I had a squeaky belt, but once that was fixed, I traded a squeak for cylinder misfires. I'm hoping to get some help from you guys in troubleshooting. Between this forum and my mechanic, we have a good shot at figuring it out.

The initial issue was a squeaky belt. The tensioner and belt were replaced. That worked for a while, then the belt jumped my harmonic balancer. Once that was fixed, everything worked great for a few days. But on my Ultragauge, the trouble codes (in the thread title) were pending. I didn't get an actual CE light until the cylinders shut down and I run on 4 cylinders for a 30-60 seconds. That happened (and consistently happens) at interstate driving speeds, but never city driving.

My mechanic has been troubleshooting. First he replaced the coil that ran cylinders 3 and 4. That didn't fix the problem. Next, he found that the belt slipping off the balancer had damaged the crank sensor. That was replaced. Still getting misfires.

We know that this all started happening after the harmonic balancer issue was fixed, and that it only happens at highway speeds. I also noticed on the Ultragauge that the O2 sensors bottom out when the cylinders shut down. I don't know if that is cause or effect, though. I am NOT engine-savvy.

So...what should I be looking for to help troubleshoot with my mechanic?

 

What about the head gasket? Have you tried anything with that yet? Like replacing it.

 

That will be my next question for the mechanic when I take it back. I understand the head gasket probability is high because the two problem cylinders are next to each other, but I'm unclear on why it would be an intermittent problem (e.g. at highway speed) instead of a constant problem. If the head gasket is bad, wouldn't the problem be constant?

I'm not second-guessing you, just wanting to understand the engine workings a little better.

 

I would think so. I am not an engine guy but from previous threads and stuff I have seen the P0303 is a head gasket issue.

 

i had the tensioner and the harmonic balancer go and then also had to replace the crankshaft position sensor as well i am having the same problem as the engine starts cutting out at over 3000 RPMs or +100km/h and only started happening after i changed these parts. i have talked to my mechanic because the codes read PO301 and PO305 PO316. the codes say that it is a misfire in cylinder 1, 5 and it is detecting it in the first 1000 revolutions. my mechanic said to change the sparkplugs and see if that works. i have not done this yet but i will keep you posted.

 

adam PO303 is a misfire in the 3rd cylinder

 

Since it's in the initial ROM count, that'll be before the controls go closed-loop... look for a hose that you didn't reconnect or a connection that you popped-off while swapping the belt...

 

just put on a sensor from carquest it is an OE cranshaft position sensor... seems to have done the trick.