TBI 350 runs poorly under load/ backfires

[livelifewideopen]

1988 chevy k1500 TBI 350. Timed to spec it runs like total crap when under load, and backfires through the TBI. Timed by ear it runs best with advanced timing, but starts hard hot or cold, runs terribly cold, and occasionally backfires though the exhaust when under load. Any ideas? I suspect the distributor because it has un even resistance in it when you spin it by hand. Truck has good fuel pressure at idle, no vacuum leaks and no CEL. Any help is greatly appreciated.

 

[livelifewideopen]

Anyone have any other ideas/suggestions??

 

[House003]

Check the fuel pressure after turning the truck off. It should hold pressure after its off for about a minute I believe. But I would suspect that your distributor is the cause.. I had the same backfiring issue and running like **** problem and it turned out to be a tiny crack in the distributor cap.

 

[silverado98]

Change cap and rotor happen to me

 

[ram1220]

Just happened to me on my 90 Sierra. New cap and rotor solved it.

 

[zepplinc20]

Another thing to check would be manifold vacuum. If there was something going on with the valvetrain it would show up as an erratic vacuum reading at idle. Also, verify TDC matches the timing mark on the harmonic balancer, just in case it slipped. I just replaced one on a 350 the other day.

 

[Rusty Nail]

No CEL *

It's actually kind of difficult to turn that on, in '88.
If we knew which sensors had the ability to do so, we would know which ones it was not. Unfortunately that doesn't help a terrible lot, but it does help.

Backfiring?
Verify engine grounds. Cylinder head, CTS at thermostat, alternator to frame.

I suspect the engine is loading with fuel. Inspect spark plugs and verify grounds.

 

[livelifewideopen]

Thanks for all the help guys. replaced cap and rotor and that fixed it. Just didnt think that was the issue because they were both only 3 months/ 5k miles old

 

[WeirdTim]

Had that happen on my 1990 C1500 5.7 a month ago. New Blue Streak Standard cap & rotor with brass contacts around two years and 3K miles ago. Loss of power, hesitation and missing. Got a AC Delco cap and rotor. Pulled the Standard stuff off and the contacts were very badly corroded with crud hanging off them. The center contact on the Standard rotor is very thin compared to the AC Delco.

After I installed it ran better but still had a little hesitation until it got warm. So I changed plugs and wires. Found one plug that had fowled badly with a lot of junk around the electrode. It was the same cylinder that had the worst contact on the distributor cap.

Used AC Delco Professional wires. Tough to find AC Delco stuff anymore. Actually got it all from Amazon.com for a decent price.

All is fine now.

So many just start throwing parts without diagnosing anything.