P38A Phantom gearbox/alternator/EAS fault

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Wazzajnr said:
I'm wondering if you've got a dodgy ecu here. 64 as a decimal number is just too convenient when talking computers etc.
Computers only know on and off and 64 just happens to be one of an array of bits being "on" (1,2,4,8, 16,32,64 etc etc etc)
I'm just wondering if something withing the ecu is failing and occasionally it makes this bit stay on and throws it all over the place?
Not sure how you could find it apart from substitute ecu.
Click to expand...

Funny you should say that. 64rpm did feel a bit too convenient a number when thinking about computer systems.

Are you thinking Engine ECU or the BeCM?

Sandy.
 
alexmcrobbie said:
Funny you should say that. 64rpm did feel a bit too convenient a number when thinking about computer systems.

Are you thinking Engine ECU or the BeCM?

Sandy.
Click to expand...
Not sure to be honest! Problem is, it's not just one system that's faulting but it does seem to always be a system that takes an engine speed signal. Whether said signals are routed through the BECM or not I'm not sure.
Might be one @Rick-the-Pick or @martyuk may know.
Still think you'd be better off if you could do some checks with a nanocom to be honest.
 
Wazzajnr said:
Not sure to be honest! Problem is, it's not just one system that's faulting but it does seem to always be a system that takes an engine speed signal. Whether said signals are routed through the BECM or not I'm not sure.
Might be one @Rick-the-Pick or @martyuk may know.
Still think you'd be better off if you could do some checks with a nanocom to be honest.
Click to expand...

I'd agree that getting it checked over with Nanocom is probably the best thing to do at this point. Sadly being up here in Glasgow there aren't quite as many folk with the kit to help me out haha.

Yeah to the best of my knowledge, the Crank Position Sensor data goes to the BeCM via the engine ECU and is then fed to other systems like the instrument cluster.
 
alexmcrobbie said:
I'd agree that getting it checked over with Nanocom is probably the best thing to do at this point. Sadly being up here in Glasgow there aren't quite as many folk with the kit to help me out haha.

Yeah to the best of my knowledge, the Crank Position Sensor data goes to the BeCM via the engine ECU and is then fed to other systems like the instrument cluster.
Click to expand...
There are some members in Scotland with nanocom I think but not sure where.
Maybe it's time to invest in one.
They really are handy. I wouldn't be without mine (although my diag port fuse is blown at the moment so it doesn't work!)
 
alexmcrobbie said:
Strangely, there's a healthy 14.2-14.3V at the battery at idle and 14.4V at the battery at 2k RPM which would suggest that the alternator and wiring (to the battery at least) are ok.

One thing I did forget to mention is that when the car is at idle and I flash the high beams, turn the steering or put the car in gear there is a slight (but noticeable) blip from the engine where the revs drop by at least one mark on the instrument binnacle before returning to normal.
Click to expand...

Do you still get over 14v with all the lights/heater on etc? Flashing high beams shouldn't affect the engine but steering or putting in gear (an auto anyway) would put a load onto the engine
 
Kev12 said:
Do you still get over 14v with all the lights/heater on etc? Flashing high beams shouldn't affect the engine but steering or putting in gear (an auto anyway) would put a load onto the engine
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I haven’t checked the voltage under full electrical load yet but will do that tomorrow and report back
 
Wazzajnr said:
There are some members in Scotland with nanocom I think but not sure where.
Maybe it's time to invest in one.
They really are handy. I wouldn't be without mine (although my diag port fuse is blown at the moment so it doesn't work!)
Click to expand...
I’d quite like to buy one, but probably can’t justify it to my better half for another month seeing as the Lynx was purchased fairly recently (along with a tonne of braking/air suspension components). I could slip it all under the radar a lot easier if he wasn’t into cars as well...;)
 
The tacho is driven by engine speed signals from ECM, in this case three pulses per RPM. That engine speed signal is then sent from BECM to EAS, Autobox and ABS etc for use by the various ECUs. If the tacho is not working the speed signal is being lost. Could take some finding. Connections to BECM maybe worth a look at.
 
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wammers said:
The tacho is driven by engine speed signals from ECM, in this case three pulses per RPM. That engine speed signal is then sent from BECM to EAS, Autobox and ABS etc for use by the various ECUs. If the tacho is not working the speed signal is being lost. Could take some finding. Connections to BECM maybe worth a look at.
Click to expand...

I was thinking along the same lines (perhaps a wire with broken insulation contacting the body or similar).

Have spent a good few hours going over all the connections and earths in the engine bay again today. Everything looked good and all the grounds were clean and tight but have used contact cleaner where there was any doubt at all.

Also had the carpet up in the driver’s footwell to check all the cabling running to the BeCM from the engine bay. It all looks good and the connector pins into the BeCM itself are clean/dry.

Feeling like I’m chasing my tail a bit now with this one haha.

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Also had the crank position sensor connector off. It all looks shiny and clean on the contacts so starting to consider ruling that out as a possible cause, but may just buy and fit a new sensor regardless.
 
So to update. Today I’ve had the cover off the fuse box and removed the fuses/relays. All looks incredibly clean in there with no charring anywhere. All contacts look virtually brand new. Can probably rule out the fuse box as a culprit at this point.

Sandy.

5DC8D3B7-3433-4EF4-A697-E5777E68847D.jpeg
 
Have also checked the harness connector under the coolant expansion tank as corrosion here apparently can lead to the symptoms my car has been suffering. But again, all clean.

Have cleaned everything with contact cleaner as I go along just to be 100% sure that it’s not a bad connection or Earth. Took the car for a drive, problem persists.

Rimmer Bros are overnighting a crankshaft position sensor so I will be fitting that tomorrow. This should allow me to see if that clears the strange “64rpm” observed engine speed reading.

5A1969F9-D1D2-4E5A-8128-BBD35BF1B846.jpeg
CA1867AE-2CE0-4CBA-96A5-0D1304B3D223.jpeg
 
Wazzajnr said:
Not sure to be honest! Problem is, it's not just one system that's faulting but it does seem to always be a system that takes an engine speed signal. Whether said signals are routed through the BECM or not I'm not sure.
Might be one @Rick-the-Pick or @martyuk may know.
Still think you'd be better off if you could do some checks with a nanocom to be honest.
Click to expand...

Sorry, only just seen the tag in this now..

I doubt that it's the BECM at this stage - mostly because if your engine speed is showing 64 in the engine ECU aswell as autobox ECU, then chances are it's being derived from the engine ECU.

Crank sensor, or No 4 injector wiring could be culprits as to engine speed, but either of them failing shouldn't cause the dash to drop out or other spurious faults. I had a diesel where the No 4 injector wiring was faulty and the vehicle would still start and the rev counter would work. It was gutless and didn't like revving, but it didn't lose the tacho.

It can't hurt to try swapping the crank sensor - they are probably the most important one - so even if it doesn't fix it, it's well worth having replaced it. They are a hall effect sensor, and even if they look ok, can get a break internally.. (Quite known for it on the petrol models where they won't start when hot, but OK when cooler ).

My first thought on this, if it's not the alternator is to check the exciter wire from the alternator to the BECM. This tells the BECM that the Alternator is running and putting out charge voltage. If this drops out, then I have heard of various strange things happening.

In the alternator, it's a Brown/Yellow wire, and goes through pin 25 of the connector under the coolant tank (that looks good on your one).. to pin 15 of C1289 on the BECM (20 way Green connector on the front edge of the BECM).

I have seen a couple of times that the ring terminal can corrode where the wiring is crimped into it (including on my own P38), and if this is the case, it could be causing an intermittent connection. I'm not sure what the BECM's response would be if it thinks there's no alternator charge when the vehicle is moving, but Alternator Fault (and probably gearbox fault) are what I'd expect to see.

If that wire checks out, then as someone else mentioned - I'd be trying to check the alternator output carefully when the vehicle is running, as to me, if there were an engine issue with something like the No4 injector or crank sensor, then I would expect there to be engine performance issues aswell.

Hope this helps,
Marty
 
martyuk said:
Sorry, only just seen the tag in this now..

I doubt that it's the BECM at this stage - mostly because if your engine speed is showing 64 in the engine ECU aswell as autobox ECU, then chances are it's being derived from the engine ECU.

Crank sensor, or No 4 injector wiring could be culprits as to engine speed, but either of them failing shouldn't cause the dash to drop out or other spurious faults. I had a diesel where the No 4 injector wiring was faulty and the vehicle would still start and the rev counter would work. It was gutless and didn't like revving, but it didn't lose the tacho.

It can't hurt to try swapping the crank sensor - they are probably the most important one - so even if it doesn't fix it, it's well worth having replaced it. They are a hall effect sensor, and even if they look ok, can get a break internally.. (Quite known for it on the petrol models where they won't start when hot, but OK when cooler ).

My first thought on this, if it's not the alternator is to check the exciter wire from the alternator to the BECM. This tells the BECM that the Alternator is running and putting out charge voltage. If this drops out, then I have heard of various strange things happening.

In the alternator, it's a Brown/Yellow wire, and goes through pin 25 of the connector under the coolant tank (that looks good on your one).. to pin 15 of C1289 on the BECM (20 way Green connector on the front edge of the BECM).

I have seen a couple of times that the ring terminal can corrode where the wiring is crimped into it (including on my own P38), and if this is the case, it could be causing an intermittent connection. I'm not sure what the BECM's response would be if it thinks there's no alternator charge when the vehicle is moving, but Alternator Fault (and probably gearbox fault) are what I'd expect to see.

If that wire checks out, then as someone else mentioned - I'd be trying to check the alternator output carefully when the vehicle is running, as to me, if there were an engine issue with something like the No4 injector or crank sensor, then I would expect there to be engine performance issues aswell.

Hope this helps,
Marty
Click to expand...

Hi Marty,

Thank you SO much for your advice.

I replaced the crank position sensor today and took the car for a run. The fault didn’t present itself and after clearing the existing fault codes everything seemed fine. The “ENGINE SPEED HIGH/OUT OF RANGE” and “SIGNAL FAILURE” faults from the gearbox ECU don’t seem to have came back either, but time will tell if the new CPS has fixed the problem.

I’m fitting a new, and even beefier battery tonight (over 100Ah and over 1000cca) just to be absolutely positive that this isn’t what’s causing the issue. Will perhaps put a new alternator in next week to rule that out too.

I’ve checked out as many connections as possible (fuse box, connector plug under coolant tank, all the wiring from the engine bay back to the BeCM (including checking and cleaning BeCM connectors with contact cleaner)). Will check the alternator exciter wire you’ve mentioned as well to rule this out.

Also, picked up a couple of decent little 270lumen LED lights off amazon which have really made it easier to work after the early winter sunsets.

9D44817B-12F4-4326-A980-9A34F9E050C2.jpeg



Cheers,
Sandy
 
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