My 305 TPI starts and idles great. Once I start to drive it, it has an engine miss/buck during accerlation that I can't seem to isolate. Has everyone experienced this problem and found it to be the TPS (even if it tested good) or the MAF (even though it seems good)? If I jumper the ALDL pins A and B it runs fine. Everything else on the engine has been tested or replaced. Recent tune-up, fuel pump (pressure fine) and many new sensors (MAF pwr rly and burnoff rly replaced, OS, temp sensor). I could really use some insight?

Also, will it damage the engine if I operate it while the ALDL is in Field Service Mode (Pins A and B Jumpered)?

thanks a ton.

Jeff

 

You can check the TPS with a voltmeter. Just make sure it increases smoothly with the throttle. Sounds like it could be ignition to me. Wires good? Plugs good? I'd be thinking of putting an ignition module and pickup coil in the dist. They are common problems and fairly cheap.

 

Yes, all wires and plugs have been replaced. Thanks for the heads-up on the ignition components. I will replace them next.

Do you know why it would run ok though with ALDL pins A and B jumpered? I've been asking this questions a lot, but can't get an answer and not sure where to go to get it.

thanks again,

Jeff

 

Oh, I did check the TPS a couple times in the past and it seems to test ok. Injectors test good cold, havent tested warm yet.

thanks,

 

I'd have to look in the shop manual to be sure, but I'd guess it disables the EST.

 

I'm drawing a blank on what the EST is?

 

Electronic Spark Timing.

 

Isn't the electronic spark timing (EST) managed by the Ignition Module (IM) (and Pickup Coil) in the distributor? I've looked through my manuals on this TPS system and I haven't determined is there is a seperate module for the EST or is it controlled by the IM as mentioned above. I do have a new IM that I haven't installed yet. Maybe I'll put it in.

Any other thoughts?

 

It's managed by an EST module which is up by the relays (above brake booster) until '88 and then built into the ECM in later years. In either case, it's enabled by the ECM. I've never seen the EST module itself fail, but I'm sure it happens.
.

 

Got it! Thanks! right where you said it was. My book called it an Electronic Spark Control Module. So your thinking this Electronic module is possibly disabled when you jumper A and B terminal in ECM? Any chance you can verify this for me? Or suggest where to find out? And if it does, is the ECM managing spark timing when the ECM is in Service Mode?

thanks a ton, Jeff