I just picked up a second 6.5 GM 4x4 extended cab from a friend. I drove this vehicle a lot this fall and it ran great before buying it last week. It has been great for almost a week now until yesterday. The problems started after driving in heavy Ice Fog on my way to work.

My 98 ,6.5 started acting up, clacking like crazy, it sounded like it just started at -30 as I took off from a a stop sign. Then it showed the check engine light, as I braked to pull over the oil pressure droped to zero and the check gauges light came on briefly.
A code scan says Crankshaft position sensor circuit A fault. I cleared the codes and all seemed fine. Back to diesel quiet.
Then when driving all seemed normal until I had to brake and the engine speed droped to idle, the check gauges light comes on, oil pressure is zero, Tap throttle to bring engine up to 700 plus and oil pressure returns to normal. Acelerate lightly and engine is loud {valve clatter} briefly until about 30 mph/50 KMH and all sounds normal , good oil pressure again.
Then it starts acting normal again at stops etc. No more codes, and oil
pressure is normal at idle speeds. No unusual noises.

The motor has about 40,000 KM since being rebuilt, and has run fine until now. It is full of fresh oil, 0W40 Synthetic, 3 days old, fresh Filter, and still on the full oil mark. Temp is normal .Idles smooth.

Is it normal for a crank position sensor to cause these things to happen intermittently? Oil pressure sending unit intermittently bad?
I am at a bit of a loss on where to start.
Pete
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Was the CSS replaced when the engine was rebuilt??if not it may be time the they decay with age and you may have a time with removing the old sensor get AC/DELCO or NAPA do not waste money on the BWD brand

 

Well it just went south , big time.
I drove it yesterday for over 100K and all was good. Today I warmed it up , went 5 miles and it coughed surged, and rattled like crazy. Pulled over and the check engine light is on, did a code check and it said Crank Position sensor circuit A malfunction. Like before I cleared the code, but it didn't clear the light, so shut it off and cleared it again, got an all clear reading, but no starting it. It tried to start but no go.
Seemed like no fuel so I opened the filter cap and got lots of fuel, . After 20 minutes under the hood looking for something it finaly starts, but rattles bad, no power and the CPS code is back along with check engine light.
I am believing the CPS is the villin, but I have never had a vehicle with one, and don't know where it is, or what it looks like or how to change it.
can someone please point me in the right direction to change out this CPS.

 

I think I already answered this @ DP but I will post here as well:

Not really a good way to test.

A multi meter set to ac milivolts should show a voltage when the engine runs across the terminals of the sensor when unplugged.
I have no idea what the voltage reading should be though?

If the CPS is not AC Delco then it is a given that it is bad.

A scan tool that shows CPS reading should also tell you whats going on.


On the drivers side of the timing cover behind the power steering pump you will see at the cranshaft centerline a 2 wire sensor with 1 small bolt holding it-thats the CPS.

Getting the CPS wires connected is pretty easy.

Do yourself a favor and loosen off the power steering pump from it's mounts-it needs to move a fraction of an inch to get the CPS in/out.

Can't stress this enough-AC Delco ONLY for CPS replacement!

 

Cold weather forced me to a shop to change the CPS. Good news is all is well and the truck is running fine after several hundred miles.I am beginning to think some of the thought to be PMD's at fault were actualy good now. It is running fine on PMD's that were changed out previously because of running problems.
It is starting to look like a bad CPS can cause lots of issues that changing the PMD temporarily fixes.
This all becomes confusing.
Truck looses power, change PMD and truck runs good for a while, and looses power again after a few thousand miles, another PMD and truck runs good. Finaly CPS code pops up, change CPS and re use thought to be bad PMD and truck runs fine.

Can the CPS be the root cause of running issues that a PMD switch out seems to fix for a short while and I have been changing out the wrong thing all along ? How the CPS / Computer/ PMD / and pump interact is all greek to me, but it is looking like I have been blaming PMD for issues the CPS is actualy causing.

I have 2 6.5's now and the other truck is doing the same thing as this one was doing by eating PMD's , and now it too is showing a CPS code. I may now have a good supply of PMD's I thought were bad but now seem to run fine when I tested them again after changing out the CPS..

 

A bad CPS will put the ECM in limp home mode,cutting power,causing smoke and rough running.
AC Delco ONLY for CPS!!!!

A bad PMD will cause stalling,no start and in some cases runaway engines.

I haven't had a PMD cause the engine to run rough or anything besides stalling or no start or runaway.