Engine Specific Info and Questions > Diesel Swaps

Gggrrrrr. TDI conversion problems.

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Baxter:
How do.
Not been here for a while.

I have a problem with a customers car that has be scratching my head.

It is a Vanagon with a AFN in it. [I did notdo the conversion, but it is quite tidy and according to the owner has been reliable]

It came as a none runner having broken it's oil feed pipe for the turbo on the motorway, oil everywhere, customer stopped and had the van recovered to me.
We've had it here and corrected the oil line, we fired it up, it idled and didn't leak and we didn't think much of it and moved on to get on with the rest of the work it needed.

Came to take it off the ramp and the throttle pedal has no effect.
Great, has a look and see if we have dislodged anything while we've changed the pipe, nothing obvious.
Plugs VagCom in and we get "00777" throttle position sensor - implausable signal", tidy, sensor has failled we'll try a known good one, no go, still kapput.

So, heres what happens.
Van will start and run, albeit at idle.
You can gently rev the engine till about 1200rpm okay, over this threshold it will go into some form of limp mode where idle speed is increased to about 1000rpm and the accelerator pedal now becomes inoperative.
Now, if you are in VagCom, measuring block group 2 field 3 there is a set of binary figures, the first I believe is the AC raised idle signal, the second is the idle switch and unsure of the 3rd.
When this problem happens then the fields got to "110" rather than the usual "010" setting it should have at idle.[van doesn't have A/C]
While the problem is happening you can move the throttle and you will get the load going from 0% to 80% no problem so the throttle signal is making it's way to the ECU, just the pedal becomes innefective.

Once the "110" is achieved, then the ECU again registers the fault "00777", the fault will not clear while the engine is running at this raided idle speed.

Now, weird bit.
if you start with the engine off, and the fault cleared and hold the throttle to the floor and then start the van it will rev normally, you can drive the van so long as you do not drop it to idle, once you get to idle it then returns to it's limp state and again the throttle pedal now has no effect and the fault code is lodged.

I have tested the sensor, it appears to check out using test data from ELSAWIN, I have tried and alternative sensor with no effect.

If you read the test data, it says that if a problem exsists with the sensor it will default to a raised idle speed, which is I presume what is happening.
I'm wondering if it does this by internally turning on the increased idle speed via the air con request and thats why I'm seeing "110" ??

Dunno.

Tested continuity between the sensor wiring and the ECU - no fault found.

Wouldn't normally post this here but I have 24 hours to fix it!!  :o

Oh, customer says he scanned for fault codes a little while ago and did see the throttle position fault code a while ago but it hasn't caused any problems.

Any ideas?
.

Baxter:
Further to this.
Continuity between ECU and sender - good.
Wiring checked for short to each other, short to earth and short to positive - all good.

the caveman:
I had similar problems with 2 VWs ,one a Beetle ,the other a Passat, around 2002, albeit gassers, but still drive by wire. Both had bad grounds.
But the signal you are getting in the measuring block sounds like shorted wires or 2 mixed up connections . Real question is whether it's a coincidence or something done while doing the sump repair.
I would also do a ECU memory kill by disconnecting the battery and touching the two big cables together for a minute or two

Baxter:
With it being a conversion, and a conversion done by some respected boffins and the fact that this van really has been around the world I'm tempted to think that it has been alright most of the time so more inclined to think that it is either something that has failed or something we have "nudged" while doing the oil feed pipe, but I've been over it and checked all the electrical connections in the vicinity and all are good.
I have repaired a few things on the way, oil pressure sender not plugged in, alternator wiring damaged etc but nothing has had any effect.

I couldn't get a wiring diagram from ELSA for the base vehicle, but I did get one from autodata and found the wires to the ECU for the air con, and duly snipped them, no effect.

the caveman:
Do you indeed have a raised idle speed while the fault is there ? If not i would still suspect a bad ground or ECU failure. I doubt the ECU failure , but ...
If you do have raised idle speed then the ECU is almost definitely seeing a failed throttle issue.
I'm sure that you know that most of the connectors at the ECU are ridiculously small and can develop connection problems due to voltage drops across such small surfaces . maybe try a wiggle test at the ECU connector while running

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