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Talk to me about timing and TDC learn

mitchedo

mitchedo

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Location
Bountiful, UT
I followed the timing instructions I could find that said to set the timing at 3.5 degrees, then perform TDC learn. I did that last night. I got perfect 3.5 timing, but my TDC was -2.46, and was setting TDC codes.

So, today I goes out to try and get TDC closer to -1.94. I moved the pump toward the passenger side about half a millimeter. The timing is (can't remember exactly) about 2.8 or so. My TDC is now -1.94 after performing a TDC learn.

The book calls for -0.25 to -0.75. It seems the ECM doesn't appreciate the -2.46 I had before. What is the reasoning behind setting it at -1.94? It is noticeably quieter at -1.94 than it was at -2.46.

This is a rebuilt engine with new timing set, new CPS. I'm using Autoenginuity to peform initial timing and TDC learn.

I've read and read and read, but I'm too stupid to get it, I guess.
 
The timing is really a PCM program thing. With the same TDCO I can have a stock chip at 3.5*, another stock chip is 8* and an aftermarket at 4.5* and another at almost 9*.

The more negative the TDCO is, the more it is advanced, fuel gets input earlier. Thats good to a certain point, but too early causes detonation too early, and it may not burn hot enough. The book may say to set it to -0.5ish, but it should say the spec'd limits are from -2.02 to +2.02. What setting the timing should really do is change the stepper motor operation to make the desired injection timing the measured, since twisting the pump changes the TDC position.

I have found that at the same TDCO, 8* injection timing is loud at idle compared to 3.5* or 4.5*.
 
The more negative you go the louder the engine will be. Bill Heath has done a lot of testing and has found that -1.94 gives approximately 3 extra HP combined w/ his chip. He also says that -1.50 will give you your best responsiveness combined w/ fuel economy.

Since (according to your signature) you want to keep your truck bone stock, I would set it as close to -1.50 as possible.
 
Time set and TDCO are 2 different things, -2.46 is too far advanced, IP needs to be rotated to pass side, will code at -2.02 or +2.02, factory is -.25 to -.75 as you state,

I've never used a AE tool for setting timing so not sure if it has time set.

What I do on my snap-on tool is set IP in time set mode for 3.6-3.7 timing, which nets me in-1.94 TDCO area once I'm out of time set. -1.50 is a good compromise setting more response than than factory but not as agressive as -1.94, which come winter time and cold oil is VERY loud.
 
Turbine Doc said:
Time set and TDCO are 2 different things, -2.46 is too far advanced, IP needs to be rotated to pass side, will code at -2.02 or +2.02, factory is -.25 to -.75 as you state,

I've never used a AE tool for setting timing so not sure if it has time set.

What I do on my snap-on tool is set IP in time set mode for 3.6-3.7 timing, which nets me in-1.94 TDCO area once I'm out of time set. -1.50 is a good compromise setting more response than than factory but not as agressive as -1.94, which come winter time and cold oil is VERY loud.
Click to expand...

Thanks Tim (and Rodd). AE does have time set, and when I set it to 3.5, the TDC offset was -2.46 (or whatever I stated). I moved the pump toward the passenger side, and timing was a little less than 3, and TDC learned to -1.94.

This was done while the engine had less than 3 miles on it. I wonder if a worn-in timing chain and gears will be different. I also have a new CPS.

I think I might go ahead and move it a little more toward the passenger side. It did quiet down significantly with the little bump I gave it. I'm looking for best longevity on this thing, and maximum fuel economy. I also have to pass a dyno soot density check once I get a few more miles on the engine. ...kinda seems like more advanced timing would make for less soot. I'm yanking the intake Saturday to reseal the stupid passenger valve cover (again), so I might just bump the pump a quarter mm or so while it's easy to see and get at. Those three nuts are a pain, especially with the dual T-stats. I don't know how anyone can time this thing without the special wrenches. I ponied up the cash for those, but welded up my own pump lever to move the pump. ...spent about eight bucks on it rather than another hundred for the timing tool.

The TDC offset was within factory spec (seems like it was around -.50) before I rebuilt the engine. The pump is now rotated a full mm toward the passenger side from the original mark from when I tore it down, yet it results in the -1.94 TDC offset. There was a LOT of slack in the timing chain when I tore it down, yet it was still within the factory limits of deflection. The new set has almost zero deflection.
 
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Also need to make sure engine is good and hot so the cold advance isn't kicking in on you, I like to do them with 180+ coolant temp, even though the manual only calls for >170 to be met, I have been in mid time setting and if at/near 170 CA/TSM did become a nuisance to repeatability from IP movement to IP movement.

If AE tool has time set mode, it could be like a GM T2 tool, if current IP position has enough "window" at 3.5 deg in time set, then you can rev the engine (wamed fully) a little push TDC learn and the TDC "captures" at the rev up position, if not enough "window" then you may need to bump the IP a little.

This is why GM-T2 (or direct clones) makes it easier, if current IP position provides enough TDC "window", then many times all you have to do is rev engine, initiate the learn and not have to mess with the IP at all.
 
FWIW snap-on Solus tool is no better than MT2500 brick for TDC offset values, I plugged in one today at a buddy's trans shop that has one for grins, it showed my TDCO was -2.11 (I should be coding with > -2.02 out of range BTW), my 96-2001 brick cartridge indicates I'm at -.9 TDCO, my 96-98 cartridge shows -5.4 TDCO, and a GM T2 last time I had access to one same IP position & learned TDCO position indication is -1.95

Ain't no wonder this gets complicated for folks.
 
The guy that set mine used a Snap-On scanner, and I've been suspicious ever since that my timing or TDC offset are off, I've felt like I've had less power since the new IP was installed. I've just never taken the time to find someone with a Tech 2 to check it. I'm going to try to get it done soon, will report back the current settings if I learn its been off by much.
 
I believe timing was 3.3 and TDC offset was -.95 if I remember correctly. I'll check with the guy to be sure. At the time I didn't specify that I wanted offset further negative, from reading here I assume I should go for -1.5. How much would mileage be affected by incorrect timing and offset? I mentioned in a thread a few months ago that my mileage went down a bit since the new pump install, so I'm assuming all this is related.

I don't know what cartridge he was using.
 
Im so happy I have GMTDScan :) I'm betting it works right.

With this variability which scanner is the known correct, the control group. This could cause a lot of the problems people have with their trucks. This could be on the scale of how moronic everyone was with the PMD on the IP.
 
From what I've seen with OBD-IIs OTC tool and GM T2 are the 2 that always agree with each other, and I've "normalized" my MT2500's readings against a GM T2,

I had a buddy of mine in NY who also compared his MT2500 to a T2, his results mirrored mine, so once you know what the variation is vs T2; the MT2500 is consistently "out of range" and the OOR can be offset to meaningful readings.
 
Such a shame snap-on should make the correction and/or send out a TSB so the variation could be calculated correctly.
Wonder if they are even aware of the problem...and if so, why.
Snap-On now has another tool called Modis, When I hooked-up to it said my TDCO was -1.94.....Now considering my IP was replaced under warranty a few years back, the last tech to set my timing was the Dealer...What are the chances that was the value he was aiming for?
Wonder if this version got it correct?
 
-4.8 to -5.4 are what worked well on my 98 cartridge, never looked at the lower value -4.8 vs my newer cart, IIRC -4.8 was near a factory recommended -.75 with a T2, following IP replacement under warranty by GM tech with a T2
 
What a PITA. Now I wont even trust bringing my truck somewhere to set it to -1.50.... argh....

Who near Massachusetts can do this with me? I'll drive to you with money for your time, or beer for your belly.
 
Thats what I'm saying, youre going to have to verify the shop has the correct scanner or dont let them work on your truck. Potential for lots of 6.5TD problems.
 
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