So, I finally got another PCM (junkyard) installed. Fixed my CEL and dead injector issue. All of my injectors are firing again but I still am having the roughness/vibration at low rpm. The jeep seems to idle fine and run good at higher rpms but any time the tach gets close to 1300rpm it just gets really shaky. I can't help but think this is related to my injector issues because they both started at the same time. Also, what would have caused my pcm driver to go bad? I wonder if my injector signal wires are shorting out due to damaged insulation? I could see that causing a driver in the PCM to burn up, but doesn't really make sense why the jeep would run rough at certain rpm and not at others.

 

Engine mount? You checked the resistance of the injectors? Any ignition issues?

 

I replaced the engine mounts and trans mount about a year ago. I did test injector resistance (tested good) and I also tried a different set of injectors. Same issue even with the new ones. The spark plugs, cap, rotor and plug wires are all only about a year old (have about 8k miles on them). Same with the TPS and IAC valve. All my vac lines are new. Can't find any vacuum leaks anywhere. The problem is there no matter if the engine is cold or hot.

 

Hm. Well you certainly sound competent, and done some good work and testing. A thought I have is, a problem with the valves or valve train. In other words a mechanical problem.

Have you checked the lifter preload? Compression test? How about a radiator leak down test? Change the coil for a known good? Just brainstorming.. Seems to happen at a certain rpm. Too bad no scope huh? How about this...Does your throttle cable rest on the back side of your crank sensor, like mine did? Bend it out of there. It can throw off the magnetism of the hall effect sensor.

 

Hey guys. So after a couple more days of failing to figure out whats going on I decided to go ahead a get a scope. I actually picked up the same one Dave has, the Hantek 1008c. After reading up on how to use scopes and watching a butt ton of ScannerDanner videos I think I might actually have an ignition problem. The only issue is I can't get my scope to show me a good secondary ignition waveform using the HT25 hook up that it came with. I'll get a glimpse of the wave on the screen but it jumps around so much I can't see it. I'm not sure if its my laptop lagging/freezing or if its just my settings. Anyway, Dave I was wondering if you had any experience with this? I've tried moving my ground clamp around to different places but it hasn't really made a difference. I think the best is just grounding it to the negative battery post.

Here's a link to a google drive with a video of what I'm talking about if ya'll are interested. Anyway, I appreciate all the help so far.

https://drive.google.com/drive/folde...nf?usp=sharing

 

To waveform the ignition, it is best to use an ampclamp on the ASD fuse (using a fuse buddy) as this fuse is the circuit that goes right to the ignition coil. It will show all 6 ignition waves on one screen (typically it will auto detect the sequence). I have a Hantek scope. Then you can use your HT25 (or even just one of your probes) on one of the spark plug wires to plot the voltage spike from a known cylinder number (like #1) so that using the order 153624 you can identify which wave corresponds to which cylinder in the ignition sequence.

Here is the clamp...it measures amperage via capacitance then converts it to voltage so that the scope can plot it for you (its also useful for a lot of other things - and well worth having):

 

Here is my ignition sequence (you could probably use it as a known-good representation):


A long sequence of primary ignition waves with cylinder 1 spark plug (secondary ignition) being indicated by the voltage spike below in blue.



A screen capture dialed in a bit closer to view 6 waves (6 cylinders).

 

IDK, the parameters you have set up should work but your trigger isn't triggering. The trigger level set on the right axis should be a nice clear T but it looks like you cursor is sitting on it. Perhaps that's messing it up.

 

Or alternatively, use a different horizontal scale.

 

I don’t have the scope but Dave is right, you need to select your trigger source. I would put the crank sensor on channel 1 and trigger from that. Then the channel 2 on the secondary ignition probe. If the secondary is still jumping around after triggering from the crank sensor, you have a problem with ignition. Specifically, your spark isn't happening when the crank is telling it to.

 

Alternatively2, set the Acquisition Mode to Single and scroll through the waveforms one at a time.

 

Yeah, but wouldn't that not show if the ignition is firing at the same time the crank sensor is?

 

To start I would just use the HT25 and run down the line and eyeball the 6 waveforms. Based on current issue:

that would be a good quick screen.

Need to figure out why the trigger isn't working. I can't make my trigger NOT work so IDK why his isn't working (yet). I shall fiddle with mine to try to duplicate that.

Then add the CPS and CKS. That's going to be a busy screen so we'll we'll need to work on the horizontal setting to fit it all in.

 

Then check all the injectors (still might be a wire or connector)(hey, you got the stuff out already).

 

This is exactly what I was trying to do last night. Just go down the line and check the secondary ignition waveform of each cylinder with a throttle snap since the miss is the worst at rpm above idle. I just can't get the trigger to work at all. I tried for several hours messing with different settings and clamp locations. I think I'm gonna try what 97Grand and Jordan said and add a current clamp on the ignition fuse and try to set the trigger off that. I won't have a chance to try it until tomorrow afternoon though.

It's weird because I can get the trigger functions to work great just using the square wave generator from the calibration output and ground that's built into the Hantek.