hello again. in the previous episodes the tdci had its pedal changed, injectors cleaned. filter changed pump cleaned / checked , map sensor cleaned, maf sensor checked and cam sensor replaced. then i went on holiday. phew. on my return the limp mode probs continued but the battery was dead, drained maybe? So ...... i replaced the battery. took the car to check there was no drain at auto electician..... all was fine. so driving around nice and steady for a whole week. no limp mode battery fine. Great. then one day I put my foot down..... limp mode. engine off and on while moving limp mode gone. drove home, parked up. Next day, car wont start. New battery was fine till limp mode happened now is drained, car wont start. HOW ON EARTH CAN THIS HAPPEN????? ANY and I mean ANY ideas on what the hell is going on greatly appreciated. to me it seems limp mode kicks something into action which drains battery. but wtf do i know :w all::wal l:

cheers for listening

steve

 

Low battery voltage will trigger limp home mode. I would second guess at alternator reg being duff !!

 

Hello !

My advice is take it to someone with a diagnostic code reader who actually knows what they are doing.

Changing parts randomly by guessing will only cost you money and piss you off !!!
Its better to pay a bit extra and get the job jobbed properly.


The non starting/battery drain symptons sound like a dodgy engine main earth fault/loose connection which could cause any of the faults you have mentioned.
Check the battery terminals are tight as well as the large thick earth wire that connects to the block and chassis.
Also check the starter motor/alternatator mounting bolts/brackets are tight and corrosion free.

 

cheers peeps. i have had it on diagnostics twice first time injector code came up cannae remember what but it got sorted . then after more probs had diag again and no codes.
so low voltage can trigger limp mode. that sounds interesting. how can this happen if the auto lectrician did a drain check and found nothing?? cheers again

 

also. he confirmed alternator was doing its job on the voltage thing. yours confused

 

Whilst starting the engine, the battery current draw will be about 200+ amps and any loose/dirty connections can cause a bad voltage drop for a fraction of a second but the ecu should ignore that unless its excessive.
You need to do a code read before and after a starting session to diagnose this correctly or use a quality volt meter in the following way....

1) Measure between battery positive terminal and engine block whlist starting.
2) Measure between starter motor power input bolt positive and battery negative terminal whilst starting.

This way, you may be able to measure the voltage drop and see which cable or connection path may be giving you problems.

I personally would use an oscilloscope to do this to measure how long any drop actually lasts as a multimeter wont tell you that and it is impossible to see the true length with any type of digital meter !

 

cheers flux. i'll look into finding someone with the right toys.

best

steve

 

The problem is two-fold - Firstly finding someone who knows about TDCis is surprisingly difficult - one Ford dealer refused to look at my car, and the other diagnosed it incorrectly. I've also had three different diesel specialists state that they don't know what's wrong, and that they can't offer any further help.

Secondly - (without wishing to patronise you, as you know way more about this shit than I do) the fault codes rarely pinpoint the actual cause, but merely the symptom. Unfortunately, such is the complexity of the common rail system that there seems to be literally no way to correctly fix the 'limp home' mode without swapping parts over until a solution is found.

Also, rather bizarrely, it's very common to swap a suspected component and the car then runs perfectly for a couple of weeks, only for the original problem to reoccur.