94ConvertibleZ

Hello! I recently started working on my sister's '99 Trans Am. This is a 1 owner car with 46k and no mods ever. It could barely idle and was puffing white smoke. The smell of gas was heavy in the air. I scanned it and got 3 codes: p0122, p0200, & p0300. I started with 0122, bad tps. I pulled the tps and found it broken, easy fix. I cleared the codes, fired it up. It still ran rough. I was out of time, so I had to put It off til the next day.

Round 2: I started the car up, and it felt smooth. Drove it 5 minutes, then it acted up again, smoking, rough idle and barely able to chug along. Scanned again, this time I got p0200, and p303. Hmmmm, fuel injector maybe? I hooked up a fuel gauge and keyed it on. It shot up to 60 psi, then immediately fell to 0. I'm thinking injector 3 must be stuck open. I pull injector number 3 wire and check for 12v on pink (KOEO), looks good. I check the other wire against a chassis ground and got infinite resistance. All signs point injector, except when I ohm the injector it comes up 15 ohms, normal.

Round 3: I notice while poking at injector wiring injector 1 is getting really hot. I pull off the connector and start probing. I find 12 volts, but this time the "ground" wire is showing resistance. So now I'm thinking bad wire on number 1. I trace the wire back as far as I can reach and don't find anything wrong. I pull the PCM connector and check resistance from inject connector to PCM pin and get a nice, low value. Weird right? I check injector 3's ground wire to PCM pin and get another low resistance value. Now I'm getting confused. I decided to disconnect the battery, and clean the 4 ground posts on the inner fenders and rad support just for the heck of it. I reconnected the batter fired it up, and it rubs nice and smooth. I start pulling injector wires one at a Tim and each time the idle stumbles indicating injectors are working fine. Sure enough 5 minute later, the stumble and white smoke comes back. I scan again and this time I get p0200, and p0300 for random misfire. WTH? So what do you guys think? Bad PCM maybe? I'm all ears........

Injuneer

One thing we really discourage is "paging" in the tech forums. If you want a reply from a specific person, send them a PM.

The "ground" wire in the injector harness connector is only grounded when the PCM provides the ground to fire the injector. If you check the resistance from the ground pin in the injector to the chassis at any ther time than when the injector is firing, you will get infinite resistance. You measure the resistance of the injector across the two injector pins, as you did.

94ConvertibleZ

Thanks for the quick reply, Fred. I didn't realize you were up to giving advice to random board members through PM. I'll keep that in mind for next time.

Anyway, I am aware that the "ground" wire in the injector harness only sees ground momentarily as the PCM commands it to. Maybe something got lost in translation, as it was a lengthy post. I did see continuity at one point when probing the #1 injector harness "ground" wire to chassis. This was during a KOEO inspection. Thus I expected to find a wire shorting against metal somewhere. When I did not find that, I checked the resistance of the wire itself by removing the PCM connector and probing the wire at each end as I described in the original post. The wire checked out OK, with no shorts. This, along with the inconsistent misfire codes is what makes me think this could possibly be a problem with the PCM.

I hope that clarifies what I was trying to convey. Any feedback is appreciated.