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Discussion Starter #1
Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

I have a number of issues with the old girl, the latest of which is GEARBOX FAULT, possibly related to a missfire but maybe battery/alternator (yeah I've done the electrical sticky). I've changed battery leads as they were causing a bit of a Volts drop (750mV), cleaned grounds, and I know I have a diode away in the alternator. It's charging ok, but has AC ripple so a new one arrives next week.

I mistakenly did a write of settings to the GEMS from the Nanocom before I took note of the adaptive air-flow rate, but I don't think this is causing my slight engine miss. I've set the AMFR to 3.75 for now as I found someone else that had that somewhere on the interwebs - happy to take advice in lieu of a CO meter check as to what others have as their Air flow rate. My 95 is a cat free model.

I have changed plugs, filter, got new leads in the post with the alternator and will take off the coil pack and have a good look at that tomorrow. I've cleaned the throttle body, IACV, TPS, MASF, (there was a lot of crap in the plenum) and reset adaptive settings. It's idling nice now but has still has a slight consistent miss as though its an HT lead. I have fully charged the battery. I may also have a slight crack in an exhaust manifold but can't hear a squeak, or feel anything with the viscous fan running.

The problem is this (with a fully charged battery and 14.2v alternator charging): ignition on, no gearbox fault, can press sport and get the light and dash message. start car, car idles, a few seconds later "GEARBOX FAULT".

The nanocom only lists a fault for the Gearbox ECU - ENGINE TORQUE FAULT. Looking at the reference manuals it looks like the miss may be causing the ECU to send the gearbox an under torque signal. Is there any more info on this fault from the Nanocom such as a P code - the reference manual has a few guides, but the code is in english text only.
 

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Discussion Starter #2
Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

New alternator, new HT leads, running a bit better, no gearbox fault message and no alternator fault message - however the red battery light flashes with ignition on. When I take the car on a high speed run I can get the gearbox fault again.

Just had battery tested and its all good, but the alternator is only putting out 14.1v between its post and the case. Suspect I've still got a dodgy earth somewhere....
 

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Discussion Starter #3
Blinking British Leyland cars.....!!!!

Ok, did the sticky again, battery after 30secs full load would return to 14.26v so new battery installed. All grounds cleaned as per sticky and the bulletin.

Missfire still there, more noticeable under load. But it’s not always there. The miss is causing the gearbox torque fault, again not always there. Head gasket checks ok. Plugs are a bit lean, exhaust is grey. Fuel consumption is good. Red battery lights blinks occasionally when ignition on, light is always off when car running. And now “Rosie”, named after the ac/dc song, has decided to go a bit incontinent on the driveway from her front seal.

Any pointers on the missfire? Camshaft sensor? I have no faults on the nano to help me.
 

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Discussion Starter #4
Checking air idle values again and the Air Intake Temperature is much lower than it should be. Reading 8C when the ambient is 19C today. My GEMS literature says above 55C it’s used to retard ignition-but couldl an incorrect low reading cause issues such as a ‘miss’? Holding a piece of cloth over the tailpipe shows a steady beat until a slight drop in pressure immediately followed by a larger puff than the steady stream.

I have a compression tester in the post to check there isn’t a gasket leak between two cylinders, but could this be low reading IAT?
 

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Discussion Starter #5
And when I disconnect the sensor the system should “default to a nominal value to nominal operating conditions” but the nanocom reads -61C. Perth is certainly not minus 61C.......anyone anyone bueller?
 

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Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

IAT always seems to read a bit low but as it only does anything when the temperature is very hot, then reading low isn't important. Any NTC sensor will read very low (-20 or -40 C are the common ones) when open circuit so it is correct. You say you've fitted new plugs, what did you fit?
 

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Here are this mornings readings post last nights adaptive reset - note this is a 95 pre-cat.

Fuelling bank 1&2 the same. OPEN, ltft% -160, stft%0, adaptive fmfr 0, fuel level 0.9 BP 98, fuel temp 21.72 a bit of a warm reading I think as ambient is about

Air idle. Throttle pos 0.68, adaptive air 0.0, current airflow 25.19, intake air temp -3 (reading low), airflow sensor 1.47v, secondary air 4, curr line run position 20, lt adapt idle 15, st adaptive idle 26, IACV 46, gearbox retard 17.2, calculated load 27.8.

Other. coolant 90C, battery 14.11, injection timing adv 15.0

Apart from the intake air temp seen some notes saying it may affect injector pulse length looks ok to me...
 

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Discussion Starter #9
Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

Correcting the iphone mistooks - BP 98 fuel, ambient is about 8-9 degrees C, but IAC is still below zero at -3.

Some say IAT has no effect unless its above 55C then it retards ignitions, but seen others say its used to (a) adjust injection pulse length or (b) used in conjunction with the MAF to calculate air flow. My plugs show a lean mix. When unplugged the sensor read -61 and the car registered the correct error code.
 

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Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

This may not be your answer but whenever my RR is acting weird I reset adaptive values with the Nano and it seems to work wonders.
Then I will troubleshoot stuff. I think everyone should do this is put rubber hose around all the wires under the fusebox as I found wires wearing thru when I changed mine out
Good Luck.
 

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Discussion Starter #11
Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

Thanks for the reply - the car has had a replacement fuse box and the transmission connector from the harness near the back of the head has been replaced at some stage with a deutsch connector - I'll go checking there too. I've found a Jag description of a similar gearbox issue attached and that suggests harness/connector or ECM fault (http://www.jaguarclub.sk/service/electrical.pdf P1781). The IAT value may be harness resistance too I guess.

So the plan is to

(1) check the voltage and ground for the IAT from the ECM (wanting the +5v), check the ohm readings from the IAT are in range, clean the IAT and connections
(2) clean the MAF
(3) check for leaks of the evap purge valve connection (haven't checked this yet)
(4) check/clean the underside connections to the fusebox
(5) check/clean the ECU connection
(6) check/clean the injectors
(7) check engine compression between cylinders
(8 ) check fuel rail pressure
 

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Discussion Starter #12
1, 2 & 3 done

5.01/5.02v to IAT. 5.05v to engine earth. 0.03v difference between ecm earth and intake manifold. IAT and MAF cleaned and operating as expected.

The sound is a ‘pop’ as though there’s combustion with an open valve or unspent fuel hitting the cat.
 

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Discussion Starter #13
Ok I think I’ve fixed it....
I found the red ecm connector had a bit of oil inside as though it’d been capillaried up the harness. Cleaned with the maf cleaner I had and an instant improvement and no gearbox fault. Did the idle set up procedure so my stepper was around 22 when hot and the idle is stable, the chuff is gone and no faults. Still a little rough so I used a can of nulon upper intake cleaner and gave the old girl a fangio tune. Better still.

I’ll monitor and update this thread if anything fixes the roughness. To celebrate and show me she’s still boss and hard to get, the old girl blew the 5A fuse 33 to the odb port. Gotta love these cars.
 

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Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

IK read a couple of times your charge voltage, my charge voltage is about 13.9, and for some reason I have no issues, so I don't think your charging is causing problems
 

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Discussion Starter #15
Gearbox fault reappeared - traced back to poor connection on YO pin 5 on c551 throttle angle signal a pwm signal between ecm and tcu. Repaired connection and all good.
 

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Discussion Starter #16
And the chuff is fixed too. Coil pack.

Running like a Bentley now. Smooth engine and imperceptible gear changes. The coils were the original 1995 and show no outward signs of problems, plugs looked good too with all pretty much the same appearance.
 

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Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

Hi there any chance you could deciefer the abbrevations on your post #15 as I have gearbox fault coming up as well & yes I need to get rave.. Thanks Jeff
 

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Discussion Starter #19
Re: Nanocom "engine torque fault" on 1995 Auto 4.6 Gearbox

Apologies - 'traced back to poor connection on YO pin 5 on c551 throttle angle signal a pwm signal between ecm and tcu.

YO Yellow Orange wire pin 5 on Connector C551 - this is the square-ish connector at the back of the right hand cylinder head around the crankshaft sensor. It sends the throttle angle from the engine control unit to the transmission control unit via pin 5. This signal is Pulse Wave Modulated i.e. it is a pulsed signal not a fixed voltage. I had a poor electrical connection on this pin. It sends several other signals.

 
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