I did full tune up and now it still has the PO300 code
But I noticed as I rev up the rpm's to 4000 it pops big time through exhaust.
Still looking to Cat.. ?

 

Ok I replaced fuel filter and it was some restriction when blowing through it
so put new on! Engine still shakes when started.
Took it around block. Car drove but it was not much power till you punch it and rpm's did go up to 5k so may not be cat!
After I got home I heard like a winning noise and I put it in park and reved it up and it surges
This one stumps me!!

 

Ok while driving car my check engine light was flashing..
when I got home I checked codes again and now I'm getting PO304 and PO118 I know PO118 was first code I had. The CTS and I replaced it then erased code and it didn't come back till now for some reason..
I had PO300 multiple miss fire but that had disappeared and now it's PO304 number 4 cylinder miss fire..
Why the CTS code came back I don't know!
Anyone with ideas on this?

 

So you got a code for cylinder 4. Because of the P0300, I would go back to pull the ICM, take it to the parts store and have them test it. Could be failing, but in theory, you should have at minimum 2 mis-firing cylinders. If the ICM passes testing, I would look at the #4 cylinder. RUn down the list (easy to hard):
- with the engine running, mist starting fluid around vacuum connections and seals. Because of #4, cylinder, I would focus on where the injector for #4 is (making sure the o-rings are sealed). If the performance of the engine changes where you mist the starting fluid, you have a vacuum leak.
Everything else is engine off.
- Verify all the connectors for the injectors are firmly connected.
- Swap the plug wires on the coil servicing the #4 cylinder. Both points on the coil fire at the same time. Swapping the wires is a simple check if a point on the coil has failed.
- Swap coils around, see if the problem follows the coil (in theory, since it is only one cylinder, odds are if the above step does not flush it out, then it's not the coil).
- Make sure the plug wire is not damaged. If it is arcing, you can sometimes catch that at night with misting a spray bottle of water around the plug wires when the engine is running (you will see the arcing flash).
- Remove the spark plug for #4. Check it's condition. Such as does it have a lot of fuel on it? Also, validate the gap on the plug is still correct. If not, that in itself could be the culprit.
- You can attempt to swap the plug with another cylinder, see if the problem follows the plug.
- Last one, start messing with injectors. I would swap two of them and see if the problem follows the injector.

Hope this helps.

 

FYI @Carloman61 Im right here with you trying to figure out this issue with my #6 misfire.. Dont think ive mentioned it.

 

Thanks for reply.. Lots of good info.
i bought new coils The others were mix matched.
One came out as 8.2 ohms other two around 5.6
I bought all three new coils. They are all at approx. 6.7 now. I changed fuel filter,old one was a bit plugged.
Didn't change anything so
I'll try the checks you mentioned and post results! Being it's now not having the 300 code but 304 I'll start with focusing on that area!
Thanks

 

Ok update.. I checked firing order.
5 and 2 were switched on coil..(my mistake when replacing coils). That shouldn't have anything to do with cyl 4
While care was running I disconnect harness plug for #4 injector and there was no change in idle.
I then tried that with the other 5 injs. And Everytime I unplugged one of the others the engine stumbled. So #4 is not working!
Now I turned key to on no start and checked Vs at each inj plug. I'm only getting 5 Vs on each connector. Even at #4
I then started car and unppluged one at a time and checked voltage. They were at 13 V's except plug 4 was only 8 or 9 Vs
Not sure why??

 

Ok update: I checked the Injector wire harness.
All injectors are getting same volts with key in on position but not starting car. 5Vs
As car is running Vs on each plug to injector 8Vs
I ohmed each injector on a setting of 200 ohms and each one is at approx 13.8 ohms
I sprayed carb cleaner around the manifold and vacuum connections and only found a small leak at connection port for FPR. At throttle body.
I even sprayed around each Injector.
I still get Popping if I try and go above 4k rpm's.
It's running smother but still shakes after 15 secs when I start it.
I erased codes and ran car for 10 mins reving it to 2k and idling. So far no check engine light on
I forgot to mention when I bought car it had gas in it for a year when it sat. I drained what I could and put fresh gas 8 gals before I started it..

 

Ok.. I took car on test drive and it ran good no check engine light on and the temp gauge was working.. Then after 3 miles the check engine light came on and temp gauge stopped working..
car hesitated and ran rough again.
I check code when home and it was the PO118 again CTS that I had changed last week.
Code says temp sensor circuit high
It's driving me crazy!!

 

If I follow, while the car is running and you check injector voltages, you are seeing the harness for the #4 injector having lower volts than the others? I'm trying to make sense of where that issue would be. I almost want to blame the PCM, but really not sure.
I pulled the shop manual data for troubleshooting P0118 and attached it.

I cannot say for the 3800, but I found out the old 3400 can run old fuel. Years ago I bought a 1999 Grand Am as a flip. Needed some work, had been sitting for about 1.5-2 years and had about half a tank of gas. I eventually started it on that tank and ran it and later topped off with good fuel. Never drained it. Ran it fine from best I could tell (even surprised me).