I have a 97 Milly 2.3 Miller cycle engine with ~115,000 miles. Engine performance is ok for the first 5 minutes, then gets progressively worse as the car warms up. Have replaced the following:
1. O2 sensors Bank1 and Bank2 (pre-cat)
2. MAP sensor
3. Throttle Position Sensor
4. Fuel Filter
5. Spark Plugs
6. Several coil packs
Air filter

Have recorded engine data with notebook based OBDii unit. The timing reads as much as 35 or more degrees advanced at times, at other times it can be way retarded. The engine knocks terribly above ~2500 RPM under load. Any ideas where to look for a source of the problem? Also, is there anyone who can read the data I logged and interpret it to see if it is normal or not?

Any help is sincerely appreciated.

Jeff

 

are you using premium fuel? was the timing belt changed a short while ago?

 

Yes, have always used premium. No, the timing belt is original as far as I know. What has me most puzzled is the fact that it runs fine when fully cold, but starts to run poorly the warmer the engine gets. When fully warmed up. there is almost no power and it knocks badly.

 

under load would certainly make me consider plugs/coils.

did this start all of a sudden, or very gradually?

what spark plugs did you use?

what prompted you to change out so many parts? did you get codes thrown? is the ce lite still on?

 

Plugs, air filter, fuel filter replaced as normal maintenence. O2 sensors replaced when we got the trouble codes for them several months ago. Also got a code for the MAP sensor a while back, so we replaced it too. Two coil packs replaced when we had misfires in 2 cylinders that moved when we moved the coil packs to different cylinders. Replaced the TPS this morning after trouble shooting according to Alldata (did some tests on voltage and continuity according to their diagnosis chart). Interesting this happened tonight when we hooked up the laptop to get some data. When we put the accelerator to the floor, the engine did not accelerate and I noted that the timing actually went to about -8 degrees instead of advancing. Engine also knocked pretty badly at that time too. Weird symptoms. We're beginning tothink that maybe the ECU is bad. Can those things be tested somehow?

Thanks again.

 

About the plugs - we used Autolite. Tried for Bosch platinums but were told that Mazdas didn't like them. Any comments abotu the best plug to use?

 

We still get CEL light - only code now thrown is P0300 - random cylinder misfire.

 

there are only a few plugs that should be used. i have always used the factory ngk PZFR5F. and do NOT get the -11. that means the gap is 1.1mm, WAY too big. you need .7-.8mm. and dont fall for the "just go ahead and regap them", mazda and even ngk specifically state to DO NOT regap the plug. dunno if autolite makes a plug for the 2.3. beware of parts stores that will tell you "yah, this'll work", because it wont. most of them have the wrong information in their database.
tps is really tricky to set up. they are very sensitive. was it new? i have heard of the ecu needing to be changed, but that was because a generic o2 sensor was used, and the wires got crossed, which fubar'd the ecu. if you are unsure of the plug gap, i would start by getting the correct plug/gap. something is causing the random misfire, you need to solve that first.

 

thanks - great info. we had used generic O2 sensors when replacing them the first time, then switched to the OEM. We were told that Mazda's did not like the generics hence the change. I'm going to try the NGK plugs and see if that helps.

I really appreciate your taking the time to help out on this. I was pretty much at a loss as to what to do next.

 

we had a similar situation on the black car, 99s with about 70k when we got the random misfire. at first, it was sure it was the gas. happened right after we filled up. i threw in a couple bottles of drigas, and it went away, but came back. then i got specific coil codes, iirc, first was #5, the worst one to get at. i ended up changing out all 6(around 134 each with discount at the time), cleared the codes, and they have never been back. i am thinking you still have some bad coils, and the ecu just hasnt pinpointed them yet. random miss can be picked up by the ecu as knock, and it will pull timing. if it was ok till you changed something, then whatever you did is suspect, also whatever connections are in the area you were working on. a simple mistake, like the fuel filter installed backwards, could cause low fuel flow under load, causing a lean condition. you should recheck all your work.