Inlägg
av hunn » sön nov 16, 2014 20:57
a) Warm up the engine over 170F, and with the scanner verify there are no DTCs.
If you have a DTC88 for timing/TDCO, clear it before running the “TDCO Learn”.
If you have other DTCs, such as DTC 17, 18, 19 for the OS or CPS you need to resolve them first.
b) While at normal idle, the lowest idle you have available, nearest to 600rpm, command the “Time Set” to “On” and observe the actual timing value.
The value should be approximately 3.5° degrees, while the desired timing is at 0°.
The value may jump around a lot, but you want an average value of 3.5° to 3.8°.
Command the “Time Set” to “Off” after about 20 seconds.
I have found that mine will sometimes go lower after performing the TDCO Learn, so if it’s a little high continue anyway.
The value you see is your “base timing”, where the IP Stepper Motor has incremented as low as possible.
c) Record the current TDCO value, and then command the “TDCO Learn” to “On” and observe the TDCO value.
This will time out after about 25 seconds, or you can command the “TDCO Learn” to “Off” and it should store the value on the screen at the time.
Occasionally the value may continue to bounce around after commanding it off, and time out later.
You can run the TDCO Learn again if it moved to an undesired value.
Compare to the previous value you recorded to see if your IP was properly timed before.
I prefer the TDCO value to be between -0.75 and -1.5. If you are getting -2.02 or +2.02 that is just the limit the scanner displays,
will set a DTC88, and you could be quite far out of tolerance.
The “Time Set” should give you an idea of how far out you are, if you run it again.
A “Time Set” base timing value over 4° will go to -2.02 and any value under about 2.5° will result in a +2.02.
If the base timing value is just over 4°,
and you are aiming for a TDCO value of -1.94 or thereabouts you can run the “TDCO Learn” again and hold the fuel pedal at 1000-2000rpm.
This can get you from -2.02, down to -1.85 or -1.94 for you to command the TDCO Learn “Off”.
OBD2 trucks can set the TDCO down to -2.5, likely because those trucks also set high idle when
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learning the TDCO and OBD1 trucks do not.
Increasing RPM also increases IP transfer pressure which affects the advance piston,
working against the stepper motor, which attempts to retard timing as much as possible.
OBD2 TDCO tables may be offset to compensate for the difference in IP position.
d) Up to now you’ve just verified if your timing was set properly in the past.
To modify the TDCO value you need to physically turn the IP.
Always shut the engine off prior to loosening the IP nut(s).
To get a less negative value the IP needs to turn towards the passenger side; more negative turn towards the driver side.
With the engine off, scribe a line on the timing cover where the IP is currently set, then loosen the IP nuts with the 12-point,
15mm half-moon wrench.
The lower nuts are difficult to get to and have limited space to turn a wrench.
It takes some finesse to get the wrench on the nuts, which you’ll have to do 2 or 3 times to get the nut loose enough.
On the passenger side you may need to unclip the turbo oil supply hose from the coolant crossover.
Once you get it figured out and done once it gets much simpler.
To turn and hold the IP you can use the large oil filter pliers, or a tool you fashion.
The IP will provide resistance to turning so you will have to hold it while you tighten the top IP nut.
Each millimeter you turn the IP will change the TDCO value by about 0.7.
Leave the bottom two nuts loose while you check the TDCO value by repeating steps (a) to (c).
Repeat step (d) with just the top nut until you achieve the desired TDCO value.
e) Once you achieve the desired TDCO value then shut the engine off and tighten the lower two IP nuts.
Once all IP nuts are tight, I recommend running steps (a) to (c) one more time to verify the IP did not move while tightening the lower nuts, it happens.
The snapshot below from GMTDScan Tech is a typical example of how the IP could be way too “advanced” towards the driver side,
so much so that the “base timing” seen in Time Set is 9.3°.
It is supposed to be 3.5°, but the PCM has an old stored TDCO value of -0.88 that is within tolerance.
When I actually run the TDCO Learn it will set DTC88 and TDCO value will show -2.02.
The same concept could happen in a way too “retarded” manner.
This would not set any other DTC and could never be noticed without the Time Set or TDCO Learn if the desired timing at idle is over 9.3°.
The stepper motor DTC34 for timing is not set until there is more than 5° difference between desired and measured timing.
There are some stock programs with as low as 4.5° timing where this situation could be seen just by looking at the scanner, but would still not set a code.
If you do have a 4.5° idle timing PCM program this error would probably make the truck much faster off the line,
since idle timing between 8° and 11° is a lot more responsive.
However, this is not good for general reliability and efficiency.
It could be a free performance upgrade for some, but idle timing that advanced is not good with a functional EGR valve.
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hoppas det här hjälper //mvh david
Funkar det så riv isär och kolla varför!!
