I have a 1997 Cavalier Z24 with approx. 135k miles on it. I recently (approx 3k miles ago) replaced the fuel filter, cleaned out the air intake, sprayed a little carb cleaner in the TB and wiped it out to clean some deposits, did an oil change and added a bottle of Rislone 4 Cylinder Compression Repair (because my car has started burning oil between oil changes), I cleaned & lubed my K&N drop in filter, and I torqued the EGR mounting bolts (because there was oil build up on the engine around the EGR).
I drove it all the way from MI to WA to relocate for a new job. I unplugged to battery to reset the check engine light before I started my trip, but it was for a different code (P0420?) that said the O2 sensor after the CAT was going bad. The O2 code wasn't affecting my performance, and it had only came on a couple of times. So, I reset it to see if it was really a problem that would come back after clearing it.
On the way out to Washington the car was loaded with most of my stuff for the move. The check engine light was off for 1/3 of the trip. I think it finally came back on in South Dakota. Anyway, I arrived in WA and the car seemed fine. I was driving around and I ended up down by the Puget Sound. I had to climb a fairly decent hill to drive back to my hotel, and as I accelerated up the hill the engine started to sputter and misfire. I looked down and now the check engine light wasn't just lit up, it was flashing. I thought ooh great! The car was running a little rough at idle, but really rough when you accelerated at low (under 3k rpm) engine speed.
I drove the car to Autozone and had them hook up the OBDII reader to find out what codes it was throwing out. It had the same code for the O2 sensor and a couple other codes (one of them was the P0304 code) for the misfire condition. I read the list of possible causes for the O2 sensor code and was fairly convinced that my O2 sensor had finely said enough. I unpluged & cleaned the connection for the O2 sensor, but it didn't help. I decided to buy the O2 sensor and replace it.
The O2 sensor was rusted tight in the hole, so, I had to take the car to a mechanic to have it heated with a torch in order to get it out. I drove the car back to my hotel, and it started misfiring again. It wasn't as bad as before, but the misfire was still there. I opened up the hood and the dumbass mechanic forgot to plug the IAT sensor back into the air intake tube. So, I thought that was the reason why the misfiring was still there.
The next day I started it up, and the idle was a little rough (maybe because it was cold) but it settled out after a minute or so. I took it for a drive and it was stuttering all over the place as soon as you gave it any reasonable amount of throttle; however, it seemed like the engine accelerated decently smooth once the rpms were above 3k. The misfire became very pronounced any time the engine had a load on it (going up a hill...Seattle is very hilly) even at high rpms. I just couldn't feel the misfiring as much at the higher rpms. The check engine light was still on and flashing whenever I tried to accelerate under moderate (20-40
throttle.
So, I headed back up to Autozone to check the codes. I thought that maybe the Bosch O2 sensor that I had just replaced was faulty, but they only found one code (P0304), which is a cylinder 4 misfire. The code is produced when the PCM has detected a misfire condition based on a velocity change shown at the crankshaft speed sensor. This was one of the codes that showed up when I first discovered the misfire condition. I asked the guy @ Autozone if the misfiring could be from running low octane gas because in Wyoming and Montana they didn’t sell 87 octane (it was 85 octane). I knew at the time that I probably shouldn’t use the low octane gas, but the midgrade (88 octane) was 30 cents more, and I was getting low on cash. The guy at Autozone thought that I had a clogged injector, and recommended that I run Lucas Fuel System cleaner in the next couple tanks of gas. I agreed, so I tried the Lucas.
I just started on my third bottle of Lucas/tank of gas. I have been running Premium (92 Octane) gas since the problem started. Last Sunday, after two tanks of gas with Lucas, I decided to try take out the Autolite spark plugs I had in there and replace them with ACDelco OE plugs. I thought that the plugs might have something to do with it. Last time I had an ignition/fuel problem it ended up being caused by the Bosch Platinum plugs I used to replace my first set (at 100k miles), so, I thought that I might as well go back to the original plugs. I also replaced the coil-to-plug adapters (the plastic connecters that clip on to the coil housing).
The hesitation & misfiring seems like it has decreased a little since the spark plug change, but it is still there. On cold starts the engine stutters a little, but just for a minute or two. If I baby it through first gear and try to keep the engine speed above 2600 rpm for the rest of the gears, while keeping the throttle under 30%, then the car drives fine.
Yesterday I replaced a vacuum hose that looked dry cracked. It was running from the EVAP purge side to the junction that is bolted on top of the AC compressor. When I finished replacing it I noticed that there is another dry cracked vacuum line running from that junction box to the throttle body, so, I’ll probably replace that this weekend for good measure, but I doubt that it is the cause of my problem. Does anyone know what controls (PCM) the EVAP system purge, or when the purge is performed (during acceleration, at idle, etc.)?
I have been back to Autozone/O’Reilly multiple times and the P0304 is the only code I have retrieved each time. The code lists possible causes as the following: vacuum leak, fuel injector, ignition coil, etc. I don’t want to have to dump a bunch more money into chasing this misfire problem. I read on this forum that some people have had similar problems and the failure ended up being the coil housing. How is that possible? I thought that the housing just kept moisture from contacting the coils?
I think that I am going to test the resistance of the coils this weekend. Are the secondary terminals for the ignition coils located on the coil housing, or do I have to remove the four post plastic housing in order to test the coil resistance? Also, is the resistance supposed to be exactly 10,000 ohms, or is there a range?
Is there a way to test the coil housing?
I also read on this forum that you can have the ICM tested at a local auto parts store. What does the test look for in order to determine that the ICM is bad?
I would greatly appreciate any help that any members have to offer. I just want my Z24 to run like it used to.
Denny
