ACV timing jumped

Hello,

I have a 99 2.5tdi T4 (Eurovan) with an ACV engine. It's been running fine - last time I set up the timing I had it pretty much spot on (65) on VCDS.

Recently the idle speed has been a bit higher than I expected (825 rather than 775) so I check with VCDS. No fault codes, apparently all the temp reading seem feasible to me. I checked the timing when warm and it is way too advanced (93). It's running fine, but I can't think what would cause the timing to have jumped in this way.

The ACV has two timing belts - one for the cam and water pump and crank, and one from the cam to the pump. This has a tensioner which can be used to advance or retard the timing. If this slips it would naturally retard the timing.

I am wondering if perhaps the pump itself has some internal problem. I am loathed to set the timing again for the pump, only for the dynamic advance to not function.

I am wondering what might have caused the timing to suddenly become advanced. Any insights very gratefully received.

thanks

It's quite the timing for your post; my T4 (albeit with an 1Z) just did the exact same thing. The pump is an 11mm from an ALH.

I was getting an 00550 code (N108 start of injection regulation). I verified the resistance of the N108 coil at about 17Ω. I reset timing (the bolts were tight; I don't believe the pump sprocket slipped) and idle is now much smoother and quieter, but the engine still sounds strange and is down on power.

I think the next thing to check is that the cam to crank timing has not changed. I have a two-year-old interrupting my every thought, so I may be way off, but it stands to reason that the belt could have slipped from the proper position of one stroke to an advanced setting of the stroke behind it (if that makes any sense). Like walking on a sidewalk, watching the position of your feet related to the cracks: if your foot was falling at the beginning of each block, taking a smaller step could cause you to now land at the end of each block.

I checked the belt timing and it appears my cam is very slightly advanced. The only way I can see this happening is that the alternator over-ran the engine and pulled the crank sprocket (and cam and IP and oil pump) forward slightly. However, I have a clutched alternator pulley with less than 6000km on it. I don't know how the ACV crank sprocket is attached (how it's keyed) and if it could spin, nor if the ACV has a clutched alternator pulley, or if yours is seized).

My symptoms started very suddenly while cruising at a constant speed about a block away from home. I'm at a loss for how the cam could advance itself slightly.

Hello,

thanks a lot for the reply. Interesting points and awesome engine and pump choice The ACV has a separate cam to pump belt - the cam to crank timing is separate. The only thing I can think in my case is that the cam pulley jumped or maybe the pump itself shifted on its bolts.

I will reset the timing and see how it behaves. Good luck getting yours running well. I remember with my AFN I had to always push the pump right up to the head to get it properly timed - didn't matter how many times I did it, that was always how it was.

I wonder what is normal timing for that rpm on your ACV? The timing will advance as the engine speed increases.

What is your IQ running?

Hello,

good question and good point - thanks a lot for pointing that out. I'll check that out and get back to you.

thanks

So iq is 4.8 at idle up to temp and timing is at 72. It was definitely at 55 when I last set it. Still confused as to how it could jump.

55 to 72 is not a tooth jump, it is probably only about two thumbnail thicknesses of travel.

You were in basic settings when reading your timing, right? Not in measuring values?

You set the timing with automatic advance off, by going to basic settings. You must check it the same way.

I had to ask...

Yes in basic settings of course. I realise it's not a tooth jump but a slip of any kind would ordinarily retard the timing - that's why I'm confused.

Thanks a lot for your help and advice. I'll reset the timing today.

I have discovered the reason for this in case anyone comes across this in a search.

My voltage regulator died in such a way as to not provide earth. I therefore didn't know the battery wasn't charging. The ECU was increasing revs often to try and increase the voltage and hence the timing was often a bit advanced.

My stupidity I realise to not check the voltage in VCDS or even with a multimeter, and a good reminder that the battery light is not a good indicator of whether the alternator is charging or not.

All is good now.

Thanks for the update, we really appreciate it.

Thanks also for your helpful suggestions...