LUVTruck.com

A couple weeks ago my truck started shutting itself off on the freeway. It just shuts off for a split second and then regains power and shuts off again, over and over again. I give it more gas and it does it worse. It doesn't do it unless at 40mph or over. This has happened three times in a few weeks. Happens after driving for an hour. I get to work and it's fine on the drive home.

I have a permanent digital voltage gauge and I moved the + lead to the coil wire, to be sure that the ignitor and coil weren't losing power. I have examined the gauge during the shut offs and it reads 14V. I have a relay directly to the battery from the coil. The coil is an MSD blaster SS. I run NGk plugs at .045. Timing is good. I have a vacuum gauge that shows the dip in power.

I replaced the fuel filter and cleaned the filter in the Weber when it first started. The Weber filter looked spotless, that's what made me move the voltmeter lead to the coil, but that's not the issue either.

I can see about having the carb rebuilt. I can probably check the float level myself, which I have not done. I have never checked the fuel pressure but the truck has run fine for two years until now. Motor has 23k miles on rebuild. New plugs, wires, cap, rotor, coil within last 6 weeks.

I have a spare ignitor I can swap on. The shut down feels like the car is being turned off, it's sort of a sputter but when it's got power, it's full power, when it's off its completely dead.

I can go back thru the ignition wiring and magnetic pick up again. I think I built it pretty securely last time I put it together. (I had been swapping between and MSD 6 that never worked right)

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1979 4wd Mikado. G200, Gemini 250 Turbo, Clive Cam, Offenhouser Intake, JE Pistons, maXspeeding Forged Rods, Blow Thru Weber, Trooper 5spd, Intercooled

Back in the 80's with my first truck I had what sounds like the same issue. My truck would die on the freeway and as soon as I pull over it would start right back up and go again. It was the fuel filter by the gas tank on mine. You said you replaced it already though. If you still have it try blowing some air through it. Has your tank ever been cleaned out?

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Three Amigos

I would suggest checking the fuel pump itself for good flow. Sounds as if the carb is using the fuel faster than fuel pump can refill it. Start engine and let idle. While idling remove fuel hose from carb and check to see how much fuel is coming out. If not much flow replace the pump. Hope this helps.
Mike.

See what happens if you take the gas cap off. There is a full line to the carb and a return line also. If the return line is crimped or clogged the tank can develop a vacuum that restricts fuel flow.

I recently got a new gas cap because I lost my old one, and the seal is unusually tight. The thing makes a large sucking sound when I open it. I'll try relieving the pressure each day.

I don't have a return line from the weber.

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1979 4wd Mikado. G200, Gemini 250 Turbo, Clive Cam, Offenhouser Intake, JE Pistons, maXspeeding Forged Rods, Blow Thru Weber, Trooper 5spd, Intercooled

You need to drill a very small hole in the new fuel filler cap to vent the tank. This may not cure the problem but the increased vacuum is certainly straining your fuel pump unnecessarily.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

Yeah this could very likely be my problem. I have been thinking that the truck acts sometimes like when I hit the gas harder I'm not getting any more fuel. The vacuum drops on the gauge but I don't go any faster. Also, when I have to press the gas harder, I don't necessarily get worse mileage on that tank. I have been thinking this is awkward because I feel that when I'm pressing harder on the pedal, and the vacuum is worse, I should be using way more fuel. I flipped the gasket over on the gas cap today and I think it's not building pressure any more but I'll know more as I drive more.

Thanks for the help, I would have never figured this out.

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1979 4wd Mikado. G200, Gemini 250 Turbo, Clive Cam, Offenhouser Intake, JE Pistons, maXspeeding Forged Rods, Blow Thru Weber, Trooper 5spd, Intercooled