1995 Jeep Grand Cherokee 4.0L

Ben wrote: Also what's the deal with your buddy's jeep that signal looks horrible?

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Haha. That's what i thought when i saw it but didn't have time to do any other tests on it.

I'm actually working on a 96 Jeep 4.0 right now with a crank sensor signal problem. Sensor is not pulling the 5v ref down for the amount of time it should between the 4 humps. Suspecting crank sensor not spaced correctly since the sensor was replaced already. I'm the third tech at this shop to look at it but I'm the only one that knows what to look for when scoping haha. Parts have already been shot gunned at this thing. Crank sensor, cam sensor, distributor and ignition coil. haha. They gave up and gave it to me.

Any waveforms you would like me to gather for you once I get this running good? I will be getting injector, coil, cam and crank as I have been watching those already.

Is those last images of the coil in your buddies jeep with the ignition wire off? Running a coil with no way for the energy to be released can damage the coil. The one coil fires a lot more then standard COPs or waste spark systems.

On your coil in the jeep your working on, at the computer, I do believe that 95 and 96 are the same. The PCM located on the passenger side of the firewall? If so check the connector closest to the engine for a large Gray/White wire on the bottom row. I found its easier to grab a signal there than at the coil. Might just be the design of my probes that was giving me issues. It would be better to check at the coil to make sure you are receiving control but either way will work. That is your ignition coil ground control. This will give you a better idea as to what is going on. If there is no control which I don't believe there is, you will read 12v coming through the winding in the coil. The waveform you got does seem to show there is no control even though its on the power feed to the coil.

In terms of injectors firing when coil doesn't, I will check this on the jeep I have, some how. I know having no CKP Sensor the engine won't start but I do think the injectors loose control too. hmm

It does look like your CKP sensor is loosing a window on the flywheel. Make sure there is no corrosion on the surface of the bell housing where the CKP sensor goes. On the verus pro, I will usually set my time base to 100ms or 50ms and then zoom out after stopping the recording to see repetition. This will also tell you if your loosing random windows or the same window every time. Either way make sure there is not major corrosion on that bell housing that may hold that sensor up to high. Remember its hundredths of an inch that can cause a concern when it comes to spacing between the CKP and Flywheel Tone Ring

The last 3 screenshots are of the ignition coil on suspect jeep control wire taken at ecm & power feed from ASD relay. The only thing i appear to be lacking for engine to run is spark from igniton coil tower. When i said with coil wire off i was referring to off of distributor cap & plugged in to my grounded spark tester. Now, looking at the last 3 ignition coil waveforms i posted, in your opinion would you say that i should be getting spark from ignition coil tower?

So those last three are ignition ground control. We should see coil activity if its a good coil since control is there.

One thing I notice with your setup is channel one (yellow) is set to "Test Lead" and not "Ignition Probe". It works better even when scoping on the primary circuit to set the scope in ignition probe mode for which ever channel is probing coil control. Change that and take another snap shot of coil control. Even if there is no spark from the tower we should still see activity on that coil.

Do you have an amp probe? It would be good to take a current measurement of that coil to see if its shorted either on primary or secondary.

Also I learned that the crank sensor goes to 5v with the windows so if you ever have the crank sensor not spike to 5v on these I would highly suspect a sensor problem instead of something mechanical. If it stays at 5v for too long or turned on to early to 5v, something mechanical like spacing would be a suspect.

Here are a couple shots. The crank sensor is a problem with this one so that large 5v turn on in the green channel at the beginning and end of the cam signal is bad so ignore that. This vehicle does run fairly smooth just hicups now and then.

Yellow: IGN COIL CONTROL AT PCM
Green: CKP SENSOR AT PCM
Blue: CMP SENSOR AT PCM
Red: Cyl #1 Fuel Injector Control Wire at Fuel Injector

Here is what good coil control looks like on a 96 Jeep 4.0


Here is a Shot viewed out with crank and cam, #1 Inj to sequence the #1 cyl ignition event.

So looking at this just looks like your time base was too long and may not be a ckp sensor dropping out.

Your flywheel and distributor look to be correct for your year. They also look like they are timed correctly.

Just so we can see everything in detail which will also tell us if something is not timing right...
CKP Sensor, CMP Sensor, #1 injector and Ignition Coil Ground Control.

1. Set your scope so the channel scoping the ignition coil is set to "Ignition Probe" and you may need to put the KV scale is high as it will go. Attenuators work good for keep ign signals under control on the scope.

2. CKP & CMP sensor channels you can set to 20v scale.

3. The fuel injector channel you will probably need to set it to 400v scale. Attenuators help with this too.

Set your time base to 50ms. Have someone crank the engine and fill the buffer and hit the stop button then save all frames. Now you can adjust zoom levels and other parameters. You can take screen shots with your phone and if you have an online drive (cloud drive) like google drive, you can upload the entire scope file. May need to use a usb drive to transfer file to another pc.

I would be interested to see what everything looks like.

Matts Auto wrote: Ok, so i removed the starter to inspect reluctor ring & found what i think was part of a sticker stuck in one of the holes. I removed it with a pick, reinstalled starter & no change. So i replaced crank sensor with a new aftermarket ( i know aftermarket isn't always a good choice) & no change. I tried adjusting crank sensor but really can't get much movement out of a one bolt sensor. Customer has no history on this vehicle as he picked it up not running. The flexplate looks new so i don't know if there's a possibilty of wrong flex plate installed.

Ok I will see if I can grab some time on it tomorrow. So you know I have a 2 channel vantage so I will try n get some screen shots for you tomorrow. I have been doing this for a long time but have just recently (last year or so) been using a scope so I'm still learning the scope waveforms & I appreciate the help in learning that l.. I have never run into this scenario with everything looking good to me & no fire from coil. I'm still trying to wrap my head around coil power good & coil signal good (so I thought) & still no spark. Thanks again for your help

Ah Sorry, I always assume everyone has a 4 channel.

Here are the shots you should grab with a 2ch
1.CMP and CKP at 50-100ms time base. 100ms is probably fine for cranking
2. CKP and #1 Fuel Injector (Injector Timing and Control Confirmation)
3. CKP and Ignition Coil Ground Control (Set the probe type to Ignition Probe) (Ign Timing and Control Confirmation)

This will tell us how everything is timing up and the condition of everything and how the coil is doing internally and if the PCM is trying to give proper control.

The ignition coil needs to have a good ground I believe through its housing to the engine. A diagram shows it grounded that way.

Yea I have already replaced coil & thoroughly cleaned coil housing & grounds to it. Again thanks for your invested interest in helping to solve this issue & help me with my learning curve. Hopefully I will get some time on this tomorrow. Also just to let you know I have plenty of time with this vehicle it's my customer/ friend play jeep he's in no hurry

This video Paul Danner created is probably one of his best at explaining ignition waveforms. If your not already, I would highly suggest subscribing to his premium channel. Its worth so much more then just a library of videos. It has changed my entire career.

I know you have a no spark situation but just some food for thought in case you haven't thought of it...You can also use an incandescent test light to check spark. clamp end to ground and probe end to coil. I think its better actually cause you can see just how far the spark will jump and this will determine how much energy that coil is capable of producing. I find most coils will jump 3/4-1" just fine. If its down around 1/2" thats usually ok but might be showing signs of weakening, should still start and run just fine. Less than that and I could call a bad coil.

I noticed your snap shot here. If the CKP sensor and CMP sensor have no drop outs at all, then your CKP and CMP sensors look good and your timing is right.



I would say just grab CKP & Ignition and then CKP and #1 Fuel Injector. In fact CMP & #1 Injector would also help to judge timing of everything since there are no major sync notches in the CKP signal that can allow us to notice 720 degrees of crankshaft rotation. I can then compare them all and judge timing.

I do believe, if you have injector control, then you should have coil control. If you have good coil control, then just to make sure its housing is grounded and you have good power to the coil which I believe you already tested.

Whats interesting is the 96 Jeep I work on only uses a 5v REF to the sensors, not 8v.

At what time base were you looking for on those waveforms?

100ms is probably fine for cranking and idle so you can try that. Plus 100ms has a big buffer so more of a chance to capture something.. Idling engines I like a little more detail sometimes so I'll use 50ms but it all depends what I am looking for. The last capture I quoted of your CKP & CMP signal correlation looks like a 500ms screen so 100ms should do.

When you scope ignition control circuits on 2 wire ignition coils, sometimes its better to go right down to 20-50ms to get a full detail of the ignition waveform. Give it a shot, play around. you can send pictures of 20,50,100 and I can let you know which ones I prefer for analyzing detail just as a reference for your scoping future. The actual "numbers" for time base and voltage scales I don't put to much thought into, its more of just wanting the right settings to get the detail or repetition you need to make a call. I do have a generic time base range which I normally go to and that is 20-50ms usually for ignition and 100-200ms for mostly everything else.

It varies from vehicle to vehicle especially when you start scoping variable reluctance sensors producing AC sine waves.

If you ever use another scope other than a snap on scope, you might get mixed up with time bases and voltage scales because most other scopes set everything "Per Division" instead of "Per Screen" like snap on does it. So depending on how many divisions (squares) are across the screen will judge your "screen" time base or voltage scales. So if there are 5 divisions horizontally across the screen and you want the same 100ms screen, you would need to set other scopes to 20ms/div. Same goes for vertical scales. Little food for thought.

Here are a couple cam & #1 injector

here is crank & #1 injector

Cam & #1 injector

It appears timing wise it looks good. Matches what I got on the 96 jeep which is now fixed.

Grab some cmp / Ign ctrl * ckp / Ign ctrl shots. We need to figure out why your coil is not firing. You should see control to your coil if you have control to your injectors. Compare control at PCM and at IGN COIL. Make sure IGN CTRL is making its way to that coil.

Do you have a low AMP Probe that measures on a scale of 1mv/10ma (20a) or 1mv/100ma (40a)? 40amp could also be 10mv/1A scale, same thing. A current ramp test could tell us if the primary or secondary winding is shorted.

Honestly If you have good control and good power to the coil and the body is grounded well, that coil should fire.

Below I highlighted the area you need to change. You should be able to tap on the probe to change it. You might need to be "recording" aka "Scope Live" to make the change. Then set your voltage/KV scale as high as you can go. I believe it will probably go off the screen a bit "if" the coil was actually firing. Make sure coil is attached to the distributor like normal.


Here is a known good from a 1995 Jeep 4.0. Wiring diagrams do show 8v REF voltage to sensors but that might only be to run the hall sensing circuit. Probably just a 5v supply on the signal wire.

That's what i've been trying to understand all along. Everything seems to be there except no coil fire. I have to believe i'm overlooking something simple somehow.