Engine/Transmission (1998.5 - 2002) Purpose of the VP-44 shaft key in regards to timing???

[Gary - K7GLD]

Since the operation of the VP-44 is pretty much fully computerized in regards to the precise timing and volume of fuel injected at each firing stroke, what is the purpose of the various specific offset gear shaft keys used and matched to each VP-44?



If the final operational timing/advance is sensed and controlled by the computer, what are the small differences between keys likely to make in timing - why wouldn't the computer (within reason) simply sense the advance timing needed, and automatically adjust for minor differences?

 

[timbo]

I'm pretty sure its to locate the window in the valve rotor (that turns in the housing) at the correct timing. TDC is based off the cam sensor, the ecm will compensate the timing piston accordingly. CTS and IAT also control timing.

 

[Gary - K7GLD]

I'm pretty sure its to locate the window in the valve rotor (that turns in the housing) at the correct timing. TDC is based off the cam sensor, the ecm will compensate the timing piston accordingly. CTS and IAT also control timing.

That's pretty much my guess as well - to "center" the rotor in the middle of it's operating range as the computer sees it...

 

[BradyWilliams]

It's all about static timing. The VP44 can advance and retard timing in a specific range. The VP44 can compensate timing in a small range +- 2-3deg. The offset key locates the timing in a place so that the inj. pump timing is very close in the window so that the system can be precise on timing. Thanks

 

[GOT-Torque]

Is there any chance that some trucks have the cam advanced from the factory one position or gear tooth such that the static timing is slightly advanced compared to most trucks? The reason I ask is related to why a few trucks (mine included) can't run a box that adds timing when it is cold outside. I'm in the process of altering the IAT signal to fool the ECM into pulling some timing out to prevent the problem. More info in this post



I will be replacing my VP44 with an I. I. HRVP44 within the next two weeks and was wondering if it is a possibility that my cam is advanced, is there anything I can do while replacing the pump to address it?



Thoughts?

 

[timbo]

Originally posted by GOT-torque. I will be replacing my VP44 with an I. I. HRVP44 within the next two weeks and was wondering if it is a possibility that my cam is advanced, is there anything I can do while replacing the pump to address it?



I was talking to a guy that is having the same issue with the EDGE ON. He installed A hod rod pump and his issue got WORSE!

 

[Gary - K7GLD]

Given the number of gears in the geartrain that drives the camshaft, Vacuum pump and VP-44, it would seem pretty easy for the timing seen by the VP-44 to differ a fair amount from what's actually happening at the camshaft and crankshaft - after all we're talking about only a couple of degrees putting the VP-44 outside it's optimum operating window. Looks like the VP-44 relies pretty heavily upon the rest of that geartrain to be pretty accurate - at least in relation to the cam sensor...

 

[GOT-Torque]

Based upon my very limited understanding of how the ECM controls timing and relates to the different pump shaft keyways, would it reduce overall static timing if the pump was retarded one position using the available keyways? (I've never even seen the shaft of one to know how many there are or how many degrees difference there is between the choices. I read elsewhere that the keyway you use doesn't really matter as the ECM will adjust timing to compensate for it? Is this true?

 

[Gary - K7GLD]

I read elsewhere that the keyway you use doesn't really matter as the ECM will adjust timing to compensate for it? Is this true?

I think that question - and the relation of specific VP-44 shaft keys was answered above:

The offset key locates the timing in a place so that the inj. pump timing is very close in the window so that the system can be precise on timing.

I appears the use of the wrong key, one the VP-44 isn't calibrated for, could place the range of advance the VP-44 uses off center, too close to either the advance or retarded side - limiting flexibility of timing and probably generating error codes.

 

[GOT-Torque]

After re-reading the posts above, the keyway gets the pump close to where is should be and then the pump can advance or retard 2 to 3 degrees when needed. What causes the pump to alter the timing? I assume this is the timing alterations coming from the ECM based upon the IAT and CTS temps?



It would appear I could just retard the pump some and hopefully my problem would go away and I wouldn't need to fool the ECM.



Does anyone have a pic of the keyway or offset keys? I assume it is one keyway with different keys to offset the pump shaft from the gear?

 

[RCenters]

scheid used a bunch of keys back in the day trying this (adden more and retard ) but it didnt work out usally above or below 3+ degress it would set it back , as for as keys go u can c the offset on some take a HO pump there keys r more advance take that key out turn it around , i dunno how much it will take it back , buddy of mine tried a HO key with a SO pump didnt really change much but he could tell some differences ,

 

[timbo]

I think that question - and the relation of specific VP-44 shaft keys was answered above:







I appears the use of the wrong key, one the VP-44 isn't calibrated for, could place the range of advance the VP-44 uses off center, too close to either the advance or retarded side - limiting flexibility of timing and probably generating error codes.

Nicely put Gary!

 

[Jetpilot]

If you want to increase or decrease timing don't look at altering the gear for the IP or different keys. Look at what signals the timing event.



Doug

 

[Gary - K7GLD]

Here's a quote containing a Sheid rep comment from a related thread on this board:

They told me to call sheid diesel for some help. I found out slotting the mount holes on the front flange will not change timing. the ecm senses TDC by the CAM sensor. Timing and fuel delivery is entirely controlled by the ecm closeing the bypass valve. Twisting of the pump body would do nothing, the ecm would just compensate for it. Thats what the guy at sheid diesel told me,and i also agree with him!

I suspect the same effect would apply in attempts to change pump timing by altering the key offset.

 

[shawn huizenga]

Doug is right, just have to offset the tone ring to change the timing. This just fools the ECM into thinking the engine is at a different position than it actually is. I did this on my 2001 w/PDR HRVP.



Shawn

 

[GOT-Torque]

Just today, I got my switch installed for altering the IAT signal to pull some timing out and allow me to run my comp box when its this cold out (15 degrees today). Works great!



Now my question is how do you know how much to offset the tone ring? Is it a trial and error method or can you read the timing on these engines with something and know exactly how much to change it?



Thanks for all the info!

 

[timbo]

Originally posted by shawn!



Doug is right, just have to offset the tone ring to change the timing. This just fools the ECM into thinking the engine is at a different position than it actually is. I did this on my 2001 w/PDR HRVP.



Shawn



i'm a machinest and also rebuild hydraulic pumps+valves. I've had a VP completely apart already. Do you mean the cam ring that the timing piston engages into? Please define tone ring. Do you mean shim the timing piston feedback sensor out. Sorry this may not be exact part names,but its what they are called on a sofistacated hyd. pump

 

[shawn huizenga]

Timbo,



I'm talking about the camshaft tone ring, this doesn't work on the older 24v's that have a different style camshaft tone ring plus a crankshaft tone ring. It's pretty much trial and error from my experience. The tone ring is what the camshaft position sensor reads engine TDC off, has a series of slots machined into it in addition to a gap with no slots, what I did was filled one slot and machined another into the other side of where the original gap was. Hope this helps a little.



Shawn

 

[timbo]

Now i know exactly what your talking about. So you mean the tone ring is removable from the back side of the cam gear?

 

[shawn huizenga]

Timbo,



Yep, just three bolts hold it onto the camshaft gear, take it off, make the changes, and bolt it back on. The catch is you have to take the cam out to do so...



Shawn