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Shem 
Groupie
Joined: 04-November-2005
Location: Hampshire
Status: Offline
Points: 51
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 Topic: Autobox thump / Sticky cold start
Posted: 04-November-2005 at 10:54 |
Hi, I've just joined the ranks with the purchase of my first 6 (1988 Highline).
I've two questions which I hope have not been covered already(I've have a search through the threads but not found anything)
1. The autobox generates a thump at the rear when changing up. The harder the change the bigger the thump. Ideas? (I believe the car has a LSD).
2. Sometimes when I start the car from cold and drive off it runs very badly, misfires, lots of black smoke and no performance. The cure is to pull over, switch off for a few seconds and restart. When you restart everything is perfect, almost like something has got stuck and been released.
Many thanks..
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Horsetan
Really Senior Member II
Say Neigh to Gatsos
Joined: 11-April-2003
Location: Please let it be Ireland
Status: Offline
Points: 6381
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Posted: 04-November-2005 at 18:40 |
 Shem wrote:
Hi, I've just joined the ranks with the purchase of my first 6 (1988 Highline). |
...and you won't be able to get enough of it. Well, at least until the rust starts coming through the wings......
| I've two questions which I hope have not been covered already(I've have a search through the threads but not found anything)
1. The autobox generates a thump at the rear when changing up. The harder the change the bigger the thump. Ideas? (I believe the car has a LSD). |
Differential mounts - UKDaveJ knows all about changing these!!! Also check your guibo / flex-disc in the drivetrain.
| 2. Sometimes when I start the car from cold and drive off it runs very badly, misfires, lots of black smoke and no performance. The cure is to pull over, switch off for a few seconds and restart. When you restart everything is perfect, almost like something has got stuck and been released. |
Not come across these symptoms - "Brucey" would be yer man for this one!
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simonr
Groupie
Joined: 31-October-2005
Status: Offline
Points: 54
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Posted: 05-November-2005 at 18:27 |
I concur on the first item; almost definitely the diff' mount.
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Brucey
Really Senior Member II
Joined: 07-March-2004
Location: United Kingdom
Status: Offline
Points: 744
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Posted: 06-November-2005 at 02:51 |
yes, and its not unknown for the body to need welding where it attaches, too, but this is more common on early cars.
Re. the running issue; there could be a lot of causes for this, but DO check;
1) the AFM vane is moving freely
and
2) check the crank position sender; on yours I think its just got the one, make sure its properly connected, and its the right distance from the toothed wheel, that the wheel runs true etc. If this sends out the wrong signals it screws everything up...
finally check the FPR if the other two check out OK- but 'known good substitution' is the only way here unless you can rig a guage up. Should be 3.0 bar on your car.
cheers
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~~~~~~~ Brucey ~~~~~~
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Shem
Groupie
Joined: 04-November-2005
Location: Hampshire
Status: Offline
Points: 51
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Posted: 06-November-2005 at 04:13 |
Thanks for the advice, the FPR is already on my list of issues to investigate as fuel economy is not great. Its certainly better now that the computer isn't set to US gallons  (thanks to this forum).
The car has not run that much over the last few years so i expect a few teething problems but hopefully mpg will improve (current avg 19mpg). It passed its MOT with CO reading of 1.77% and a HC of 134. From what I've read here thats a little too rich but nothing major?
The rusty wings and TRX issue I'll deal with after it runs ok 
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Brucey
Really Senior Member II
Joined: 07-March-2004
Location: United Kingdom
Status: Offline
Points: 744
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Posted: 06-November-2005 at 07:16 |
a duff AFM will ruin the fuel economy too;
I had a sticky AFM at one point; mine stuck open after more than 3/4 throttle and 4000rpm- after it would hardly run at all, but sometimes the AFM freed itself up after a complete stop.
hope you get it sorted out
cheers
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~~~~~~~ Brucey ~~~~~~
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AndyS
Really Senior Member II
The Last of the Few
Joined: 21-August-2003
Location: 55 � North
Status: Offline
Points: 1365
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Posted: 06-November-2005 at 11:43 |
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Actually 19mpg isn't too bad - depends what road conditions are.
I had similar problems with plug fouling - all down to the fuel
pressure regulator. Cost £35 from main dealer, 2 mins to fit. Improved
consumption from 16mpg to 20mpg.
I believe there is a cold start circuit on the injection. This may be sticking too. I'll check the Bentley manual.
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AndyS Live each day as if it's your last - one day it will be. 
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Horsetan
Really Senior Member II
Say Neigh to Gatsos
Joined: 11-April-2003
Location: Please let it be Ireland
Status: Offline
Points: 6381
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Posted: 06-November-2005 at 12:15 |
AndyS wrote:
Actually 19mpg isn't too bad - depends what road conditions are..... |
...but it is possible to improve on this.....
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Shem
Groupie
Joined: 04-November-2005
Location: Hampshire
Status: Offline
Points: 51
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Posted: 06-November-2005 at 14:50 |
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19mpg when mostly cruising on the A303 around 70mph.
In fact I reset the computer whilst on cruise control around 80 and after 10
miles it read 21mpg. Based on other posts in this forum I would have
expected high 20's? maybe over 30?
What is the AFM Vane? is it easy to check?
Many thanks
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AndyS
Really Senior Member II
The Last of the Few
Joined: 21-August-2003
Location: 55 � North
Status: Offline
Points: 1365
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Posted: 06-November-2005 at 17:30 |
I think over 30mpg is wishful thinking unless you don't go over 55mph.
On a long run from Windsor back to Tyneside at 75-80mph I managed
28.5mpg. This is very good when you compare it to my E30 316 Touring
which managed a trip to the NEC & back at the same speed & only
managed 33.7mpg 
"Around town figures are harder to quantify. Depends on the speed of
traffic, time standing at lights etc but 18-21mpg is a ball park.
On faster A roads with some spirited driving, ie box in Sport mode you
could expect 19-24mpg. Again, it's what your definition of "spirited"
is.
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AndyS Live each day as if it's your last - one day it will be.
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Horsetan
Really Senior Member II
Say Neigh to Gatsos
Joined: 11-April-2003
Location: Please let it be Ireland
Status: Offline
Points: 6381
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Posted: 06-November-2005 at 17:39 |
AndyS wrote:
I think over 30mpg is wishful thinking unless you don't go over 55mph. |
60mph (after o/d 4th has kicked in).... assuming downhill all the way! I don't have an "EH" auto, so no "sports" setting for me.
Next 3,000-mile oil change due soon, so will recalculate consumption over next 3000 miles.....
Edited by Horsetan
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Shem
Groupie
Joined: 04-November-2005
Location: Hampshire
Status: Offline
Points: 51
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Posted: 07-November-2005 at 05:21 |
How accurate is the computer?
I'm trying to best the best fuel econmony on a dual carriageway without holding up the traffic and the computer is now reading 16.5
I
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What fuel crisis?
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Brucey
Really Senior Member II
Joined: 07-March-2004
Location: United Kingdom
Status: Offline
Points: 744
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Posted: 07-November-2005 at 14:49 |
jeez.... if mine read that it would mean a real....
14mpg.....
once fully warm (50 miles plus) instantaneous readings of 35mpg at a steady 70 are common, and 30mpg on a long steady run is quite possible.
But spirited driving gives low twenties, and short runs give sub 20mpg, easily.....
The AFM vane is accessible once the airbox and its hose are shifted....
cheers
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~~~~~~~ Brucey ~~~~~~
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Horsetan
Really Senior Member II
Say Neigh to Gatsos
Joined: 11-April-2003
Location: Please let it be Ireland
Status: Offline
Points: 6381
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Posted: 07-November-2005 at 16:58 |
Shem wrote:
How accurate is the computer? |
Close, but no cigar. I brim each tankful and calculate from there....
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Shem
Groupie
Joined: 04-November-2005
Location: Hampshire
Status: Offline
Points: 51
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Posted: 08-November-2005 at 08:21 |
The car is booked in this weekend to be looked at with the fueling issue at the top of the agenda. Weird this is that the emmissions test doesn't show anything wildly out.
many thanks for all the advice which should help at the weekend.
I'll let you all know!
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What fuel crisis?
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UKDaveJ
Really Senior Member II
Joined: 18-November-2004
Location: Bromsgrove, Worcestershire
Status: Offline
Points: 529
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Posted: 08-November-2005 at 17:57 |
Your two points;
1) thumping from rear. yes I changed my diff mount, a right PITA to do,
should be simple, but these things rarely are......! Depends on your
tools, ease of access.
I also had my axle bushes changed, they were well & truly bollox'd.
However, I still have a thump from the drive-train. When the bushes
were changed, I got the mechanic to check the centre-bearing, that was
fine. No guibo on an auto - not on mine anyway.
My Highline has done just shy of 200,000 miles, so I don't know if my
limited slip diff is worn or likewise the gearbox. There may be other factors
involved which I've yet to suss. But I plan to!!
2) economy - my Highline has never shown me more than about 28'ish. I'm
not particularly light-footed, I've no idea whether the afm is set-up
correctly, or any other particular area of the engine. But I do know
that since I've had it chipped it FEELS so much more gutsy!!
Might even change the plugs soon.......!!
Might even take it to a good indy & make sure its set-up correctly
from a mechanical point of view, but hey, its a 3.5 litre straight six,
never designed with economy at the forefront of the performance parameters
IMHO! That big old lump is powering similarly a big old lump!
If you are in double figures, great!
Just my few penneth worth!
By all means chase some more economy but these cars were designed to be
driven by 'fat' businessmen/retired guys who didn't give a fig about
how much they spent at the pumps, or at the stealers......., they just
put their hands in their pockets!! A LOT!!! 
Edited by UKDaveJ
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My 635's.
 
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Horsetan
Really Senior Member II
Say Neigh to Gatsos
Joined: 11-April-2003
Location: Please let it be Ireland
Status: Offline
Points: 6381
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Posted: 08-November-2005 at 18:03 |
I think it is possible to drive economically.....
....it just helps if you have loads of downhill stretches 
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UKDaveJ
Really Senior Member II
Joined: 18-November-2004
Location: Bromsgrove, Worcestershire
Status: Offline
Points: 529
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Posted: 08-November-2005 at 18:17 |
or the engine in neutral.......
or a few plug leads disconnected......
or on the back of an AA recovery truck......
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My 635's.
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Horsetan
Really Senior Member II
Say Neigh to Gatsos
Joined: 11-April-2003
Location: Please let it be Ireland
Status: Offline
Points: 6381
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Posted: 08-November-2005 at 18:37 |
UKDaveJ wrote:
....or on the back of an AA recovery truck...... |
Not familiar with this! 
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UKDaveJ
Really Senior Member II
Joined: 18-November-2004
Location: Bromsgrove, Worcestershire
Status: Offline
Points: 529
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Posted: 09-November-2005 at 03:06 |
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Nor me as it happens!!
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My 635's.
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Autobox thump / Sticky cold start
