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PhatBob
17-09-2009, 09:35 AM
My second question in the same number of days...

My wife's Leon (S reg approx 90k miles) has gone from being a fizzy little TDi to a boring sluggish yawn recently.
It wont rev over 4500 in 5th, it has no power in so much that the acceleration is barely noticable and that I had to change down a gear to go up an incline.

There's nothing actually wrong with the engine from what I can hear, no check light, and you can hear the slight noise of the turbo's whistle. One of my mechanic mates reckons that I should change the nozzles - but this is his stock answer to any TDi problem.

Is there anywhere else that I should look for a fault?

Thanks in advance.

Rob

shark_90
17-09-2009, 09:45 AM
I suggest you change the MAF sensor as they don't often give any warning lights and can cause poor performance as you describe.

Eshrules
17-09-2009, 10:01 AM
Grab hold of someone with vagcom and do some logging before you drop £60 on a MAF, it's odd that your revs are limited in only one gear.

is the car expressing any other symptoms?




Air system part I: MAF


Go into Engine measuring block 003
Start Logging data
In a high gear (4th/5th), give full throttle from 2500 rpm up to 3500rpm.
Find and Open the Log file in Windows Explorer
Graph MAF actual -vs- rpm in Excel
The MAF is OK if the actual value is at least 850-900 mg/h at 3000 rpm.

Taken from here (http://www.ross-tech.com/vag-com/cars/tdi.html)

PhatBob
17-09-2009, 10:31 AM
I mentioned 5th gear because its most noticeable then, but the symptoms are the same regardless of which gear its in.

With other MAFs I've been able to back probe the plug and scope the voltage reading, I don't suppose that there's any voltage tables and MAF pin-outs knocking around are there? (I'll have a good search too)

shark_90
17-09-2009, 10:45 AM
A quick unscientific test is to unplug the MAF and drive the car. If it is no worse or better than before, then it is likely to be the MAF. If the car is noticeably better with the MAF plugged in then it's likely to be something else.

PhatBob
17-09-2009, 10:45 AM
Found a MAF checking PDF:
http://www.kuiack.net/Files/GenDUB/Bentley/P0103/MAF_Sensor_Checking.pdf

And this handy little thread:
http://forums.vwvortex.com/zerothread?id=4474516

At least I can give that a go, thanks to you both

PhatBob
17-09-2009, 10:46 AM
A quick unscientific test is to unplug the MAF and drive the car. If it is no worse or better than before, then it is likely to be the MAF. If the car is noticeably better with the MAF plugged in then it's likely to be something else.

I'll take quick and unscientific over complicated and slow every time:)

Quick thought - my AWX engine doesnt have this problem - how compatable are the MAFs? I could swap mine over to test if they're the same unit.

shark_90
17-09-2009, 10:52 AM
I'm almost certain they won't be the same, and even if the connector is the same and it physically fits the scaling in the ECU will no doubt be different.

PhatBob
17-09-2009, 10:55 AM
Cool, I'll just try your test and not complicate issues with stupidity :D

PhatBob
18-09-2009, 10:15 AM
Drove the car for a while, then pulled the MAF plug, car felt sluggish beyond belief.
Re-attached the MAF car felt quicker than when I started the exercise:o
That MAF plug has never been removed but my SoP Dyno seems to suggest that theres an improvement.
I shall get Mrs PhatBob to test it.

PhatBob
22-09-2009, 08:44 AM
On sunday after about an hour of town driving we got onto the A14 and I put my foot down to get some speed up to join the dual carriageway. I was rewarded by an engine that wouldnt rev above 4K...
Pulled off on the next junction and the car felt gutless, so I pulled the MAF plug to see if it was any different, and 2-3miles later we agreed that it was marginally worse on acceleration but it seemed to rev above 4K in 3rd gear (couldnt rev above 4K in 4th or 5th - on an A road so speed limited). Reconnected the MAF and the car was restored to a decent level of power - reving upto the red line in gears 1 to 3, and much better response.

Could it be that the MAF overheats, and that 3 miles of unconnected driving cooled the thing down enough to start responding properly?

I need to find someone in the Cambridge area with Vagcom - any clues where to look?