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OBDII

Matt Bachand said:
What year vehicle? The 96+ with dual thermostats are ALOT tougher to turn vs the pre 96 with the singe t-stat housing. The later dual t-stat housing makes it alot tougher. If you can fabricate your own wrench with a torch giving it a radius and a 1/2 offset , then I'd say your more than capable of doing this job easily. The only tough part of the entire job is getting that bottom bolt loosened.

If your already stuck with the thought of bending your own wrench to imitate a specialty wrench to reach the lowest bolt on the IP, then have the dealer do it! :) Clean it real good, and make a good scribeline so you can make sure, and it will help the guy too. Make that engine spotless, make mechanic happy!

Also, is this an area where if you went into TIMESET and read the actual timing in car-code to find base timing would help determine how much movement required? What numbers do you have there?

When in TimeSet the stepper motor isn't changing timing via PCM command. Its actual base timing. Once time-set is over, the PCM resumes control of the timing via the stepper motor, and the timing readings between the two should be completely different.
Click to expand...

See what a little under hood time will get ya, that was a pretty lucid response, somebody been schooling you :D
 
buddy said:
Do you also have DTC for TDCO, telling you its out of tolerance. If so then yes you need to retard it towards passenger side. If not then Carcode must not be reporting it correctly.
Click to expand...

FYI some observations reconfirmed

Iv'e used CC 2x now I borrowed from Quintin once, and Matt & I used his a few weeks back, seems to work well, while it's not ideal & takes some time to navigate the screens I'd buy it if I was only planning on using it for a 6.5, I'm probably going to get the full Auto Engunuity software set to go with my new netbook as I'm always working something oddball gasser or Diesel and want max capability .

Mine was right on edge of being too far advanced I had coded TDCO out of range a couple of times right after installing a test ATT oriented reflash from Bill.

We had a TDCO school/clinic at Aces house, I wasn't coding after setting with my MT2500 until I did a relearn with car code scan tool.

It looks like CC has ability to use a "window" like the GM T2 tool does to where depending where the IP is set mechanically there is some offset to let the scan tool bias the TDCO within "window".

Matt's was set too far on edge of it, we moved his IP and were able to set TDCO with the CC scan, so it now has ability to be slightly over or under the -1.5 with TDCO learn activated, which is where I think that we finally left it at, prior to moving IP Matt was locked at -1.9 I think and CC did not have any ability to change TDCO.

Trick that I have found that makes it a little easier to set with the MT2500 is to do a time set so that instead of a 3.5 deg avg actual time as called for in the service manual, if I bump to a 3.8 avg and lock IP for that, when I come out of time set, shut down then ko/ko to set the TDCO learn command, I'm right around -1.5 to - 1.95 TDCO.
 
Hi
With all the talk about setting TDCO do you have to clear the codes in the computer.
I put in a new pump and the truck runs great but I have a trouble code p1260 timing. So do I have to clear the code before I start.
Thanks
Mike
 
I think I agree with Tim. I'm gonna go for AE simply cause it can work on other vehichles and I don't see a Snap On Modis in my financial future.
 
So I'm sitting here looking at car code runing my TDCO.

Here's what I've got

IP 3.5 on timing set

IP on 11.0 running

TDCO at 1.41

What am I looking at?

The positive numbers are not so good right?

I need to start rotating to the passenger side, correct?
 
ak diesel driver said:
drivers side to get a - TDCO#
Click to expand...

Just reading my 98 service manual, vol 4 of 4, page 6-2637:

rotate pump towards drivers side; a positive(+) number, rotate toward passenger side (1mm equals 2 degrees) to achieve a negative (-) number.
Click to expand...

Passenger side it is....unless GM is wrong.....:dunno:

I also believe a positive number is advanced, not retarded :nana:



Seems the 3.5 is what I should be seeing on timing set also, according to the book. Apparently, it's just base timing and you go from there with the pump...
 
Rotating IP to the driver side makes the # more negative, if your manual says otherwise it is wrong. IE if TDCO is @ factory spec -.25 to -.75 then to advance timing for a -1.5 TDCO then you rotate IP to the driver side.

The 3.5 avg seen in time set is a baseline setting, I like to set for a 3.8 avg which gets me close to the -1.5/-1.94 performance TDCO setting the 6.5 likes
 
great white said:
Just reading my 98 service manual, vol 4 of 4, page 6-2637:



Passenger side it is....unless GM is wrong.....:dunno:

I also believe a positive number is advanced, not retarded :nana:



Seems the 3.5 is what I should be seeing on timing set also, according to the book. Apparently, it's just base timing and you go from there with the pump...
Click to expand...

Don't go confusing yourself or others with this nonsense.

-1.94 is more advanced than 0.
 
Turbine Doc said:
Rotating IP to the driver side makes the # more negative, if your manual says otherwise it is wrong. IE if TDCO is @ factory spec -.25 to -.75 then to advance timing for a -1.5 TDCO then you rotate IP to the driver side.

The 3.5 avg seen in time set is a baseline setting, I like to set for a 3.8 avg which gets me close to the -1.5/-1.94 performance TDCO setting the 6.5 likes
Click to expand...

Ok, maybe this is just my gasser background coming out, but this is how I've always understood it:

Advanced timing is getting further from TDC, retarded timing is closer. To follow that reasoning, Pos would be further from to tdc, neg closer. Unless its different in a diesel? Dunno but an explanation would be appreciated.

I'm probably not understanding the neg and pos part here with relation to diesels, but can't see how it can be much different.

Matt; "just do what I tell ya" doesn't work with me. It's not "nonsense". I need to understand things, I don't just accept them at face value when someone says so. Remember the statement "there are no stupid questions"? This is one of those times.
The factory service manual clearly contradicts what's been put forth. Maybe it's an error, maybe not. I'm a Flight/Technical instructor and many a time I've had a student question "the bible" or the way it's done only to find out we should be re-examining how things are being done or what we think we know rather than beating a student into a mold. I guess questioning things has become a side effect of my work. Questions are always good, it leads to new knowledge, even if it's something we all think has been fully explored or "known".
If all I learn from this discussion is the manual is wrong (or right), it will have been worthwhile. If I learn a few tidbits about how a diesel works, it hasn't been nonsense and has been worthwhile.
If I read a "tone" into your response and there was none, my apologies. There was no tone intended in mine, either that post nor this one.

As to which way is advanced and retarded, my service manual does indeed say what I posted above.

I'll try it TD's way and see what i get.

Cheers
 
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You are moving the IP further from TDC when setting this don't fixate on TDCO # as that # is for setting of a "window" of operability for the PCM to tweak the IP when in PCM control,

When moving the IP to driver side you'll see overall timing does come more positive in relation to the crank when doing time set, and PCM is commanded to not adjust timing.

Which manual are you using ??? BJ you have me at a disadvantage as I am without mine right now, PM me after the 17th I'll be home and can access my 98 GM manual to see what mine says, but I'm 99% sure it shows moving to driver side as a timing advance
 
Turbine Doc said:
You are moving the IP further from TDC when setting this don't fixate on TDCO # as that # is for setting of a "window" of operability for the PCM to tweak the IP when in PCM control,

When moving the IP to driver side you'll see overall timing does come more positive in relation to the crank when doing time set, and PCM is commanded to not adjust timing.

Which manual are you using ??? BJ you have me at a disadvantage as I am without mine right now, PM me after the 17th I'll be home and can access my 98 GM manual to see what mine says, but I'm 99% sure it shows moving to driver side as a timing advance
Click to expand...

I guess the question isn't whether you're moving the IP from TDC, it's a question of which way. I'm thinking the problem is my understanding of the relation between "advanced" and a negative value.

Falling back on my gasser/recip training, advancing the timing is moving spark (I'm guessing in the case of a diesel the injection pulse) in advance of TDC (gasser terms: BTDC). This allows better flame propagation and better burning before the piston reaches TDC and higher peak pressures for the beginning of the down stroke. Not quite the same as a diesel, but I can't see the principals being so completely different. I guess I'm just not grasping how a negative timing number relates to advanced timing. Dunno, that's why I'm asking....

My intent is not to "catch you out" brother, not at all. Just looking for some understanding and better knowledge of the inner workings.

The book I'm looking at is from a set of four books (vol 1-4) and labeled as such:

1998 C/K Truck Service Manual, GMT/98-CK-4, Volume 4 of 4. Includes Engine and Transmission/Transaxle.

It's "two tone" blue in color. GM Authentic technical Service Information "seal" in the bottom LH corner. All vol's are 3 hole punched. Here's a pic:

BqNv1QBmkKGrHqIH-CgEu50zckjBLu0Zf6Hw_12.jpg


Information page inside:

1998 C/K Truck Service Manual Volume 4. Published by North American Operations. General Motors Corporation. Warren, Michigan 48090. Copyright 1997 General Motors Corporation. Information cut off date 3/26/97.

Here's the ref for the adjustment:

Chapter 6, Engine Controls - 6.5

Page 6-2636, Para - TDC Offset Adjustment, sub para 13. (not trying to beat you over the head with a detailed ref, it's just an occupational hazard and such. An ex-Military tech should understand ;) )

Here's the passage as written in the manual verbatim:

13. Slightly (1mm equals 2 degrees) rotate the injection pump (use tool J 29872) and tighten injection pump flange nuts. Rotate pump toward drivers side; a positive (+) number, rotate toward passenger side (1 mm equals 2 degrees) in order to achieve a negative (-) number
Click to expand...

Not sure why it's different from what you gents are saying really happens, all I can say is that's what's in the factory service manual I have in front of me right now. Could be an error I suppose. Wouldn't be the first time I've seen a technical manual with an error in it......




So, in gasser terms, can negative be thought of as BTDC and positive be thought of a ATDC?

If this is the case, a negative value being "advanced" makes sense to me. But positive would have combustion chasing the piston down the bore ATDC, which doesn't seem right in an internal combustion engine....just doesn't fit in with my recip training models of internal combustion. Unless diesel is a really "weird" beast for a recip design.

Admittedly, my diesel exposure is pretty limited. I'm mostly recip (auto and aerospace) and turbine (all aero-centrifugal/axial flow/etc).....basics are all there though:

Suck-squeeze-bang-blow.......

):h



:edit:
Hmm, maybe this is better discussed in a separate post?
 
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I always looked at the offset as a delay. Whether its in tiny fragments of time, or distance, the neg number makes it more advanced, and the pos number would make the Delay or Distance OFFSET larger, thus the negative number would happen FASTER (shorten the Delay, or Distance to TDC SOONER, thus making the inj cycled SOONER), and the Pos Number would INCREASE the DELAY, or Distance to TDC Inj Cycle, thus making the inj cycle Later (retard).

And it seems the BASE TIMING goes UP, the TDCO goes Down. (I hope I didn't just confuse myself by saying this now :)

The OFFSET is just that. A slight adjustment room for the PCM to fine tune the INJ Cycle. Shortening that OFFSET makes the INJ cycle happen sooner. Thus Neg number is more advanced.

Thats how I understand it in my head, and I'm sticking to it.
 
I've often wondered if it was because of the extra gear used to drive the ip. Basically it would reverse the rotation.
 
Hold on a second.

"TDCO" is top dead center offset.

Is this the crank angle offset they're referring to?

If so, the positive and negative values make sense to me when dealing with injection during peak cylinder pressures and relative piston/crank movement during TDC.

Where as the neg value would be injection prior to the crank angle breaking over the zero degree mark and entering the positive (or downward) stroke, thus being "advanced" timing while being represented as a "negative" value.

I think that might be the jewel of information that lets TDCO and the required values fall in to place for me. I was reading through a few journal papers and it kind of gelled in my mind.....

Wrong?

Right?

Totally lost?

):h

*edit*
Here's the paper I was reading that sparked off the light bulb if you care to look:
http://www.ifac-papersonline.net/Detailed/40983.html
 
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