1998 K3500 5.7 Misfire No code

[BigAustin]

1998 K3500 5.7. Misfire with no codes. Idles fine. The misfire starts at about 1400 rpm to about 4500. It clears up with high throttle and wot. Replaced all plugs, wires, cap, rotor, distributor, coil and ignition module. Changed a fuel filter but i really dont feel like its a fuel delivery problem. Im a ford guy and new to chevy. Any help would be appreciated, im really out of ideas for what to do to fix.

 

[Betty the Burb]

You need a misfire count, obd Bluetooth scanner from the jungle site and torque app has a good data logger and will count them per cylinder if you dont already have one. That can really help chase down your misfire and looking at a live data stream can really be a god send when no codes are being set. I would start by checking your live data with car on engine off to see if something is out of wack like coolant temp, intake temp, maf, tps, map.

 

[Schurkey]

The usual advice is to verify all the typical "tune-up" items, and you've mostly done that.

Vortec small-blocks are known for distributor problems--worn bushings, failed caps, worn distributor gears. Verify "cam offset" within + or - 2 degrees at 1100 rpm.

Vortec small-blocks are also known for failed intake gaskets, (generally a problem at idle, and yours idles well) and failed injector spiders. The upgraded electronic injector spider is recommended, but only from a proper brand-name/reliable source.

Verify fuel pressure.

And, yes, connect a scan tool to verify ALL the sensors and computer outputs, fuel trims, and misfire counts.

How old are the O2 sensors? They don't age well.

 

[emarkay]

The usual advice is to verify all the typical "tune-up" items, and you've mostly done that.

Vortec small-blocks are known for distributor problems--worn bushings, failed caps, worn distributor gears. Verify "cam offset" within + or - 2 degrees at 1100 rpm.

Vortec small-blocks are also known for failed intake gaskets, (generally a problem at idle, and yours idles well) and failed injector spiders. The upgraded electronic injector spider is recommended, but only from a proper brand-name/reliable source.

Verify fuel pressure.

And, yes, connect a scan tool to verify ALL the sensors and computer outputs, fuel trims, and misfire counts.

How old are the O2 sensors? They don't age well.

All of this. Strange it's not throwing a code, or not yet.

Mine ran pretty similar '97 5.7 until I dialed in the cam offset. I would check into that. Also, AC Delco cap and rotors only. The other cheap amazon stuff does not last at all I've found.

Related: https://www.gmt400.com/threads/scanner-tool-to-set-the-timing.42183/page-8#post-1320079