VE Pump Major (temporary) Stumble

[twentyeight]

I have had two different engines now, both 1Z blocks, that have exhibited a temporary stumble issue and I'd like to figure out why. The first was a B4 with RC2 in a GQ ecu (max pump voltage ~3.8v at 3500 vs 3.6v stock). The second is my T4 running GL programming with an 11mm ALH pump. I just so happen to also be running about 3.8v at 3500, although at what I'm telling it is 64 mg/s. Both engines were running .205 nozzles. I never get a code. The B4 had a rebuilt pump (but exhibited this issue far worse).

Symptoms: It loses 99% of power and smokes like a tire fire. It stumbles terribly. If i push in the clutch (which I initially did in the B4) it would die and be very difficult to restart. If I floor it and let the engine spin in gear, it eventually clears up and runs just as before. The 1Z (smooth body) pump cleared up much slower. The ALH pump has only done it once and it was very brief and seemed more like a switch was flipped when it came back on. It also didn't smoke as badly, which I attribute to higher pressures atomizing better.

Causes: The only two conditions that I have been able to identify are a fairly heavy throttle on a somewhat cold engine, such as the first time pulling onto the freeway in the morning. When hot I can flog the bus without issue. I seem to remember the B4 would do it even when hot, but I think it had a bad thermostat so I can't say for sure.

The T4 did it a few mornings ago after I upped the pump voltage slightly on the high end of the map, which is why I mention it above. I am fairly certain that the two engines ran completely different sets of nozzles; the only things they shared would be unrelated (like a power steering pump) and the ECU. However, the B4 exhibited the issue with a different ECU as well.

Is this a QA getting stuck wide open? That's the only idea I can come up with. I need to reseal the 11mm pump so as soon as that seal gets here I'll have a look inside. Any other ideas?

 

[andy2]

Assuming that this is not a fuel starvation issue I might have a clue.

I'm going out on a limb here and guessing that it could be the exhaust and/or intake valve(s) hanging open causing a loss of compression.This is much more common when the engine is cold and will cause grey smoke,loss of power/stumbling and possibly stalling if the clutch is disengaged at the right time.

If this is the case you would notice that the engine sounds different while cranking over like it has lost compression on a couple or all cylinders.After waiting a couple minutes to let the lifters bleed down it then fires up like nothing is wrong.

Sometimes the valve guide to valve stem clearance is made too tight but most of the time its due to the stock single valve spring.The fix is to install dual valve springs and I'd recommend using aftermarket ones.The cyl head does not need to be removed to swap out the springs.

I've had this happen on my modded AHU and seen it happen on other modded engines even ones with stock dual valve springs like the AAZ. It can be a combination of cool engine oil,higher engine rpm and higher than stock exhaust manifold/boost pressure.

 

[twentyeight]

That's an interesting take. The new engine in the T4 has a rebuilt head with ~600 miles on it.

I thought of this thread today because I soldered in a new 4 bar MAP sensor, and while logging it happened again, albeit very briefly. I was unfortunately logging group 11 when it happened, and nothing out out of the ordinary showed up.

Maybe I should build a rolling logger, like a security camera for KW1281. Keep the last x minutes of data and save it when you hit a button.

 

[algirdas]

I've had this happen on several tuned VE engines. AHU and ALH.
It's always, like your experience, fairly heavy throttle on a somewhat cold engine,
I think it is related to the old "warp field collapse" which was too high of IP voltage.
Adjusting IQ with VCDS from 2-3 up to 4-6 seems to help. But can still happen.

 

[mk1-83]

Check case pressure valve and ad a liftpump to feed the ip.
What oil you running ?

 

[Sc0]

Try a different Injection pump, had a similar issue with two different pumps before they grenade. One pump had metal chunks in it and the other was flawless but still didn't work properly due to something in the QA assembly.

 

[GTiTDi]

Isn't this the rocket chip shudder talked about in many threads?

 

[Abacus]

No. Not even close.

 

[tdi-mk2]

Hi, i'm not glad you are having this problem but I am glad that you have described exactly what mine has been doing for a while now, My first engine and pump never ever did this, but the 1z I have fitted now has done this a few times, always when not fully warm/hot, it will even do it if you statically rev it when cold and like you said it will stop dead and then be hard to start, It turns over almost like the engine is hydraulically locking. If you are moving when this happens it smokes real bad and then as long as you don't let it stall will come back to life and clear completely.
I don't have a lift pump on mine, but the other engine/pump never had this problem, and besides it does seem like an overfuelling issue rather than under.
Andy2 seems to have described it to a T to be honest

 

[tdi-mk2]

Any further on with yours twentyeight?
Andy2 you mention the valves being stuck open, and then say about allowing the lifters to bleed down, is that a suggestion that the oil pressure to the lifters is a cause?
Or that the oil pressure in the lifters is somehow fighting the weak valve springs?
If so, would recreating the problem and then removing the valve cover show the problem? (providing I could remove it quick enough that is)?
Thanks in advance

 

[andy2]

The oil pressure will be higher when the oil is cold and will help overcome the valve springs much easier.

There is no test for this condition other than knowing that there is a lack of compression while cranking over on one or more cylinders or there is a loss of power and lots of exhaust smoke.The engine would sound different and possibly have compression on some cylinders and none on others.

Aftermarket gasser Dual valve springs should be a must on any of the older 028 vw AAZ/1Z/AHU that have been modded somewhat heavily.

This issue is not common on the ALH 038 and later engines.That could be related to oil pressure? The later modded TDI's ALH - current should benefit from a stronger valve spring.Even if an engine doesn't have a distinct stumble or completely stall out doesn't mean that it couldn't benefit from a stronger valve spring.

 

[twentyeight]

I've only had it happen once since the last time I posted. It lasted a longer time (15 seconds? Hard to tell in traffic) but still smoked a lot less than the more stock 1Z in my Passat. I'll need to give it some more thought, but this difference either implicates the injection pump or absolves it .

The thought being that higher injection pressures (and maybe more air; VNT17 vs GT15) atomizes the fuel better to begin with. I really need to log the IQ voltage when it happens. Maybe I'll try to trigger it tomorrow morning.

andy2, What kind of duration are we talking with regard to valves hanging open? There's obviously not a lot of room in there at TDC. On that note, though, both engines did start doing this after being rebuilt. A cold engine with tight tolerances and high oil pressure would be the time for it to happen. On the other hand it feels like it's connected to the accelerator pedal.

I'll see if I can get logs. That'll tell the story.

 

[andy2]

andy2, What kind of duration are we talking with regard to valves hanging open? There's obviously not a lot of room in there at TDC. On that note, though, both engines did start doing this after being rebuilt. A cold engine with tight tolerances and high oil pressure would be the time for it to happen. On the other hand it feels like it's connected to the accelerator pedal.

I'll see if I can get logs. That'll tell the story.

Its still possible that you have a fueling issue.If you can't find a problem then look into my suggestion.

The lifters can take a while to bleed back down no different than when a camshaft is installed and needs to sit for length of time to let the lifters bleed down.It doesn't take much valve float to lose compression and still not have piston to valve contact.

Some mechanical engine issues/faults can't be logged and just need to be figured out.It doesn't take long to swap out valve springs and they are not too much $$$.

I used one of these kits in the red box.. along with some old camshaft bearing caps.

https://www.google.ca/search?q=vw+v...UIBygB&biw=1173&bih=803#imgrc=EopmvMnaBOO4DM:

And vw 8 valve HD springs of choice.

http://store.concept1.ca/Autotech-HD-V.-Springs-8v-AT10.109.600K/