single cylinder misfire

Good evening guys I need a little help. I have a 2007 Chevrolet Tahoe with a 5.3ltr engine. It has a single cylinder misfire on the #5 cylinder. The spark plugs, coil, fuel injector and AFM system lifters have been checked. Power and ground circuit, intake manifold (for leaks) have been checked also. Not sure where to go next. Any ideas?

Compression issues tend to give a compeletly dead cylinder at idle but smooth out at higher RPM
Ignition coil pack and spark plug issues are often most notieable at wide throttle openings at low or medium RPM in high gears.

Compression test or cylinder leak down test would also be my next step,

Is it a dead miss or random single cylinder miss?

Scope the control (I’ve highlighted blue)
And scope the low ref (I’ve highlighted red)

Checking to see if the computer driver may be dropping out here.

Post a capture here.

If that checkouts out relative compression is the way to go, but if it’s not a dead miss make sure to do an extended crank time. Compression gauges can miss low compression in some instances. Relative compression will show if you have an intermittent compression issue which is why I’d recommend a long crank time.

Just to gather a little data, what are your LTFT and STFT at idle and while holding 3k RPM?

Nissan Technician

They were verry close to zero. Probably a 5 to 8 % spread. Now the vehicle has the #1,4,7 fuel injectors opening when the key is turned on without attempting to start. The injectors are not stuck open because i switched the harness connector to one of the ones not opening and it opened immediately. Trying to narrow that down now.

So your filling those cylinders up with fuel?? Are you comfortable using an ohm meter to find a short to ground? Or bad pcm driver?

Does the computer think you’re getting an RPM signal when they engine is off for some reason?

Are you sure you don’t have a harness issue. Maybe the injector control wires rubbed through and are finding a path to ground.


Try test light on B+ and backprobe the control wire then wiggle the harness and see if your test light goes out. If you don’t find anything then unplug the ecm and see if connector and see if the test light comes out. It should shut off. If it doesn’t it’s a harness problem. Tap test on ecm to see if it’ll stop providing constant ground to injectors?

I used the test light to positive and probed one of the injector harnesses and the light came on. I then unplugged the ECM and the light went out. I purchased another ECM and programmed it and now the injectors are fine. Engine runs ok but still has the cylinder 5 misfire along with Bank 1 lean code P0171 and a bank 2 rich code P0175. I really dont understand that one. I guess all the fuel that was dumped into the exhaust either clogged up the O2 sensors or catalytic converter. I will look at that tomorrow.

Lean on the same bank as misfire only when cold or at all times? What are your fuel trims at idle? I see you posted them at 3000 rpm. Bank specific makes me think intake manifold gasket.

If you’re concerned about a clogged cat, aside from a back pressure test you can go WOT while monitoring calc load. It should go above 90% if volumetric efficiency is fine.

oh, this is really crazy. I just did another scan and im getting a lean code P0171 and a Rich P0172 code on the same bank. which happens to be the bank with the misfire. I must be jinxed. time to try another scanner. Need to clear my head and start from scratch.

The po172 might be due to oil contamination. With the injectors leaking fuel probably got passed the rings and got in the crankcase. I’d change it reset trims and go from there.