Do I need to do a crank / cam re-learn after removing OPDA

[OldBuzzard]

I don’t like how it’s out of sync at start

I've seen screenshots from other OBDII readers, and they all say it's out of sync at start, too. I think that's the way the PCM does things. I wouldn't worry about that. It cranks, sees it's out of sync (as expected), and applies it's correction value to get it to run.

and the learned value is 6753.40

Do you mean 6553.5 ? That's because the firmware writer doesn't understand signed vs unsigned binary values. He's reading a signed 16-bit value as unsigned. 65535 = -1, and then shifted into the decimal place (OBDII is awkward that way) it's -0.1. So I think the Cam Crank Learned value in your screenshots should show -0.1. After you tweak the OPDA, read it again and see if the value changes a little.

 

[Jwhite]

I've seen screenshots from other OBDII readers, and they all say it's out of sync at start, too. I think that's the way the PCM does things. I wouldn't worry about that. It cranks, sees it's out of sync (as expected), and applies it's correction value to get it to run.



Do you mean 6553.5 ? That's because the firmware writer doesn't understand signed vs unsigned binary values. He's reading a signed 16-bit value as unsigned. 65535 = -1, and then shifted into the decimal place (OBDII is awkward that way) it's -0.1. So I think the Cam Crank Learned value in your screenshots should show -0.1. After you tweak the OPDA, read it again and see if the value changes a little.

When I had my cam crank difference of 6.7 the learned value was still 6553.5. Now I have it at .400 or so and it’s still 6553.5. Do you still think I should adjust it even at .400? That was the closest I could get it to be to zero. If I turned it counter clockwise any more than I have it, it would read 6553.5 which the car didn’t like.

 

[Jwhite]

I've seen screenshots from other OBDII readers, and they all say it's out of sync at start, too. I think that's the way the PCM does things. I wouldn't worry about that. It cranks, sees it's out of sync (as expected), and applies it's correction value to get it to run.



Do you mean 6553.5 ? That's because the firmware writer doesn't understand signed vs unsigned binary values. He's reading a signed 16-bit value as unsigned. 65535 = -1, and then shifted into the decimal place (OBDII is awkward that way) it's -0.1. So I think the Cam Crank Learned value in your screenshots should show -0.1. After you tweak the OPDA, read it again and see if the value changes a little.

Also I should mention that the jeep has all its power and does not set off a check engine light when I floor it or any other rpm. I just don’t want it to be unreliable because the learned value is different from the cam crank difference.

 

[mrblaine]

When I had my cam crank difference of 6.7 the learned value was still 6553.5. Now I have it at .400 or so and it’s still 6553.5. Do you still think I should adjust it even at .400? That was the closest I could get it to be to zero. If I turned it counter clockwise any more than I have it, it would read 6553.5 which the car didn’t like.

The PCM compensates by about 10 degrees either side of 0. It can't get better inside the range, it only gets worse when it moves past the amount it can compensate for.

 

[Jwhite]

The PCM compensates by about 10 degrees either side of 0. It can't get better inside the range, it only gets worse when it moves past the amount it can compensate for.

Should I take it to a shop or dealership for a crank cam relearn now that it is almost 0?

 

[mrblaine]

Should I take it to a shop or dealership for a crank cam relearn now that it is almost 0?

I wouldn't. I'd dig around and find the manual version that clears the adaptive memory in the PCM and follow it to the letter. If you don't find the one that involves turning on the headlights, it isn't the correct version.

 

[TEZZA]

After assigning the relearn with the scan tool you need to do a drive cycle for the PCM to learn the new sync value.

 

[Chippy]

Does that one do the relearn?



Thank you

Yeah, the thinkdiag2 is the only thing that worked to relearn for me. People say disconnect the battery, touch the terminals together, etc. none of it worked except that scan tool

 

[Vtx531]

Yeah, the thinkdiag2 is the only thing that worked to relearn for me. People say disconnect the battery, touch the terminals together, etc. none of it worked except that scan tool

Costs $100 per year after first year free? Argh

 

[mrblaine]

Costs $100 per year after first year free? Argh

Ya'll are making this a lot harder than it needs to be.

 

[Vtx531]

Ya'll are making this a lot harder than it needs to be.

Last I recall, I used a toothpick to align a couple of holes with engine at TDC 15 years ago and it's been fine ever since. So I don't really understand anything going on here but trying to learn.

 

[mrblaine]

Last I recall, I used a toothpick to align a couple of holes with engine at TDC 15 years ago and it's been fine ever since. So I don't really understand anything going on here but trying to learn.

I'm referring to the obstinance about finding the manual relearn procedure that involves doing a few things and turning the headlights on to clear the adaptive memory. That was available long before it was common for home mechanics to have any sort of scanner.

 

[sab]

I'm referring to the obstinance about finding the manual relearn procedure that involves doing a few things and turning the headlights on to clear the adaptive memory. That was available long before it was common for home mechanics to have any sort of scanner.

Interesting. I was not aware of it, but with a bit of searching, I found this:

https://search.brave.com/search?q=c...ersation=08d3fb7e55fbf9bad4cbb192b4d7c9e4babe

 

[Chippy]

Interesting. I was not aware of it, but with a bit of searching, I found this:

https://search.brave.com/search?q=c...ersation=08d3fb7e55fbf9bad4cbb192b4d7c9e4babe

I tried that too and it didn’t work for me. The link also says to fully reset “This typically takes around 500 miles of varied driving.”

That’s like a year of driving for me. No waiting when you just reset it with the tool lol.

 

[sab]

The link also says to fully reset “This typically takes around 500 miles of varied driving.”

That's to reset all the adaptive registers, which are data values in memory that it learns over time. The cam/crank offset is just one of those registers, and that one wouldn't take but a few seconds for the PCM to measure and set.

 

[Steel City 06]

I'm pretty sure it was determined in a previous thread that disconnecting the battery on an 05 or 06 would cause the PCM to relearn the cam/crank difference.

I've never done a scan tool relearn on my 06. If it throws a code, tweak the OPDA one way or the other till no code, then disconnect the battery to relearn.

The NGC3 literature out there actually notes that the cam-crank relationship is stored in non-volatile memory, and is not wiped by a loss of power. Unplugging the PCM will result in the loss of fueling adaptive tables and similar data, but can-crank relationship is not reset.

I suspect it is set up this way so that the computer can monitor for long-term drift in the relationship. If it left the factory at one angle and then 5 years later is more than 10 degrees out of spec, there is likely a problem that should be reported. If unplugging it reset it, the computer would not know about the long-term drift, or an owner could simply unplug the PCM to erase a code that is actually still a problem.