Lag/Judder

[philj]

This tdi isn't quite right. Fitted the earlier t2 turbo not the t15 just to get the car going.

There's a massive lag, doesn't get any boost untill 2.3k rpm, and every now and then it jerks quite violently, as if fuel is cut for a split second, whatever throttle is being applied.

I've checked cam timing is correct, pump timing is advanced but in spec. It's like it doesn't get enough fuel till 2k. Upped the injection quantity no difference. Took out the tuning box and it was 10 times worse with the jerking and dog slow.

All the fuel pipes at the front of the car have been replaced, including leak off pipes. Filter upgraded to the late a4 style. All the vacuum hoses have been replaced with silicone, including the little one in the ecu.

Cruise control turns itself off every now and then. Read the speed sensor causes similar jerking issues somewhere, could that be the issue? Petes suggested to cut a wire, worried that might upset the cruise even more.

Anyone got any other ideas?

[targus]

there is a wire under the bonnet at the back (blue/white from whats been posted on here before) that stops juddering at idle.
Sounds like it needs mapping for the turbo.

[stocious]

Sounds like it needs mapping for the turbo.

its were i would start, if you have access to equipment. before snip snip

[philj]

I read they have different maps for fuel and boost, and I know its not ideal, but surely if the map was wrong, it would overfuel at lower rpm when its expecting boost? It idles fine, just every now and then when driving it jerks, and the massive lag.

[prj]

It will not over or under fuel, because the fuel is put in according to the air via the smoke limiter.

However, it will fuel cut and boost cut if you reach those thresholds.

As for massive lag, are you sure all your intake is tight? No leaks?

[philj]

Fair enough, yeah intake is ok, have double checked all the intake pipes. Hadn't replaced the pipe to the ecu, did the one in the ecu and this improved things a bit. Then the throttle pedal snapped off and it got a bit faster again, but mainly seemed to improve off boost and get on boost quicker/smoother. Hopefully the adjustment on the arm will fix things for the moment.

Whats the best way to increase boost pressure? Actuator arm? Bleed valve on the n75? Bleed valve on the map sensor? Tried the last 2 and it seems to flutter a bit, does hold 13-15psi though.

[prj]

Fair enough, yeah intake is ok, have double checked all the intake pipes. Hadn't replaced the pipe to the ecu, did the one in the ecu and this improved things a bit. Then the throttle pedal snapped off and it got a bit faster again, but mainly seemed to improve off boost and get on boost quicker/smoother. Hopefully the adjustment on the arm will fix things for the moment.

Whats the best way to increase boost pressure? Actuator arm? Bleed valve on the n75? Bleed valve on the map sensor? Tried the last 2 and it seems to flutter a bit, does hold 13-15psi though.

The best way to increase boost pressure is to map the ECU instead of screwing with all of it's inputs and outputs.
These old ones are so easy that a baby could do it

As for the intake pipes - you must pressurize the inlet. Visual inspection is a waste of time, might as well do nothing.

[Acidburn]

One other thing since your having issue's with the pedal. There is a 13mm adjustment on the pedal box that you can adjust till you hear the engine note change as the rev's slightly increase then it will be setup. I had to do it to my green one before I started modding it.

[philj]

Took an extra turn to start today, stalled a couple of times, didn't think too much of it until it did it 200 yards away from my house and wouldn't restart.

I unplugged all the sensors and tried it - nothing, plugged them all back in - nothing. About to give in and it stutters into life, got it home and now it won't start - same as before.

Probably to do with the above issues, anyone with any wise ideas on what the process is now? Seems like no fuel.

[rynaqui]

Doesn't seem like any sort of sensor problem, FPR perhaps? Could be many things... Must be fuel pump related, hope you get this sorted soon

[audinut]

...

[philj]

Wouldn't mind knowing exactly which wire it is as well Audinut. Don't think that's my issue here though.

[audinut]

VSS Vehicle Speed Sensor - Jerking/Juddering

Great to see all the interest! Bare in mind my car is 80 Avant 1994 1Z TDi, not sure if it applies to all, so please check first.

You can either remove pin 43 (White/Blue wire) on the ECM (which is located behind the glovebox, behind the heater fan). I found the pic/pinouts here;

http://www.hasenwerk.ca/tech/wiring/earlypassat1z.pdf

But it would be easier to cut the wire from the dash, I found that it goes to pin 18 (White/Blue) on the blue connector at the rear of the dash. You will find the markings for pin numbers on the socket of the dash, just count along to 18, then check the colour, cut the wire (insulate, just in case). To remove the dash remove the cowl (two screws underneath), then the two screws for the dash. You don't need to remove the steering wheel (disconnect battery if your unlucky enough to have airbag).