'88 TBI 350 problem PLEASE HELP!

[crashandburn]

My truck is acting strange......It runs great cold, then once it warms up it bogs and spits and runs like total crap! It just gets worse untill it can barely stay running. If you shut it off and start it back up it runs ok for 30 seconds or so. It was throwing codes for the O2 sensor and the TPS. I put in a new MAP, O2, TPS, and the fuel filter and pump are pretty new. I also pulled the vacuum line off the EGR since it's not in use, but it just ran the same. I compressed the EGR with my fingers, and the motor almost died, so that's working. Here's where it gets really weird... If the truck sits for a long time, like months, it runs great for a few days. I am at my wit's end. GM TBI is the simplest fuel injection setup in the world, and I am pretty good with a wrench, so why does this elude me? Anyone else ever have this problem? I am about to put a carb on the stupid thing, as much as I don't want to.

 

[eagle mark]

Check fuel presure when your having this problem. I have seen the sock in the tank acumulate so much rust it will prevent the flow of fuel. When you let it sit the rust falls off and your run good until it sucks up enough chips to clog.

That would still not explain the TPS code?

 

[chevyuser74]

id start by pulling the vacuum off of the egr, just cause the egr works doesnt mean its not being held open a bit. plus its free and easy to do. then i would also get a scanner and see if anything is lying when it is warm

 

[Jason4x4]

maybe plugged exhaust

 

[crashandburn]

That is a good point, but I had the tank out of it about a month ago, and it is sparkling clean, and the strainer is new. There is no place to hook up a fuel pressure gauge without disconnecting the fuel line. How do you check pressure while it is running?

 

[crashandburn]

Tried pulling the line off the EGR and plugging it, no difference. Exhaust cant be plugged, I dont think....brand new headers to about 3 feet of pipes, mufflers, then turnouts. That wouldnt explain why it runs perfect when cold. I appreciate the responses. Bouncing ideas around eventually leads to the answer, so keep them coming!

 

[Thunder]

2 things I can think of off hand are
1. the distributor module/pickup coil. When they go bad a common symptom is running good cold and running problems after the engine warms up and internal resistance in the electronics builds.

2. The coolant temp sensor. It might not be working and keeping your fuel mixture cold start rich. Which is similar to having a stuck choke on a carb

 

[BillyBob]

That is a good point, but I had the tank out of it about a month ago, and it is sparkling clean, and the strainer is new. There is no place to hook up a fuel pressure gauge without disconnecting the fuel line. How do you check pressure while it is running?

If the tank is clean, check the fuel filter. Sounds like it may be getting clogged. You sure it's not just running lean?
I had an 87 that had a butchered harness for the fuel pump. One day the truck started to sputter, and eventually died. Turns out The connector to the fuel pump was broken, slowly disconnected, and finally left me stranded. So check the connector located on the frame as well. I forget where it is exactly, but it's fairly easy to spot.

 

[crashandburn]

Interesting! Would that be the temp sensor in the side of the drivers side head? If not I am sure I can spot the other one. But just in case where is it?
I put up the same post on pavementsucks.com the same time that I made this one to get more opinions, and got the same results. After cutting through the basic stuff, it looks like we are down to the ignition module or the temp sensor, just like you guys are saying! Both possibilites make a lot of sense. Basically the ignition is cutting out as heat builds up, or the computer is not getting the heat signal and therefore not changing the mixture as needed. I think you've pointed me in the right direction. Well 2 of them, but thats a whole lot better off than I was yesterday. Thanks a lot guys, you really helped out. If this doesnt fix it, I'll be back for more brainstorming.