Hoping for a quick diagnosis

longdog

longdog

Member
My 2002 tdi 1.4 passed its MOT on Thursday with no advisories. This morning, 15 miles later, it started as usual on the first compression when I moved it out of the garage to the front of the house. An hour later it took three sustained goes on the starter to get going, which has never happened before. I set off on a journey and the engine ran perfectly normally for the first 10 or so miles but I then noticed it cutting out momentarily. Very occasional hesitation continued and, not wishing to be stranded, I turned for home. After a further 10 miles or so the hesitation got much worse, I think mainly but not always when I pressed the accelerator. At the same time the ABS light, the handbrake warning light and what I think is the ESP light came on. I turned the ignition off and on again and got the OK message with no warning lights. Just now, after standing for 40 minutes the engine started on the first compression and revved freely, again with OK and no warning lights.

My first thought was fuel starvation or air in the fuel, but I don't see how that could account for the warning lights. Perhaps they were totally unconnected with the cutouts but they haven't happened before. Is there anything in the MOT test that might have disturbed something?

Clearly I need to get a scan but I don't have a scanner, so I was wondering whether anybody might recognise the symptoms?
 
Sounds like a bad earth to me, I had the exact symptoms you describe on my 1.4 petrol and a second earth fixed all of them.
 
Many thanks, Kleynie and mcauleyj. I've cleaned up the earth behind the n/s headlamp but it's made no difference. Is there another earth point at which I should look?

Is it possible that the problem lies in the injector loom?
 
longdog said:
Many thanks, Kleynie and mcauleyj. I've cleaned up the earth behind the n/s headlamp but it's made no difference. Is there another earth point at which I should look?

Is it possible that the problem lies in the injector loom?
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There is only one engine earth point I believe. Worth noting though, just because it's clean does not mean it's good, the cables themselves are known to corrode and cause a bad connection. If I were you, I'd order a new earth strap on eBay, and take it from the engine to the body of the car somewhere else. I have done this to both the A2s in the house, and it has cured poor starting on both of them.
 
Thanks again, Kleynie. I've fitted an additional earth strap but it made no difference. Having read all the threads I can find on the subject I'm thinking again about fuel starvation, and particularly about the tandem pump. I understand this supplies vacuum to the brake servo and wonder whether a failure there was the reason for the brake warning lights coming on at the same time as the engine was losing power. The pump is a fairly expensive item to replace, so I want to be as sure as I reasonably can be that the symptoms are consistent with it having failed.
 
I am having the same problem, intermittently. I suspect a injector control issue, will be checking the connectors and spraying with contact spray. I will update on Thursday
 
A scan throws up fault 16706 engine speed sensor (G28) no signal P0322 intermittent, which fits with the symptoms. Some threads seem to imply that replacement of the sensor involves removal or at least disconnection of the oil cooler. Others that it doesn't. Grateful for advice because I'd like to know before I start whether I'll need to get in a new gasket for the oil cooler. It's a 2002 tdi75.
 
There's a post in vwaudiforum years ago from someone with a Polo Tdi 1.4 that suggests you can swap the G28 from underneath without removing the oil cooler - but just by shifting one of the pipes and collecting the oil - so you might be able to undertake this without unbolting the cooler itself - I should stress that I'm not an expert, and it may also be slightly different on an A2.

>The good news - For those of you may want to know how I changed the Engine speed sensor without to much hassle.
>From underneath the car (remove the engine cover) remove only the oil cooler section from the oil hosing unit (its the square looking part with 2 >pipes attached to it) You will see a large black plastic looking nut from underneath the car looking up. Undo this carefully and remove. Be carefull as >oil will flow out once the oil cooler comes away from the housing, so have something to catch the oil in would be best to avoid a mess. By moving >this out of the way it will give you enough clearance to undo and remove the sensor.
 
2002 car, 165K miles. I've had it for two years. No knowledge of any sensors or loom having been replaced before that but I think unlikely.
 
Thanks to those who offered guidance. In the hope it may help others avoid my mistakes I will post the rest of the story.

Wisdom on the net was that the problem nearly always lay with the crankshaft sensor itself rather than the wiring. The sensors stated on the internet to be correct for the car didn't look right, and none were available on the forum, so to be sure I was getting the right thing I asked the ebay seller gijen4e to take one off a tdi75 he was breaking. He worked really hard to get it to me next day. He appears to be breaking several A2s and I most strongly recommend him.

Getting the old sensor out of my car wasn't easy. It appeared that it had been done before as the bolt was rounded. A boat mechanic who shifted it for me said it was 9mm bi-hex rather than the expected 10mm. I really think this job is best done with the oil cooler removed.

Anyway the replacement sensor didn't cure the problem, and I had no idea how to check the wiring. I wasn't totally confident of any local garage achieving a quick diagnosis, and had visions of the car languishing in some yard where I couldn't do anything about it. Also, none of them would look at the car in situ - it would have to be taken to them on a transporter. So I turned to auto-electricians and mobile mechanics claiming particular diagnostic skill. All of the three in the area were booked up for about a fortnight, so there's obviously a need for more of them.

So, having wasted many days, I reluctantly had the car transported to Racecourse Garage in Totnes, whose expertise and fairness I respect and who only had a four day waiting list. They soon found that a wire in the male part of the connector for the crankshaft sensor (in a clip on the front n/s end of the block) had parted. The car now starts on the first compression and everything has gone back to normal.

It was good that the humble VCDS Lite correctly reported no signal from the crankshaft sensor. The garage told me that virtually no diagnostic equipment will indicate whether a fault is, for instance, in the sensor or its wiring or, even better, where in the wiring it is. Is this true?
 
Wow, glad you got it sorted. Doesn't sound like it would have been easy to find and great that you had a garage who did! Thanks for completing the story.
 
longdog said:
Thanks to those who offered guidance. In the hope it may help others avoid my mistakes I will post the rest of the story.

Wisdom on the net was that the problem nearly always lay with the crankshaft sensor itself rather than the wiring. The sensors stated on the internet to be correct for the car didn't look right, and none were available on the forum, so to be sure I was getting the right thing I asked the ebay seller gijen4e to take one off a tdi75 he was breaking. He worked really hard to get it to me next day. He appears to be breaking several A2s and I most strongly recommend him.

Getting the old sensor out of my car wasn't easy. It appeared that it had been done before as the bolt was rounded. A boat mechanic who shifted it for me said it was 9mm bi-hex rather than the expected 10mm. I really think this job is best done with the oil cooler removed.

Anyway the replacement sensor didn't cure the problem, and I had no idea how to check the wiring. I wasn't totally confident of any local garage achieving a quick diagnosis, and had visions of the car languishing in some yard where I couldn't do anything about it. Also, none of them would look at the car in situ - it would have to be taken to them on a transporter. So I turned to auto-electricians and mobile mechanics claiming particular diagnostic skill. All of the three in the area were booked up for about a fortnight, so there's obviously a need for more of them.

So, having wasted many days, I reluctantly had the car transported to Racecourse Garage in Totnes, whose expertise and fairness I respect and who only had a four day waiting list. They soon found that a wire in the male part of the connector for the crankshaft sensor (in a clip on the front n/s end of the block) had parted. The car now starts on the first compression and everything has gone back to normal.

It was good that the humble VCDS Lite correctly reported no signal from the crankshaft sensor. The garage told me that virtually no diagnostic equipment will indicate whether a fault is, for instance, in the sensor or its wiring or, even better, where in the wiring it is. Is this true?
Click to expand...
Wow they did well to find that well done ...it’s so annoying when a small thing like that can throw up so many possibles ..great job.
 
longdog said:
The garage told me that virtually no diagnostic equipment will indicate whether a fault is, for instance, in the sensor or its wiring or, even better, where in the wiring it is. Is this true?
Click to expand...
Yes. How? The sensor has either no voltage or reports no information. Both just say "here is a problem": they cannot say where the problem lies as it's just a "signal transferred" or not.

- Bret
 
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