Okay, my 1987 GMC Jimmy TBI 4.3L is on it's way out. WHen pulling out rom a dead stop the thing will bog for a couple of seconds, almost like its gonna die and then take off and run fine until you try to pull out from a dead stop again. It has no power whatsoever now and horrible gas mileage (14 - 16 mpg). I have replaced the o2 sensor, coil, plugs, wires, distributor cap and button, and transmission fluid. The injectors seem to be firing fine with a good conical pattern and no drips. What is the deal here??? Do you guys think it could be the IAC, TPS, ECM, or the fuel pump? Oh yeah, 1 more thing, I'm having to run 91 octane to prevent spark knock. Any ideas are appreciated.

 

Low fuel pressure can cause many different problems, I would check it out.

Lonnie

 

i would have the ignition timing checked, also check all connections to the ECM, EST distributor, then if that checks out ok i would recommed you find somone that has Winaldl and check everything out if you can of course, but it sounds like timing, but then again the computer controls your timing as well, so double check connections an try to time it, and if thats okay the computer based program for diagnostics will show what needs replaced!!!


mike

 

maybe your cat or muffler is cloged?

 

sounds like the fuel pump to me...mine did the same thing

 

My first move would be checking the Fuel Filter. My 82 did that and replaced the Filter. No problem afterwards.

Hope this will be of good use.

 

The fuel filter is a good idea. But let's keep it simple guys OK? I follow several Astro van websites....This is a common problem for these engines when the air filter gets plugged up.

For some reason the 4.3s appear to be extremely sensitive to having a clean air filter....

 

I agree, that would be the first and simplest thing to do. Mine got pretty dark and would die at stop lights unless I kept reving it.

 

Thanks for all the ideas. The air filter only has 4000 miles on it so it can't be that... and the fuel filter likewise. I'm thinking that it's probably a combination of things. I know that the cat is damn near dead cause the exhaust smells like rotten eggs most of the time. I'm going to check the timing on my next day off and see if I can dig up an ECM to try out. Last but not least will be checking the fuel pressure.