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73JPS

Speedometer(?) Issues

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After a bit of research I have decided to put out the call to all who have had speedo issues in an attempt to consolidate some info and hopefully find some answers to my problem:

My speedometer is tends to bounce around quite a bit at low speed, 10-20 MPH variations. It tends to be more steady at cruise, though it still bounces a bit, say, 2-5 MPH variations. The problem seems to take a while after start up to take hold, in other words, the speedometer tends to behave itself for the first few minutes of driving after start up.

The speedo will occasionally show 20 MPH when the car is stopped; this will also lead the odometer to click up the mileage.

I always keep the car on a trickle charger when it is parked, and the battery is fresh. This could mask an alternator problem, which I understand sometimes leads to speedo issues?

I don't think I am having any other driveability issues, but am not 100% on this due to the limited amount I have driven the car in the past few weeks.

If the alternator is bad, shouldn't the battery light come on? If not, what is the best way to test the operation of the alternator?

Well, there it is in a nutshell... Looking for bigger brains than mine to suggest probable or at least possible causes. :wub:

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Usually the battery light is linked to voltage and depending on how long you drive your car at one time, it may not draw down the battery far enough to trigger the light. With the trickle charger on all the time, you never give the battery a chance to completely discharge, signaling an alternator problem. Feel free to correct me if I'm wrong.

I would go about testing the alternator by use of a voltmeter. Don't know if the alternator terminals are very accessible on the car, if not, can test on battery terminals. Simply disconnect trickle charger and test voltage of battery. Then have someone start the car. If the alternator is working, the voltage should jump up. I think normal is around 14v give or take 1v.

Have you ever noticed an ABS light come on? I know these cars get their speed reading through the ABS sensors that goes through the ABS block and ECU.

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Well I accumulated a bit of information today.

Steve, I took your suggestion and voltmetered the battery; it did indeed show a good 14 volts with the engine running, and 12 with it off, so everything seems okay there. Re-tested after running the car for a while too, to see if it was heat related; battery still showed a good 13.5 volts. Would it be correct to conclude that the alternator is okay?

I also used the OBD II. I had the car stopped at a couple of points with the speedo doing its 20 MPH dance; OBD II indicated that the ECU was senseing 0 MPH, even though my speedo was showing about 20 MPH, so I would deduce from this that the sensor is not the problem. Is this a correct deduction?

Does this mean the actual speedo is the problem? There is mention in one of the references given on this forum to a capacitor in the wiring loom behind the speedo; does anyone know anything about this?

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I would have to say it sounds like something funny with the speedo itself or the wiring from the ECU to the speedo. As the ECU is always reading a steady 0 mph while the speedo is jumping around, I would think the sensors are not to blame for this issue. At this point, I would have to pass you off to someone else on the forum who is more familiar with the actual wiring of the speedo as I have not dealt with this or read anything on it.

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I've heard of this, and for some reason recall it's related to a blown fuse in the rear fuse box. Sorry I don't have more info, but you may want to check your fuses.

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Thanks for the input so far guys...

Paul, I did read that someone had had an issue with the speedometer similar to my issue, and he had cured it when he discovered his rear fuse box to be loose; I will check the fuses back there however.

I can determine that the speedometer is driven directly from the ECU, but I am not 100% certain if the speedometer unit itself decodes the SAE protocol. I figured this out from this description http://www.egauges.com/pdf/vdo/0-515-012-051.pdf which is worth saving for anyone planning on having speedometer issues in the future :) .

There is no sign of the "capacitor" described at the bottom of this one http://www.gomog.com/allmorgan/VDOCALIBRATION.html which I think is from a Morgan forum.

So this probably brings me back to something at the fuse box (bad ground?) or within the speedo itself. Since the problem takes a couple of minutes to appear, which suggests some sort of heat related issue, I am guessing the speedo.

Anybody got a spare one kicking around? Are they available from Lotus for a price that won't leave me bankrupt? :lol:

Edited by 73JPS

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Problem solved.

Thanks for the advice, Paul. I did what I thought was an extensive search, and could find no reference to a blown fuse in any previous threads, but when I phoned JAE to find out how much a replacement speedo would be, Jeff mentioned that a "fuse on the back of the speedometer" was what he had heard might be the problem. I knew there was no fuse on the speedo back as I had already had the speedo out, but this coupled with Paul's recommendation led me to study quite extensively the electrical schematics for the speedo circuitry... to the best of a very limited ability.

The bottom line is this: if your speedo sometimes reads 10-30 MPH when you are at rest, and "bounces around" by plus or minus 10 MPH at all other times while driving, replace this 5A fuse in the rear fuse box. It also links the positive battery terminal to the recirculation pump relay, and to one input pin on the EGR sensor, so why other things didn't go wrong when this thing blew I'll never fully understand :yes: .

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Nice result!

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THANK YOU, THANK YOU, THANK YOU!!!!

Timing is everything. I read this thread and a day later my 98 Esprit

was doing 40 when parked. ( I know they look that way LOL )

So 2 minutes and $1.50 later all is well with the spedo!! Saved no doubt

$300 at the dealer and a trip into Atlanta

Thanks

Mike

PS anyone have and idea why this fuse did not cause any other issues???

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The only thing that I can conclude is that occasionally voltage will backfeed through a circuit, in particularly one with a blown fuse. Perhaps this backfeeding of voltage is enough to cause issues with the speedometer. I know at one point I had an issue with the trunk light on my '86 Fiero in which it would glow at partial brightness as well as the footwell lights in the passenger compartment also glowing at about 1/4 normal brightness. Come to find out, it was backfeeding voltage through the fuse that normally operates the roof main lamp/map lights. The only difference in my case that I can somewhat see is that the interior roof light is operated by the same door pin switch that controls the footwell lights, but that still didn't explain the cause for the trunk light since thats on a different circuit controlled by a separate pin switch to operate that light.

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Thank you Paul for the suggestion and Patrick for the picture. My speedo was doing jiggy hop ever since I purchase my car two years ago. I simply chalked it up to build quality since each Esprit is hand made. After stumbling across this thread, I figured it wouldn't hurt to check. I pulled the fuse clearly pointed out in Patrick's picture and sure enough - it was blown. A quick 5 amp fuse replacement and my speedo is behaving like it should. Wish all repairs were this easy. Thanks again!

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Another thread i'm gonna re-awaken!

Must admit when i saw this (read the title & the posts) i was smiling because this sounded just like an issue that my dad's car is having, But having just gone & looked at the 5amp fuse pictured- the fuse is good!,but the speedo is still reading about 20mph whilst stood- Also according my dad when traveling he didn't think the speedo was bobbin about at all either???- it's just that it's reading 20mph high all the time, and 20mph when stood (not even running!)

There is a bit more of a story with the old man's car that will end up relating to several problems i'll end up posting about on here- so just bare with me while i tell it in as short as possible terms as i can! Basically him n my mum were coming back from Newark (a good few months ago now), & to put it bluntly the old man lost the back end after exiting a round-about (i assume they must have been going reasonably quickly!), and the car swapped ends ends on them and from what i can gather they ended up bouncing backwards up a kerb & onto a grass verge where the car finally came to a stop! Now from what i can gather he'd spun on a diesel spill (or so he thought) because he said he could see something on the road surface where they'd just lost it, and just a little bit further down the road from where they were was apparently a pile of glass and fresh'ish looking skid marks- so it looks like they weren't the only one's that had been caught out that day! (that's the story & blame apportioning bit out of the way :hrhr:)

Anyway- back more to the speedo, Basically my old man after getting home from the above (the car was still ok to drive seemingly) noted that the steering wheel was now slightly off centre, and for what-ever reason he decided to try N get the wheel off! The steering wheel was apparently on it's splines VERY tightly abd he had to resort to belting the steering column (whilst someone else pulled on the wheel) in an attempt to try n jar the wheel free! Now my dad knows next to naff all about the car itself, and didn't have any kind of reference material to work with/too (workshop manual etc) so he just did what he thought was right!

Basically after all that little tale- I guess what i'm asking IS- Has the old man knackered the speedo in some way by his belting the steering column to get the wheel off??, Or could it still be something else!??? As i say- i popped that 5amp fuse out n it wasn't blown (and the speedo is still showing 20mph), the one thing i didn't do was put the ignition on or try starting the car though!, But would this have helped reset anything anyway (me removing the not blown fuse n then stuffing back in!?), or do you peeps think that my dad's messing is what's to blame n he's basically shafted the speedo unit!???????

Sorry for the long'ish post, but i thought i'd spell it out as best i can as i'll no doubt need to refer to this story in other threads- for his "other" issues (which are all probably related in some way to the above :wine: )

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Will that be of any use to our car though- afaik the car is a 98/99 V8se, and the speedo doesn't have any digital elements to it- it's all analogue!????

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If it's got a analog odometer (old style with numbers on a series of wheels) then no, this wouldn't help in your case. However, if it does have a digital odometer/trip then the calibration procedure should apply.

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Yeah, don't know what you can do on that unless it's a matter of "removing the needle and repositioning it to zero" (making sure the ignition is on to "zero" it out that is). That might work as long as it's a consistant 20 mph over, and the odometer is reading accurately.

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not sure what an analogue will cost, bud i have the same 'digital' VDO speedo in my 'Cobra Kitcar' as on the '98 GT. These VDO speedos are pretty common& not to expensive in the aftermarket for Kitcars, boats, and so on.

Basically there is nothing else on the back as an positive voltage, earth and an 'impulse' signal. The same is it on the Kitcar - I use an self fabricated 'impulse wheel' and sensor on the propeller shaft and positive/earth . No capacitor so far ! If it comes out with my *dancing trip counter* (the digital element) again -than i will use the other speedo out of the Cobra to verify that the fault is in the speedo, not in the wiring of the Esprit.

Mentioning your 'analoge' speedo: have you opened it, to see if there is some kind of magnet-coupling like it was in the old 4-pot speedos with manual drive ?

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I have again problem with my Speedo, as you see. Mechanical odometer is in stuck. I think that my sppedo is electronic and ecu driven, except those silly numbers.

post-2215-1254845581_thumb.jpg

Steve from SJ Sportcars told me that this speedo is not availlabe anymore.

I have got an good offer about VDO Speedo 437-015-008 G.

55_Elektronische_20Tachometer_20vision.pdf

But I not 100% sure that this works in my car. What do you think?

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Jukka, you link refers to the later (small cockpit) fully electronic speedo (of course, there still is an stepper-motor in..). These speedos are the one that i mean with my *dancing digits* on the digital trip counter. So you will have the Chance to come from one fault to the other. Bud anyway, the VDO speedos are still available (mostly the digital ones..) in the Kit-car scene. It is common to use them for various types of Super 7 /Cobra replica types. And they are available in different diameter and designs (chrome, black, modern gauge style/classic lettering and so on.. .)

Not sure that the ECM will support the 'impulse' rate for the speedo. Can you undo the cockpit and pull the speedo out !? Firstly to see what type of reference is used to show the speed (as the old 4 pots have the cable driven types..) -and also to see if there is mechanically something wrong. Maybe some cheap plastic stuff is coming loose or so... .

+++

there is an full instrumentation listet in, if you want to change the speedo to the later version

http://www.espritism.com/espritelectrical.htm

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Thanks for quick answers.

I have opened cockpits upper cover and there is no cable to speedo. So that speedo must be electric. But I have not yet removed the speedo. But I will do it on next winter. On next weeks wednesday we will start our 'autumm holiday' and I will not do any extra repairs before that. I have limited time to spent with car and I'am very 'slow' mechanic.

I have tried to find suitable old style VDO in internet, but can't find nothing.

May be that best alternative is repair my old Speedo.

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Jukka, you need no speedo -all you have to do is 'get sure that all the others are bhind you' , that's the right speed for an Esprit :devil:

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