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99 gs misfire codes stumped

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eclipsekid1013

10+ Year Contributor
162
0
May 9, 2010
hudson, New_York
Ok guys I have a 99 gs Bought with bad motor has a donor 96 420a in it. Got 5 misfire codes One code was for misfire unknown cylinder then a code for a misfire in each cylinder. Replaced coil pack plugs x2 and wiresx2. Brought it to a mechanic he said he can't find anything wrong that would cause it. It seems to run fine I dont feel any lose in power or anything. I'm stumped I need help with this. Could it be the fact that the ecu is for a 99 and the motor is a 96? Any help would be appreciated
 
If you feel no difference then I could be the ecu. I know in the turbo models they are different between the 95-96 years and the 97-99 years.
 
No the motors are the same. Check for loose connectors on crank and cam sensors as well as injectors. Add electric grease as needed.
 
Ok thats the next thing I'm going to try. Because its not like it's running like garbage. It seems to be running fine.
 
If the connections were not good wouldn't that cause it to not run well? Not being negative to your post or being corrective I'm just asking? Have you tried another ECU in it? It could be the ECU itself is just bad
 
I have not tried a new ecu yet if I do such will I need a 99 since its ob2 or a 96 obd1
 
96 is still OBD2. As for what 96 420a said all the 2g n/t ECU's are the same so you can use any year 95-99 ECU
 
What's the consensus try a new ecu? Open up the old one? Check wire trails from where to where?
 
You would have to trace the trails from the pins where the connectors connect to the ECU to where they go on the circuit board. You would have to find a diagram of the board. (That could be hard) I've never seen one. If you clear the codes do they automatically come back on or do you drive it for them to come back? If you have an ecu or can borrow a friends then I would deffinately try that
 
Ok thank you for the clarification fotowntalon. So would that be the cause of the misfire codes?
 
It sounds like there's something mechanically wrong. Lots of people have already stated that the engines are interchangable.

I would be willing to look at it for you, but my shop is at the opposite end of the state from you.

Do you still have the injectors from your old engine?
 
So since its a 96 in a 99 would the ecu cause the problems that I an having?

Not a 100% sure, but I am guessing it would depend on the harness used on the engine, I'm not the greatest with the electronics. I can tell you misfires are the most fun thing in the world to try and diagnose. A number of different sensors could cause it, as well as something mechanically being off. I tried forever to diagnose my own, and for performance purposes replaced springs and retainers, and it took care of the problem, not saying you should but. Best of luck :p
 
When the swapp was done all the sensors and connectors from the 99 were swapped to the new 96 motor. Now If I'm actually misfireing it wouldn't run as good as it does correct?
 
This is why it leads me to believe it is a sensor or an ecu issue. But another question if it was a loose Cas or such wouldn't I throw a code for that and wouldnt it also run like $&it? I'm planning on bringing it to a place a town or two over that is top of the line for diagnosis cels. I would have rather fixed it my self but I need to get an inspection already got 2 tickets for it. :ohdamn:God dam Nys emissions
 
Took it to a shop and had it diagnosed had a cracked coil pack change it out with new plugs and wires. Light came back on again. My ps belt popped off a s on the process of replacing it I noticed the crank pully is pushed out a little bit which is causing the alt belt to ride off the pully and the ps belt to rub and jump off. Would this be causing my CPS to throw my misfire codes? And to get to the CPS it where? Or could it be clogged injectors?
 
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