I used the search option to look up information on the SES code 42. TO start off I have a '87 IROC-Z that originally came with a 305. I replaced the 305 with a 350 from jasper. I tried using the stock 19lbs.injectors from the 305 but it spark knocked (wasn't getting enough fuel). I called Howell EFI in michigan and they sent me a chip that fixed my spark knock problem. However after that chip i decided to install the recomended 22lbs. injectors. I am still running the chip used for the 19lbs. injectors with the 22 lbs. The problem i am having is a misfire and a fluctuation in the rpms that can be seen with the tachometer. It is fluctuating between 1200 and 900 rpms when i first start up the engine. while the engine is running you can here a "popping" or a misfire sound if you stick your ear next to the exhaust. I have replaced so far the distributor, coil, ECM, plug wires, spark plugs and checked a couple wires. What else is there that i can check or replace?

 

Anyone? I'm in desperate need for help.

 

did you install the 350 knock sensor? I think that's a necessity. You swapped the injectors, but still have this funky chip? What about a 350 chip, since you now have 350 injectors? are you sure the noise "at the exhaust" is not simply an exhaust leak? If you think it's misfiring or backfiring, check electrical - check continuity on all plug wires - just because they are new doesn't mean they are good.

I'm assuming this is a TPI induction car - might get better answers on the TPI board.

 

I have replaced the original knock sensor with a new 305 sensor. What us the difference between the 305 knock sensor and a 350 knock sensor? Also i was not sure on where to get a 350 chip. I might try to contact the GM dealer tomorrow 8/13. The misfire that i am hearing is not and exhaust leak. i know that for sure.

 

Just wanted to say, i got the 42 code. What fixed mine was replacing the distributor. 100bucks but well worth it. Car runs 100% better. Corrosion was on the sensors when i took the cap off. I guess it got a little wet somehow.