Chevy 454 backfire at speed - Page 2

leomarcotte · 07-23-2003, 12:22 PM

I think it is intake because the sound seems to be focused under the engine hump.

Power under light load seems to be fine; which is probably why the dealership mechanic thinks it is okay. When cruising on a level highghway at 65 it runs great. Going uphill is when it gets into trouble.

jim8860 · 07-23-2003, 01:42 PM

When the motor backfires under load though the intake that means a few things. 1 bad cam, not it because the power feels good or 2 running lean ( not enough fuel) I had problem 2 and I am also still fixing the problem. The problem is is the fuel system One problem: cloged fuel filter is my problem because dirt inthe tank) .That my be your as well its from sitting with a low tank . Two: You may have a bad fuel pressure regulator you will need a fuel presure tool to check it while you are driving under load. I did a quick fix with a few bottles of Amsoil fuel ingector cleaner or you may have a bad injector as well. Again look at the fuel pressure regulator .Any more question write back.

jaiman · 08-07-2003, 08:48 PM

Do you notice any irregularities with your guages when it backfires. Esp. the voltage. This could indicate an electrical problem with the main cable from your battery. I had similar problem a while back I discovered that the ground cable running from my battery to the starter had loosened and had been grounding out against my headers. It ran fine without load but the hills would cause backfireing and loss of power. Worth a look.

Silvertwinkie · 08-07-2003, 09:11 PM

I'd check the EGR valve among the other great ideas posted so far.

Eric

59toaster · 08-07-2003, 09:26 PM

Quote:

Originally posted by jaiman
Do you notice any irregularities with your guages when it backfires. Esp. the voltage. This could indicate an electrical problem with the main cable from your battery. I had similar problem a while back I discovered that the ground cable running from my battery to the starter had loosened and had been grounding out against my headers. It ran fine without load but the hills would cause backfireing and loss of power. Worth a look.

Uhhhh that's not a bad idea of soemthing to watch for.
I just had a Alternator go. It had a bad rectifier that was intermitantly sending A/C voltage. Kepet poping fuses and the engine would miss a few beats then run fine.

ALANSD · 08-12-2003, 03:15 PM

The new edition of Motorhome magazine has an article on the same situation. A P30 Chevy chassis with a backfireat speed that is occasionally there. The tech writer says to check the rear fuel pump.

He also states that the 454 runs ok on regular 87 octane gas, which suprised me, as I always run mid grade or high octane. Are you all using reguar?? Could save me some $$$$$$$ but maybe only $$$

59toaster · 08-12-2003, 05:36 PM

Quote:

Originally posted by ALANSD
The new edition of Motorhome magazine has an article on the same situation. A P30 Chevy chassis with a backfireat speed that is occasionally there. The tech writer says to check the rear fuel pump.

He also states that the 454 runs ok on regular 87 octane gas, which suprised me, as I always run mid grade or high octane. Are you all using reguar?? Could save me some $$$$$$$ but maybe only $$$

Yep Reg is fine. 454 is a relatively low compression engine. I think it's under 8:1.
Now if it has sat for a while I would recomend putting a tank of mid in it to try to get the octane back up. I suspect a lot of these engine failures folks have on relatively low mile engines is fuel related. Gas goes stale in about 30days. Typically your best to keep a full tank of fuel to help prevent condinsation in the tank. You MH folks have such a large tank it would take a LONG time to burn through a stale tank of gas. I wonder if you would be better storing with empty tank if it's going to be for more then a month. Then dump some line dry in and 5-10 gallons of fresh super.

jaiman · 08-12-2003, 05:42 PM

Mine runs fine on good old and less expensive regular. I stored mine full of gas all winter about 6 months. she started and ran fine my first trip this year. I never thought about the full tank idea. I will definately do it again this year.

Jai

74Argosy24MH · 08-12-2003, 05:47 PM

Quote:

I wonder if you would be better storing with empty tank if it's going to be for more then a month.

Stabil works great for long term storage. Might not be as good as fresh gas but it doesn't varnish and runs fine.

John

thenewkid64 · 09-14-2003, 06:42 PM

Well, I got mine fixed.

The 76 was missing at speed or heavy throttle. The issue was that the centrifugal timing adjustment in the distributor was seized.

It would start fine and run fine until warmed up. Then if driving I would give it a full throttle push, it would miss/backfire.

Idle timing was perfect, so I had the distributor replaced and the power is back! It slowly went bad, and I had not realized how much power was gone. 200.00 bucks and it was worth it. BTW I got close to 9MPG to GA towing the Saturn.

Orland Dewey · 09-14-2003, 07:34 PM

I realize its kind of later for your question. I looked at all the answers and none were the solution a friend of my had on is sob Chevy 454.
He actually blew one muffler to pieces.

His problem was the A-I-R injection pump at the exaust manifolds was working on only one side.

It took him a long time to figure it out. He said that after that was repaired it ran good.

ODD

thenewkid64 · 09-14-2003, 07:40 PM

The A I R pump would make that happen, of course that would mean I have smog controls. I don't think the smog stuff was added until the early 80's. I LOVE my 70's vintage stuff easy to fix, no emmission controls stuff, no computers, easy to fix (in most cases)