Noise in gearbox area and strange gear changing

[130camper]

1998 P38 4.6 litre had it 6 months been going good. New to P38 ownership.


Any body got an ideas of where I could look for the cause of a loud whining noise that I think is from the gearbox area and strange gear shifting that has started?

Driving back home doing 90/100 km/h flat road, I heard whining noise a bit like a noise associated with
accessory belt. It only did it when moving the accelerator down, back off no noise.
Didn’t do it when stationary at home, but next day I took the belt off, checked all the pulleys for play and free wheeling, no problem so replaced belt.


Couple of days later took car out, noise now much louder again under acceleration. Got out of town and floored the accelerator, pick up very good along with the not so good increasing noise.
With window down noise appears to be just underneath, not coming from the front.


Now seems NOT to change up a gear, or two, just stays in a lower gears, a lot of loud whining.

Pitch varies with speed. Floor the accelerator and it seems to kick down and go to what I think must be engine revs limiter, gearbox will only change up if the accelerator is released and then goes up, I think, two gears, revs drop down but noise still there.


Sport mode is not pushed and no light is visible. I have used sport mode some times and it was working okay.

When I purchased it I changed all the oils and filters.
The auto box was not changing smoothly some times, but after draining it for a few days, I got 8 litres out and fresh oil and new filter in the box and smooth shifts again.

Thanks


Andrew

[Scouse]

If it appears to be underneath, the first thing I'd be checking is the condition of the flex plate. I can't see how it would really affect the gear change but it has been known to produce all sorts of strange noises when it's on it's way out.
The crank sensor uses the flex plate for it's signal so if something is amiss, then it could just be sending strange signals to the auto/engine which might affect your changes.
There's an inspection cover that's behind the sump. Once that's off, you can see the reluctor teeth for the CPS. Look for bent/missing teeth or the whole ring loose on it's rivets. Check the whole plate for cracks/rust stains, well, as much as you can.

[130camper]

Thank you Scouse.

I have seen the cover that I think you are referring to, so hopefully at the weekend I will remove it and see if I can see anything that looks out of place.

Andrew

[130camper]

Took the plate off at the weekend. Chalk marked what was visible, started then stopped motor several times until I had seen all the way round.

To a home mechanic that has never owned an automatic gearbox vehicle it all looked okay to me. Area was clean, no rust marks, nothing loose, "U" shaped pieces looked good no sign of any damage to them.

Engine starts very easily every time and runs well on idle and all through the revs range.

If car is driven only using light pressure on accelerator there is no noise, gear changes are good through all 4 gears.

Press the accelerator and the noise starts harder pressed louder the noise. Press accelerator down doing about 80 km for gearbox kick down and it operates. Hold down and revs go up until limited, keep held down max speed 100km. Let accelerator off loud noise stops and I think the box goes up 2 gears.

Will now see if I can find somebody I can trust and knows auto boxes to drive it and see what opinion I get from them.

Thanks
Andrew

[130camper]

I finally got time to get a second person involved and one with a hoist. Yes he agreed the noise sounded to be was just under in the area of the maybe the bell housing. Yes it gave a varying pitch related to speed. On the hoist I was to increase the revs considerably source of noise was easily found by the second person.

A very small jet of exhaust gas from between manifold and tail pipe flanges joint drivers side.

Disassembly when cool showed where gas was passing the deformed metal sheet gasket making it act as a reed thus the very varied sounds.

The heads had been taken off the engine and replaced just before I purchased the car, the guess was that the old sheet metal gaskets had been put back on and a problem with 2 of the 3 studs in the manifold had been bogged up and had loosened off.

The problem of the gearbox not shifting beyond 2 under hard kick down acceleration has improved after contact cleaner was sprayed onto the contacts in the plug socket of the throttle position sensor.
It still gives the impression it is sport mode, but button and light are not on, changes are okay.
Driven more sedately the gearbox changes are very good.

So totally usable again, but will probably, as time allows, try and follow up on the different kick down effect.

Andrew