1997 GMC 3500HD with 6.5. Yesterday I was driving all over and it had been pouring out and big puddles all day that i'd been splashing through. (im not sure if that has anything to do with this) It was running fine and starting fine all day but the check engine light came on. It still started fine and seemed to run fine after. Later in the day I stopped by O'Riley's and used their scan code which came up with a code for Crank Position Sensor. I bought a new one and installed it that night. Went to start it and it turns over for at least 15 seconds before it starts and the code is still there. I try to clear the code with my own scan tool and it immediately turns back on. It revs fine and drives fine but takes a long time to start! If anything is different while its running it might be that its a bit louder then normal with its rattling engine sound. If I shut it off I can clear the code and as soon as I start to turn it over the code appears again even before it starts. I'm not familiar with this problem and was reading about how sometimes after you put one in that you might have to try the "KOKO" but that did not change anything after I tried it with a cold engine and after I tried it with a hot engine after a 20 minute drive. Today I disconnected the plugs from the computer behind the dashboard and plugged them back in. It took a long time to start and when it did it would Rev wide open till i shut it off, then tried again and same thing. I disconnected the computer again and plugged it back in and it went back to idling but taking a long time to start. I put a new injector pump, lift pump, fuel filter and oil pressure switch on about 2 1/2 months ago and it has run fine since with no codes. I can hear the lift pump working when I turn the key on and i'm assuming the injector pump is working since it does start and run fine after a long cranking. Now I think the starter went out trying to start it while i've been messing with it. When I turn the key it just clicked a few times then finally started after a couple turns of the key then next time i shut if off it will only click no matter how many times I try it. The batteries are charged and I had my other truck hooked up with jumper cables to keep from going dead. Any ideas that I should look into? thanks.

 

AC Delco ONLY for CPS and all other electronic parts on these trucks.

Parts store CPS are often bad right out of the box and are notorious for making things worse(BWD).

Seems you are starting off the OS only,as a test unplug the OS and try starting-if no start then CPS is bad(extended cranking normal),then try with OS plugged in and CPS unplugged-result is likley how it is now.

 

I did get a BWD CPS. I will return it and see if they have an AC Delco or try a different parts store. Whats the OS? Im going to check out the starter also, so later today when I change the started i'll try unplugging those and see how it does and let you know. Thanks.

 

OS is the optical sensor,located on top of the IP with 3 wire harness if I remember correctly.

Most likely problem is the BWD CPS though.

When the CPS fails it can only run from the OS in limp mode.

 

Im hoping its the CPS, i just picked one up from the dealer for $70 and a new starter from O'riley's for $180. If this doesnt work out i'll look into the OS. If it is that then it should be under warranty because I just put a new injector pump, PMD, and OS because it comes on the pump.

 

As sure as I can be over the internet that the CPS is the problem-TDCO needs done but should be checked with a proper scan tool if KOKO is done.

 

How exactly does the KOKO work? I've read key on for 1 minute and key off for 1 minute all while holding down the pedal, then start it. Is it turn the key on, then press and hold the pedal or press and hold pedal and then key on and then key off then try to start it with out letting off the pedal or let off the pedal then try to start it? All this is done after the motor is warm right? I dont have a scan tool that reads anything other then codes. Maybe O'riley's auto parts scan tool reads TDC?

 

originally posted by gmctd:
Stanadyne specs call for specific mechanical Optic Sensor adjustment relative to camring.


A reference line is scribed on the camring at that specific location, probably representing Top Dead Center position in internal pump timing.


Inj Pump is then placed on the flow bench to measure output for any adjustment required.


Minor offset adjustment from this line may be required by mechanical pump\shaft\housing tolerances, and a resistor value is specified to fine-tune Fuel Solenoid control of injection fuel rate, based on that mechanical offset and Fuel Solenoid efficiency.


When the Inj Pump is installed on an engine and timed, it must then operate within a set of specs determined by General Motors to provide sufficient power within warranty considerations, while meeting emissions criteria.


Factory timing spec is +3.5deg advanced, with -0.5deg Top Dead Center Offset, a value which the PCM has capability of 'learning', or, storing in memory.


TDC Offset Learn has been variously described as allowing Timing Stepper Motor to seek middle, or optimal, position of it's mechanical adjustment limits, and\or to allow PCM to correct back to TDC.


Based upon what I've read, looked, listened, and observed, I believe this is what actually is -


Pcm sets an injection window, based on the mechanical Base timing adjustment to +3.5deg, where the cylinder #1slot on the Optic Sensor Encoder Wheel on the Inj Pump drive shaft is compared to the Crank Position Sensor output for cylinder #1.


Timing Stepper Motor advances the Optic Sensor\camring as rpm increase requires.


Start of injection within this window requires a specific rate of pressure increase, where the rollers are riding up the camring ramps.


Stanadyne's mechanical Optic Sensor-to-camring spec results in delayed pressure rise, where injector 'pop' occurs late in window.


PCM program compensates for this electronically by assigning the Optic Sensor a negative number, which allows the camring to be advanced toward the oncoming pump plunger rollers.


The Inj Pump drive shaft, rotor, rollers are timed to crankshaft TDC for cylinder #1. The Inj Pump housing\distributor head is +3.5deg advanced to the shaft and rollers, but the Optic Sensor\camring is now at +4deg (-0.05TDC Offset, corrected). The rollers are further up the ramp, increasing pressure is higher, rate of increase is quicker, injection now occurs at designated degree within window.


When Inj Pump is mechanically advanced to +8.5deg Base\Desired, injection pressure rate\increase must also be advanced accordingly.


PCM fuel rate\timing matirix has an offset value for each degree of base, or Desired, advance, to ensure injection occurs at correct degree within window.


Each TDC Offset value is optimal for range of advance required by Base\Desired mechanical adjustment to the Inj pump.


+8.5deg mechanical advance will run with -0.5deg TDC Offset, but not well - if not reset via 'TDC Offset Learn', PCM will re-learn the required Offset within about 50 starts.


The Tech-II scanner\ programmer will enable TDC Offset Learn, and various manipulation will result in various negative values up to -1.94, generally considered best for highest output.


At +8.5deg, if left to learn TDC Offset on it's own, PCM will learn a value of -1.5deg, indicating an optimal value programmed in memory.


A manipulated "Learn" thru the Tech-II writes a replacement value to the memory, which will then not relearn to -1.5deg value.


As you can see, this is the electronic version of TDG's Optic Sensor 'bump', but with Base\Desired Timing adjustment.


PCM is aware of this change, so throttle sensitivity, surge\runaway, and poor idle quality are not effected.


To be objective, not all Optic Sensor 'bump's result in those problems - depends on 'state of tune' of any particular engine and system.


So - 'TDC Offset Learn is allowing the Timing

KOKO TDCO relearn:
Originally posted by Turbine Doc:
"Timing is best set with a tech 2, that said it can be done on a 98 & 99 for sure without T2, as I've done it myself several times using just a Snap-On MT2500, I've done it only on those 2 years which are theft deterrent equipped systems.

What I don't know is if this works for all OBD2 PCMs or just the ones with theft deterrent. It is for this reason I've not posted what worked for me in detail.

That said, for the general population, what follows is what is in the manual for my year model truck and is paraphrased for simplicity.

From what I read there are 2 different routines 1st is setting timing following pump replacement, this one requires a 2 directional scan tool, start engine bring to normal Op temp 170F or > coolant temp, use time set command to command timing desired to 0 deg, actual timing should read 3.5 deg on avg.

MARK IP BEFORE MAKING ANY ADJUSTMENT SO YOU CAN GO BACK TO WHERE YOU STARTED IF NEED BE. Also (1) mm rotation roughly a scribe line width = 2 deg. timing change, make small moves.

If above 3.5 avg., shut down engine, loosen mounting nuts and rotate pump toward pass side, if below 3.5 rotate toward drivers. These are hard to get at I moved the AC compressor off of it's mount hoses still connected to get better access, also I don't think you can access them without making a custom wrench or buying the Snap-On set which I did. IP turning wrench is also an asset. Continue this until 3.5 avg. is satisfied.

Best as I can figure this is the base timing, once out of time set commanded to 0; the computer commands where the timing needs to be. Can be greater than 3.5 avg seen in time set command mode.

The next procedure is the TDC offset which can be done independent of time set, and can be done with just a reader that displays TDC offset reading. Nothing in the manual directs that both be done at same time, but I did the time set before doing TDC offset just to see if I was in the correct ball park.

Snap On MT2500 TDC display is incorrect vs. a Tech 2 tool a T2 -.25 to-.75 setting is -4.8 on a MT2500, a T2 -1.76 to -1.94 setting is displayed as -5.4 MT2500 only carries to 1 decimal place.

Bring engine coolant temp to 170 or above, see that all codes are clear (clear codes before proceeding).

Shut off engine, then turn key to run not start and accelerator to floor minimum 45 sec,(this activates TDC learn), then key off 30 sec.

Restart truck if coolant is above 170 and rpm below 1500 PCM automatically relearns offset, may stumble on start 1st run until new offset is accepted.

If you want TDC to go more negative(-), shutdown truck as before and rotate pump toward driver side, if you want a more (+) offset go toward pass side, same (1) mm =2 deg be frugal with adjustment.

Bolt all down do key on key off routine pedal to floor as before, and restart to do learn, and repeat until at desired TDC offset."

In my experience the snap on mt 2500 will give a correct TDCO value if the model year is entered as 2000 no matter what year the truck is from 96+.

 

Thanks for that info.
I put the new CPS in and new starter in and all it would to was click when I tried to start it. I pulled up both my trucks and hooked up 2 jumper cables, 1 to each battery from each truck and let it charge for a bit and still nothing. Then tried to jump the starter with a screw driver and all it did was make a TINY spark and nothing. I checked the grounds and they all looked clean and tight. Out of curiousity I took one of the jumper cables of jumped it from the negative post on the battery to the motor, then tried to start and it fired right up! Turned over less then 5 seconds then it started. I took it for a drive around the block and after about a minute of it running it started blowing lots of white smoke and running rough, I guess its what people describe as loping. It did that for about 30 seconds maybe and then came out of it and ran good. I shut if off and it starts back up now with out any jumper cable from the battery to the motor, so im not sure what was the problem in the first place when it needed that jumper. Now the truck runs awesome and starts up less then 3 seconds, I think its not as noisy now also, but maybe its just in my head. Thanks for all the help and advice.

 

Sounds like you need to invest in some new battery cables.

PT wiring soloutions sells sets on ebay that are way better quality than new but pricey-FYI.