengeance. It filled the bowl, the float stopped the flow... then it started seeping around the needle. I pressed the float down, and the gas positively JETTED into the bowl. When I let go, it stopped briefly, then started seeping around the needle again. I let go of the return line, and it stopped pushing as it resumed flow back to the tank. I put the works back together and got it the last 100 yards or so home.

So now, the fuel pump is running with decent flow, but most of the flow is going back to the tank rather than into the carb. And it does generate enough pressure to overwhelm the float needle, so I can't just run a single-outlet inline filter, but it's sending more fuel back to the tank rather than pushing it through the filter.

The local APS has an Edelbrock inline electric pump that does 38GPM at 4-7psi max (this one supposedly does 25GPM at 5psi max). Should I replace the pump, or try to find some way to restrict the flow back to the tank without shutting it off altogether? And why did this all happen now, with no other changes?

Nick

 

[N9VIW]

Well, it seems @TSB8C 's suggestion was right. Even though the new pump was, well, new, it was the issue- decent pressure, but insufficient flow.

I suppose I could have tested it by putting a restrictor into the return line so that SOME fuel would go back to the tank, but it would be a period of trial and error that I simply shouldn't have to do if the system were to work properly as designed.

I went to town and got the Edelbrock pump. The instructions said to mount it within a foot of the pump, at a level at or below the bottom of the tank. With a 20-gallon tank that's not going to happen, so I bolted it to the frame at the front spring mount of the rear spring.

I ran both power and ground wires back to the pump rather than grounding it at the pump, so I could tie it to the bonded lead that went back to the negative battery post. Because the new pump had an inline filter on the intake side, I eliminated the inline filter that used to be just before the pump I had mounted to the frame up by the engine, which is good and bad- I like those clear inline filters so I can see if I'm picking debris up from the tank.

After starting the pump and doing a leak check, I took it for another test drive. I went to a gas station about 10 miles away, and it didn't give me a lick of trouble- no hesitation, no stalling, no bucking, just power. I topped off the tank, took a pic at a new billboard by the livestock auction yard, then came home. Again, not a bit of trouble.

Thanks, @TSB8C, you win! And so do I!