Hello, I am in need of any advice on this I can get, First off the truck is a 1993 GMC Sonoma 4x4, with the 4.3 VIN Z Engine (Non Vortec) and the 4l60e Trans. PCM 16168625. I just bought the truck and try to drive down the road and the truck runs fine then basically cuts flat out until I feather the gas a bit and goes some more, off and on while trying to drive. Sometimes it throw code 33 or 34 while doing it for MAP too low or high. I have done the following, all Brand NEW MAP, TPS, IAC, Distributor shaft cap and button, Ignition Module, Coil, Spark plugs and wires, as well as tested the Map sensor for correct power ground and signal function. EGR is good as well. Oh and the throttle body has been completely rebuilt. Even switched the PCM using my original PROM. Checked all vacuums finding no leaks that I see and checked out as much wiring that I possibly could and all seems fine?? I am at a total loss I may even be forgetting some things I tried. Any advise or something to try next would be greatly appreciated and thanks in advance!
93 Sonoma 4.3 Vin Z MAP Code/Crazy Issues Help?
- Thread starter Minix69
- Start date
Went ahead and changed all the vacuum emission hoses just in case but still the same, checked timing and advance to no help, But discovered one thing If I manually shift through the gears It doesnt cut out? Tried once in drive instead of over drive and was ok after the manual shift but from dead stop in drive still cuts out. Only when I manually shift. Still code for MAp high or low randomly? Very Confused with this truck?
OnlySonoma
Member
Have you checked the Fuel Pump? My Sonoma acted similarly when when fuel pump was going. The pump still worked and I drove it for about a month while it was on its way out. The truck would run fine when it wanted to, but from a stop it would almost always stall. Your fuel pump should be capable of 13psi. Worth a check, but I doubt this is your problem.
Seeing as you sometimes get code 33 or 34 it makes me think its definitely something to do with your engine vacuum, are you noticing any black smoke from your exhaust?
Seeing both 33 and 34 would indicate your TPS may be wrong.
You should look into this throttle body rebuild, as it could be the culprit.
Specifically the fuel pressure regulator if you're Throttle Body Injected.
Seeing as you sometimes get code 33 or 34 it makes me think its definitely something to do with your engine vacuum, are you noticing any black smoke from your exhaust?
Seeing both 33 and 34 would indicate your TPS may be wrong.
You should look into this throttle body rebuild, as it could be the culprit.
Specifically the fuel pressure regulator if you're Throttle Body Injected.
Thanks for the advice, I was considering the fuel pump too, I mean i do get gas when its unhooked but thinking of renting the proper gauge to make sure. The TPS test correctly and it had that code only before I changed it. Now just the MAP sensor. randomly yes some smoke blows shortly before the stall. And I agree as well with the throttle body think I'm gonna try one from a good running ride and see what happens. Thanks again!
OnlySonoma
Member
Also, if it is Throttle Body Injected then I would clean the injectors. Some dirt may cause them to spray irregularly causing strange compression/vacuum scenarios.
Another thought, Check the PCV Valve.
If your PCV valve is stuck closed then there will be crankcase pressure which will result in leaking seals and gaskets, and could also force oil into the intake manifold. If the PCV valve is stuck open then you will experience hard engine start, misfires at idle, Rough idle, and a lean air-fuel mix. A PCV valve stuck open can trigger the "check engine" light due to increased in air flow. However, a diagnostic computer may point to a Mass Air Flow or Oxygen Sensor failure instead.
This is, at most, a $10 part.
Another thought, Check the PCV Valve.
If your PCV valve is stuck closed then there will be crankcase pressure which will result in leaking seals and gaskets, and could also force oil into the intake manifold. If the PCV valve is stuck open then you will experience hard engine start, misfires at idle, Rough idle, and a lean air-fuel mix. A PCV valve stuck open can trigger the "check engine" light due to increased in air flow. However, a diagnostic computer may point to a Mass Air Flow or Oxygen Sensor failure instead.
This is, at most, a $10 part.
I will pick up the PCV for sure, like you said its so cheap and I have went to far not to, but I am thinking your right the injectors don't seem to be spraying like I want, Going to give them a try cleaning and see what happens.
OnlySonoma
Member
Let me know how that goes for you! I'm going to take my Throttle body apart this weekend. I plan on cleaning then entire unit as well as the injectors and replacing all the gaskets. I'm also going to remove the tabs/ flanges on the top and smooth out the openings to allow for better air flow. The link there is to a really good write-up about taking a TBI unit apart and the youtube video gives you a good idea as well.
http://www.gmc4x4.com/topic/1035-1991-57l-bored-tbi-upgrade-write-up-warning-lots-of-pics/
https://www.youtube.com/watch?v=SeoQdQVWhCI
The injectors are quite pricey so cleaning and re-sealing the TBI unit and the injectors is a cheaper and more realistic solution, as long as the injectors still work.
http://www.gmc4x4.com/topic/1035-1991-57l-bored-tbi-upgrade-write-up-warning-lots-of-pics/
https://www.youtube.com/watch?v=SeoQdQVWhCI
The injectors are quite pricey so cleaning and re-sealing the TBI unit and the injectors is a cheaper and more realistic solution, as long as the injectors still work.
The PCV didnt help but like I said it was worth going ahead and doing since so muche else was new, I cant understand why if I shift manually I have no problems whatsoever with it cutting out. Only when I allow it to shift on its own does it cut off. also the 4x4 actuator is trying to kick in on its own now too, something I didnt notice before, really dreading this is going to turn out electrical. I'll check out the guide I am planning on ordering a kit and re redoing the Throttle body since pretty sure when I open it up gasket will break. I'll keep it updated as I get through.
OnlySonoma
Member
Did you ever solve your problem Minix69 ?