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MG MGF Technical - World's slowest MGF, please help.

Think my car has a slight problem that has been slowly getting worse.

I've have noticed over time, my top end speed has slowly been getting worse, figured might have been due to modifications etc.

However now the problem seems to be getting much worse.

Although, this seems as though it may not be what it first seems.

As today on my way to work, i was hurtling passed everyone on the motorway at 60 mph.

60???

Thought i'd give it a quick test.

Redlined 2nd gear doing....35-40 mph??
Redlined 3rd gear doing....50ish mph.
Redlined 4th gear doing...65-70 mph.

(Then I ran out of motorway.)

Can someone tell me is my speedo fecked, or am i really driving a corsa?



paul weatherill

PS.

It's a VVC redlining at 7000 revs.

Could it be a coincidence that in kilometers per hour.

the speeds relate to:

2nd Gear about 60.
3rd gear just under 90.
4th gear about 110.

????

paul weatherill

Paul

Could be your clutch is on its way out, or constantly slipping for some reason. When you accelerate hard, do the engine revs go up rapidly but you seem to go nowhere, and then drop back as you pick up speed? I had similar symptoms on a V6 Vectra some time ago. It had 5 complete replacement clutches and flywheels over a period of 3 years.
David Dewick

Sounds more like a speedo fault when Paul says > , i was hurtling passed everyone on the motorway at 60 mph.<

Ted



Ted Newman

This recently came up on the Lotus board, I personally think this is too much of a coincidence and shows a clear link between aliens and the american war effort.

The americans are clearly using a special 'speedo jammer' first found after the Roswell incident.

They are using it under the close supervision of Tony Blair whos governemnt are sure that speed kills.

Being american they can't aim the thing.

QED
Will Munns

can anyone tell me where the sensor is for the speedo?

does it share a sensor with the rev counter.

the rev counter seems perfectly ok.

btw, still testing I have a top speed of 85-90 mph!!!!

paul weatherill

The speedo needle seems to "wave" about a lot, if it goes over 80.

Will, thanks mate, it seems most likely cause so far.

paul weatherill

Paul, when was the last time you cleaned the air filter?
Rob Bell

its got a nice new pipercross viper one fitted now.

however, problem was occuring before i fitted that.
paul weatherill

i think its definately the speedo, just need to work out, if i can fix it, or whether its back to the garage.
paul weatherill

speedo is crap anyway. Mine is always off by 10/15 kmph.
Bram

Any ideas on how i can measure speed without a speedo?

something about standard distance between lamp-posts on the motorway?

paul weatherill

The police often have calibrated 1/4 mile lengths marked out on the verges of motorways, so they can check their speedos. I'm sure that there are likely to be some near you Paul...
Rob Bell

Those little red topped things at the side of
the motorway are 1/10 th of a mile apart.

If you time how long it takes to go past ten of
then this should give you an idea of how fast
you are going.


Paul;
Paul Waine

Paul why don't you check your speedo against one of the other Fs on Sunday. Also, you should be able to check your revs against another VVC at a particular speed to see if they are the same - this should tell you if your clutch is slipping and if they are the same you can then work out mph/1000rpm in top gear.
David Clelland

Paul

Do you have a GPS navigation unit. (Like an e-trex or something)?

That will measure your speed pretty accurately. If not I'm sure someone you know has one or perhaps a fellow Fer will have one on Sunday?
Billy Bob

Billy Bob,

We share one mobile phone between six cars on our runs :-) You've no chance of anyone having fancy GPS navigation gear.
David Clelland

Paul at least yours works albeit badly. Mine gave up the ghost totally this morning. I usually judge my speed by watching everyone else :-)
D Jamieson

guess we better stick to the back of the convoy on Sunday then ;-)

The more i read up about this, the worse it gets.

So far.

Sensor in gearbox feeds information to ECU, ECU then feed signal to Speedo (and EPAS).

so..

Cheapest..to Most Expensive.

Loose cable.
Faulty Speedo.
Faulty Sensor.

daren't even suggest..Faulty ECU.

Question is how to progress from here.



paul weatherill

what i haven't found out yet, is whether rev counter and speedo use same feed.

if they do it must be a faulty speedo as the rev counter seems fine.

will do some more "testing" tonight, but working til 6.
paul weatherill

Ref Sunday, do you meet up often and if so where abouts is it usually, I've now got the tuning bug and wouldn't mind seeing what you guys have done, not many modded F's locally!!!

Thanks

Arron
Arron

Paul, what age? are you sure the ECU gets a speed reading?
Will Munns

Long way from Kent, usually meet up in Stirling.
You're still more than welcome tho ;-)
Think other peeps on here, might be able to advise on a closer one.

Anyway, had a lunchtime tinker, and thing have improved.

Couldn't properly test, as too far away from the motorway.

But Speedo now showing..

Redline 2nd gear...55 mph.
Redline 3rd gear...80 mph.

couldn't do 4th gear due to speed restrictions.

Anyway, all i did was...

remove black covering.
located cable going into back of intrument display.
follow cable down, until i found join.
disconnected.
checked out cable.
(oddly enough, the inner core, actually pulled clear of the instrument display. is this right? shouldn't it be connected to something??)
anyway, threaded core back thru, and went for a drive.

not totally fixed, but a lot better.

paul weatherill

What age? me? 30 :-)

Car is a '97 P-reg VVC.

paul weatherill

Paul, see JT's theoretical top speeds for each of the gears- http://www.mgcars.org.uk/MGF/vvcrpm.jpg

According to this, JT predicts 65 and 91 mph @ 7500 rpm in second and third. Looks as though you are within 10% of these values, so I think you've fixed the problem :o)
Rob Bell

heh, thanks Rob.

will give her some "loving abuse" tonight, and see if there's any fluctuation.

certainly seems as though i've found where the problem is anyway.

Thanks guys.

paul weatherill

Paul are you remembering that you have 17" wheels and different size tyres. This could explain the 10% discrepency.
David Clelland

A clear proof that it's no good having the size if you can't control it !
JohnP

David,

I have 17" rims, but lower profile tyres ;)

Rolling radius is almost identical.

paul weatherill

IIRC, my VVC redlines at 90 MPH in third. I dread to think how fast you were actually going when you redlined in 4th, and got to your top speed!

Leigh
Leigh

I always thought the speedo on the F was mechanical and not electric. Well at least on the 95-99 generation. An easy way of telling is to see if it reacts to reverse: if does it's electric, if not it's mechanical.
Anthony Braham

Paul
How's the odometer readings ?
Is work now closer than it used to be ?
Are you only getting 200 miles to a tank rather than 300 ?

If the odometer reading is OK, but the speedo is wrong then I'd say that's a big indicator that the speedo instrument is bust.

If the odo's wrong (and you've not indicated this) then something is up with the drive to the instrument - though I can't imagine what !

Steve
Steve

Haven't checked Steve.

will check on drive home tonight.

Thx for info.
paul weatherill

Even though the speedo has a mind of its own Paul your car was going like a rocket yesterday. Nice One mate !
D Jamieson

:-)

I was just trying to keep up with Gerry's MGBGT V8.

Not once did i go above 50 mph, well not according to my speedo anyway.
paul weatherill

This thread was discussed between 27/03/2003 and 31/03/2003

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