1Z/AHU stumbling under part load

Chris Bell has all good points and advice, but I have to say again I tried them.

It took me about 3 years of fiddling before trying the vss sensor trick.

greenskeeper said:

Chris Bell has all good points and advice, but I have to say again I tried them.

It took me about 3 years of fiddling before trying the vss sensor trick.

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I had a similar experience. I have moved the IQ from 1 to 7 with no change in the stumble.

http://forums.tdiclub.com/showthread.php?t=294613

My final fix was injector balance. I was able to improve my balance with the IQ but you may consider sending them out to have a mechanical balance or it could be a pump issue. What is your injector balnce range at?

Well I didn't clean the ring terminals of the ground wires, I cut them off and soldered new ones in place. I cut apart the old ring terminals and the entire connection was greenish corrosion. I did all three. Afterwards I added a ground lead from the terminal to the body. I have my IQ set at 4.8 now and seems to run very well.

I bought a pop tester with dual scale gauge a while back, tested the injectors and they all popped at the same pressure and none leaked down. all spray patterns were good. I cant recall the exact pressures they popped at but it was around 2600 psi or so.

Just as I was going to recommend spraying the engine with Stumble-B-Gone...

The original ground lead connections are terrible on mk3 VW's, They should have been soldered or at least covered with heat shrink to prevent the ingress of corrosive contaminants..there is no path to ground through the green buildup that completely envelops the copper wire where it is crimped to the ring terminal.

Well the stumble is still there but not as bad..seems to be worse before the engine is up to full operating temperature. I never noticed it do anything like this until the temps started to drop around here. I haven't done any winter driving with a TDI yet. The coldest weather I drove it in was when I completed the swap and was test driving the car last year, but that was before I installed Srint 520's and later RC3'd the ECU.

GTiTDi said:

Well I didn't clean the ring terminals of the ground wires, I cut them off and soldered new ones in place. I cut apart the old ring terminals and the entire connection was greenish corrosion. I did all three. Afterwards I added a ground lead from the terminal to the body. I have my IQ set at 4.8 now and seems to run very well.

I bought a pop tester with dual scale gauge a while back, tested the injectors and they all popped at the same pressure and none leaked down. all spray patterns were good. I cant recall the exact pressures they popped at but it was around 2600 psi or so.

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You need to check the balance with the VAG-COM and let us know what it says. I think it is number 16 in the measuring blocks.

Houpty GT said:

You need to check the balance with the VAG-COM and let us know what it says. I think it is number 16 in the measuring blocks.

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That doesn't just tell injectors, you could have balanced injectors but a problem (wear, compression, etc) in a cylinder and be show as an "imbalance"

FWIW I've tried everything, and the wire bypass is the only thing on my car that got rid of it. I don't want to sound like I am disagreeing with great advice/suggestions that are being posted

I am having a very similar problem in 4th and 5th gear only. So I am in progress of cleaning the connections/grounds but would like input on the VSS (what it stands for) and/or part number.

One other clue to add if it is the VSS: My cruise control randomly shuts off. It is not very frequent and does not happen during stumbling but is this another indication of a bad VSS?? Or no relation whatsoever

Thanks!

Well VSS stands for Vehicle Speed Sensor. And when mine is disconnected, the stumble never manifests itself. I am going to double check all the connections at the back of the fuse/relay panel. I drove all the way to Warwick and back today, on the way I had the VSS hooked up, stumbled consistently at low rpms and high load, ie accelerating from a low rpm. Once I stopped and disconnected the VSS it was absolutely fine, actually seemed to pull better than with it hooked up. Weird

I only seem to have the stumbling under load (up hill) in 4th or 5th gear and not in any other gear. I was already in process of upgrading to new 520 injectors prior to this stumbling occuring so lets see if there are any changes in a few weeks.

One other question: Where is this sensor located so i can try it myself?? If you have a pic that would be an awesome christmas present!

Thanks in advance

Look for the small red stripe in the middle of the photo..it is located above and to the left of the green item in the photo (the seal of the axle flange) keep in mind that when you look under the hood of your car it will be in the back in the middle of the engine bay. Good luck and Merry Christmas!

thanks for the pic........Have a great Christmas!!

tested the VSS disconnected today (easy enough to find with the picture) and noticed no differnence.

Before the hesitation/stumbling started a few weeks ago I had already ordered new injectors as it is time to change anyway. The current ones now have 300k miles on them. Additionally I have seen a drop off in milage of about 3 to 4 mpg at the same time of the hesitation/stumbling.

I have been driving around w my VSS disconnected and it has ran flawlessly. One thing I noticed however is my fuel gauge acting flaky..I need to check all the ground connections at the ground point behind my dash as a I had the whole dash apart recently and may have inadvertently knocked a wire loose.

Has anyone spoken to Jeff Robertson about this topic? I wonder if there is a modification that can be done to the ECM that will allow for the VSS to stay plugged in and eliminate the need to cut a wire at the fuse block.

taken from The TDIFAQ....

7. Drivability limitations. The engine control module contains a program for maintaining a steady engine speed at idle and during part-load constant-speed conditions. If the response characteristics of the system are changed too much (e.g. by increasing fuel delivery), unstable operation can occur, which the driver will feel as an extremely annoying shuddering. Aftermarket fuel-adding devices that have an "on/off" characteristic (as opposed to a smooth response to increasing engine load) WILL result in extremely annoying abrupt response.

I have reconnected my VSS and disconnected one of the blue and white wires at the blue TV connection on top of the fuse/relay panel, and now have a working speedometer but obviously no cruise control. The engine is smooth and responsive at all speeds, and will easily cruise along at 1500 rpms.

more from the FAQ...gotta ask Jeff how the EGR was disabled..
"Shuddering", "misfiring", "stumbling" at highway cruising conditions:
- Fuel pump delivered quantity may be out of specification (or if your vehicle is modified, it may require a different setting than standard which will have to be determined by experiment). Refer to section 7.i of this document. - Some vehicles may have had a device fitted in the electrical circuit from the MAF sensor to the ECU, which tricks the computer into thinking that the EGR system is operating when in fact, it is disconnected in order to avoid intake clogging, thus avoiding a MIL or "check engine" light. Malfunction of this device can cause shuddering under certain speed and load conditions. Check security of electrical connections associated with this device, if the vehicle is so equipped. Calibration of the vacuum switch may have some effect. Rather than installation of this device (which is not legal for on-road use), it is recommended that the EGR system be recalibrated according to section 7.g of this document such that the EGR is operating at the minimum level that the original specifications will allow - i.e. that the amount of intake air is at the maximum that the original specifications will allow, which is 370 mg/stroke at warm idle in neutral with all major accessories off.
- EGR valve, or EGR solenoid valve, may be sticking. See sections 7.h (recalibration), 7.g (cleaning).
- If the vehicle is modified beyond stock, the modifications may be such that the ECU in the vehicle is not compatible with the modifications. In some cases, modifications to greatly increase the amount of fuel delivery have resulted in shuddering. Some compensation may be possible by recalibrating the fuel pump per section 7.i of this document. You want a larger reported amount of fuel delivery at idle than standard in this case - this is actually a "leaner" pump, because the actual amount of fuel required to keep the engine going is not changing but you are telling it that it is delivering more (bigger number) than it really is ... i.e. it is actually delivering less than it is telling the ECU. But in extreme cases, the only solution to the shuddering may involve un-doing some of the modifications so that the ECU is capable of dealing with the situation.

Houpty GT said:

You need to check the balance with the VAG-COM and let us know what it says. I think it is number 16 in the measuring blocks.

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It is measuring block 13. Check it and tell us what the range is.

My mods are similar to yours and I was able to fix my stumbling. Disconnecting the VSS may help but it is definitely not a repair. My car actually had a different set of problems in lower gears with the VSS disconnected.

Houpty GT said:

It is measuring block 13. Check it and tell us what the range is.

My mods are similar to yours and I was able to fix my stumbling. Disconnecting the VSS may help but it is definitely not a repair. My car actually had a different set of problems in lower gears with the VSS disconnected.

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Well I did some data logging with Burpod today, and it appears my injector balance is well within spec. I can't recall the exact numbers but maybe he will chime in. Also the car seems to be running very well, is very responsive, in a small car the GT15 performs nice it just cant flow enough air to keep the EGTs down apparently.

greenskeeper said:

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

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I found post #7 in this thread:
http://forums.tdiclub.com/showthread.php?t=160189&highlight+passat+shudder

(2006) that discusses correction of the shudder using the hammer mod and adaptation. Did this end up not working for you, Greenskeeper?

I believe that was before installing larger injectors (RC chip only), if I recall.

No Stumble!

Well i cut wire 2 on U2 at the fuse block and put a switch on the wire. I am amazed at how much smoother the car runs through all of the gears. No stumbling in 4th or 5th. I do hear the cruise circuit relay behind the ash tray clicking away with different throttle positions.

When i need to cruise, i just get it to speed and flip the switch. Thanks Greenskeeper for you investigation. Please let us know when you have the relay circuit figured out.

my 96 passat has had this problem off and on for a while. Finally got worse(shudder at most cruising speeds)Tried adjusting IQ,etc. Nothing worked.
unplugged vss and it has behaved perfectly for 2 weeks. Except for the fuel gauge being very sensitive to minor changes in fuel level (cornering, starting/stopping)
Does anyone know the cause/fix for this other than cutting the wire.

My car has started stumbling more than it was and in 4th gear now too. It may be related to winter fuel and it seems to reduce as the engine warms up. I had moved my IQ up to 5.2 by adaptation a few months ago hoping to help with injector balance but the range was still over 1 (the tolerance is 4 but way to high). I am going to recheck my injector balance and see what it looks like.

I have always had this in 5th gear below 2k rpm. It doesn't stumble at that speed in another other gear, but from 1700-1900 rpm in 5th gear always causes bucking if you try to accelerate even a bit.

I just came across this thread. Does anyone have sample waveforms for the VSS? Good V. Bad?

Tony

Houpty GT said:

My car has started stumbling more than it was and in 4th gear now too. It may be related to winter fuel and it seems to reduce as the engine warms up. I had moved my IQ up to 5.2 by adaptation a few months ago hoping to help with injector balance but the range was still over 1 (the tolerance is 4 but way to high). I am going to recheck my injector balance and see what it looks like.

Click to expand...

Seems like most of my recent problem was from the fuel filter. I started noticing hard starts and worse stumbling. I check the fuel line and saw I had air bubbles. I changed my filter and it runs alot better but I would say that the winter fuel is still a factor. My filter was also half or more full of water. I had never seen that before. My injector balance range is 1.8(1.4 to -.4) and I think If I can get this to less than 1 it will run better. I was also talking to Jeff from Rocket Chip about the stuttering and he seems to think that it could help to try the ALH injector bodies. My injector bodies and nozzles came from another car that ran fine at 40-45 mph in 5th gear. Also this car had stuttering with its old bodies and nozzles and the old bodies and nozzles did not cause stuttering in the other car.

I'm going to ressurect this topic, does anyone have a picture of what wire to cut or where it is located!

Yes, on the back of the fuse panel you will find two blue electrical connectors that have all white wires going into them.

Look up where the connector is on the CE2 diagram.

Find wire U2/2 and either cut it like other people have, or remove it from the terminal and install it on a switch. I put mine on a switch so I could still use the cruise control when I wanted.