Kalali

That was also my understanding that the PCM is reading the CPS signal from the marks/notches on the flywheel as it rotates. An engine misfire affects the flywheel 's rotation and depending on which notches are out of sync the CPS will determine which cylinder is misfiring. I'm sure someone more knowledgeable can correct me if I was misinformed.

cruiser54

That is true.

I guess I'm saying that's about as good as a scope reading...

A scope reading would show a line on the screen indicating a misfire also.

Will a scope reading definitively tell you whether it's an injector, loss of compression, spark plug issue, or lack of fuel?

Or, will it lead you down a diagnostic path?

skife

This is a square wave, It's graphing the voltage reading from a hall effect sensor and a tone ring, the up parts are when you're getting a reading from the sensor (hi spot on tone ring) and the low spots are from a gap in the tone ring. when the PCM notices a slowdown between 2 points it calls it a misfire.

cruiser54

Makes sense.

skife

to be honest, i never questioned how the PCM knows there is a misfire until you asked, then i did some research. i said the same thing as you.

cruiser54

LOL. It's called learning. Old school meets new school.

DFlintstone

Sort of a side note I suppose. It seems he is watching that "square wave" but stopping, just turning it with a wrench. A three wire HO type CPS.>>> http://troubleshootmyvehicle.com/jee...crank-sensor-2

turver

I didn't see this posted yet, so I'll chime in quick. In regards to looking for a crack in the head between cylinders 3/4, it won't always be visible to the naked eye.

In some cases, a crack in the head will only open up once the vehicle is at operating temp. It might be worth your time to take a peek under the oil cap while the jeep runs.

cruiser54

While all this cracked head info is interesting, it's between cylinders 3 and 4, doesn't affect compression, and surely doesn't cause a #1 cylinder misfire.

synergy58

I'm paying close attention to this thread because I am currently experiencing a similar issue, which recently began. Most recently, yesterday in fact as I'm trying to solve my noise issues (which I think has been solved - electric fan shot, old belt replaced and new belt needing proper tension) I run to the auto parts store, about 10 miles, run inside for about 20-30 minutes, come out, start the jeep and it acts like... there's not enough power to move, press on the pedal and I felt like I was going to choke it out, its still started but won't go...it moves out of the parking space, leave me choking in the middle of the lot, sputters, chokes, wants to go, doesn't, then it clears its throat, spits it out and takes off like a bat out of hell! Weird!
A similar thing happened a few days ago, where I ran it to the store, came out, started it and it ran really ruff, really ruff! in a few feet, it smoothed out...which has happened a couple of time. Did this to my wife the other day and she won't drive it till it's fixed, that and the noise, which hopefully thats fixed now.

If my issue is something entirely different, sorry for the intrusion, but if anyone has any ideas for me, and I'm going to try the BG44K thing today too, HELP!

Firestorm500

Yours sounds more like a fuel problem. Over-rich, maybe. Could be an injector(s) heat-soaking and leaking into a cylinder(s).

cruiser54

No codes? CEL?

md21722

This sounds a lot like heat soak, or dying crank sensor or dying throttle position sensor?

synergy58

None, nope not a one. This thing bucked like a bronco for a few seconds too. Hasn't repeated that since this one time. I drove it around yesterday for just a few miles and all seamed ok. Gonna drive it again today and see.

Rogue4x4

Have you verified fuel pressure?