Timofo24

Hey guys, was wondering if I could get a little help with my Bird. It's 1989 Trans Am, 305 TBI, Auto Trans, no major upgrades except for exhaust and open eliment filter/intake. I will be driving down the road, car is running great, get into a situation where I have to give her a little more throttle then back off right away, pretty much just normal driving. Every once in a while, when increasing throttle and pulling off of it right away, the CEL will come on and the car will start running like total ***. Keeps running but power is greatly decreased, car heats up, does not overheat though, very rough acceleration, and a slight smell of engine coolant. At idle, the engine idles very low and rough and a very different exhaust note is apparent. I will pull over and turn the car off, no wait, turn it back on and CEL is gone, car runs fine until next time it decides to do it which may be five minutes or five days. I'm thinking that I can replicate the problem by specific movement of the accelerator, that it may be a TPS problem. What do you guys think? Thanks in advance for any input.

ex-x-fire

Get the trouble code & start from there.

Motopsyco

yea, sounds like a code got set, and put it into limp back home mode, had it happen once with my old bird. turned it off started it back up and it was fine, never set that code again either, mine was a knock sensor code.

Timofo24

Thanks for the thoughts guys, this week I will get the car on the road, legally, and will get it to screw up again. On my way home I'll stop by advanced auto parts and have them read the codes. That should help point me in the right direction. Kinda off topic, anyone know where I can find good information on my heater/ac controls, they have been screwed up for years, thanks.

RBob

iTrader: (1)

Sounds like the forced knock test is failing. This test is run at heavy load once the engine is up to temperature. When it fails code 43 is set and some spark advance is pulled.

Can check the codes with a paper clip between A & B on the ALDL connector, key-on, engine-off, and count the blinks on the SES light.

The forced knock test can fail from running too high an octane fuel, improper distributor base timing, or a fault in the ESC system.

RBob.

Timofo24

Thanks for the reply RBob. So let me get this straight, when the engine gets up to temperature, the ecm creates a knock in the engine and is looking for detection of it from the knock sensor? If it does not detect the knock then it goes into a "run like crap" mode? I have had the car now for about 12 years, not a daily driver, I have never changed the knock sensor. When I do drive it, I do fill it up with premium fuel, pretty much the last thing I would suspect but I know that you know your stuff. Going to get out today and get it cleaned up and inspected, hopefully will have the code by Friday. Also, will investigate some of the wiring on the car, the previous owner or owners did all kinds of retarded crap with audio, alarms, and other poo. Remembering back, I can't tie the problem to any particular repair or modification. Thanks again for all of your support guys.

RBob

iTrader: (1)

Yes. The run bad mode is from the ECM removing timing across the board. The cost is lack of power and mileage.

In the forced knock test the ECM advances the spark timing and looks for knock. It will run the test a second time with more timing if the first test failed. If the second attempt to force knock fails, boom, code 43 and the removal of a bunch of spark advance.

Can key-off for at least 10 seconds to reset the ECM back to the proper SA. So if you are on a road trip pull over and key-off. Then restart and try to avoid heavy loads, just cruise to get good mileage.

If you want to stay with the premium fuel, can try bumping the base timing up a few degrees at a time until it will knock. Or go back to 87 octane fuel and see if that does the trick.

Can test the ESC system easily. With a warm engine and running, open the throttle to about 1200 RPM and hold, then rap on the block with something like a broom or screwdriver handle.

The RPM should dip down for a moment then recover. The dip is from the knock retard.

RBob.