Volkswagen crankshaft sensor

[FlyingDutchman]

A friend of mine has a 5 cylinder Volkswagen Marine engine in his boat. I think it is a 75 hp one. Two weeks ago, the engie refused to start. He had to get an expert to come to his boat who analysed the problem using a computer. It appeared to be a loose cable connection in the wiring of the crankshaft sensor. The engineer told him, that when starting the engine, a check is performed and if something is wrong, the engine does not start. He also told him that if the connection would have come loose with the engine running, it would have kept running.

Can this be true? I woud think that this sensor somehow determines the timing of the fuel injection?

 

[savageseadog]

I don't know which engine you're talking about but many older VW engines have a pretty standard mechanically coupled and timed injection pump. I know from my Audi diesel that sensor failures often result in the ECU reverting to a "limp home" mode. I don't know about the specifics of starting or not with that sensor failure but it's quite possible.

 

[--ice--]

The ECU could be programmed to prevent the engine starting if the programme deemed the failure of an input necessary for safe operation. This could be extended to engine temperature and fuel pressure.

So in answer to your question, yes the ECU can prevent the engine from starting if the ECU has been programmed that way.

 

[DownWest]

VW made a 5 cylinder that was common in some of their LT vans and also used in Volvos. But back then it was with mechanical injection.
The idea of relying on an ICU to get things going in a cruising yacht make me a complete luddite.
At the last La Rochelle show, I drifted through the engine section and most of the big stuff was common rail injection with the neccessary electronics. The engines most likely to be used in cruising yachts (up to 50 hp) were still mechanical. No surprise that people try and hold onto their old slow reving marine units.

 

[david_bagshaw]

A friend of mine has a 5 cylinder Volkswagen Marine engine in his boat. I think it is a 75 hp one. Two weeks ago, the engie refused to start. He had to get an expert to come to his boat who analysed the problem using a computer. It appeared to be a loose cable connection in the wiring of the crankshaft sensor. The engineer told him, that when starting the engine, a check is performed and if something is wrong, the engine does not start. He also told him that if the connection would have come loose with the engine running, it would have kept running.

Can this be true? I woud think that this sensor somehow determines the timing of the fuel injection?

Yes this can happen, as crank and cam sensor are used together to determine which cylinder is on compression & therefore to inject. Thereafter it is done by rate of change rather than a particular point. & yes if something fails on an initial start,the ecu will lock out start permission till the fault is cleared. With Man truck it even stops the starter motor turning until certain faulta are fixed.

 

[FlyingDutchman]

Thanks for your replies!

I have checked it and it is the SDI 75-5.
The engine is something like 4 years old and has the ECU.

I would personally prefer an old fashioned system, but in cars and trucks it is all electronics and it has proven to be reliable so it is probably more a feeling than a rational thing.

What still puzzles me is how the engine can run without the crankshaft sensor. Will it run on the camshaft sensor only? If it works on the rate of change (of rpm?) then I would think that after a while a fault would accumulate which would lead to a big error in the timing?

 

[savageseadog]

Thanks for your replies!

I have checked it and it is the SDI 75-5.
The engine is something like 4 years old and has the ECU.

I would personally prefer an old fashioned system, but in cars and trucks it is all electronics and it has proven to be reliable so it is probably more a feeling than a rational thing.

What still puzzles me is how the engine can run without the crankshaft sensor. Will it run on the camshaft sensor only? If it works on the rate of change (of rpm?) then I would think that after a while a fault would accumulate which would lead to a big error in the timing?

The electronics will fine tune the timing but there is a default limp home as I said. perhaps the lesson is that if you get an engine alarm, don't switch off!

 

[Latestarter1]

Yes this can happen, as crank and cam sensor are used together to determine which cylinder is on compression & therefore to inject. Thereafter it is done by rate of change rather than a particular point. & yes if something fails on an initial start,the ecu will lock out start permission till the fault is cleared. With Man truck it even stops the starter motor turning until certain faulta are fixed.

Spot on!

VW marine engines are real quick and easy to trouble shoot using VagCom, the marine engines even use standard automotive OBD diagnostic socket.

VagCom http://www.vagcom.co.uk/

 

[FlyingDutchman]

Wow!

Does that mean you can just buy the software, put in on your laptop, connect it with the engine and perform a diagnose?

That sounds too simple to be true!

 

[Latestarter1]

Wow!

Does that mean you can just buy the software, put in on your laptop, connect it with the engine and perform a diagnose?

That sounds too simple to be true!

I have not updated mine for years, still use old OBD2 to serial adaptor, together with clunky old Panasonic Toughbook £80 off Ebay. The latest genuine OBD2/Hex-USB+CAN PC interfaces are a little pricy, however copies available from other sources....

This is far more powerful tool, far more than just a code reader. You can set it up to say read live sensor data take your vessel/car out for a run and use it as a 'flight recorder' then take a detailed look at the logged data in the comfort of pub/home, real cool!

 

[jimmcgee]

so what he is looking for is this ,

http://www.ebay.co.uk/itm/USB-409-1...iagnostic_Tools_Equipment&hash=item2c59af6ec2

 

[SJF]

Wow!

Does that mean you can just buy the software, put in on your laptop, connect it with the engine and perform a diagnose?

That sounds too simple to be true!

In principal yes, VCDS as its now known (by www.ross-tech.com) is designed to plug into the OBD-II socket so if you can locate one on your engine you should be laughing. May take a little more effort however if you don't already have the right socket.

As the previous poster suggested, it is fairly pricey to buy but if you also own a VW, Audi, Skoda, Seat group car then I have found it to be extremely useful for diagnosing the odd engine management light before taking it to a dealer as needed so has easily paid for itself as far as I'm concerned. Also allows you to do things like add cruise control and Driver information system if it wasn't installed from the factory and setup tow bar ECUs correctly to name a few.

SJF

 

[FlyingDutchman]

Sorry guys, I am only interested because my friend has had this problem, I do not intend to buy diagnostic software myself.
I can fix old fashioned engines, take them apart and put them together again without having many parts left!

But I am amazed by your responses. It means that on modern cars (and boat engines) you can not do much without these diagnostic tools!
The world has changed, in my young days most things could be fixed with hand tools...

 

[david_bagshaw]

T ......... If it works on the rate of change (of rpm?) then I would think that after a while a fault would accumulate which would lead to a big error in the timing?

the rate of change is not so much as in RPM but more as in change of crank angle per 1,000 of a second! It is possible to measure the rotational rate change as the engine comes up to compression and the rate change as the fuel burns,even giving time to workout and inject the required fuel in 5 shots per cylinder according to the power requirement. (hence there is no accumulating error after the first bang)