Novak Conversions Jeep Wrangler TJ engine mounts

P0320 dead on road

4BY4ADV

4BY4ADV

TJ Enthusiast
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Jan 2, 2020
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280
Location
Oceanside, CA
I had a p1391 error code yesterday. Decided to replace both the distributor pickup and the crank position sensor yesterday.

Fired up perfectly and ran better than before.

Today, leaving for a trip, it stalls and dies.

Swap both sensors back since I kept them in the jeep. Now it’s cranking a bit better but a couple exhaust pops and still won’t start.

Now p0320, nothing else. I’m thinking the wires are damaged. Hoping someone can tell me what diag I can do… I’ve got a multimeter with me. Spare wire, etc. IF I need to do a roadside bypass of the wires I can. But would like to know ohms at the connector, etc to test first?
 
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5v at pin 3/ supply
5v on occasion at pin 1/ sensor signal
(I’ve blipped the throttle and checked voltage)
Ground at pin 2 sensor return

I’m flummoxed. Yesterday all that was done other than an oil change was replacing CmPS and CkPS. Jeep ran perfect for 10-15 minutes then nothing.

Changed both sensors back and still stuck at P0320.

And all packed up for two weeks of beach camping in Baja.
 
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So… brand new sensor catastrophically fails after 2 miles of running great… swap back to the previous and no change. Not doubting you, but isn’t that weird?

I was thinking that my fiddling with the wires trying to pull them away from the exhaust might have caused problems, but having all three wires pass for continuity (even while jiggling) tells me that’s not the issue.

Oh well. I have two weeks in Mexico before I have to deal with it.
 
4BY4ADV said:
So… brand new sensor catastrophically fails after 2 miles of running great… swap back to the previous and no change. Not doubting you, but isn’t that weird?
Click to expand...

Not one bit. New parts are shit. What brand did you install? Try a Standard Motor Products or Napa Echlin.

-Mac
 
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Saw a hack on a YouTube video. Dude sprayed some water from a water bottle on the crank sensor and his Jeep fired right up. Hard to believe but I saw it on YouTube so it’s gotta be true. I figured if I’m ever in this situation I’ll try it. Guess it cools it down a bit and gets it working? I dunno. It’d be great if you tried it and let us know. It’ll take longer to lift the hood than try the hack.
 
Think it's more to do with cleaning the tip. Basically the flywheel is a big reluctor wheel with gaps.

It's also entirely possible it's wiring. Might want to pull the connectors to your PCM and inspect for corrosion. And since you'll have them off check continuity and ohms.

The FSM with wiring diagrams is in the resources section. That'll tell you the pins to look for...

-Mac
 
I checked continuity yesterday. Connections at the PCM look clean.

While testing continuity I moved the wires all over the place. Continued to have a tone.
 
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So... Back from Baja and doing some testing when I have time. I swapped for a new echilin CKPS. Also purchased a tool similar to power probe that has an oscilloscope built in. I tested the signal wire and I'm seeing a waveform.

Still no start and the occasional pop/puff when cranking. I'm going to swap the CMPS again to see if that's the culprit(both were changed together the day before it all went down).

My only other thought... audibly this all sounds the same as when I installed a new distributor and it wasn't lined up properly. So I'm wondering if the distributor has gone bad.

Any other ideas here before I rent a trailer and struggle to push the jeep up onto it? Or do I just risk destroying my starter with another starter creep?
 
Make absolutely sure that the square wave is pulling all the way to ground. Many cheap aftermarket sensor’s wave forms will look fine at a glance, but the devil’s in the details.

Another known issue with cheap sensors, is they get hot, and start giving the PCM a nonsense, fuzzy, looking signal. This can often trip dtc’s for the wrong sensor. Most commonly, the cam sensor will get fuzzy, it kills the engine, the engine loses crank signal, and ends up throwing a crank sensor code because it was “seeing” a crappy cam signal. Our PCM’s weren’t programmed with the capability to detect an “implausible signal”.
 
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macleanflood said:
No RPMs means bad Crank position sensor.

-Mac
Click to expand...

No RPM's CAN mean a bad crank position sensor.

Fixed it for you. It can also mean a broken signal wire, intermittently losing 5v at the sensor, bad signal wire connection at the PCM or sensor, bad sensor ground, etc...

This is your go-to response. Stop.
 
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ItchyDong said:
Make absolutely sure that the square wave is pulling all the way to ground. Many cheap aftermarket sensor’s wave forms will look fine at a glance, but the devil’s in the details.

Another known issue with cheap sensors, is they get hot, and start giving the PCM a nonsense, fuzzy, looking signal. This can often trip dtc’s for the wrong sensor. Most commonly, the cam sensor will get fuzzy, it kills the engine, the engine loses crank signal, and ends up throwing a crank sensor code because it was “seeing” a crappy cam signal. Our PCM’s weren’t programmed with the capability to detect an “implausible signal”.
Click to expand...

First time using an oscilloscope. As techy as I am, this one is a bit new to me. I'm assuming here that I'd look at the vMin and want to see a zero value here?

Other thing, I'm assuming the waveform is not going to be consistent, correct? I don't have it in front of me, but I want to say that I saw something like 4 square waves then a gap before 4 more waves repeated. That sound correct? Maybe I'll try to make a video this evening after I'm done with work.

I'd *rather not take it to my mechanic as his shop is always busy/full of Jeeps and I'm not sure how long it will be there before it's next up. I really like taking the time to get to know my Jeep and doing the repairs myself. Makes me feel more confident in both the repair and that should I have future issues... I'll know what to do.
 
Here’s the CPS waveform. Does this give any clues? Depending on your browser... you might have to change the resolution settings from auto to 1080P to see it clearly. Also... tried to rotate 90 degrees... but for whatever reason even though it's correct on my iphone, the PC reverts it back. :/

20240910_001300000_iOS.MOV
 
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ItchyDong said:
Make absolutely sure that the square wave is pulling all the way to ground. Many cheap aftermarket sensor’s wave forms will look fine at a glance, but the devil’s in the details.

Another known issue with cheap sensors, is they get hot, and start giving the PCM a nonsense, fuzzy, looking signal. This can often trip dtc’s for the wrong sensor. Most commonly, the cam sensor will get fuzzy, it kills the engine, the engine loses crank signal, and ends up throwing a crank sensor code because it was “seeing” a crappy cam signal. Our PCM’s weren’t programmed with the capability to detect an “implausible signal”.
Click to expand...

It's showing a zero value for minimum during crank. As for getting hot, this one... and the previous, both Napa Echlin, neither had a chance to get hot.
 
The signal looks fine from what I can see.

No, the signal won't be consistent. It's varied by the pattern cut in the tone wheel so that the PCM understands it's position.

Where are you testing to get that waveform? At the sensor? It maybe time to move your test up to the PCM. You need to make sure the PCM is receiving that signal. That is, after all, the definition of the DTC. The PCM isn't happy with the signal.

Also, you say "CPS". That can easily be confused as the Cam Position Sensor. Just making sure that you are, in fact, testing the Crank Position Sensor.

After a quick search, it could be an issue with the cam sensor, or cam sensor wiring. Need to check that stuff too.
 
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ItchyDong said:
Also, you say "CPS". That can easily be confused as the Cam Position Sensor. Just making sure that you are, in fact, testing the Crank Position Sensor.
Click to expand...

I typically see "CPS" used for the cam position sensor and "CPK" for the crank position sensor.
 
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