ARicci6792

Hey all, I'm having trouble trying to figure out the cause of the misfire on my car. 99 GT with a motor from an 02 GT, was swapped due to rod bearing in last motor ): anyway, couple weeks ago I had a Coil On Plug die on me so I swapped with one from the old motor, car runs awesome.

Now out of nowhere it started running like total ****, mainly in lower RPM/Idling. The motor shakes, sputters when taking off. I replaced the other 7 COPs today with ones from old motor and its a little better but still acting up. I'm not throwing any codes so idk what else it could be...

I know unplugging each COP 1 at a time is the way to test them, but since the motor already has a shake to it, it's hard to tell if any of them would be dead. For those who don't know when you unplug a GOOD COP the motor will cause a shake and change in idle...

Any help would be appreciated! I just hope it's nothing major I've put too much time and $$ into this car recently I just want a break lol.

Bman2000

is it just at idle? is it possible your iac is having issues, common problem for our cars. Honestly, i had a random hard to track miss/stumble, and it never really seemed to be the cops, but finally i upgraded to weapon x stuff, cuz it was in my plans, and problems went away. Sometimes old cops are any good, if they are the suspect id consider getting ebay ones. Of course throwing parts at it doesnt mean it will fix crap.

cliffyk

Have you checked the spark plugs?

That said, do not focus exclusively on the ignition system as the cause of the misfire as the EECV misfire monitor only knows that a misfire has occurred, not what caused it, it could be any one or more of spark, fueling, compression or ??.

Here is a description of how the monitor system works.

A failing Crankshaft Position (CKP) sensor can create the symptoms you describe.

swarthyfellow

I agree with cliffy (not that first time that has been said in this forum) check the plugs themselves. Might have messed them up with the bad COP.

uberstang1

I'd also check the plugs to start.

Eduardo Molina

i recently started having this problem with my gt and its becoming a headache, ive already replaced all my spark plugs and wires also, also both coil packs and its doing it specially while driving the engine shakes the whole time

cliffyk

There are only three things needed for a spark ignition internal combustion engine to run; a combustible fuel mixture, compression, and a spark. So work the list.

You need to monitor the AFR and see if it is running lean or rich--really running lean or rich, not what the narrowband O² sensors might report. To do this you will need to buy or borrow a wideband O² system, or have the engine checked by someone who has one.

Next you need to check the engine's compression, search here or on the web to find out how--the lowest cylinder should produce 135 psi or better and be no less than 75% of the highest cylinder's reading. If you do have a low cylinder do a wet compression test. If the compression improves your likely have worn/broken piston rings;p if not then is is likely one or more leaking valves.

The overall mechanical condition of the engine can be gauged by monitoring the manifold vacuum, compare the readings with this chart and pay heed to the suggested issues.

Testing the spark can be done while doing the compression tests. Use an adjustable spark gap tester to see if each COP can fire across a 3/8" to 1/2" air gap--if it can then it is OK. Do not fire each COP more than 5 or 6 times in quick succession as they can overheat and be damaged.

With all of the above done you will know what the problem is, and be on the way to fixing it--just throwing parts and money at the engine and hoping to get lucking is not a viable or sensible appraoch...