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rough idle/missing a litle

R

robjr80

New member
my 98 grand prix gt 3800 has been running great and 2 days ago it started idling a little rough and is missing. you can here it in the engine as well as the tail pipes. I got ahold of a code checker and came up with po301 which is misfire on number one but I also got po336 and po446. what could go wrong for to suddenly start running that way and throw out those many codes?
 


I read on another site on how to test the crank sensor for the 3800 series 2 and it said if I'm getting fire than the crank sensor is good. I've switched out and tested the coil packs and checked all the wiring and all looks good. Is it possible a bad injector could cause this? Also my plug looks good as far as coloration but the little piece of metal that the fire comes from looks to be rounded on top and is smaller than it was new. They were flat on the top new. Could that cause this? Maybe I need some hotter plugs? I don't know I'm just guessing now.
 
if you got a crank code its a crank sensor, that code hardly ever shows its self unless its been acting up hard core. they are wonky working, good now, bad a hour later.

or the crank harness is chewed up.


id dive in and change the crank sensor.
 
I found the source of my problem. The wiring harness that connects to crank sensor and the coil packs had melted down near the crank sensor and 5 wires were naked and touching. I got all that fixed and the crank sensor code has went away but now I'm getting a po300 code multible misfires. I'm assuming some of the coil packs might have been shorted out because of the wires touching. is there any thing else this could have shorted out?
 


The plugs and wires are brand new. The coil packs are the only other thing I can think of. Which I picked up a set at the junk yard and after I put on that set the car ran good sitting in the driveway but I took it up the road and it started missing again and that's when the engine light came on and I got the po300 code. After all that work and got mad at the damn thing is when I pulled the harness and found the naked wires because that's the only thing I didn't change or check. That's why I was thinking the wires touching might have mess those coils up too. Do you think that's a possibility?
 
you could have a clogged cat too. does the cel flash when you floor it? then set the p0300? then the cat could be clogged or it needs a tune, you did the rune up, so cat is next.

especially if the car feels super gutless. aka no power.
 
yes the cel did flash on and off before it stayed on and I did have catalyst show up on the code checker but I didn't know what it meant since there was no code to it. I bet it messed up the cat when I had that that upper intake leak that was blowing all that water out the exhaust.
 
upper intake failure is its own issue, your clogged cat is another one. time to replace it.

being a 98 you could buy a new down pipe, and pop in a $50 hi flow cat if you need a cat where you live.
 


I have to have a cat if it's a 96 or above around here. I can't just gut it like my 93 blazer. can you give me a link to give me an idea of what the down pipe looks like and where to get one. sorry if I sound dumb. I've worked on my own cars all my life and I still don't now what every part is called. I just tear it apart and put it back together the same way it came apart lol.
 
After all that work and parts I threw at this thing and cleaning the cat the problem with the misfire ended up being a faulty plug wire that was brand new. The only good thing that came out of this was I found the wiring harness was melted and wires were touching which is probably what started this whole chain of events to start with. You talk about mad I gave that dude at auto zone a hard time which I feel bad about now lol. So she's all fixed up now. I even did a burnout at the bottom of the road to show the little punk next door his little honda black marks ain't s**t.lol
 


At least with all the parts I put on it I know it's going to be good for awhile (I hope) and the cat probably needed cleaning anyway. You could see thru it but it looked pretty dirty. It's got 180,000 on it.
 
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