rough running....backfiring 350

Ken B · Apr 22, 2026

So here is my issue....my truck which has a 350 runs good if the trans is in park....rev it up and it runs good. Put it in gear and try and drive and it coughs and backfires and shimmy and shakes...any ideas??

bucket · Apr 22, 2026

Still a Quadrajet?

Ken B · Apr 22, 2026

i put a rebuilt on it but yea

Sad Sack · Apr 22, 2026

First things first- fuel pressure and vacuum readings at idle.

Ken B · Apr 22, 2026

I do not have an answer to either of those questions. Very limited knowledge of the actual setting/readings/pressure.
I could drop on a carb and that's my true knowledge.

Sad Sack · Apr 22, 2026

Ken B said:
I do not have an answer to either of those questions. Very limited knowledge of the actual setting/readings/pressure.
I could drop on a carb and that's my true knowledge.

Stock engine idle vacuum at 21hg and fuel pressure 4-7 psi. The tools to check these are cheap and lots of YouTube vids on how to do.

Ricko1966 · Apr 22, 2026

Check firing order especially make sure 5 and 7 aren't crossed. Most back fires are ignition.

Sad Sack · Apr 22, 2026

Got a spare ignition module?

Ken B · Apr 23, 2026

Thanks for the starting points.
Body shop said they had a mechanic that could do stuff for me but maybe he was too young and didn't have lots of experience on old sh!t

Ken B · Apr 23, 2026

I didn't have this issue b4 new plugs wires and vacuum booster addition and "cleaning up engine bay of "extra stuff" including Charcoal cannister removal.

Sad Sack · Apr 23, 2026

Ken B said:
I didn't have this issue b4 new plugs wires and vacuum booster addition and "cleaning up engine bay of "extra stuff" including Charcoal cannister removal.

Ok, helpful info. Like @Ricko1966 said check wires for firing order. Removing the charcoal canister will have ramifications and not good ones.

Ken B · Apr 23, 2026

thanks. I think i am going to learn some things by necessity....firing order 1st.

74Blaze · Apr 23, 2026

Also could be bad gas.

Ken B · Apr 23, 2026

Please allow me stupid questions....I just dont know but really want to figure this out.
Why would this vacuum line be plugged?
Shouldnt that have vacuum hose to the front of the carb???

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Ken B · Apr 23, 2026

Gentlemen does it look like I have these labeled correctly...sorry the pic isnt the best....
trying to look at things one step at a time I have not moved or removed anything yet , just trying to label and learn right now

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rough running....backfiring 350

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