Misfire when warm.

[grouch]

Well, what ever the problem is, it's getting worse. I cleaned the last of the grounds I could find today. Each ground was cleaned and reattached one by one so I know I didn't leave anything undone. Fired the truck up and got half a block before I had to turn around. It was bogging BIG time and nearly died on me 4 or 5 times in a one block drive. I talked to the dealer service department and they think it may be the IAC or TPS sensor. The parts should be here tomorrow. If that's not it, I believe the fuel pump is trying to die. I'm not a fan of throwing parts, especially ones like the pump, at a problem but the problem has gone from an annoyance to making it undriveable.

 

[grouch]

I'm thinking I have a bunch of problems. I replaced the IAC and TPS today. It idles better and doesn't miss at idle. I don't see how the old TPS functioned. I still have a stumble when accelerating. It bogs down and spits like it's not getting enough fuel. I think my fuel pump has pressure but isn't providing volume. The filter is new and no change. So either rebuild the TBI injectors or a new pump. I'm not looking forward to replacing the pump.

 

[OR VietVet]

The fuel pressure should be at 12 psi, so your 11 is slightly low but I would bet that after all this, you could have a fuel pressure regulator problem.

https://www.rockauto.com/en/moreinfo.php?pk=10911080&cc=1033108&jsn=929

 

[grouch]

The fuel pressure should be at 12 psi, so your 11 is slightly low but I would bet that after all this, you could have a fuel pressure regulator problem.

https://www.rockauto.com/en/moreinfo.php?pk=10911080&cc=1033108&jsn=929

Specifications for a TBI is 9-13. My pressure is fine. I was over at a friends house and was talking about it and his ELEVEN year old son asked how old the parts and truck are. It's probably the original pump so everything is 28 years old. He then said the pick up tube on the pump may be rotten and collapsing under demand. Geez! Talk about being put in your place! After thinking about it, I'm pretty sure that's the problem. New pump on order. I could replace just the rubber but it'll be apart so why do it twice.

 

[exp500]

Have you done the IAC relearn? I don't remember the exact procedure, but it is two plugs one is IAC. The object is to find zero and 100 percent and the sweet spot for neutral. If IAC drops below neutral, then idle suffers up to stalling when in gear. Night/day difference when correct. It is a plug/unplug start engine, plug in last plug, takes 3 tries. Other thing you can do is remove welch plug on throttle body and set minimum idle with IAC at zero to about 450-500 rpm so that IAC closing does not affect low Idle as much. There were many different IAC's used and only a few are sold now.
I hav never had to replace a throttle body or Injector on this vintage, only one IAC and that one the motor wouldn't move. Had to rebuild several fuel pressure regulators on throttle body, The GM kit was about $30.00. Hope this helps.

 

[Tonyrodz]

Specifications for a TBI is 9-13. My pressure is fine. I was over at a friends house and was talking about it and his ELEVEN year old son asked how old the parts and truck are. It's probably the original pump so everything is 28 years old. He then said the pick up tube on the pump may be rotten and collapsing under demand. Geez! Talk about being put in your place! After thinking about it, I'm pretty sure that's the problem. New pump on order. I could replace just the rubber but it'll be apart so why do it twice.

That kid is off to a good start! I can't believe he'd even know about it.

 

[grouch]

That kid is off to a good start! I can't believe he'd even know about it.

As adults we often get focused and lose the sight of alternative issues. The kid has been racing go karts since he was 6. His dad and I insist he learn to wrench on his equipment. In a year or two, he's hoping to start racing dwarf cars. He's had problems with ethanol fuel rotting his fuel lines.

I did the procedure for IAC relearning. I might have been able to clean the old one but it was looking pretty sad and the spring was at an angle. I had a new part so I replaced it.

 

[exp500]

Humor me, Have you checked timing? With the wire by Brake booster unplugged? A few advanced ok, retarded not.

 

[grouch]

Humor me, Have you checked timing? With the wire by Brake booster unplugged? A few advanced ok, retarded not.

The timing chain was off by 2 teeth so it's been replaced. The distributor was set with my light. The old distributor was pretty rough inside so it's been replaced.

 

[George B]

Just throwing this out there. Years ago I had an OBDI truck and built a cable to connect to it with my laptop. I went and found my writeup in a different forum. Maybe it will help with seeing what's going on...

https://www.gmsquarebody.com/threads/connecting-with-a-laptop-with-tuner-pro-rt-and-diy-cable.13194/