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P0203 and P0303 help??

MattGTP04

MattGTP04

New member
My Comp-G just started throwing a p0203 and a p0303. It's got 145k on the original engine. It idled pretty rough, shaking the car actually. The exhaust also smells different than normal, which brought the thought of a bad cat to mind, but can that cause misfire? I've tried doing research on my own on forums, but I'm still not sure where to begin. Any help appreciated. Thanks.

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Edit: Also, I do mainly highway driving, and my fuel economy is worse than I feel it should be. I'm averaging 22 mpg right now. I feel like it should be way more for mostly highway driving. Not sure if related to this.
 


Both those codes are pointing at the exact same cylinder.

You have a cylinder 3 injector issue and a cylinder 3 misfire. So either it's not getting fuel or it's dumping fuel and causing the exhaust smell.

I would swap the cylinder 1 injector with cylinder 3 and see if the misfire follows. Also inspect all the wiring and connectors.

This thread from a different forums describes the same problems.

http://www.automotiveforums.com/t1067919-p0203_amp_p0303_when_engine_is_warmed_up.html
 
Checked the resistance on the #3 cylinder, and it kept reading zero. Is that accurate for a bad injector?

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try a test light, one end to ground, the other inside the plug, the light should flash if the wires are working right.

or you can use a side marker bulb out of the head light, bend the wires back on the bulb and stick it in the plug, it will also flash if the wires are good.

engine needs to be running to see this really, it only flashes for a second when the key is first turned then starts up after its running.
 
So I just put everything together to leave it sit, and thought hell let's see what happens. Turned it on and no misfire. Could it have just been a bad connection? No codes, just running like normal. I'm going to replace the #3 fuel injector anyways, because it was reading abnormal resistance, but for now it seems to be working oddly

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You should definitely be seeing resistance on the injector. Did you check another? There's not really an exact resistance you are looking for, just want them all close. Loose connector can definitely give you fits. When i first fired up my top swap I had 2 bad injector adapters that made me think my injectors were bad, once I soldered in new connectors my misfires went away.
 
In response to bandook, some wiring must be bad some where. I drove it home last night and everything was fine. Drove it to work this morning and everything was fine. Just went to move it (storms coming) and its misfiring again. Should I be looking at the harness or the injector for problems at this point?

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I guess both. I'd want to do something with the injector with no resistance first. Are you positive you probed the terminals right? Just asking, it would be a quick double check. Then you could pull one injector wire at a time with car running and check the adapter for voltage.
 
Just checked again, reading 10-11 on the problem cylinder, about 14-15 on the working one. Of course, I went to start it up and it wasn't misfiring. So it must be electrical. If the injector was bad it wouldn't keep working then not working right? Wouldn't it stay dead?

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You would think... Electrical problems scare me. Technically an injector is an electronic device, so I suppose they can have intermittent problems as well. Not sure man. Best I can suggest is thoroughly go over all the wires in your engine bay. Look for any breaks in the plastic conduit stuff and make sure wires look good under it. Do as suggested and swap plugs, plug wires, injectors from 3 to 1 or 5 and see what the misfire follows. Do them one at a time. I'd probably start with plug wire, then plug, then injector. If the misfire stays with cyl 3 then you know it has to be the wiring harness or something mechanically with that cylinder.
 
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