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Engine dies at 3000 RPM

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fried_guy

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Fallbrook, CA
My truck always stumbles, back-fires every now and then, and sometimes dies at 3000 RPM. Sometimes I can get the engine to keep going and if I lay off it's ok. But at other times, no matter what I do the truck dies and won't start for like a minute.

This has happened once just cruising and I thought it was out of gas since the original gauge was at 1/8. So I went and got gas and it started up fine.

My carb's jets, squirters, cam, transition, and idle have been tuned. My timing is set at 34* total. Vacuum advance is on full manifold vacuum. I have a decent carter mechanical fuel pump that SHOULD supply this no problem. I have a cheap in-line electric that I use when the floats are empty to aid startups. I have a good fuel regulator with a return line. 4-hole spacer on my manifold to keep the fuel cool. Both in-line filters and the carb filters are spotless. Plenty of gas in the tank.

I haven't been home in a few days, but this seems fuel related to me. Any ideas? :confused: I want to get this in the snow damnit! :D
 
What kind of carb? If you get it to die, check that there is fuel in the carb. If there isn't, you've got a fuel delivery or needle/seat/float issue I'd think.

I'd run my Q-jet out of fuel when I ran it for a prolonged period at high load, stepping the secondary rods down a step took care of the problem.
 
It's a 670 truck avenger. I'm suspecting my fuel pump and I'm going to probably end up replacing it with a high quality electric pump.

When time allows I'll drive it down the street and try and get it to die so that I can check my bowls. Needle/seat seem fine as I've already opened up the carb and cleaned it all real well a few times already.

I have a rubber gas tube that is in a 90* bend to the inlet of the mechanical fuel pump that could be collapsing as well I suppose.

Any other things I should check?
 
Put a fuel pressure gauge on it. Backfires are usually caused by a lean condition. If the gauge shows 5+ pounds of pressure, then its time to look at the carb. Maybe step up in jet size, if the carb checks out good.
 
check your power valve circuit. It could be possible that your power valve is killing your engine by not opening when your engine needs the fuel. The reason why it would keep going when you romp on it is your accelerator pump is compensating for this by shooting fuel into the engine.
 
Thanks, I thought of the PV already and replaced it. And I've got a pressure gauge on it, but it's in the engine compartment so I can't see it :)
 
I'm curious how well the mechanical pump can suck fuel through the cheap electric inline pump. It could be too much restriction in the line with the electric pump turned off. Are you running the electric when this happens? It sounded like you only run it when you're starting the truck from your description.
 
throttleissues said:
I'm curious how well the mechanical pump can suck fuel through the cheap electric inline pump. It could be too much restriction in the line with the electric pump turned off. Are you running the electric when this happens? It sounded like you only run it when you're starting the truck from your description.
Click to expand...

We have a winner. A fuel pump is made to push fuel not suck fuel which is exactly what you're making the mechanical pump do by having an inline electric pump as well. There is a way to keep the electric pump without affecting the mechanical one but it would require a couple Tee's to make it work.
 
I had a problem before with my carbed burb. It would quit running or act like it was starving for fuel and wouldn't go up any inclines in the road. Every time it would quit running the glass fuel filter would be empty, so I thought it was fuel related. Changed fuel pump, the lines to the tank, dropped the tank and it was spotless and changed the sock, even bought another Edelbrock carb, problem still there. I finally changed the pickup coil in the distributor and that solved my problem.
Just my 2 cents thrown in.
Tarey
 
Sounds like something similar to what mine was doing. The floats on my carb were set all kinds of wrong. Unfortunately, I can't say what the root cause was. I set the engine on fire while adjusting the rear float. It's about to get torn down to get fitted for MPFI now... :D
 
Is it an H.E.I.? The modules are supposed to be good to 4000 rpm or less. Can you try to put a spare in there to check it out?
 
is the tank vented,is there something letting the air entering the gas tank?
there should not be any vacuum inside the tank or pressure when u open the gas cap


a bad gas cap??

just my 2 cents!!
 
I doubt it's the pickup coil as it's a brand new distributor. And yeah it;s HEI, but I'm using an off-road ignition box so it should go beyond 6000. As it's dying, if I pump the gas it'll go again, which says it likes gas, but is only getting it from the squirters and not the bowls. So I'm pretty sure it is carb related. Gas tank is vented fine too. I was actually thinking the sock as well. The gas tank was sitting quite a while.

I'm gonna drop my tank when I get some time off work and take a peak in there. If the tank is fine I'm going to put in one of the new quiet 120gph edelbrock electric pumps. Anyone tried these yet?

I'll be upgrading my altenator and some wiring in the mean time too.
 
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