Re: Help! '95 backfiring problem

Aug 09, 2003 5 Replies

How old is the cap, rotor, plugs, and wires???



Nick


Hey guys, hope someone can help me out....
>
> I have a '95 TBI pickup with a 305. It has been running great for a while
> but occasionally, it has started to backfire through the intake at low RPM
> when trying to accelerate. The rest of the time it runs fine.
> This problem has started to happen more frequently and now when its in
> its backfiring mode it will idle and run a little rough.
> It seems to be temperature related also. Doesn't do it when cold, and
> usually happens after driving on the freeway for a bit, and driving back on
> surface streets it'll often backfire. It is definatly an on-or-off problem.
> no in between...
>
> I've checked for vacume leaks, checked and cleaned the EGR valve, replaced
> the fuel filter and looked for loose electrical fittings under the hood,
> With no improvement.
>
> Also, when its running poorly it'll bog and backfire at low RPMs, run rough
> up to about 2500, then clear right up and run strong above 3000. >
> Any answers or ideas what to look for????
>
> Thanks a lot, Brian.
>
>
> --
> Brian C. Moore
>
>

Just a wild-assed-guess on my part, but it seems to me from the conditions that you describe, that an intake valve might be hanging open, that's the only thing that would cause backfire thru the intake, and it would account for the rough running and bog. Can anyone shed any light on why a valve might hang open when engine's hot? Ed

backfire through the intake. Dont go and pull the heads off yet!

Brian,

When is the last time you did the following:

1) Tune-Up (Plugs, Wires, Cap and Rotor) 2) Checked Ignition Timing 3) Scanned the ECM for DTC's?

Doc

Oh yes, try disconnecting that MSD for sure. The check engine light will come on if it has a TDC.

Brian,

When troubleshooting an ignition problem, step #1 in the GM service manual says (paraphrased) "disconnect all non-stock equipment before begining the diagnostic procedure."

So yeah, yank the MSD and see if she runs better.

Doc

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