Misfire when warm.

[OR VietVet]

Check this link out: https://www.fixmyoldride.com/Chevro...e7e5cd24ed24635&at_ab=per-2&at_pos=3&at_tot=4

 

[iamdub]

If your ignition parts are the house brand, and especially if Autozone (Duralast), you can't rule out a faulty ignition component yet. If you can/do rule out ignition, then check fuel pressure. Fuel pump is an electric motor and it could be heating up. A heated motor gets weaker. If not the pump itself, then it could be the circuit feeding it. A poor ground can cause a motor to heat up. A truck that has been sitting could have a poor ground... See where I'm going with this? GM's factory wiring (including grounds) is, IMO, undersized. So, it wouldn't take anything more than a cruddy connection to deem the circuit heavily insufficient.

 

[grouch]

I found a rental pressure gauge kit with the adapter I need. $160 but I'll get it back when I return it. It's a 27, nearly 28 year old pump and it looks like it's been in there a while.

I have another issue with the truck that I finally found a cause/effect connection. Sometimes the radio doesn't power on. The old radio didn't work but would sometimes power on. When I opened the hood with the release, the radio cut off for a moment when the hood popped up to the safety catch. So I have an electrical issue that may or may not be related. This is a nice basic truck and except for the color (I hate white, it's so bleak) it's what I need.

 

[iamdub]

I found a rental pressure gauge kit with the adapter I need. $160 but I'll get it back when I return it. It's a 27, nearly 28 year old pump and it looks like it's been in there a while.

I have another issue with the truck that I finally found a cause/effect connection. Sometimes the radio doesn't power on. The old radio didn't work but would sometimes power on. When I opened the hood with the release, the radio cut off for a moment when the hood popped up to the safety catch. So I have an electrical issue that may or may not be related. This is a nice basic truck and except for the color (I hate white, it's so bleak) it's what I need.

Factory radio? That could just be a loose connection in the dash or, unfortunately, 100 other places. The sharp jarring from that big ass hood popping up could've shaken the harness just right to make the radio lose power for a second. Next time it's off but should be on, use your fist to bump the radio and to beat the dash around it. Maybe gently but slowly move and pull on the wire harness under the dash.

 

[exp500]

Check the engine to body ground wires, battery to ground, disassemble battery ground cable if 2 piece at battery, disassemble positive batt cable at battery, clean inspect reassemble or replace.

 

[grouch]

Factory radio? That could just be a loose connection in the dash or, unfortunately, 100 other places. The sharp jarring from that big ass hood popping up could've shaken the harness just right to make the radio lose power for a second. Next time it's off but should be on, use your fist to bump the radio and to beat the dash around it. Maybe gently but slowly move and pull on the wire harness under the dash.

Beating didn't do any good. I suspect a loose connection on the fuse block. I tested the fuel pump and it's supposed to run between 9 and 13 psi. A steady 11 running, static and under load. The pump is good.

I started cleaning grounds. Man, there are a lot of them. Each of them so far has been pretty dirty except for the ones I cleaned when I first got the truck. On some GM products in the early 70's there were ground issues from fireall to block straps missing. I'll add a couple between the firewall and the engine and one from the fender to the engine.

 

[exp500]

That fuel pressure is on the low side, I like to see over 16 on these. Many have been over 20. Try a Quantity test. Pump into a bucket at fuel filter for 5 minutes. You need a minimum of 5 gal/hr. Also check your connectors at injectors. Good Gaskets and tight. Wires twisted. If untwisted twist them. I forgot how many turns but I think 7/ft minimum. It makes a difference.

 

[grouch]

That fuel pressure is on the low side, I like to see over 16 on these. Many have been over 20. Try a Quantity test. Pump into a bucket at fuel filter for 5 minutes. You need a minimum of 5 gal/hr. Also check your connectors at injectors. Good Gaskets and tight. Wires twisted. If untwisted twist them. I forgot how many turns but I think 7/ft minimum. It makes a difference.

If I dead head the pump, it might get to 18 psi but it's where it's supposed to be. I've spent a week chasing grounds and I've gotten most, if not all, of them. The radio isn't playing games anymore and my lights are brighter so the grounds needed cleaning.

I still have a misfire when warm. I've narrowed down when it does it though. At idle in gear, it blips at times. Idle in park it idles smooth. Driving down the road, it pulls good but in overdrive it misses under any load. In drive it runs smooth. I'm wondering if my fuel pump has plenty of pressure but not volume. If so, it could be on it's way out. Especially since this began driving down the road at a steady rate.

 

[exp500]

Why I suggested Bucket test. Make sure you are not feeling OD lockup. I might be wrong, but I think the only fix for that is converter.

 

[grouch]

If it wasn't for a blip at idle, I'd think that was it. I found a kit with the IAC and throttle position sensor and a friend who still runs a shop mentioned those have a service life of 20-25 years. I'm not big on swapping parts but the shudder doesn't happen when the engine is cold, OD or not, and the parts look original. I've had other failed sensors so I figure even if they aren't the problem, they probably need replacement. The temp. sensor made a huge difference in driveability when I got the truck.