Broke down again away from home. P0336 crank sensor code.

[big bird]

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[big bird]

Sensor came apart during removal. Now some of it is in the hole.

 

[someotherguy]

Sensor came apart during removal. Now some of it is in the hole.

It just fits in there semi-snug with an o-ring for a seal, and the bolt on the bracket of course. Have you got a pick or something you can pop the broken part out with?

I'd say that's pretty good confirmation of a bad sensor!

Also, the one Road Trip posted looked pretty horrible. I had one starting to kiss the reluctor on a 7.4 - replaced it before it went bad. This was forever ago and I was unaware of needing to do a crank relearn. I'm sure they wouldn't mention that if it wasn't important, but the truck ran fine (well as fine as a beat high-mile big block could) without the relearn. You'll want to do it, no doubt, but my hunch is that once you get the sensor replaced and shimmed properly so it's not making contact, you'll be up and running reasonably well again.

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Richard

 

[big bird]

Sensor came apart during removal. Now some of it is in the hole.

Sensor out.

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[big bird]

Old sensor doesn't show tip wear, but I imagine it is fried since it came apart.

Going to take some measurements and see if I need to shim. I'm good to .020 with my pocket scale and eyeball.

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[big bird]

We're within at least .010. New one feels like it is a hair longer. I'm going to put grease on the tip and see if there is contact but I think I'm good.

 

[big bird]

Big Bird lives! Talk to y'all on the flipside. We got miles to go. Thank you much for the help!

 

[Road Trip]

Instructions that came with new sensor state: "To prevent misfire detection by computer system a crankshaft variation relearn must be performed ... Diagnostic scan tool is required to perform this procedure. Failure to perform this procedure will result in a false trouble condition."

Boy, that's an interesting wording of the potential benefit you can derive from improving the accuracy
of the misfire detection/cylinder identification algorithm. My favorite misinterpretation of what they wrote
would be, "Hey, I can prevent misfire detection by performing a CASE (Crank Angle Sensor Error) relearn?"
(You know, for those that prefer the Ignorance is Bliss theory? :0)

NOTE: In the Optional Reading section below I'll try to explain when a CASE relearn is worth the effort to thread that needle.
In particular, when would I performance a CASE relearn even though the '98+ P1336 DTC isn't being kicked?

...Is the sensor relearn actually required?

Based upon what's in the FSM plus the real-world experience in this forum, the short answer
is based upon what year Vortec you are driving. More specifically:

* '96-'97 GMT400 Vortec VCMs don't have the P1336 DTC, and AFAIK there's no CASE relearn functionality in the
code for a Tech 2 scan tool (or equivalent) to interoperate with. No CKP DTCs? No CASE relearn worries.

* '98+ GMT400 Vortec VCMs do have a P1336 DTC, and if this test runs and fails, then the CASE relearn
procedure must be run in order to clear the DTC / turn off the SES light.

****

As reinforced earlier in this thread, once the actual signal from the CKP sensor degrades past a certain
threshold it literally becomes a showstopper. Being risk averse (ie: being on the side of the road sux) ...here's a list
of the CKP-related DTCs extracted from the '98 FSM. Note that not all the CKP DTCs actually cause the SES to be lit:

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DTC 'Type' legend:

* A = SES light lit when it occurs, DTC stored.
* B = SES light not lit until error detected across 2 separate driving cycles, DTC pending > stored.
* C = SES light never lit, but DTC is stored.
* X = SES light never lit, plus DTC not stored. (Test not run.)

NOTE: If you read through the P1336 DTC description (see attached .pdf file) you will notice that
the P1336 DTC is blocked from running IF there is either CKP -or- CMP DTCs kicked, And given
the reporting types, it's possible to be riding around with CKP DTCs that aren't lighting the SES.
(Think RFI atop signal causing a spurious circuit high frequency? Marginal grounds in the RFI-rich
engine bay is one way of possibly causing this kind of heartache. (!)

****

To recap, you are driving a '98 3500. If after this CKP sensor replacement you are driving down the road,
no SES light, *and* no misfires needing accurate troubleshooting...you are good to go, keep on truckin'!


**** Optional Reading ****

For anyone wondering if they should plow through the following, if you are part of the pre-'96 TBI community then
this has no direct value -- you have to troubleshoot misfires pretty much as it was done back in the carburetor days.

If you have all the diagnostic toys, then a cylinder balance test, followed by reading plugs being pulled for a compression
test, and further refinement with a leakdown test is pretty much the state of the art. The TBI computer can sense out of
range sensors that have strayed into the high or low guard bands, as well as wonky A/F ratios, but you are pretty much
on your own when it comes to actual misfires.

The EPA decided that starting in '96 that uniform terminology, identical OBDII connectors, and standardized DTC codes
would be implemented across the entire new car/truck marketplace. And that each vehicle's computer would be able to do things
like constantly monitor & identify catalytic converters that were no longer providing baby's breath exhaust. And since the
cats were so easily damaged by even a single misfiring cylinder, the manufacturers were directed to implement real time
monitoring and test strategies to help the mechanic identify which cylinder(s) are misfiring.

The short story is that our VCM, being so fast, is constantly monitoring just how much each individual cylinder is
contributing to the spin speed of the crankshaft. IF all cylinders are contributing equally to the load, then they
will all compare the same to each other, and life is good.

But if a misfire occurs, the missing push from the misfiring cylinder is detectable by the computers capable of
performing literally millions of instructions per second. (By comparison, a V8 engine idling at 600 rpm is spinning only
10 revolutions per second, and giving the computer exactly 40 power strokes to slice/dice/compare/contrast/throw
a P030x DTC/light the SES bulb once the calculated amount of pollution is 150% of the emissions calibration. :0)

OK, the above is pretty much the standard boilerplate when discussing On Board Diagnostics, level II. So what
does all this have to do with the CKP sensor? First of all, remember that all this mandated emissions-related
self-testing was new, without the benefit of any real 20/20 hindsight. So some things worked better than expected,
while others didn't fare so well.

Reading between the lines, it looks like the cylinder misfire identification algorithm looked good on paper for the '96 & '97
model years, but fell a bit short in the real world. If the computer gets the misfire wrong by 1 cylinder in the firing order,
then this naturally causes the mechanics to doubt what's supposed to help them keep the cats from melting down. (And
since the General had to warranty the emissions for at least 70,000 miles by law, there was a vested interest in keeping
this stuff working for at least that long.)

****

Now that we've set the table, this is pretty much why the CASE (Crank Angle Sensor Error) relearn came to be, along with
a new 1000-series OEM optional DTC: P1336. Essentially if corrective maintenance forces you to replace anything in
the computer / CKP sensor / crank / reluctor ring space, there is a special diagnostic routine that allows the computer to
detect any signal variations caused by manufacturing tolerances in the involved components and store that away in
volatile memory.

This is done by getting the mechanic to spin the engine up to ~4000 rpm, the VCM cuts the fuel, and then measuring
the CKP signal while the engine does a coastdown back to idle speed. Subsequently to storing this info across a power
cycle, now the computer can perform the equivalent of an "Add/Invert" function, subtracting the 'imperfect part' signal
distortions from the incoming raw signal, thereby improving the dynamic Signal/Noise ratio.

All this in order to maximize the accuracy of the VCM when trying to associate the misfire to the correct malfunctioning cylinder.

****

Q: Why bother typing all this in?

A: Reading through this forum & others, observing the plight of GMT400 owners who are struggling
to troubleshoot a tough misfire and being misled by either their test equipment or the VCM (or both)
getting it wrong is no fun. Especially if they are driving a '98+ GMT400, *IF* they are plagued by
reported misfires that can't be felt, or keep working on cylinder #3 (P0303) to no avail, etc., then
it may pay to stop and perform the CASE relearn in order to make the misfire reporting as accurate
as possible. Obviously if a P1336 is being kicked, but even if it isn't, for the thresholds aren't
published.

In English, if your engine never has a reason to kick a misfire DTC, then all of this is just counting
the number of angels that can fit on the head of a CKP sensor. But if an engine has a history of
misfiring, isn't responding to the normal repair efforts, and you are asked to help troubleshoot
the problem, and want the clearest troubleshooting picture possible, then it might be worth the
effort to line up a Tech 2 scanner (or jump through the necessary hoops in order to get an app
set up) to perform this diagnostic accuratizing.

big bird, if you are still reading this I sincerely hope this answered your question. So I guess that
the real answer is a Definite Maybe. :0)

Here's hoping that your truck settles down and starts to fly right.

Cheers --

 

[someotherguy]

Good info on the 96-97 vs. 98-up. I had both for a little while - the '94 3500HD with the '96 7.4 full swap, and the '98 7.4 yard wrecker that I eventually took apart as a wrecker unit donor since the truck itself was so beat.

So now I know why I didn't have to do the relearn on the '96 when I replaced the sensor.

Richard

 

[big bird]

Road Trip, thank you for the very thorough explanation. I really do appreciate it.

We're busy moving furniture and building animal pens and such, so I'm being brief.

Truck felt like it ran a little sluggish at first, but then picked up after a few hours. I'm assuming it was doing its fuel relearn as I had the battery disconnected. This is a very subjective feeling and it may have been normal and I was just not pushing it hard due to nerves.

It's running well enough that I'm not going to do a crank sensor relearn while we're still moving. When I get around to fixing the stuck O2 sensor and other minor fixes, I'll probably do it then.