Posted on another site but didnt get any answers. I sure hope someone can help me out with this. I bought a 98 v6 camaro awhile back as a project. The car sometimes has po300 and p1870. However, i have changed the ICM (2 times), all 3 coils (2 times), the o2 sensors, ckp, cmp, egr, ect, fuel pump, injectors, not to mention the engine with a remanufactured one. sure i`ve missed something somewhere. The car doesn`t seem to be missing and I have tested spark with a spark tester. there`s no shaking, hesitation or anything that's normally associated with a misfire. the only time po300 is pending, or set, is when it runs 65-75 mph. Is it possible that p1870 is causing the ecm to think the car is missing when really its not? thanks in advance for any help.

 

did you replace plug wires?

 

yep, changed those and plugs. have changed almost everything ignition and fuel related.

 

How quick does the 300 set? Will it set without the car being driven? I have not read about a transmission issue causing the 300 but I guess it is not impossible.

If I had to play the odds I would guess a connector issue. I had a P300 in my 96 that turned out to be the MAF sensor connector. I got lucky finding it. I bumped the harness and the engine stumbled and it reset the code. I tried to reproduce the stumble but could not. I figure for what it cost I solder in a new connector, that was a year ago. No misfire since. Since I drive highway miles I never felt the miss, but since it was a MAF issue it must have been a lean miss.

 

hard to say because sometimes its like almost immediately set. then others i can go like 10 mi. before it set.

saw something on the gm diagnostic sheet for po300 that was dealing with the TCC (think it was step 23 or something). made start wondering if maybe the p1870 and 300 maybe connected. never heard of it myself that`s why im puzzled.

 

yes they could be. the misfire causes the ecm to turn off the tcc lock. dont know if that would set that code though.

 

The way the system detects a random misfire is it looks at how smooth the engine accelerates/idles. If the PCM does not see a smooth acceleration it assume you have a misfire or a weak cylinder. If there was something in the transmission cause a quick grab and release then I could see the PCM thinking it was a miss. The fact that P300 set while it was not in gear even once kind of eliminates that as a possibility. I guess while it is out of gear the torque converter could be grabbing, but I find that hard to believe. Torque converters fail but 99% of the time once they start grabbing they have a very limited life its not something that hangs on for months with no change.

You need a data logger. Clear the codes and drive with the data log on and check all sensor data for a change right before the code sets.

 

This could be as simple as a cracked spark plug.

 

what about the distributor I am thinking you changed it I would have,i forgot its the v6 so not sure where its at

 

The 98 v6 doesn't have a distributor cap.