I have a 91' z28 1LE, 305 tpi w/ 5-speed manual. the car seems to have like 1/2 the power it should. it's just slow now. i hooked it to my friends auto x-ray EZ-link , to the onboard computer. it said it had a code 43 spark controll failure. i have replaced the plugs, wires, and cap and rotor. it still runs the same, i am suspecting the distributer is bad. the owner before me put in a jacobs performance ignition, it's fairly new, could he have installed it wrong or do you think the distributer is the prob. any one who knows about this code 43 please help me out.

 

Code 43 means the computer is seeing excessive knock. 4 possible causes:

1- real excessive knock. Unlikely, but it's possible if you have some bad gas, or the timing way off, or dirty injectors, etc.

2- False knock. This could be all sorts of things, anything from an exhaust leak to loose bearings in the engine, to a loose accessory brakcet, etc.

3- Bad knock sensor. These do go bad, and when it does the ECM thinks you have lots of knock and sets this code.

4- Bad wiring / ECM, if the wiring to the ECM is bad, or the ECM / ESC filters on the memcal then it also is getting a false signal.

The knock sensor can be easily bypassed by substiting a 3.9K ohm resistor to ground in it's place. This way you can drive it and see if you're getting real knock.

If not, well, it'll be one of the other things...

 

I had code 43 in my iroc and i had to replace the whole harness becouse of a short

 

i don't think it is a real knock, i put injector cleaner in it and tryed differnt gas. it does have an exhaust leak where the headers go into a y-pipe. do u think that could be a prob. where is this knock sensor at? maybe it does have bad wireing or a short or something. i'm just clueless on what is go'n on. I don't want to bring it somewhere n have some place try to make me replace alot of **** that doesn't need to be replaced. so i'll check out the wireing myself and the exhaust leak is gett'n fixed soon.

 

camarochic, how much was the harness? and was it hard to replace?

 

Just because you ran injector cleaner through and some different gas doesn't mean you've solved for real knock. Still, it is a highly unlikely prob. at this point.

The exhaust leak at the Y-pipe is 93.2% your culprit, either by giving a false knock signal or having burnt the knock sensor wire. If the latter was the case you could just splice a new piece of wire into the harness, not a new one.

Actually, even if the break was somewhere in the harness that you couldn't get too, i'd still just run one new wire for the knock sensor. Gutting the whole electrical system is really a little...excessive.

edit - Whoops, posted too soon. A last chance is that the ECM or memcal itself is bad. But those are last resorts, and are best checked by borrowing / swapping in a known good one rather than buying one.

 

ok, the exhaust leak is now fixed and the exhaust doesn't rattle one bit anymore. the knock sensor is gett'n replaced next week hopefully so we'll see if that solves this prob. i heard from a performance shop that if the sensor goes out or senses excessive knock it tells ur computer to go into a "safe mode" so ur engine doesn't get jacked up. it pretty much cuts the horse power in 1/2 when this happens so that explains y it is soooo slow now.