Hi guys,
had a very peculiar problem the other day with the XJS I had starting issues with a couple weeks ago.
I had been fitting a new stereo and CD changer so was parked on my driveway a few days. I had run the car a few times to check the cooling system had been purged properly (the elec fan seems to cut in awfully early but spot readings with a pyrometer seem fine - I'll keep that one for another day!) so maybe run for 30-45 mins in total.
Each time from cold start (ambient 18C), the engine would run for a 3-4 mins and the the idle would suddenly increase to 1000RPM and stay there. I had previously repaired the extra air valve so was sure this was ok. Removed it and checked again and its fine.

So I wanted to move the car inside my garage, got in, started up, selected "D" and let off the P brake and the car rolled backward, wouldn't move at all in any selector position including "R", but would hold in "P"!!??!!
I thought about it for a while, then bought some Dexron II fluid and topped up the ATF about 100cc at a time and testing out each time. Being aware the car is on a slight slope I disregarded what the dipstick was showing. After putting in about 1 litre the drive engaged so I slowly inched the car into the garage.
Checking the dipstick on the level its way above the "cold" MAX mark. I haven't tried driving it yet - I wanted to ask you guys if you have experience of this before?

The car is an 82 5.3 HE with a GM400 gearbox.
Would the RPM increase be the torque converter emptying of fluid on the slight incline perhaps or just a coincidence? Given I am in N.E Scotland, inclines, or braes as we call them go with the territory!

Would it be safe enough the test drive with extra fluid in the gearbox?

sorry about the long post!

 

My first best guess is that the o/ring on the trans filter has split (old age does that), and the pump is sucking air, as it can. The torque convertor cannot fill with oil, so the trans cannot build up operating pressure, so the car stays put (level ground scenario), or rolls down the incline (Scottish scenario).

The increase in fluid has "closed the gap", as we say.

The "overfill", although not recommended, will do NO harm. The trans will need to be at least 5ltrs above that full mark before the whizzy bits inside actually make contact with that oil.

My advice would be to add a trans pan drop, new filter, o/ring and fluid to the "Bucket list". When in bits, check the plastic suction spout that the said o/ring fits onto, as some report them cracking, bugga.

My HE runs about 750ml above full, and just does. When on the full mark, by the book, blah, blah, blah, it appears sluggish with the changes, dunno. The other V12 runs 1ltr down, coz it leaks if I fill it properly, but at 1ltr down never drops any further, again, it works.

Not sure on the emissions junk Scotland gets, but that idle hunting is possibly the TPS out of range.

 

Grant,
reckon you are right on this one, tried moving the car again today and no drive again which probably means it is sucking air. No point pouring more fluid in - I'll have to give up on this one as I don't have the kit to get under the car and carry out the pan drop etc. I couldn't get it onto the ramps for a start!!
I'll hunt for a good garage locally that could do this for the owner.

TPS switch repairable or is it better to replace it?

thanks again for the help

 

Bugga,

Tps is usually better to replace. Some have tried to repair, most have failed, me included.

There is an update, and that requires a kit to fit it, and DUMB $.

I nicked an XJ40 3.6 TPS from a wrecking yard, and fitted it to mine a very long time ago. Best upgrade I ever did.

Test yours first, it may NOT be the issue, but age is certainly getting at these things now, and the design was not really the best way back then.

My write up on the replacement is attached.

If you need the testing procedure ask, and I will write it up for you. I thought I had it, but cant find it.

There a couple of other write ups attached that do address the TPS settings.

Throttle Position Sensor Replacement.doc

HE Tune up.doc

SETTING THE THROTTLE CAPSTAN AND RODS GRANT.doc

 

so an update of what I found this weekend......

1/ The ATF fluid will splash up out of the filler tube when you put the car in P if the dipstick is out

2 The TPS fitted to this car doesn't conform to the ones I've seen on this and other sources for a V12 1982 car. I've attempted to upload pictures below

I adjusted this one after some consideration to make the TPS get to the starting position of its rotation while the throttle capstan is at rest, with the throttle cable slightly loose. This TPS was centred on its slots when I removed the platform.

Of the three wires exiting the TPS, one appears to be a ground, the other increases in resistance as the capstan rotates and the other reduces.

Is this consistent with the $$ upgrade TPS mentioned earlier?
The car seems to run at a lower idle, perhaps even too low, but the idle adjust screw on the extra air valve seems to make a difference now while turning it out from fully in by approx 1-1/2 turn. Never seemed to make a difference before.
Exhaust fumes smell very rich - is there an adjustment on the ECU for mixture?
Looks to be a hex shaped recess on the side of the ECU - does this adjust with an allen key? clockwise for richer?

 

The high idle is nothing to do with the TPS unplug it and see what your idle is running at I would guess its the AAV or you have an air leak if the AAV will not adjust down the idle your sucking in air from somewhere, the UK V12's have cold start injectors dumps more fuel into the engine to start and get the car up to operating temp if your just fooling with the car and not running anywhere that's why its rich, try turning the car around on the slope so the pick up tube get full of ATF but defiantly change the fluid and filter you will find a thick sludge type stuff in the oil pan if it not been changed for a while.
good luck

 

The oil pick up is towards the front of the car so if your facing up hill you might get some oil starvation

 

Grant, is that an official Oz technical term?
I Love it!
Adding to my lexicon.
(';')

 

Yep.

Every language in the world understands that one.

Any more info, and most have NO idea what you are attempting to describe.

I have many.

Some ask for "The best tyres for my .......?". My reply, "Round, Black, predeerably with some tread", and surprise, some dont quite get it.

Guy at work the other day asked, "whats the best oil for my old Camry". My response, "CLEAN".

All makes perfect sense to me.