post #16 of Old 09-16-2013, 06:14 AM Thread Starter
worth
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Thanks 86cj74.2L ....... Have been struggling to find a 'break' etc.... If its a common earth issue (to those sensors) could hurt to take a new earth from one of the 'paroblem' sensors straight back to battery /thus giving a good common earth??? Is that logic sound????

D

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post #17 of Old 09-16-2013, 06:17 AM
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Or straight to the nearest Good ground location would be your best option.

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post #18 of Old 09-16-2013, 12:07 PM Thread Starter
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Originally Posted by 86cj74.2L View Post
I would trace out the 5v supply to all the sensors or look for the sensor ground.

It may be a bad sensor ground.

It may be the harness is lying on something that gets hot and has melted the wires and shorts out on occasion.

A volt meter on the 5v supply to a sensor effected at the time the MIL comes on will tell you next step.

Check 5v to the engine somewhere and also check the 5v to the sensor common pin on the connector.
Okay, have just had a brief play.... and am a bit confused!

One of the 'faults' is for the MAF sensor and another for the Turbo sensor.....

4 wires to the MAF connector....brown is ground. Getting a 14v reading when running at MAF sensor. Tried Turbo sensor.... brown ground here also...... Getting 14v here also..... Should this be part of the 5v system /running 5v? It is a merc unit so poss different to the petrol ones????

Confused!

Anyhoo, ran in a new ground to the MAF ground and back to battery and also body....neither cleared fault.....

Thanks for any help /thoughts on the above....
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post #19 of Old 09-16-2013, 12:25 PM
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Without a FSM for diesel model I can't rightly say it should or shouldn't be 5 volts.

When you read the 14v on the brown wire.......tell us where your meter leads were placed.

There should be a supply and ground in each connector.

With ignition on and connector pulled you could read across those two pins and see what you got for volts.
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post #20 of Old 09-16-2013, 12:27 PM
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My sensors run 12.5ish volts when engine off and 14 ish engine running so I would suggest this is normal at least for those two sensors. Others such as the fuel rail pressure sensor def run at 5 v.

If you can't fix it with a hammer, you've got yourself an electrical problem!
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post #21 of Old 09-17-2013, 01:11 AM Thread Starter
worth
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Quote:
Originally Posted by 86cj74.2L View Post
Without a FSM for diesel model I can't rightly say it should or shouldn't be 5 volts.

When you read the 14v on the brown wire.......tell us where your meter leads were placed.

There should be a supply and ground in each connector.

With ignition on and connector pulled you could read across those two pins and see what you got for volts.
Thanks for your continued help! Tried as you describe (pulled connector) and for MAF get (ground brown wire, supply green and red stripe) 12.5ish not running and 14+ish running..... Ditto turbo sensor.

Quote:
Originally Posted by alfaitalia View Post
My sensors run 12.5ish volts when engine off and 14 ish engine running so I would suggest this is normal at least for those two sensors. Others such as the fuel rail pressure sensor def run at 5 v.
Thanks Alfaitalia Same as mine..... Guess I'll keep working through the sensors showing on the fault list

Keep the suggestions coming all....really appreciated!
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post #22 of Old 09-17-2013, 05:05 AM
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May be it would be better to back probe the connector with it still connected. That way your seeing what the PCM is seeing.

Some MAF sensors are 4 wire and include a inlet air temp.
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post #23 of Old 09-17-2013, 05:56 AM
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Quote:
Originally Posted by 86cj74.2L View Post
May be it would be better to back probe the connector with it still connected. That way your seeing what the PCM is seeing.

Some MAF sensors are 4 wire and include a inlet air temp.
CRD's do have a 4 wire sensor. But they also have an air intake temp sensor on the bottom of the alloy intake manifold on the other side of the motor. I got so fed up cleaning the oily crap off it (it gets contaminated by the oil in the PCV and makes the car hesitant just off idle and at very high revs) that I vented the PCV to the atmosphere......have not cleaned it since!

If you can't fix it with a hammer, you've got yourself an electrical problem!
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post #24 of Old 09-17-2013, 09:05 AM
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Vent the PCV to holes in the unibody.

Rust proofing
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post #25 of Old 09-17-2013, 09:14 AM Thread Starter
worth
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Quote:
Originally Posted by 86cj74.2L View Post
May be it would be better to back probe the connector with it still connected. That way your seeing what the PCM is seeing.

Some MAF sensors are 4 wire and include a inlet air temp.
back probed both the turbo and MAF sensors...same readings (MIL on all time now). Our MAF is 4 wire. but think I've ID'd the supply and ground correctly (?).... strange one isn't it!?!
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post #26 of Old 09-17-2013, 10:54 AM
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Wonder where Tom is? He would have something of an answer for this one.

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post #27 of Old 09-17-2013, 11:53 AM
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Vent the PCV to holes in the unibody.

Rust proofing
No need....euro WJs are galvanised so we don't suffer much with the old golden body lightener!

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If you can't fix it with a hammer, you've got yourself an electrical problem!
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post #28 of Old 09-17-2013, 12:38 PM Thread Starter
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Quote:
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back probed both the turbo and MAF sensors...same readings (MIL on all time now). Our MAF is 4 wire. but think I've ID'd the supply and ground correctly (?).... strange one isn't it!?!
Okay.....

just a quick update:

Crank pos sensor also 14ish volts.....

Has me stumped...as with the other two, surely this is the correct supply /must have okay ground????

Anyone know where the swirl motor actuator connector is (to check)? Can't reach the air con pump plug easily.....

D.
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post #29 of Old 09-17-2013, 06:02 PM
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Quote:
Originally Posted by worth

Okay.....

just a quick update:

Crank pos sensor also 14ish volts.....

Has me stumped...as with the other two, surely this is the correct supply /must have okay ground????

Anyone know where the swirl motor actuator connector is (to check)? Can't reach the air con pump plug easily.....

D.
May be the fact you have 14v volts instead of 5v is your problem.

Unless the fact its a euro diesel and a overseas vehicle I don't know why it wouldn't be 5v for the sensors.
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post #30 of Old 09-18-2013, 08:55 AM Thread Starter
worth
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Quote:
Originally Posted by 86cj74.2L View Post
May be the fact you have 14v volts instead of 5v is your problem.

Unless the fact its a euro diesel and a overseas vehicle I don't know why it wouldn't be 5v for the sensors.
Alfaitalia may be able to shed some light on that? I know his prev post indicated 14v at the turbo and MAF.....

Anyone know what each should run at on a CRD /is there a list anywhere?

Possibly a slight red herring, but whilst testing (and its not on my 'fault' list), but the sensor going to the rear of the viscous heater pulley (I think) gave no reading /0v....is that correct?

D.
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