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guy99 · 03-13-2010, 09:11 AM

Definitely replace all the fuel filters. My rig has three, one at the rear pump, one under the step, and one in the carb at the fuel inlet.

But, if you heard backfires, I'll give odds your problem is ignition.

thecatsandi · 03-13-2010, 09:13 AM

Sorry your trip was cancelled.
Check (replace) your vaccum lines. The spark advance/retard may not be working. When you put the pedal to the floor is sounds like flooding or ignition bad timing. Have the carb inspected look under the cap for signs of arcing. A fuel filter will cause a sluggish response. However it usually does not cause backfiring.

Diesel1 · 03-13-2010, 09:24 AM

I'll jump in on the cap roter combo. Chevy's HEI seem's to be prone to roter/cap failure. Your symptems seem ignition to me,not fuel. Adios, John

kmpro · 03-13-2010, 09:32 AM

My $ .02 worth. If it sputters under 45mph=Ignition. Over 45mph usually fuel.

Phoenix · 03-13-2010, 10:43 AM

We had an old Chevy crewcab with a 454. Rebuilt the carburetor twice over the years, because the float went bad (sank) and overfilled the bowls, which flooded the engine. It would run, but no power. The big clue was a really strong gas smell from fuel running out of the carb. It's getting harder and harder to find anyplace that rebuilds carburetors anymore...

garry · 03-13-2010, 10:59 AM

I have had the problem twice both times fuel filter.

What I do not understand is the loss of power in reverse but no problem going forward unless you got on it. Mine did the same thing.

Always carry a spare as they can go out with little notice.

DaveFL · 03-13-2010, 08:39 PM

Quote:

Originally Posted by Buttercup

no power to the MileMarker Overdrive.
was sputtering,
zero power
backfiring
wasn't enough power.

Had same, but at highway speed, second time on takeoff from light.

Turning key off and back on, it drove home, motor runs fine, proceeded to replace parts recommended by others and did tests, did a 2500 mile trip never to happen again, my problem is I don't know which item fixed it. So I hope you try motor after each procedure, then you will know what fixed yours as your problem isn't intermitant. Mine didn't have any symptoms outside of the two times losing power

.

kmpro · 03-14-2010, 01:28 PM

Just thought I would fire up my 454 and suddenly I had a BAD CASE of the Sputters. Could'nt figure it out for a minute, then hit the boost pump switch and viola! sputters gone. Seemed like ignition but when I hit the Auxillary pump everything went back to normal. The extra 3 feet added to the chassis when AS built it is more than the mechanical pump on the engine and the tank pump will handle on my rig, so the boost pump just back of the step has to be on or it's no go period.

guy99 · 03-14-2010, 01:47 PM

I've never heard of a third pump. My 84 310 sure doesn't have one. Is your tank pump in the tank or external?

kmpro · 03-14-2010, 07:55 PM

I'll have to check the shop manual from Chevy, but I think the tank unit has a pump built in as part of it. Could be I'm thinking of the Ford chassis, so I'll check the manual. I do know I have auxillary pump amidship and the mechanical pump on the engine.

choctawmel · 03-15-2010, 06:28 AM

Water in the gas tank. Add some 'Heat'. I had this problem with the Silver Bullet. One day I was putting gas in her and I noted gas running out on the ground. The fill hose had a hole in it. I replaced it that night in an RV park. Fixed that problem.
mel

Buttercup · 03-15-2010, 01:18 PM

Well, I think we have found the problem(s). First the simple things, new plugs, wires, filters all the way around. In changing the plugs and wires (not an easy task actually, I discovered that the #3 cylinder wire was probably burnt up. When I removed the wire the internal connector stayed on the plug. When I yanked that off the plug and examined it I saw some carbon burnt stuff. I think the wire just failed.
The fuel filters were replaced. Did you know that on the 1990 345LE there are 3 of them? One by the gas tank on the suction side of the forwarding pump, one just forward of the stairs and the last on the carb body (for normally aspirated engines). I got 2 of the 3 changed. The one by the stairs was too hard to get out and not worth my time.

The cap and rotor looked clean enough to skip replacing.

Bottom line, it runs and we will head out this weekend for Death Valley. Sure hope I don't have to post from the road for help.

ROBERT CROSS · 03-15-2010, 01:27 PM

KISS usually works...keep post'n

Good Luck...

Safe Streams..

3 Dog Nite · 03-15-2010, 03:40 PM

Yahoo!! Glad to hear it was an easy fix for you. Don't regret the parts you replaced. They're all just part of routine maintanence. I went through that near Roswell, NM. It turned out I had bad gas somewhere. A bit of carb cleaner & topping off the tank twice with high test got me going. But only after a complete tuneup w/ new cap,rotor, & wires.

Ricky