Chevy Blazer 2001 LT
190,000 miles

I am experiencing a cylinder 1 misfire, according to my obd scanner and service engine light.

The first time the service engine light came on it was intermittent for a while and then eventually it was always on. If I cleared the code with my scanner it would seemingly stay off until I accelerated extra hard or went up a hill fast.

I replaced the plug and that only solved the issue for a few days.
After that didn't work I put on a new distributor cap and that worked for a few days.

Then just a few days ago I brought my blazer into the mechanic for a temp sensor and wire harness replacement, and he replaced the wire for cylinder one as well

Up until today there was no problems and now once again I have a service engine light on and my obd scanner gives me the code P301.


The truck does not run rough or backfire nor does it have a rough idle. It did seem to start worse than normal after the light came on today though, but not to much of a difference from the last few days.


TL;DR
-p301 code,service engine light
-replaced spark plug, worked for a while
-light came back on, replaced distributor cap, worked for a while
-light came back on, replaced wire, worked for a while
-light came back on
-truck seems to run normally even with service engine light on


I am not that experienced with vehicles but the only thing I think that would be left to try is a new rotor.
Any suggestions?

Thanks a lot.

 

I had the same issue with my GF blazer. And did the same things you did Exactly.
this is what I did after all that...Replaced rotor, replaced all wires and plugs(make sure gap is correct). cleaned the MAF sensor with MAF cleaner. Make sure the intake is mounted securely and properly on the TBI( hers was missing the tall wing nut and the intake cover was on the TBI half way, I think this was the issue the whole time). i put a small bead of gasket sealer around the bottom of plastic intake cover and replaced the tall wingnut (since it was gone) with a nut and tighten down. All symptoms went away, now running like new....

 

If it doesn't seem to be missing, then make sure the PCM can correctly recognize a misfire. Induce a miss into another cylinder and see if the misfire counter goes up for that cylinder. If you pull a plug wire from the distributor, be sure to ground that distributor terminal.

If it can recognize the induced miss, then find and fix the slight miss on the original cylinder.

If it can't recognize a miss correctly, then do a crank sensor relearn. If that doesn't fix it, start looking for mechanical things that are whacking out the crank sensor or the crank sensor itself. Mine was a bad crankshaft thrust bearing causing a false P0304. Only took an engine rebuild.

 

Do you have access to a scanner that can monitor streaming data from the B1S1 oxygen sensor? The data will tell if it's a lean misfire or a rich misfire. Knowing that will eliminate a ton of possibilities. For example, if it's a lean misfire, that would eliminate the entire secondary ignition system as being the problem.

 

First off, thanks for your reply.

Ill check the TBI and make sure everythings secure, should I clean it as well?

 

I believe the torque app on android that goes with my OBD scanner can give readings on that. Not 100% sure but ill post results tomorrow if it can.

The mechanic said it was running rich prior to my coolant temp sensor and cylinder wire 1 replacement.

 

yes I would still clean the MAF unit. I also wrapped the new coil wire and 1,3 & 5(at the cap to the hold down clip) wire in wire loom because the coil wire touches places and will arch in time and 1,3 &5 cross each other and will arch in time.

 

Still think the place to start is to verify that the PCM can correctly identify an induced miss. Otherwise, the PO301 can be a false code and lead you down the yellow brick road. All I'm going to say.

 

How do I induce a misfire?

Im thinking I should wipe my obd codes,
Induce a misfire on of the other cylinders and see if it reads it correctly, then see if it reads it on cylinder 1 as well.

 

The only possible problem with that, is IF #1 is actually misfiring, and you induce another cylinder misfire, the PCM is liable to set P0300, (multiple cylinder misfire). You could spot it if your scan tool shows individual cylinder misfire data. Other than that, crankshaft sensor relearn data and camshaft retard need to be correct.