On going 406 tickover issue

[lakemaligne]

Hi mjb, it's not the braking so much as the steering,like you said i have a couple of pumps left in the system,and i am slowing down as much as possible on the approach to a junction/roundabout. The bit i dont like is when the car stalls,the steering locks up solid instantly .

Funny thing is it is currently behaving itself and performing fine,so what ever it is has decided to work again,which is a shame because out of desperation i have booked it in next monday with the master tech at my local dealer,and i wanted it mis-behaving while he plugged in his laptop.

Somebody on this forum mentioned that when a coil pack goes,like mine did recently,it sometimes damages the ECU,particulary Sagem types. Problem
is i cannot remember at the moment what type mine has ,and my fault started way before the coil pack went.

I live in Rugby in the midlands. If you send me your phone number or email address ,praps we could arrange for me to call in sometime in the new year.

ps

what is a Tubby,and do you know off hand what the highest mileage currently stands at for a 2Ltr 16v petrol 406,just curious .

[mjb]

Somebody on this forum mentioned that when a coil pack goes,like mine did recently,it sometimes damages the ECU,particulary Sagem types. Problem is i cannot remember at the moment what type mine has ,and my fault started way before the coil pack went.

Interesting

what is a Tubby,and do you know off hand what the highest mileage currently stands at for a 2Ltr 16v petrol 406,just curious .

'Tubby' is the name we've given to the XU10J2TE engine - a very lazy but loveable 2 litre 8 valve turbocharged unit

I believe the current mileage record for a 16v is about 240,000 miles? Really, the petrol engines tend to out-live the cars as they're that cheap and disposable nowadays that owners get to the point where they decide a new vehicle is better value than a set of tyres, a few new brake pads and a good service...

[lakemaligne]

MJB, as the tickover on my 406 got really bad during this last cold snap recently,I decided to let the master tech at my local dealer take another look. I asked him to plug in his laptop before starting the car ,as this is when it revs up and down,to see if it showed anything up. He said all the parameters were spot on and it ticked over normally, typical !!! He did however reset all the adaptives as i had had the stepper motor out and tested it,and cleared the usual "irregular fuel distribution" fault code. He also notice that the battery was not performing well, and said that during cranking was reading only 9 volts. He said this could be causing the ecu to not initialise properly on start up sometimes and not set up all the parameters correctly ,which could cause the tickeover and stalling issue. This he said "may" be why this fault is intermittent

What do you think mjb ,could my battery be causing this,i might as well get a new battery as the old one is geting on for 7 years old and does crank the car slowly,but she always fires up instantly.

What amp hour rated battery should i go for ? I cannot find any info in my hand book concerning amp hour rating .

[lakemaligne]

Just to update you all,I decided to bite the bullet and have the ECU replaced.Before the guy replaced the ECU,he connected up his diagnostic gear and told me that the Oxygen sensor was "lazy " and needed replacing. After the ECU had been replaced , the fault light still came on and was still showing up on his diag gear as responding far too slowly. Having now had the ECU and O2 (lamda) sensor replaced ,all the previously mentioned symptoms still occur now and again,but the most persistant fault is the "stalling " issue if i engage neutral while rolling up to junctions,or if the engine is just idling. (Just in case it helps),but I have noticed that once i am in neutral and the revs are bombing downwards,if I blip the throttle quickly ,the revs pick up and then slowly glide down to the normal 950rpm and it idles smoohtly from then on !

I am wondering now about what mjb and Welly said about it possibly being related to the fuel rail pressure in some way,and i quote

"Given the fault (with the symptoms), I'd suggest one of the following (from cheapest to expensive):
1) Clogged fuel filter. Cheap and easy to replace
2) Shot fuel rail pressure regulator valve
3) Failed tank purge valve
4) Knackered fuel pump"

MJB,can your PP2000 measure the fuel rail pressure,and are there any tests i can carry out myself.

[mjb]

Just re-read the thread. I'm a spanner. I reckon the fault is with the speed sensor in the back of the gearbox (or diff). Does the speedo ever flinch or drop occasionally?

Reasoning is that when stationary, the idle speed is 650-900rpm depending on engine. When the car's in gear and moving along, the idle speed is about 1200rpm (poor man's 30mph cruise control = shove it in 4th and let it idle)

Now, the thing is, when you're engine braking - off the accelerator and driving along in gear above 1200rpm (which the ECU knows because it compares the engine RPM, road speed and throttle position), the ECU will cut the fuel to the injectors. If you're stationary and this condition occurs, it is because:

1. The TPS is saying you're not pushing the accelerator (correct)
AND
2. The crankshaft sensor is reporting the engine is running over 1200rpm (possibly correct)
AND
3. The speed sensor is reporting movement (incorrect. It only needs a few incorrect voltage spikes to cause this though)

When this happens and the RPM drops below 1200rpm (which it will because it's not getting any fuel and isn't being turned by the gearbox), it will chuck some more fuel in, which will raise the engine above 1200rpm triggering the cut-off again. This is why it could be having mad idles. If one time it doesn't respond quickly enough when deciding to put fuel in, the engine will stall.



As an aside from this, PP2000 does not report fuel pressure as it is not monitored by the ECU (at least on the petrol 406s I've seen)
The above list of causes I suggested don't match the symptoms as well as my speed sensor theory.

The speed sensor is best reached from underneath the car. It is on the driver's side of the gearbox just above where the driveshaft enters and probably has a fabric heat shield around the connector. IIRC it's held in by a 10mm screw or similar. You shouldn't need to dismantle anything else to be able to change it. New parts are expensive, so I'd recommend grabbing one from ebay or a local breakers yard. A seller called "Ade2211" on ebay should be able to sort you out for a fair price - he's a 406 coupé specialist breaker and a very nice chap.

Here it is on my V6 with the subframe and driveshafts removed.


With the gearbox removed from the car you can clearly see the sensor as the ivory coloured plastic bit on the left next to where the driveshaft goes in

[lakemaligne]

MJB,I have discovered something else regarding my tickover/stalling problem on my 406,and wanted to run it past you to see if my new findings effected your theory on my fault being caused by the"Vehicle speed Sensor" being faulty.With the engine ticking over normally at 950rpm,if I let the car roll backwards ,the tickover climbs up to about 1100rpm,then drops again once I stop the car rolling.I recently spoke to the guy who replaced my ECU about my cars tickover climbing if i let the car start to roll,and he said this was perfectly normal and was meant to happen.He said the engine revs are intentionally raised in order to maintain power for the power steering,braking and help smooth out gear changing,which i seem to remember now, some one else on this forum saying something similar. The funny thing is ,all through out the 15 years I have had this car,it hardly ever raised the tickover while rolling in neutral,which i reckon now backs up your theory MJB about an intermittent fault with the vehicle speed sensor after all.

Tomorrow I am going to get the car up on the ramps to see which type of speedometer drive it is ,a cable or transducer. Then I am going to get one and swop it out asap.I am guessing that it is the transducer type as there was no cable going into the back of the speedometer gauge when i took it apart to resolder the connections to stop the needle doing daft things,which worked by the way!

[lakemaligne]

I had the car up on the ramps yesterday,(hate that bit) and found the connector thanks to mjb's picture(thanks),and discovered the vehicle speed sensor connector was missing it's heat shield and was a bit dirty inside.So i cleaned it up and then experimented to see how difficult it was to remove the whole thing.I got the allen key headed bolt out and managed to wiggle the unit ,but stopped because i realised i had not got a new "O" ring in case I buggered the old one up getting it out. i have a couple of questions.
1.Do I need to renew the "O" ring and heat shield when i renew the unit.
2.I intend getting a new unit from Ebay(if any one reading this has a new one I could have ,let me know please),but does the fact that my speedo is behaving fine all the time mean that the vehicle speed sensor is not faulty,or could it still be causing my fault and not effect the speedo.

My car ran a treat on the way to work this morning by the way !

Thanks.

[lakemaligne]

Hello mjb, Just to let you know where I am up to on my car.
I have replaced the VSS and heat shield, and the car started fine, ran well, with no faltering or hesitating or stalling until i went round a roundabout with the car in neutral and the engine died. It started back up ok, but then started to rev up and down for 5 seconds , trying to die, but then settled down and idled ok. The car then hesitated and tried to die a few times on the way back home. So I reckon the VSS was not causing the fault ,do you agree?.
I have been thinking about the theory that my problem may be caused by lack of fuel pressure, especially as i keep getting the "Irregular fuel distribution" fault recorded by the ECU. I think that my engine may be stalling because the steering pump is sapping power from the engine ,and it stalls because the revs are not high enough to keep it going due to lack of fuel pressure? Do you agree?
I have pulled off the vacuum pipe going to the FPR/Valve and blocked of the pipe to see if the FPRV is the culprit. On the way to work yesterday morning , it didnt stall or hesitate ,but I did get the delayed jerk as I came on and off the throttle, and the revs remained high each time i coasted in neutral, and the revs only dropped down to 950rpm once the car had stopped moving. This morning the car was not jerking or ticking over high, but did hesitate and try to die a few times.
Now for the weird part . Since I pulled off the vacuum pipe , the fuel gauge started wavering up and down as i was driving along. The needle rose as i came off the throttle and dropped when i went back on the throttle, but the needle remained in the correct place if I revved the engine with it in neutral. I think this may be caused by the excess fuel being pumped back into the tank via the return pipe now that the FPRV is no longer shutting off the fuel.? Do you agree ?
If so why does it not waver all the time though.? This needle movement coincided with the high tickover while coasting and the jerking . On the way home however , still with pipe disconnected, there was no high tick over, or jerking and the fuel gauge behaved itself, in other words everything was perfect. Then later on that evening, with engine hot ,it started fine ,but faltered that badly that someone nearly rear ended me!
Strangely enough ,since removing the vacuum pipe ,I have not noticed the fault light come on. I really need some help with this , as I am near the point of driving it off beachy head!