resistance problems 2002 jaguar S type

Dave rainey · May 8, 2019

Hi bit of a strange one as load is put on my electrical system the resistance across body earth increases if I measure negative battery lead resistance it rises from 0.1 Ohm to about 10Ohms
Any ideas how to fix

Cheers
Dave

telectrix · May 8, 2019

bad or corroded connection

static zap · May 8, 2019

Try measuring DC volts ,and may get to grips with what is going on.
Between Battery -ve and body work(earth tags) near things misbehaving !
( With them turned on.)

Dave rainey · May 8, 2019

all terminals have been removed wire brushed down to bare metal greased and tightened back down see no PD across anywhere earth to earth

static zap · May 8, 2019

Whats miss behaving ,engine cranking ,lights ..other ?

(May be witnessing small DC pd in cable interfering with DC ohms measurement ... will go other-way/weird if reverse connections)

PEG · May 8, 2019

Hi,easiest way to find bad spot,is to get your DC meter (any little yoke,will do),put load on,and place probes across each side of any connection or earth strap. Any voltage measured,means a problem.

Dave rainey · May 8, 2019

static zap said:
Whats miss behaving ,engine cranking ,lights ..other ?

(May be witnessing small DC pd in cable interfering with DC ohms measurement ... will go other-way/weird if reverse connections)

Hi MAF is playing up getting a DTC P0102 which I think is due to a high resitance on the ground wire which only happens with ignition turned on and cannot start the engine

static zap · May 9, 2019

I know MAFs can die ,but not if it's a safe substitution test . (or how clever ECU is without it)

Dave rainey · May 9, 2019

New MAF fitted

static zap said:
I know MAFs can die ,but not if it's a safe substitution test . (or how clever ECU is without it)

Bobster · May 9, 2019

Dave rainey said:
Hi MAF is playing up getting a DTC P0102 which I think is due to a high resitance on the ground wire which only happens with ignition turned on and cannot start the engine

Never known a MAF sensor to stop a car from starting, put it into limp home mode sure.

I think you may have other issues.

Dave rainey · May 9, 2019

Yes I think you are correct but I do not know if this rising resistance is also causing engine start problems

Rob said:
Never known a MAF sensor to stop a car from starting, put it into limp home mode sure.

I think you may have other issues.

Shoei · May 9, 2019

Dave rainey said:
all terminals have been removed wire brushed down to bare metal greased and tightened back down see no PD across anywhere earth to earth

How are you measuring resistance with load on the electrics? If it's with a meter on ohms you'll get false results.

Dave rainey · May 9, 2019

Hi using a mulitimeter manual tells me to test for resistance with ignition on when it is turned on the resistance rises

Shoei said:
How are you measuring resistance with load on the electrics? If it's with a meter on ohms you'll get false results.

Shoei · May 9, 2019

Dave rainey said:
Hi using a mulitimeter manual tells me to test for resistance with ignition on when it is turned on the resistance rises

That could explain the change in resistance reading, the multimeter injects a small current to measure resistance, if a current that it doesn't 'know about' is flowing in the same conductor it will indicate a high resistance. As SZ suggests, it may be better to measure voltage to work out if there's a problem.

ruston · May 9, 2019

Poor starting and poor running could be lots of things , but as I suspect your MAP sensor has shown a fault and replacing it has not helped, it may be the EGR valve as the diagnostics are cumulative. A diagnostic sweep may save you hours of time searching for faults that are not there.
Is the air filter clean? Is it diesel?

Dave rainey · May 9, 2019

only DTCs i am getting if for the MAF sensor ERG has its own DTCs yes checked filter all okay and no it is petrol

Cheers
Dave

ruston said:
Poor starting and poor running could be lots of things , but as I suspect your MAP sensor has shown a fault and replacing it has not helped, it may be the EGR valve as the diagnostics are cumulative. A diagnostic sweep may save you hours of time searching for faults that are not there.
Is the air filter clean? Is it diesel?

Shoei · May 9, 2019

As others have said modern engines have a long list of ways to go wrong. Just a couple of comments, it's best not to grease connections until after they're assembled and tested, grease doesn't conduct. I doubt that's a problem but one to bear in mind.

If you suspect the MAF, most engines will work pretty well with its cable unplugged, the ECU does a fair job of guessing airflow so seeing how the engine runs without it connected is worth a try, to eliminate the MAF as a problem.

PEG · May 10, 2019

Hi,there are other factors which will cause the ECU to assume a MAF fault,even if it is functioning correctly. This gives the ECU information regarding the amount of air,passing through the intake system,in relation to other factors.
For example,a blocked or restricted exhaust,could flag such faults.

You may require the services of a clued up dude with a proper machine,not just a code reader.

static zap · May 10, 2019

PEG said:
For example,a blocked or restricted exhaust,could flag such faults.

..Ah expensive memories ,an unexpected hissing noise ,just after cranking .. (that was even before ECU's, cats & dpfs came along)

ruston · May 10, 2019

An old diesel engine was the simplest most reliable economical engine ever, just look what they have done to it. As for ecology , scrapping good roadworthy cars because they are electronically beyond economical repair does,to me benefit the manufacturers not the earth .
Sorry @PEG got me into the rant mode.