New to me 2000 K2500 missing at idle, occasional stalls

[Nicman201]

I just got this thing and I could use some pointers. First 454 and the first OBS I've had. I've always had a gmt800 truck and I put a cam and stuff in one of them so I'm somewhat mechanically inclined.

First off, I hear no ticking or valves train noise.

The cats were cut out because they were clogged by the guy I bought it from.

I noticed it never got up to operating temp so replaced thermostat and coolant temp sensor. I know if it doesn't get up to temp the computer dumps more fuel in it, maybe clogging cats.

Also did spark plugs and wires. Some of the worst I've ever seen. 6/8 cylinders, the spark plugs were completely worn down til the electrode was gone.

It still misses at idle, but not enough to throw a code.

Sometimes at a stop light or just idle in the driveway it acts and sounds like it's about to stall. The idle bounces.

Even more rarely it does this while I'm driving. As I'm accelerating it seems like it stumbles and wants to stall.

It didn't start this oddness until after I did all this work. I even noticed some plug was undone up behind the intake by the distributor when I was replacing wires. So I plugged it back in. I don't know what it was. Couldn't see it. I disconnected the battery thinking maybe the computer had to learn how to run with everything in such disrepair, it didn't know how to run with everything working. It ran fine for almost a week and just started doing the cutting out thing again.

Where to start?

 

[Nicman201]

I just got this thing and I could use some pointers. First 454 and the first OBS I've had. I've always had a gmt800 truck and I put a cam and stuff in one of them so I'm somewhat mechanically inclined.

First off, I hear no ticking or valves train noise.

The cats were cut out because they were clogged by the guy I bought it from.

I noticed it never got up to operating temp so replaced thermostat and coolant temp sensor. I know if it doesn't get up to temp the computer dumps more fuel in it, maybe clogging cats.

Also did spark plugs and wires. Some of the worst I've ever seen. 6/8 cylinders, the spark plugs were completely worn down til the electrode was gone.

It still misses at idle, but not enough to throw a code.

Sometimes at a stop light or just idle in the driveway it acts and sounds like it's about to stall. The idle bounces.

Even more rarely it does this while I'm driving. As I'm accelerating it seems like it stumbles and wants to stall.

It didn't start this oddness until after I did all this work. I even noticed some plug was undone up behind the intake by the distributor when I was replacing wires. So I plugged it back in. I don't know what it was. Couldn't see it. I disconnected the battery thinking maybe the computer had to learn how to run with everything in such disrepair, it didn't know how to run with everything working. It ran fine for almost a week and just started doing the cutting out thing again.

Where to start?

Ok closer inspection of the spark plugs, show 2 different models of AC Delco plugs. So maybe they aren't as worn as I thought, just a different style. But that also makes me say wtf lol

 

[Schurkey]

Verify fuel pressure, under load if possible. Assure that the fuel filter is in decent condition.

Connect a scan tool, find out which cylinder(s) are missing. Verify that the O2 sensors are working like they should, and the IAC responds.

 

[Nicman201]

Verify fuel pressure, under load if possible. Assure that the fuel filter is in decent condition.

Connect a scan tool, find out which cylinder(s) are missing. Verify that the O2 sensors are working like they should, and the IAC responds.

Umm brake line busted so I was under there today and the fuel filter looked new and shiny.

I did have my torque app open and graphs were showing 3 cylinders occasionally misfiring, did not really record which cylinders cause I basically saw it and said well **** and shut it off lol

 

[Nicman201]

Umm brake line busted so I was under there today and the fuel filter looked new and shiny.

I did have my torque app open and graphs were showing 3 cylinders occasionally misfiring, did not really record which cylinders cause I basically saw it and said well **** and shut it off lo

Verify fuel pressure, under load if possible. Assure that the fuel filter is in decent condition.

Connect a scan tool, find out which cylinder(s) are missing. Verify that the O2 sensors are working like they should, and the IAC responds.

This is a totally new motor for me. So I'm completely ignorant. But after looking at pictures of the distributor, that random wire that was unplugged felt like the 3 pin connector that goes into the distributor. Unless there is another sensor back behind the intake and distributor I'm unaware of. Not sure how I made it back from Wisconsin with this thing unplugged with no codes if that's the case.

Anyways, I'm going to look at the misfires again soon and update this with which 3 cylinders are misfiring.

Ok so on a cold start, torque didn't report misfires until it warmed up a little and idled down.

It's showing maybe 4 cylinders misfiring. Can't tell cause it chose the color red to report cylinder 1 and cylinder 8. Missing in the pic, was cylinder 3 was slightly misfiring too.

Guy said he had a new distributor put in... Did they maybe not have the dizzy angled right for timing with this cam offset you're supposed to look at with a fancy scan tool?

 

[Nicman201]

This is a totally new motor for me. So I'm completely ignorant. But after looking at pictures of the distributor, that random wire that was unplugged felt like the 3 pin connector that goes into the distributor. Unless there is another sensor back behind the intake and distributor I'm unaware of. Not sure how I made it back from Wisconsin with this thing unplugged with no codes if that's the case.

Anyways, I'm going to look at the misfires again soon and update this with which 3 cylinders are misfiring.

Ok so on a cold start, torque didn't report misfires until it warmed up a little and idled down.

It's showing maybe 4 cylinders misfiring. Can't tell cause it chose the color red to report cylinder 1 and cylinder 8. Missing in the pic, was cylinder 3 was slightly misfiring too.

Guy said he had a new distributor put in... Did they maybe not have the dizzy angled right for timing with this cam offset you're supposed to look at with a fancy scan tool?

After watching it for another few minutes. Basically every cylinder is randomly missing

 

[someotherguy]

Past experience says that the cam retard can be pretty significantly off without triggering the P1345 code, so confirming that first would be wise, especially since we know the distributor has been out/replaced. I haven't had to do one in quite a while; back when I did I had a dedicated scan tool with the capability - others may have cheaper solutions (bluetooth/app based) these days that I'm not aware of. Within 2 degrees of 0 while holding RPM's to at least 1,000 to ensure a good reading, that's what you are shooting for.

If this was a small block Vortec we'd be immediately suspicious of fuel pressure. They are very finicky about it due to the poppet valve injector setup. Your big block has real injectors and it will run reasonably well even with marginal fuel pressure, though testing it is smart while you're troubleshooting. 58-62 is the spec on that engine.

The fuel pump relay can be a trouble spot on the Vortec trucks. When the pumps begin to go bad they may draw more current and exceed the circuit design; sometimes the connector inside the sender burns up, but frequently the relay and its socket burn up. You can tell which one is the fuel pump relay because it'll be the hottest sumbitch in the electrical center. Next time your engine starts stumbling like it's going to stall, give that relay a wiggle; if it briefly clears up you're probably dealing with burnt relay / relay socket pins.

Richard

 

[Nicman201]

Past experience says that the cam retard can be pretty significantly off without triggering the P1345 code, so confirming that first would be wise, especially since we know the distributor has been out/replaced. I haven't had to do one in quite a while; back when I did I had a dedicated scan tool with the capability - others may have cheaper solutions (bluetooth/app based) these days that I'm not aware of. Within 2 degrees of 0 while holding RPM's to at least 1,000 to ensure a good reading, that's what you are shooting for.

If this was a small block Vortec we'd be immediately suspicious of fuel pressure. They are very finicky about it due to the poppet valve injector setup. Your big block has real injectors and it will run reasonably well even with marginal fuel pressure, though testing it is smart while you're troubleshooting. 58-62 is the spec on that engine.

The fuel pump relay can be a trouble spot on the Vortec trucks. When the pumps begin to go bad they may draw more current and exceed the circuit design; sometimes the connector inside the sender burns up, but frequently the relay and its socket burn up. You can tell which one is the fuel pump relay because it'll be the hottest sumbitch in the electrical center. Next time your engine starts stumbling like it's going to stall, give that relay a wiggle; if it briefly clears up you're probably dealing with burnt relay / relay socket pins.

Richard

Good to know! Thank you! The guy said he replaced tank and the sender. It's a steel tank and it's shiny. So you may be on to something with that relay.

If it was indeed the distributor computer wire that I found disconnected and I plugged it in, I'm not very hopeful that they used a scan tool to verify timing. Lol.

I don't think Torque has this capability, does anybody know?

Edit: the relay looks new. It's black, not gray like the others, and not dusty. Doesn't seem like the socket fried

 

[Nicman201]

Good to know! Thank you! The guy said he replaced tank and the sender. It's a steel tank and it's shiny. So you may be on to something with that relay.

If it was indeed the distributor computer wire that I found disconnected and I plugged it in, I'm not very hopeful that they used a scan tool to verify timing. Lol.

I don't think Torque has this capability, does anybody know?

Edit: the relay looks new. It's black, not gray like the others, and not dusty. Doesn't seem like the socket fried

I just reached behind the intake to see what it was I plugged in and I'm positive it WAS the distributor computer wire.

So many questions, how did it get me from Wisconsin to the twin cities with that unplugged. With no codes.

 

[smokymtn65]

I don't think any of the BT apps will do it. Tech2 or one of the bit higher end bi-directional scanners