4 HP18 auto box prob

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Deanxm
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4 HP18 auto box prob

Post by Deanxm »

Hi gents

The titled autobox gave some trouble this evening although it may have been engine related i doubt it.
After coming down the dual carrageway at about 60 ish i came off on the slipway and upto the traffic lights where i stopped........and the engine nearly stalled, the warning lights all flashed up briefly then it idled away smoothly again, it feels like as i pulled up it wasa manual car and i had forgoten to depress the clutch.
Now i have recently replaced the valveblock to releave my harsh gearchanges due to a broken spring which worked a treat, this problem was evident on the old block though, although never as bad.
All the way home after this evenings incident though it was faultless again so im thinking of blaming the lockup clutch in the torque converter.
Im thinking it locked on the dual then stayed locked as i reduced speed and came to a stop thus nearly stalling the engine, the trouble is im unsure where to start looking because im not sure how it works.
Is it controlled by the governor directly ie without passing fluid via the valveblock although if it was the governor i would expect to have gear change problems which i dont.
It would be very helpfull if someone could explain the operation of the lockup mech so i can think more about what could be the problem and save me having to strip my spare box just yet in search of answers

Thanks
D
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Post by citroenxm »

Dean,

Yur probably the only fella that knows the HP 18 so well, after dooing yur own strip down and repair which I admire greatly!!

As for yur quest, I cant answer that for you.. :-(


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Post by Deanxm »

Hi Paul

Although i did strip it a bit, i had to stop before i went all Citrojim on it due to other projects and stuff :lol:
thanks anyway, looks like i may have to get the spare box stripped after all in a bid to find out exactly how it works.
CITROJIM!!!!! i know your very busy but did you cut open your spare Torque converter and see exactly how the lock iup clutch itself works?

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Post by CitroJim »

Hi Dean,

I've not yet opened my spare TC as I want to make sure what I think is the best of the two is in fact a good'un before I take an anagle grinder to the other one :lol:

The clutch will be very similar to the 4HP20 one and the friction works on the face of the TC nearest the flex-plate (i.e. the pump half). When disengaged, the TC is supplied with pressurised oil from an orifice at the extreme front of the input shaft. This has the effect of forcably keeping the friction away from the TC body. Oil exits the TC by flowing along the gap between the input shaft and concentric stator sprag shaft. To engage the clutch, the direction of oil flow is reversed by the valve block so that incoming oil pressure forces the friction against the body. Oil exits via the orifice on the end of the input shaft.

Since you've changed the valve block it's hard to see what else could cause this fault except for a problem within the TC itself which prevents the clutch from immediately releasing.

I'd also suspect the engine itself may be stumbling after a long, fast run rather than it being a TC problem par-se. I wonder if the idle control valve is a bit sticky and is not properly setting the idle speed fopr a split-second after a long run? The symptoms would be very similar. Also, running down from speed, the fuel injection will be shut off and will not resume until the engine is sensed to be no longer on the over-run and needs to be fuelled again. The fuel pump could possibly be a bit lazy in firing up and maintaining fuel system pressure. Yet another possibilty is that road speed information is not correctly reaching the engine ECU so it remains blissfully unaware of when the engine is on the over-run and thus "forgets" to reinstate fuelling for idle.

As a test, can you knock the box into neutral as you come down from speed and see if the same fault is ever apparant?

It's an interesting one Dean :D
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Post by Deanxm »

It's an interesting one Dean Very Happy
Very helpful Sir, thanks.
If the clutch is fed fluid via the valveblock then that cant be the problem, the spare wasnt duff i drove on it in the car it came from sooo, either a mechanical fault with the T/C itself then which would be hard to diagnose or a management problem, the thing is you could feel the car forcing against the brakes if you see what i mean, and when it does it is fairly juddery coming to a stop although it hasnt done it so far today.
Cant see its the idle valve, i dont get any hunting or general idle stability problems apart from the fact it sometimes runns a little wooly, mostly after a hot start.............what about the lambda sensor? might not be switching properly causing this problem? and the car sometimes throws up a labda control fault on my cr***y gunsons fault reader dispite 4 new sensors.
I feel an investigation coming on, good thing i have the week off 8)

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Post by DickieG »

If you think that there's an engine management problem take a close look at the MAP sensor as they are prone to getting "gunged up", in particular if the sensor is mounted remotely blow through the connecting hose to ensure it has a clear flow of air, any less and it will cause all manner of running problems to the extent that the Lambda sensor may be triggering a fault as it cannot keep up with the exhaust gas mixture emitting from the engine, thereby triggering a fault code.
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Post by xantia_v6 »

A problem I have seen on other cars is a fault in the fuel cut-off detection such that the fuel is not cut-off on the over-run. This is exacerbated if the engine also has an over-run air valve that stops the manifold pressure getting too low on the over-run (purpose to stop oil being sucked up past the rings).

With this combination, you can end up with the engine producing significant power, fighting the brakes, which with a 285BHP Jag v12, you tend to notice... One of my Jags left the factory in that condition (due to the engine being built to the wrong spec), and was a real handful to drive, particularly in the wet.
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Post by Deanxm »

Hi gents

The MAP sensor on these are mounted in the management ecu, the hose is clear to it though and i swapped with another ecu to be sure.
Just trying to cure this wooly running now as what i thouhgt was the lockup clutch happens so rarely its impossible to trace.
How does the ECU know when to cut the fuel pump on over run? is it via info sent from the map sensor? or from the lambda sensor or both?

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Post by xantia_v6 »

The fuel cut-off just cuts the signal to the injectors, the pump keeps running. It will be triggered by a throttle position potentiometer, which is a likely cause of failure. It will also use engine speed and MAP signals which are less likely to be the problem here (without causing other symtoms). The logic itself is all deep inside the ECU.

p.s. also check that the throttle is cleanly returning to the idle position.
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Post by Deanxm »

Ok ive just been out for a play, i double checked the map hose, all clear, i swapped the idle control valve for a spare but it seems the spare is dead, it just stays closed and she would only run if i held idle manualy with the throttle but the orange light of death was flashing away madly on the dash, read the fault codes but none had been recorded so i cleared it anyway.
Cleaned the old idle valve out and added some light oil, refitted and it fired up sweatly and idled as normal, no hunting and it returns to idle smoothly but misses/stumples for a fraction of a second when the throttle is snapped open again.
I took it for a run and it felt smooth and progresive maybe more so than usual, just as i got back home, coming to a stop and it sort of shudders as if its still trying to pull while im braking, no stalling but it just doesnt come to a stop smoothly.
I forgot to knock it into N as i stopped, i will have to try that tomorrow.

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Post by lexi »

Who makes the box in these models?
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Post by CitroJim »

lexi wrote:Who makes the box in these models?
ZF make the 4HPXX 'boxes whilst the AL4 'box fitted to late Xantias is made by Siemens.

They're basically German but made under licence in France I believe.
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Post by Deanxm »

Isnt ZF one of the many arms of Bosch too?
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Post by CitroJim »

I'd not be suprised at all Dean..

I have a vague thought that Siemens might be related to Bosch too, at least as far as autoboxes are concerned...
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Post by lexi »

Yes . As I thought. There aren`t really that many players in the auto box market. ZF in Europe and Jatco in Japan. Borg Warner are under a new name I think. Nissan own Jatco and Toyota own the other big Jap player who`s name I forget .These are fitted in Landcruisers. One of the few manufacturers who make their own auto boxes from design to finish are Honda.
Of course the Americans have a ream of boxes that we don`t see much of.
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