vw sharan tdi low power ahu engine

[landroverbob]

Should this be a fresh post as it may detract from the OE post.?
The car is a Sharan TDI belonging to a financially challenged friend -Its left hand drive and in france
Engine AHU, first reg 17th august 1998. Car vin number is: wvwzzz7mzxv013***. Would this be an NVT turbo?, on the turbo plate is 11989/600-30K J1075/1820. -Could be the odd incorrect number due to reading in a mirror lying on the garage floor upside down with head and arm jammed round the driveshaft. .

I now have the car with me today and have spent this morning on it. Road testing last week from cold it dropped power for the first time part way up a hill after a 20k drive (thrash). I came back ,had a quick look, replaced a section of worn vac hose (under bonnet - to MAP sensor in ECU) Road tested again and power dropped off again at exactly the same place as before (sneaked another scan,clear and res-can with original fault code reappearing), back to base,another look round, disconnected and reconnected turbo valve and all the other sensors I could easily reach. Road tested again and exactly same result. Working on it again today I road tested it and exactly the same as before but found if I switch off then back on (read to try this on forum) then it is ok until next high boost demand then power goes down again. When it does this it is instant and very obvious, feels just like a turbo hose has blown off

I then replaced more vac hoses as ness, had the codes read, cleared and read again comes up with 65535 035.on one scanner and "permanent ecm fault" on another - neither proper VW scanners. Asked for turbo boost readouts but circumstances (garage boss came back) and the only one we had time to record was "desired boost 795, -"boost pressure 979". Seems a fair difference does that confirm it's overboosting? Got back to base and then checked the turbo operating valve which gave the correct figures according to Autodata
Another problem I encountered was the engine cut out as I braked to 10kph to turn down a side road after driving about 30k (the last 2k up a long uphill gradient at only 65/75kph due to the power loss). Wouldn't fire at all on the first attempt to start, fired intermittently after a while on the second attempt, better on the third attempt then eventually picked up properly and revved ok. Sneaked probably the last free scan ever, no other fault than the previous one still recorded.THe owner says it has done that before and is doing so more frequently.Last thing I did was replace the fuel filter I had ordered days ago (this is france). I did notice the fuel pipe in at the filter was perished / split so I shortened it slightly and do wonder if it was drawing air in before and causing a problem. Sneaked the very very last free "clear and reread" scan - no change, same fault recorded

Logic tells me ECU wants replacing but they are expensive and look a b*ga to get out and I have read that others have done that and been wrong

Just read the new post and will check actuator tomorrow but could do with knowing how to ID the turbo type if the number above can't and also does the ecu control limp mode by reducing turbo boost or fuelling ????.
Got involved with this to help out and I obviously know all about VW's as amongst my fleet I have a golf mk2 diesel na and a passat '93 tdi (GO SLOW BUT GET THERE CARS)!!!

[chittychittybangbang]

post moved to mk3 forum because of the engine. We didn't have that engine here so not 100% sure but I checked the parts catalog and I'm pretty sure it's not a VNT turbo.

The ecu fault is the hose inside the ECU. EVERY mk3 TDI will have it. http://www.myturbodiesel.com/1000q/a...-tdi-65535.htm See this writeup for details, classic error code, fix it first and see if it makes the difference. The vac line goes to the sensor.

[landroverbob]

After posting last night googled the turbo numbers I had and when I reversed them (duh-me) found they referred to the non NVT turbo so can discount the sticky vane problems and so assume it's got to be 1 -the hose in ecu, 2-the ecu/ mapsensor, 3-the n75 boost valve, 4- the wastegate adjustment or 5 -wastegate diaphragm and re -"If you are getting a check engine light (CEL or MIL) and see "65535 - Internal Control Module Memory Error" with a VCDS tool, it's most likely caused by this leaky hose"--No check light coming on this car. Also I looked at the link given in your reply thanks and that is right for this car



1 - Re --"There is a hose inside the ECU that will wear out. This hose connects to an air sensor inside the ecu. If an air leak occurs in this hose, the car will not run correctly". - I checked before and the hose holds vacuum but it's a pressure sensor on this model of turbo so unles told not to I'm going to see if I can test it tomorrow using around 1000mb/ 14psi pressure from the airline and a leakdown setup I have.
2 - can't test this myself
3 -N75 valve - have checked it's resistance and thats correct
4 -wastegate adjustment -got no info on that
5 - wastegate diaphragm, put around 1000mb / 14psi to it this morning and it operates ok

If the map sensor pipe was leaking how does our ecu know the boost pressures are wrong as the boost readings (as in previous post "desired boost 795," -"boost pressure 979") let me think the sensor is working to be able to make this comparison. They were not taken when under load but stationary in the car and I'd have thought these would be much higher when under load. Ive Tee'd in a boost guage and am going to road test again tomorrow and see what boost presure under load is achieved.
As regards the cutting out when I braked -any idea if it could be to do with the brake pedal switch
Any more thoughts are most gratefully received!!

Moderator, when this was moved to the Mk3 section it didn't email me with an update to say it was moved, not a winge just thinking of others in the future.

[landroverbob]

Just been on road test, different route to previous runs but approx same distance, stopped for half hour at pals house, went to fetch some bread from shop -15 minutes- then back onto the hill that it always looses power on which it did in exactly the same place! I had a boost guage on which was peaking at 10psi when the power drop occured (reached that pressure many times before during this run without drop of power)but after the drop it would still run around 4/5psi and boost to 10psi even though the performance was just as if there was no boost. Switch off and then on again and power back on till under heavy load again (10psi of boost). Knock it out of gear and it would rev up to 5000 freely even though the power was still in "poor mode" Am I right in thinking this isn't "limp mode"
So obviously it is resetting something -anyone any ideas? I suppose I could believe the fault code that says permanent ecu fault and admit defeat replace it but my time is free and an ecu is very expensive for a one parent friend to buy. Going to play with maf sensor now.

[audi1z]

Hi,
The error 65535 may but must not mean a faulty ECU. It may also be a communication problem.
Which diagnostic tool do you use, original VCDS? Which version and which interface? Potentially you must check the communication settings.
From your descrption one can only guess that the charge pressure control of the AHU Wastegate Turbocharger works incorrect, but one needs a correct communication with he ECU, a readout of the error codes (behind ECU "failure"), and a readout/log of measurement blocks during driving, mainly #11.
Do not "test around" with too many items, it will not help.
(BTW, I drive a 1Z Engine, which is identical to the AHU, with more than 350 Tkm).
Brgds,
Audi1Z

[landroverbob]

AUDI1Z Thanks for input, scanner was auto-diag which I don't have access to very often so can't obtain the information you mention. The first time but not since the code recorded was 65 535 035. As regards the message and fault code not been taken too literally as a permanent ecu fault and possibly being communication problems or one that is not recordable thats really what I'm trying to establish.
I figured as the boost pressures don't vary whether performance is proper or after it drops in power showed the problem doesn't lie in the valve or sensor or pipework

[audi1z]

Hi,
My input was only an advice. Itīs your car. I only see that you do not have available the data from the workshop manual, nor a proper VCDS version for failure search. And, I do not want to be unpolite, but your writings indicate that your understanding of the engine control is not complete.
Brgds,
Audi1Z

[landroverbob]

Compliments on your english but be as impolite as you wish if it helps me to mend this car and I'm sure my knowledge isn't complete or I wouldn't be asking questions but what part have I got wrong so far? I am quite happy to told where I'm going wrong.

[audi1z]

Hi,
Please take my apologies if my words were too hard. If you still like, letīs go back to the problem.
What you observe is symptomatically for an engine going into limb mode because of a temporary error observed by the ECU, lasting for some seconds and classified dangerous for the engine.
Once you stop and re-ignite, or even let go the gas pedal and then throttle up again, the limb mode is left, and the engine comes up again.
Typical fault conditions are a too high manifold pressure (overshoot), or a misrelation between manifold pressure and intake air mass. The latter would happen if e.g. the ECU internal hose to the pressure sensor would have a leak, but other reasons are credible, too. I personally had this situation with defective intake hoses, but also with oil in the hose going from the intercooler to the pressure sensor in the ECU. When you reach a certain load condition, engine power is suddenly gone.
For the case you can not find a broken intake hose, or another evident mechanical defect, the search becomes more difficult.
Without having measurement equipment, you can perform a driving test with the N75 regulator valve electrically disconnected. When the fault disappears, either the valve or its supply is defective (I have read that you measured the valve resistance), nevertheless do the test.
For further checks, you need to read out the ECU during defined driving conditions, particularly the requested/real values for the intake manifold pressure, and the control level of the N75 pressure boost valve.
Manufacturers values for turbocharger check are:
Full throttle acceleration from 1500min-1 to 3000min-1. Manifold pressure to be reached at 3000min-1 is 1550 mbar to 1750 mbar w/o N75 operating, 1800mbar to 2050 mbar w/ N75 operating.
Note that this test must not detect all faults when done with an external pressure gauge, it is important what the ECU reads.
Error 65535 is imho no indication for a failure in the intake pressure tubing. The ECU can not distinguish between a leak inside, and a leak outside, in the sensor tube or in the intake hoses. All is connected together.
Brgds,
Audi1Z

[chittychittybangbang]

Originally Posted by audi1z

Error 65535 is imho no indication for a failure in the intake pressure tubing. The ECU can not distinguish between a leak inside, and a leak outside, in the sensor tube or in the intake hoses. All is connected together.
Brgds,
Audi1Z

Correct.

landroverbob, have you removed the tubing inside the ecu and visually inspected it? Perhaps testing under vacuum the hose cracks pulls tight but under pressure the crack is exposed? You say you vacuum tested it but I have to ask if you visually inspected it since it's such a common problem.