1995 Jeep Grand Cherokee 4.0L

tps 5 volt is good.

That capture is exactly what were looking for! Notice the points of the crank sensor that we only see 3 humps it's likely that the air gap is to big however these fail enough that I would replace it as it comes with the felt tip to set the proper air gap as well . Also the tapering humps are also a sign of excessive air gap but I've seen them on 4.0s that run fine so that alone isn't enough to condemn it but that capture is a model bad crank signal.

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So with a bad crank sensor I would still have injector pulse & power n signal at coil?

Also with time base at 500ms why does crank signal look better & shows all 4 points on the last one but only 3 on 2second time base ? I haven't done a lot of crank sensor scoping

You just weren't seeing enough of the events to get a full pattern it's important to look at low time base for detail and longer time base for repetition the pcm isn't getting enough information to fire correctly it doesn't like the tapered signal either I thought it was possibly a scope setting till I seen the missing events . And yes it's possible to still have injector pulse (it may not be in time and it may not be consistent) I would bet if you scoped the injector signal while cranking you'd see inconsistency as well

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I will change out cps & let you know how I make out. I'm still on the green side of scoping. Thank you for your time & explanation. It is very appreciated.

No problem assuming thats the only problem and it runs after changing the CKP take another look at the coil trigger it should look better as well (also CKP= crank position sensor, CPS= cam position sensor) just so there's no mix up with your parts supplier.

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Pull the crank sensor and use a borescope to inspect the teeth of the reluctor ring it looks like sludge has built up in the gaps

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.

Decided to do a few tests on my buddy's older jeep wrangler that he installed a 4.0L from a 99 cherokee. One thing to note (not sure if it matters) he installed a cps kit to move CPS to read from the front crank pulley. The installed crank pulley also has the 3 sets of 4 notches.

Here is his coil cranking with coil wire off.

Try that coil control at 100ms or so so we can see some detail to the control

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

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Make sure whatever your adjustment is on your crank sensor that it looks good on the scope (I'm sure your checking at the sensor connector by master cyl it might be a good idea to check at the pcm and see if the signal makes it all the way back there...

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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?