3.9EFi revs dropping too low when drive & reverse selected

doesnt drop the revs when tbox in neutral:

but does drop the revs in hi or low would indicate to me clutch or clutches dragging in gear box

does this mean a new tbox? or is the clutch repairable? amasingly this never occourred to my garage that had the car for a week!!

transfer box is okay ,gear boxes are often very repairable ,you cant say till its opened up its not allways usual suspect, would be worth removing sump to see if any obvious clues

cheers mate, i was planning on an oil change anyway as i have no idea if it has ever had one in 90,000 miles. incidently the drive is lovely, gear changes smooth and kick down perfect. the fault occours stationary or waiting in D for a while maybe 2-3 mins or more.

check sump and oil carefully and let us know

Ianski said:

are we taking unstable idle or revs droping when put in gear at ide (loading the engine) the engine needs to know its in gear to compenste the load:beer2::beer2:

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Unstable idle mainly.


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Gear inhibitor switch, i'd put 20p on it being that!

When you put it in D or R the inhibitor switch tells the ecu that the engine is coming under more load and that it should up the revs to keep it from stalling under the extra load of it being in gear. If this isn't working right it could cause the revs to drop too low or too stall.

i have found a diagram showing this switch located on the gearbox, is there any testing i.e continuity etc to try before I replace said item. if it is that i'll buy you a pint or two....

if engine dont turn over in p or n switch is faulty it splits ingnition feed to starter unless in p or n ,inside the box on slector shaft is a cam wheel that presses plunger in or not depending on whats selected ,also puts reverse lights on

engine starts fine in p and n. the issue is only when idling then selecting d or r. just reading up on the switch and it seems this switch inhibits starting the engine in gear etc and reverse lights. I dont have this issue with starting. At 100 squid for a new switch, Id like to be sure!!!!

The switch does stop it from being started in any gear apart from N or P but i spoke to mark adams about it awhile ago and he said they can still work but give a poor signal to the ecu. Might be worth searching for a 2nd one if you can't find any other problems

cant see how switch could give poor signal ,it either works well enough for starter and reverse lights or not ,i wasnt aware any signal was taken for ecu ,there is signal from speedo transducer to let ecu know vehicles moving or not ,but system works without that input

jamesmartin said:

cant see how switch could give poor signal ,it either works well enough for starter and reverse lights or not ,i wasnt aware any signal was taken for ecu ,there is signal from speedo transducer to let ecu know vehicles moving or not ,but system works without that input

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On the p5 efi I cut a wise so it thought it was in gear-it previously suffered stall problem

Ecu orange and white wire if manual then to earth with 510 ohm resistor otherwise cut it will think in drive from memory.on phone so check diagram

Also make sure service adjustments timing and if non cat co adjusted

I got told the exact same info about earthing via a 510ohm resistor too. wire can be found at the white/clear multi plug under the drivers side dash by the pedals. might be worth just trying to cut the wire so it can be rejoined after.

Not much of an update but gearbox oil, AFM,TPS all fine, stepper motor fine. Really stuck on this one. So I'm gonna buy ECUmate

Ecumate Ltd

And see what happens, if it can get me any closer to solving this bloody annoying fault/quirk. Anyone used one?

I've been messing with my V8 for a few weeks now, also has a simliar problem but im on LPG..... So far as I have a (or had) a complete car in spares as a donor that was a good runner, I have swapped out stepper motor,AFM,Thermo sensors, bought a complete Brand New Plenum chamber with all new butterfly mech on, that actually made a nice difference when I rebuilt all that lot and the old plenum was minging inside. However this idle problem remains except its not actually an idle problem really.... I start the car on petrol, blip the throttle and it switches to gas, I then have a nice solid idle of around 800-900rpm and then I select D or R and it drops to around 550-600rpm all OK its nice and solid and smooth. Then as im driving as I let off the throttle to roll up to a junction or a set of lights the rev counter goes right down to zero and the motor cuts out. It will start again no probs but its a pain as I have to start on Petrol and the fuel pump is currently on a manual switch that I have to engage to start up, blip the throttle then switch off again!
Anyone got any ideas on this one?
Cheers

PS Timing is correct for gas and I have not done the T-box oil, car has a genuine 87K on the clock.

dirtydiscov8 said:

I got told the exact same info about earthing via a 510ohm resistor too. wire can be found at the white/clear multi plug under the drivers side dash by the pedals. might be worth just trying to cut the wire so it can be rejoined after.

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Ok got ecumate plugged in and no fault codes, everything is running sweet.
Until I put it in gear, or staright after cranking, it still bubbles around 200-300 revs before dying. Recovers if I blip the go pedal then steps down to normal revs. (I have an Auto zf gearbox) So having had a look at your suggestions for the 510 ohm on pin 34 orange/black this will tell the ecu its a manual gearbox. How will this affect an auto? will it start in gear? will it affect changing up/down? just wanna be sure before I go cutting stuff up!! and go to Maplins in the AM..

ok another bloody update before i torch the thing........
checked inhibitor switch at pin 34 ECU 0v in N/P and 5v in D/R exactly as it should, then went to maplins, 26p 510 ohm resistor in orange/black wire. ecumate correctly showing the resistor showing as manual gearbox according to ECU 2.5v across resistor.

Same issue when selecting D or R from neutral revs still dropping so reconnected wire Orange and Black.

So, inhibitor switch ok, stepper motor ok, soon it'll be for spares/repair at this rate!! shame cos its in bloody good nick too.

ECUmate, says all systems ok, no faults recorded. also tried a pals ECU 14CUX, started exactly as mine original one did, so ECU ok too!!!