1Z/AHU stumbling under part load

GTiTDi · Dec 19, 2011

I have noticed my GTI stumbling/skipping under a partial load..It doesn't run roughly like this any time other than cruising at legal highway speeds..if I back off it smooths out and if I add more throttle it smooths out..IQ adjustment perhaps?

greenskeeper · Dec 19, 2011

disconnect the speed sensor on top of the trans and see if it goes away. You won't have speedo for this test.

G60ING · Dec 19, 2011

What is the IQ at?
Where is the timing set to?

GTiTDi · Dec 19, 2011

The timing is right in the middle of the graph, checked that not long ago. I haven't rechecked the IQ setting at idle yet though, I have been very busy. The temperatures around here have dropped considerably, it had been a mild winter so far. The only change I have made recently is installing a different lift pump. I reinstalled the A3 TDI sending unit and mounted a lift pump under the hood.
IQ was set at 326.88 or 3.6 mg/h last time I took notes, but that was back in July

GTiTDi · Dec 19, 2011

greenskeeper said:
disconnect the speed sensor on top of the trans and see if it goes away. You won't have speedo for this test.

G60ING · Dec 19, 2011

Yeah I know the feeling about not having much time. Another thing to check is the temp sensors when the car is cold. Check the coolant, fuel and air before the car is turned on. Make certain they all read roughly the same. Another thing to watch for is a vacuum hose leak.

Seatman · Dec 19, 2011

What about the maf? Could that cause this sort of thing? Might be worth checking the figures for it.

Abacus · Dec 20, 2011

I have heard of this with the 1Z and larger injectors. I'm interested in what you find out since I have a similar issue at 1600-1650 rpm's.

GTiTDi · Dec 20, 2011

Well I had an opportunity to check some live data with my Mac Task master this morning, there isnt a heading for fuel temp but the IAT and ECT sensors both read 39*F, and it started right up no problem after sitting outside all night. Going to check my IQ in a bit.

greenskeeper · Dec 20, 2011

GTiTDi said:

did you try the test? There is a way to have speedometer and eliminate the stumble if it goes away when disconnect the speedo.

GTiTDi · Dec 20, 2011

greenskeeper said:
did you try the test? There is a way to have speedometer and eliminate the stumble if it goes away when disconnect the speedo.

It seems to have gone away before I tested it with the speedo disconnected..was low on fuel so got some winterized petro d...had been running on the fuel that was still in the tank from last summer when I melted a piston...would running summer diesel in cold weather have caused this situation? I also noticed the QA housing seals leaking a bit more, I am thinking it is time to reseal the pump.

Also my IQ is set at 32686, which is around 4.0-4.2 mg/h. It seems to like the IQ set on the high side, might try hammer mod after replacing the QA seals..Already have a seal kit and metalnerd tamper proof bolt socket

Seatman · Dec 20, 2011

Summer fuel can wax a bit I would've thought if the weather's cold enough, my mates Landrover's fuel went solid and that was winter diesel! It had the stupid fan that just blew cold air straight onto the filter but he's since fitted a fuel heater and an elctric conversion for the fan.

bigrichard · Dec 20, 2011

disconnect speed sensor

greenskeeper said:
did you try the test? There is a way to have speedometer and eliminate the stumble if it goes away when disconnect the speedo.

I have a stumble that is noticeable in 4th and 5th and does go away when i disconnect the speed sensor on the trans. How can i 'have the speedometer and eliminate the stumble' with the speed sensor disconnected? the stumble appeared after i did a GLX conversion with slightly bigger injectors. adjusted the IQ up and down, etc.

GTiTDi · Dec 21, 2011

So last night I took a long ride in the GTDI on local highways and the stumbling started happening again. I pulled over and disconnected the VSS again and the symptoms didn't reoccur. What does that mean? I want to have my speedo and cruise control to function but dont want the stumble. whats the solution?

GTiTDi · Dec 21, 2011

Green Geeker! what did you do to solve this issue?

RIP TDI · Dec 21, 2011

Try cleaning the 3 grounds (ECT, VSS & cluster secondary) shown here.

GTiTDi · Dec 21, 2011

Hmm interesting I will check out the ground connections...My speedo never acted up but its worth investigating. Thanks Chris
-Chris

greenskeeper · Dec 21, 2011

GTiTDi said:
Green Geeker! what did you do to solve this issue?

ahmm....it's greenskeeper

but anyways.....

The vss input to the ECU is the culprit. Why? I have a number of ideas* but this is what I did.

On the edge of the wiring block you can find the U2 connector. On that connector the wires are labeled, cut the #2 wire (#1 goes to the cluster, #2 to the ecu)

The U2 connector should be blue and the 4th connector from the passenger side of the block.

The drawback is you won't have cruise control. However you could run a switch to the #2 wire splice to "turn on" the ECU vss signal for the cruise control which is what I ended up doing.

When I get around to it I will hook a relay to the cruise stalk to "close" the cut wire for the vss signal

GTiTDi · Dec 21, 2011

greenskeeper said:
ahmm....it's greenskeeper but anyways.....

Oops..don't know how I made that mistake

greenskeeper said:
The vss input to the ECU is the culprit. Why? I have a number of ideas* but this is what I did.

On the edge of the wiring block you can find the U2 connector. On that connector the wires are labeled, cut the #2 wire (#1 goes to the cluster, #2 to the ecu)

The U2 connector should be blue and the 4th connector from the passenger side of the block.

The drawback is you won't have cruise control. However you could run a switch to the #2 wire splice to "turn on" the ECU vss signal for the cruise control which is what I ended up doing.

When I get around to it I will hook a relay to the cruise stalk to "close" the cut wire for the vss signal

What are the potential causes that you have in mind? I like the idea of wiring in a relay to close the contact of the VSS wire when cruise is switched on, but would rather have it work the way it was meant to! I didn't have any issues like this until recently.

RIP TDI · Dec 21, 2011

Clean those 3 grounds first. If no luck, check vehicle speed output in VCDS, then replace the VSS.

I think you have either a somewhat dirty VSS signal to the ECU which is dirty enough to cause an ECU issue but not dirty enough as a passthrough signal to the cluster to cause a speedo problem or you have a bad ground to the head that is causing a reverse ground path through one of the other two grounds at that point.

greenskeeper · Dec 22, 2011

Chris Bell said:
Clean those 3 grounds first. If no luck, check vehicle speed output in VCDS, then replace the VSS.

I think you have either a somewhat dirty VSS signal to the ECU which is dirty enough to cause an ECU issue but not dirty enough as a passthrough signal to the cluster to cause a speedo problem or you have a bad ground to the head that is causing a reverse ground path through one of the other two grounds at that point.

All good advice and I did all that before going at the wiring for the signal. But the problem was still there.

This "fix" works well for me, although some may want to solve it completely which is fine as well.

bigrichard · Dec 22, 2011

grounds

I've also spend time cleaning those three grounds and verifying intergritry of the wires from the VSS--but the stumble is still there. It's very reproducible. I'm inclined to start in the direction of Greenskeeper's approach but would still like my cruise.

As soon as i finish the injector o-ring project on my F350 I'll probably get back to the stumble.

RIP TDI · Dec 22, 2011

Bigrichard, do you have an RC as well?

GTiTDi · Dec 22, 2011

Chris do you think it is related to the RC software?

I have a hard time thinking it is since my car ran flawlessly after the swap and after the Rocket chip...This is definitely something I have not felt before.

bigrichard · Dec 22, 2011

Rc

Chris Bell said:
Bigrichard, do you have an RC as well?

Rocketchip-no. I have been thinking of driving up to Jeff for a tune, though

greenskeeper · Dec 22, 2011

GTiTDi said:
Chris do you think it is related to the RC software?

I have a hard time thinking it is since my car ran flawlessly after the swap and after the Rocket chip...This is definitely something I have not felt before.

I can't recall if RC does it alone, but the larger injectors probably amplifies the stumble.

It almost acts like it's hitting the an electronic fuel limiter and cutting fuel, then adding fuel. So you get fueling of on/off/on/off/on/off

Are these cars speed limited? Thats the only thing I can think of since this involves the vss signal.

greengeeker · Dec 22, 2011

GTiTDi said:
Green Geeker! what did you do to solve this issue?

greenskeeper said:
ahmm....it's greenskeeper but anyways.....

GTiTDi said:
Oops..don't know how I made that mistake

Might be the first time that's happened...usually it's the other way around!

bigrichard · Dec 22, 2011

fascinating

greenskeeper said:
I can't recall if RC does it alone, but the larger injectors probably amplifies the stumble.

It almost acts like it's hitting the an electronic fuel limiter and cutting fuel, then adding fuel. So you get fueling of on/off/on/off/on/off

Are these cars speed limited? Thats the only thing I can think of since this involves the vss signal.

My stumble started with my VR6-->TDI conversion. I bought a set of injectors with T-4 nozzles from Frank Irving. I checked the injector balance and even sent them back to Frank for further tweeking to no avail. If i had a set of stock injectors swapping them in might be an interesting test.

I just looked at my 3 grounds on the head and all is well.

Still stumbling away.

GTiTDi · Dec 22, 2011

Well my grounds look corroded as heck, am going to add a ground lead to supplement the connection at the bracket rather than relying on the bracket to be a ground..I will re do the ground terminals once I finish replacing the QA seals..

RIP TDI · Dec 22, 2011

It would be better to either bypass the bracket ground connection entirely or keep it as is (cleaning it, of course!) rather than create multiple ground routes.

If the ground work doesn't make a difference, be prepared to adjust your IQ up. Since you're going to change the QA seals, make sure that you set the IQ mechanically in a position that will allow as much electronic adjustment (adaption) of IQ as possible in the range that you need. 1Z/AHU ECUs have a relatively narrow range of IQ adaption and you want to make sure that you're right in the sweet spot of where you ultimately want to be with IQ mechanically (i.e., hammer mod) before you fine tune with IQ adaption in VCDS.

Before you do anything else, I would see if you can make any difference with the symptom by adapting IQ up.

1Z/AHU stumbling under part load

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