1994 454 GAS MOTORHOME CANT FIGURE OUT WHATS WRONG WITH IT WONT RUN BACKIRES MISSES SURGING HARD STARTING SOMETIMES RUNS PERFECT FOR A SHORT TIME

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Asked by Apr 25, 2014 at 11:09 PM about the 1994 Chevrolet C/K 3500 Crew Cab 2WD

Question type: Maintenance & Repair

i am a mechanic that is at the end of all options i have traced one problem to the next all of them changing it for the better in a way but ultimatly still far from a fix. let me tell you what i have done so far i was driving the motorhome up a slight grade when it starts to miss and at the same time would backfire this goes on worsing very quickly to a stall situation and on the side of the road >> think i located the prob a bad coil and some burned wires just for saftey also replaced the distrbutor module..wont start acts like its to advanced so i crank the distributer about a quarter turn starts right up perfect but only for a sec had to put it back to previous location but it runs now .  well that was good enuff to limp it home with it running very bad lots of backfires and a lot of power short of normal wouldnt go above 50mph ... next morning go by new spark plugs ceramic boot sparkplugs cap rotor with the new coil and module start it still feels rough so i time it go to hit the gas huge backfire and  fireball so i replace the knock sensor since it seems to be timing related no help i take the distributor apart repalace the pick up coil looked freyed no differance replace fuel pump filter rabuild tbiALSO VERIFIED FUEL PRESURE AND IS AT 30 PSI ROCK SOLID and replace the computer ran a new ground to the block frame batterys are brand new and replaced the map sensor there was codes that lead me to replace or investigate all these areas currently no codes starting it you have to press pedal slightly to get it to fire then will idle very low when its cold it does a wierd thing and sounds almost like its like a tractor shakes rough 45 sec like its stalling but stays running wierd .. anytime you drive it it has no power wants to die your  constantly fighting it to stay running backfires alot if your on the gas at all everyonce and a wile it clears up and will run so perfect full power nothing wrong untill it flips back to shit mode feels like im dragging a ancor backfires no power HELP ME SOMEONE IM GOIN NUTS

18 Answers

101,815

How long had the fuel been in the tank before it started acting this way? Also was tank full or almost empty? Sure sounds like it could have condensation in the gas causing the issue. If fuel was old I would drain all the fuel and refill with good fuel and fuel treatment. (Sea foam is what I use). This will also clean any carbon build up on the valves that may not be closing all the way shut. (Back fire) just a thought.

2 out of 2 people think this is helpful.
16,255

Has it jumped timing? It wouldnt be a bad idea to check. Have you shot ignition timing and set your base ignition timing since the new distributor. I know on all the trucks there is a tan/black wire to disconnect in order to do this. Idk where it would be on the motorhome

2 out of 2 people think this is helpful.
11,425

All the above sounds good. My first guess would be the timing or a short or broken frayed wire. Is the timing belt still good? If it is getting worn, or from the back firing, it may of slipped time. I had a older car with the chain timing chain, and it stretched and the cam go off on or two gears. The old 350 carburetor style, old point distributor engine did what your describing.

16,255

The 454 has a chain.

56,855

If the motor has a valve tap the knock sensor may be picking it up and severely retarding the ignition timing because it "thinks" the motor is pinging. Is it running hot? If so I'd definitely look into that. My '93 Caprice did that once it developed a valve tap. I disconnected the knock sensor at the knock sensor module and it ran fine. HTH. -Jim

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thank you all for the responces i the gas was totally drained and replaced when i did the fuel pump so thats not it the timing has been set and stays putwith the tan/black wire disconected.. i would seem if the chain was streached it would wander the timing mark under a light .. the knock sensor i thought was a major player in my problem but disconected it still runs bad .. it doesnt have a valve tick i can here but does have a exaust leak from all the backfiring its violant on backfires

1 out of 1 people think this is helpful.
10

I can tell you this. If you ran it out of gas or drained all the fuel out of the tank it will take a good 20 gallons sometimes before it will pick fuel up again. I just but a really nice 86 Itasca with a 454 that has only 2400 miles on it. They could not figure it out for anything. (the neighbor kids had been stealing the gas out of it) They had put five gallons of gas in it and figured that should have worked.Then they replaced the fuel pump and filter. Still no fuel. I picked it up for $875. I put another three fives of gas in it before it would pick it up. They were so pissed off when I drove it out of there an hour later.

1 out of 1 people think this is helpful.
95

I am having this same issue with my worrier..

1 out of 1 people think this is helpful.
95

It seems to have a long crank time before starting sometimes it starts and dies. Sometimes it starts and surges before dieing and other times it starts and seams to idle fine. But it always stalls when put into gear unless you have your foot on the accelerator. If you try to Rev it when it doesn't want to idle it will stumble then pick up but will only come up to about 3/4 of its power band and act like it has a Rev limiter. It has done this since I acquired it. I kinda thought fuel pressure but after sitting last winter the fuel pump locked up. So it is now new along with the fuel filter. And it definitely has gobbled 25 gallons of fuel up so being primed isn't the issue. .

4 out of 4 people think this is helpful.
10

Top intake is the problem it has to be removed and replaced with new gaskets and this would solve your problem to it missing and surging do your math gentlemen im SaintJoseph from Phx,Az 85041 and if you feel up to the complete job do the headgaskets as well take your time and use new head bolts and new intake bolts.Thank you gentlemen have a pleasant day. Qwickness@yahoo.com

1 out of 1 people think this is helpful.
95

Nope, wrong fuel pressure was my issue. . The new ac pump I bought to replace the original (which was frozen from sitting and evidently hurt when I bought the wennabego) was only making about 18 psi. I dropped the tank again and installed a Bosch pump making close to 30 psi and now she runs grate! So dude thanks for the input but you would have just mislead me to dump allot of money and not fix my problem.. I sprayed the intake and vacuum lines down with starting fluid early on with no change in rpm so i knew it wasn't sucking air..

I have this exact problem . I'm a mechanic and I have done everything you can think of some things I have done twice . Not one bit of improvement seems like its going to run fine when it's in park but as soon as I put it in gear it shits the bed . It backfires surges stalls etc. So I'm left with 2 more things I have been trying to avoid . Jumped or stretched timing chain or valve's not seating properly . Just My theory . Gary the mechanic

10

Did you find your problem Chris because I'm having the same one

1 out of 1 people think this is helpful.
10

I have done everything everyone said from changing the fuel pump and rebuild the throttle body. It was a poor fitting fuel cap......

10

A quick way to test smear grease or Vaseline on the rubber ring. It should take care of your hot start problem.

1 out of 1 people think this is helpful.

Im having the simular problem my 89 Rv with 454 big block Chevy engine starts idles good for a while then later if gas not pushed dies ..but it drives good at 25 miles per hour but if you press the gas harder it sputters then shuts off

11,425

Do you have a carburetor? You may have a float needing attention. If it is a FI, you may have a air leak, or dirty injectors. It sounds like a fuel flow issue.

the valves are stuck open somewhere

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