89 k3500 454 rough idle

[itzjoe]

Just bought a '89 k3500 1 ton for a good price to add to my gmt400 army! It has a 454 and interestingly enough its paired with a SM465 4 speed. Ok back on topic. it was sitting since about '07 or so and i got it running on Friday. Before Friday it would not start at all, it would backfire through the throttle body. I figured the gas in there was bad because the PO tried to start it, and yes it ran rough when he tried it, he was also using fresh gas at that time. that was in about April this year. there was only like 1/8th a tank so i dumped in like 3 gallons of premium gas and she pretty much fired right up. So it Idles rough, sounds like its missing. almost dies sometimes. But once i give it throttle it sounds fine, I was even able to drive it around and it did just fine except when it fell flat on its face and almost died but once i go back to idling it idles rough and backfires aswell. ill try to get a video tomorrow if i can.

Heres a list of whats been done so far:
-O2 Sensor
-Cap and Rotor
-New Plugs
-New Plug Wires

No codes or dummy lights. If anyone has any ideas id appreciate it! Thanks in advance! Sorry for the miniature novel.

 

[RichLo]

Probably fuel related since you upgraded the ignition already, first thing I would do even if it wasn't running rough is pull the throttle body and do the ultimate TBI mod. You'll probably find a problem when you do this, either a bad fuel pressure regulator or sticky injector. I would run a bunch of seafoam through one tank of gas to clean the injectors first though.

 

[itzjoe]

I put some Chem tool in the tank aswell as some more gas today. I think it smells like it's running lean. It's still backfiring through the exhaust I think. And sometimes when cranking it backfires through the throttle body with such force that it blows the lid of the air cleaner lid off because there's not a wing nut on there. Would that be the cause?

 

[RichLo]

That would be running rich

Rich = Backfire through exhaust when running, fireballs out of intake while cranking over
Lean = Coughing out of intake when running, cranks over for a long time before starting.

I would definitely rebuild that throttle body and probably put in an adjustable pressure regulator too.

 

[itzjoe]

Would that be causing the misfires and rough idle? I tried to get a video this morning but my phone wasn't working right but now it's at the point where it won't run at all for the most part. I was driving it and it just completely fell on its face and died today when I was going to repark it and go get parts. I couldn't get it to start and stay running it'd bog down and die and backfire over and over again just like before I had it running. Exept this time it'll start up and actually idle roughly I must add then die within seconds. It was backfiring through the throttle body when trying to crank it back over. I did have a buddy take a video but it's with the air cleaner on and it flying off. I'll see if I can have him come on Friday and get one with the throttle body up close with out the air cleaner.

Edit #1: Already got a rebuild kit on order. What else should I look for? Any other fuel delivery issues or ignition issues. What about the pickup coil? Maybe the dizzy it's self is causing the misfires? Uploading video currently. It used not to backfire through the throttle body when running and bogging out, just the exhaust. It backfired through throttle body only when starting every now and then but now it just bogs out and backfires and dies

Edit#2: Here's the video. Too bad this wasn't when it was shooting fireballs through the throttle body as it did after the video

https://youtu.be/K_-9-40TSkI

 

[itzjoe]

Please anyone have any ideas. I got a video of the throttle body its self and will upload in a bit and add on here!