timing and random misfiring

[Jim Williams]

I have a 94 k1500 with a 350 and a 4l60e. It runs pretty bad and it gets about 10 mpg right now. When I first start it up and the engine is cold, it runs fine, but as it runs longer it starts randomly misfiring while cruising at a normal speed and it stumbles going up hills. Sometimes it tries to stall when sitting at a stop sign or a red light. I have replaced every sensor on the engine, the whole distributor, the iac valve, the throttle body, the intake gaskets (they were leaking coolant out the back), the egr valve
(was stuck), and pretty much every vacuum line on the thing. Every time I replace something, it gets a little better but it's still not right. My MIL is not on, and I know the bulb isn't blown out.
I was trying to set the timing this weekend after replacing the intake gaskets. I disconnected the wire so the computer wouldn't adjust the timing and set it at 0*. When I reconnected the wire, it was still showing 0*. I have an obd scan tool, and that was showing the timing at about 20*. As the truck ran longer the timing would creep down little by little, but I'm not sure if that's showing the actual timing or if it's showing what the computer is telling it to do. Either way, the timing light shows it at 0* regardless. What am I missing? Could it be the computer?

 

[RawbDidIt]

I have a 94 k1500 with a 350 and a 4l60e. It runs pretty bad and it gets about 10 mpg right now. When I first start it up and the engine is cold, it runs fine, but as it runs longer it starts randomly misfiring while cruising at a normal speed and it stumbles going up hills. Sometimes it tries to stall when sitting at a stop sign or a red light. I have replaced every sensor on the engine, the whole distributor, the iac valve, the throttle body, the intake gaskets (they were leaking coolant out the back), the egr valve
(was stuck), and pretty much every vacuum line on the thing. Every time I replace something, it gets a little better but it's still not right. My MIL is not on, and I know the bulb isn't blown out.
I was trying to set the timing this weekend after replacing the intake gaskets. I disconnected the wire so the computer wouldn't adjust the timing and set it at 0*. When I reconnected the wire, it was still showing 0*. I have an obd scan tool, and that was showing the timing at about 20*. As the truck ran longer the timing would creep down little by little, but I'm not sure if that's showing the actual timing or if it's showing what the computer is telling it to do. Either way, the timing light shows it at 0* regardless. What am I missing? Could it be the computer?

What's your short term and long term fuel trims, both banks? Also, is there oil in your coolant, or coolant in your oil?

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[Jim Williams]

I'll check out the fuel trim when I get home from work, I haven't looked at it yet. No oil in the coolant, and no coolant in the oil before or after the intake gasket replacement.

 

[PlayingWithTBI]

When I reconnected the wire, it was still showing 0*. I have an obd scan tool, and that was showing the timing at about 20*. As the truck ran longer the timing would creep down little by little, but I'm not sure if that's showing the actual timing or if it's showing what the computer is telling it to do. Either way, the timing light shows it at 0* regardless

If your timing light shows 0* and your PCM says it's at 20* I would think something's wrong with your EST (black and tan) wire connection or your ICM in the distributor (not likely your PCM is bad but, maybe). Trace that wire from the PCM to your distributor and check for continuity.

I know you said you replaced the dizzy, what brand did you use? I've seen multiple times the ICM goes bad almost immediately (my Spectra Premium did in less than 2000 miles), here and on other forums.

BTW - TBI engines only have 1 O2 sensor so you won't see STFT and LTFTs on both banks, unless you put in an L31, you'll see INT and BLM.

 

[Jim Williams]

If your timing light shows 0* and your PCM says it's at 20* I would think something's wrong with your EST (black and tan) wire connection or your ICM in the distributor (not likely your PCM is bad but, maybe). Trace that wire from the PCM to your distributor and check for continuity.

I know you said you replaced the dizzy, what brand did you use? I've seen multiple times the ICM goes bad almost immediately (my Spectra Premium did in less than 2000 miles), here and on other forums.

BTW - TBI engines only have 1 O2 sensor so you won't see STFT and LTFTs on both banks, unless you put in an L31, you'll see INT and BLM.

Probably about to get read the riot act on this, but I got a chinesium distributor off of ebay

EDIT- this one
https://www.ebay.com/itm/NEW-Igniti...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

 

[Jim Williams]

I just took this screenshot of the data from my scan tool after I let the truck run for a little bit. Hopefully someone with a little more knowledge on tbi systems can tell me how it looks

You must be registered for see images attach

 

[Supercharged111]

How's fuel pressure? I had a plugged filter make my 88 run like crap warm. Can also try unplugging O2 sensors

 

[Jim Williams]

Not sure about the fuel pressure, I'm going to get a gauge tomorrow but I replaced the fuel filter right after I got the truck. The o2 sensor is unplugged right now but it didn't seem to really affect it too much. Plugs and wires are also new

 

[Supercharged111]

My filter plugged itself quickly after I did a fuel pump swap. Must have gotten some dirt in the tank from that.

 

[Kris901]

Would definitely suspect that distributor, the pick up coil was going out on mine and giving me the hesitation at high way speeds. I ordered all good parts pulled and just rebuilt it, it’s not very complicated and as long as you have no shaft wear or gear wear just replace all electronics. Also, did you disconnect the battery while doing the timing reset? You can’t just simply disconnect the wire. I tried doing just disconnecting the wire and still kept sending my timing all erratic.