454 Back fire thru exhaust

[saulfun1971]

I have an 88 Gulf Stream Sunsport that I recently bought. It has been sitting for 2 years and it runs good except at about 50 to 55mph it back fires thru the exhaust. E have changed plugs and wires and rebuilt carb. Does anyone know if it has an inline fuel filter? Also the distributor and coil looks new inside?

[Gale_Hawkins]

wa8yxm wrote:
Though I do admit that on many vehicles the exhaust is to the rear and thus "BACK FIRE" might be proper.

In automotive terms a back fire is a fire backwards (Out the air intake instead of the exhaust)..

That said.. Good advice above.. I can not improve on it.

I guess I call After Fire Back Fire 🙂

[wa8yxm]

Though I do admit that on many vehicles the exhaust is to the rear and thus "BACK FIRE" might be proper.

In automotive terms a back fire is a fire backwards (Out the air intake instead of the exhaust)..

That said.. Good advice above.. I can not improve on it.

[Gale_Hawkins]

saulfun1971 wrote:
It does the back fire during acceleration of 50 to 55. It did it before and after changing new plugs and wires

Had back firing twice with our 1992 454 TBI. First time it was the pick up coil under the distributor. We did the labor and the part cost $13 but I would just with a rebuilt distributor next time I think.

The second time it turned out to be a dirty fuel filter .

Both problems had the identical symptoms. As noted with a carb you should have two fuel filters.

[Jayco23FB]

Does your truck have an air pump as part of the emmisions system? A bad diverter valve and or check valves on the air manifold will cause this. This is a 1988 and it still has a carb? Most of GM trucks switched to throttle body injection in 1987.

[ernie1]

GM distributors are known for the centrifugal advance, which is fastened to a rotating plate, gumming up and not rotating anymore or being balky. Grab the plate by hand and see if it'll rotate. If not, the distributor has to be disassembled and cleaned. You can also check the operation by removing the vacuum line to the vacuum advance and then using a timing light and revving the engine to see if the timing changes.

[powderman426]

darsben wrote:
454 engines are notorious for collapsing the vacuum advance tubing. Please replace the tubing going to the distributor with new tubing.

X2 and listen for vaccum leaks.

[darsben]

454 engines are notorious for collapsing the vacuum advance tubing. Please replace the tubing going to the distributor with new tubing.
EDIT:
Also to answer your question My carb has a filter at the inle

[saulfun1971]

Thank you for you help! Will try these things and get back with you both. Hopefully I can get this fixed by wed nite. Suppose to leave on a short 2 hour trip on thurs morning?

[enblethen]

Crossed plug wire.
Verify firing order and wiring.

[saulfun1971]

It does the back fire during acceleration of 50 to 55. It did it before and after changing new plugs and wires

[ScottG]

A filter isn't going to make it backfire through the exhaust.
Did it do that before the new plugs? Does it do it more under a load? Is there a stumble feeling? (EGR)
If a plug gets cracked during installation it can act like that.
You could also have one or more valves sticking because it sat so long. Running some good fresh fuel with a can or two of Seafoam through it may take care of that if it's the case.

[enblethen]

There should be a large in line filter along frame rail just in front of right rear wheels.
Carb getting rebuilt should have taken care of filter in the inlet port there.
Backfiring is more likely to be electrical. Check to make sure the plug wires go to the correct one.
Check the EGR valve and vacuum control lines.
Does the back firing happen during acceleration or deceleration?