Eratic rev counter

[shaun]

Can anyone give me some ideas to where my problem is? My Fiat 124 ish rev counter doesn't work until 1000, gets erratic from 1000 to 1500 and works fine from 2000 to 4000 after that no idea. Engine is Lancia volumex on standard ignition, loom a homebrew but using std Lancia on the engine side.

[chris.richard]

Sounds the same as me, except I'm Alfa ECU. It happens with 2 tahos, so I think it's a loose connection/bad earth problem.

[shaun]

I think it was ok about two weeks ago so may just have to look inside or try another. Thanks anyway.

[rutthenut]

Sounds the same as me, except I'm Alfa ECU.

Chris, from the wiring diagram I've got, there appear to be two connections from the ECU loom back to the tacho. Which connection(s) have you used?

[chris.richard]

I've attached up the wire from G154 pin5 to the tacho. I seem to remember thinking that the wire G154/3 to the 164's instrument cluster was something superfluous, but I might well be wrong! :rolleyes:
Further investigation shows both these wires as for "revolution sensor"... :eek: HELP! Chris Savage - what do I wire this to on the tacho? :confused:

[CorseChris]

Chris,

Use the wire that fed the dash tacho on the donor car. Data I have to hand suggests ECU pin 74 is the right one. Chase that to the connector you are using.

To be honest, the problems you chaps are having leave me somewhat mystified. Standard 124 tacho works perfectly on my current standard TC motor (also tested some on the 164 and the Jeep in the past). My modded tachos work perfectly on the 155 whch has the same ECU as the early 24V V6 motors.

I take it from your comment Chris that the new test unit I sent you isn't working either?

Triple check your earths.

[Sando]

Can anyone give me some ideas to where my problem is? My Fiat 124 ish rev counter doesn't work until 1000, gets erratic from 1000 to 1500 and works fine from 2000 to 4000 after that no idea. Engine is Lancia volumex on standard ignition, loom a homebrew but using std Lancia on the engine side.

Hi Shaun
I had exactly the same problem on my Vx. I couldn't find anything or change anything so I just put up with it ;)
Worked fine over 2k Revs so when you really needed it at the top end it was fine. Must admit I just go by ear once you get used to the car anyway so hardly ever looked at it! :eek:
Hope the build going well.
Rob

[shaun]

Just about to take that B..... vx lump out and push it off a cliff. Now the whole lot is playing up, it's backfiring thru the exhaust and the inlet manifold and running really rich. A smart man has put money on the carb float having a hole in it, timing is ok, plugs & leads new, tried different coil, ign module and even had a cup of tea. Symtoms worse when hot. I think the cams are timed in ok and it is only the offside exhaust that spits flame. As ever the problem is very simple, I've just got to find it to merit the reward.

As for the rev counter, I'm sure it worked ok when I first put it in when the loom wasn't loomed. The only other instrument problem is a dead oil temp guage.

Everything will be ok tomorrow night after a good days rest at work, three weeks I have hoped to drive it out the garage and tighten all the suspension up and......... well you know what, quick blast up the road.

Hows that Lancia V6, there one for sale near chantilly but no price as yet.

[David May]

I agree with your diagnosis Shaun. All it needs is a stronger cup of tea and maybe another days rest! Stay away from those cliffs though...

[Sando]

Hows that Lancia V6, there one for sale near chantilly but no price as yet.

Stick with it mate I'm sure you'll sort it. Brent (BAS) had my standard Vx carb bits, if you pester him he might sell it you if you get stuck?

The V6 is still not fully in, I've had to miss a few Saturdays worth of fettling recently so I'm a bit behind. Everything looking good though, only last bit to fabricate is the exhaust, but the final fuel and water plumbing is going in now so the engines out again at the mo so I can get to the bulkhead. I'm still aiming to get it started up by Chrimbo if I can. Exhaust or no exhaust....... :D

Rob

[chris.richard]

I'm still aiming to get it started up by Chrimbo if I can. Exhaust or no exhaust....... :D


So we'll all hear it if you succeed! :cool:

[shaun]

Several cups of tea later and no change for the tacho but everything important is working.

I've been out for my first Driftwinkel in the devils plaything. I can't stop grining and it was only a few minutes worth. Thanks to the lack of inner rear arches mud is everywhere but it runs, it goes, it bl...y works. The hot engine even heats the workshop. Back to work now, you shouldn't run too fast until you can crawl or something like that.

I'm a happy puppy.

[strat6v]

Looks like next year will be a bumper year for finished kits. Should be over for a visit at some point but don't hold your breath!! I'm trying, i'm trying!

John

[chris.richard]

Well done Shaun! That grin will last for days!

[SUSIT]

Several cups of tea later and no change for the tacho but everything important is working.

I've been out for my first Driftwinkel in the devils plaything. I can't stop grining and it was only a few minutes worth. Thanks to the lack of inner rear arches mud is everywhere but it runs, it goes, it bl...y works. The hot engine even heats the workshop. Back to work now, you shouldn't run too fast until you can crawl or something like that.

I'm a happy puppy.

Fantastic news Shaun. A trip to the UK early in 2006 for an SVA ?? :)
Well done. Any chance Abingdon 06 for the sprint :)

[Sando]

Well done Shaun! Was the Mrs impressed? ;)

Won't be long before you are Driftwenkeling up the Col de Rousset! :D ..... Bet its cold up there at the mo.

I bet its the Christmas pressie you've always wanted too :)

cheers
Rob

[shaun]

Car should be back in the uk before 2006 due to a restructuring here at Aubenasson, Abingdon is a distinct possibility so is the Mulltour a forced sale is on the cards if I do not find a second income.

The Mrs didn't know as she was away with her horse and thought I was working, the kids knew as I was late to pick them up from school.

I'm trying to fit the windows for the trip back, now they are a fiddle.

One last thought, I was so excited I forgot to take a photo!

[Chris J]

Abingdon is a distinct possibility so is the Mulltour a forced sale is on the cards if I do not find a second income.

Well done with the car Shaun. Sell everything else before the Stratos.

Is this Mull tour on?? I'd like to see it happen.

[John]

Shaun,
if the tacho worked fine before you loomed it all together, then perhaps you should consider using a screened cable for the tacho feed? Maybe the signal is getting interference from other cables? I'm thinking this could be so because elecctronic speedo's require a screened cable to work properley, and they work on the same principal (I think)
Anybody else out there think this is worth a try?

[chris.richard]

Chris S suggested interference as a possible cause of the erraticness (?) that I'm seeing, so maybe a screened cable is the answer.

[David May]

Its got to be a pretty crude rev-counter circuit if it can't tolerate a bit of line noise. (Noise pickup tends to add pulses, not lose them.) I doubt if that's the root problem anyway, since it works at higher revs, when the noise is doubtless much greater.

[CorseChris]

I suggested checking earths but as Dave say's interference tends to add pulses not remove them. I had an electronic speedo on a car once that indicated 150mph when you switched the heater fan on.......

The circuit in the latest iteration of my tacho mods is basically the standard LM2917 application and is pretty good for noise immunity.

[shaun]

The answer is here somewhere, I just need to read it again to understand.

http://archive.mirafiori.com/show.php?fid=2&msg=134609#top

Found buy accident, buy the way, while trying to find the size of volumex valves without taking the head off.

My rev counter would have worked with the old alternateur which wasn't working.

[shaun]

Quote "Kelly do as Trent says....sometimes these conversions work without the capacitor
sometimes not,on my electronic conversion I had to install a 0.68uF/400v cap.on
the tach wire...all is well now...BTW my '69 has the 8K tach."

Easy then!

Still haven't found valves sizes though.

[Sando]

Still haven't found valves sizes though.

Hi Shaun. I think it's in the Guy Croft book. I'll have a look tomorrow unless someone else has it to hand.

Bobster

[chris.richard]

Quote "Kelly do as Trent says....sometimes these conversions work without the capacitor
sometimes not,on my electronic conversion I had to install a 0.68uF/400v cap.on
the tach wire...all is well now...BTW my '69 has the 8K tach."

Easy then!

Still haven't found valves sizes though.
Surely we can do it with transistors nowadays? ;)

[shaun]

Royal we was that?

[guy mayers]

According to the Guy Croft book 43.5/36 but I can't tell you which in inlet and exhaust! Hope it helps.
Guy

[shaun]

Thanks for that, 43.5mm inlet compared to 42mm on a std head.

[CorseChris]

Surely we can do it with transistors nowadays? ;)

That tacho I sent you to test is full of them...about 100 in a small black chip......

...but seems to have failed.

FWIW, I put it back on my 155 the other day...works just fine and tracks the cars own tacho pretty much perfectly. It does do the 'kick' when cranking which I hadn't noticed before, but immediately settles to the correct reading once the engine is running.

To clarify...you have a 24V motor with coil-per-cylinder igniton and are driving the tacho from the pin of the M1.7 ECU I specified??

[chris.richard]

That tacho I sent you to test is full of them...about 100 in a small black chip......

I meant as an alternative to the valves that Shaun was looking for.....


To clarify...you have a 24V motor with coil-per-cylinder igniton and are driving the tacho from the pin of the M1.7 ECU I specified??

That is correct. What do you make of the capacitor in line suggestion?

[CorseChris]

Given that your ECU delivers a nice tidy 0-12v square wave I don't see it helping to be honest. One thought that just occured....try adding a pull-up resistor. Try adding a 1k from the ECU tacho feed up to ignition switched +12. It's possible the ECU output is an active low rather than a full rail to rail driver.

[chris.richard]

It's possible the ECU output is an active low rather than a full rail to rail driver.

Absolutely, just what I was thinking! Eh?? :confused:

[rutthenut]

Given that your ECU delivers a nice tidy 0-12v square wave I don't see it helping to be honest. One thought that just occured....try adding a pull-up resistor. Try adding a 1k from the ECU tacho feed up to ignition switched +12.

Que?

My 24v modded tacho didn't work when I first wired it up, and I just disconnected the feed to look at it another day. If I need to do this sort of mod, have you got slightly more detail for a non-electrician?

I'm happy enough working on general wiring loom issues (i.e. keeping smoke in the wires), but know naff all about electrical components of this sort.

First of all, where would I even get a pull-up resistor?
I guess Maplins would have this sort of thing?

[CorseChris]

It's a possibility the the tacho drive in the ECU uses the same kind of output as the coil driver - it shorts the connection to earth as required, but can't make it go up to 12V. My tacho design assumed a proper signal. By adding a pull-up resistor from the signal feed to 12V, this would then force the signal line to go to 12v until the ECU pulls it to ground. Using something like 1k limits the current to a small and safe level but can drive the input to the tacho.

Physically installing this is probably easiest to do at the back of the tacho - add the resitor between the trigger input and the igniton switched 12v

I've only ever tested tachos on my 155 with the original one in circuit so it's quite possible that the standard tacho provides this pull up, hence they work fine when I test them.

...Maplin would do you a suitable resistor. Worth buying a few in case... try a 470 ohm, 680 ohm and 1k ohm. Start with the biggest value one and work down. You'll only need a low wattage type - 1/3 watt or thereabouts is fine.

Meantime, I'll see if I can disconnect the original tacho on my 155 and test a modded one on it's own.

[rutthenut]

Thanks for the explanation - makes sense to me.
Will attempt to make some time to test this out, after getting required parts.

[chris.richard]

Try adding a 1k from the ECU tacho feed up to ignition switched +12.

Finally escaped the festive nonsense and got back to the garage this afternoon, before proper celebrations begin tonight ;)

The 1k pull up resistor works a treat. No fsd on cranking, and a smooth progression across the rev range - well, up to 5k rpm anyway, the engine was cold and i don't want to skip a tooth on the cambelt now do I? So a small soldering job tomorrow, (hangover permitting :( ), and the binnacle can go in permanently. :)

[rutthenut]

The 1k pull up resistor works a treat.

Thanks for the confirmation Chris.

Now which little item should I get?
Maplins list small 'metal film' resistors
http://www.maplin.co.uk/search.aspx?MenuNo=13798&MenuName=Metal+Film+Resistors&FromMenu=y&doy=2m1
as well as 'high power wirewound' resistors
http://www.maplin.co.uk/search.aspx?MenuNo=513&MenuName=High+Power+Wirewound&worldid=3&FromMenu=y&doy=2m1

I guess the latter type would be a better choice?

Regards,
John

[chris.richard]

No, the former is fine - the one you want is M1K , just over half way down the page.
I soldered mine in between the black +12v feed to the alternator light and the brown tacho signal input, but it could equally well, and probably more easily go on the yellow/black +12v instrument power feed

[CorseChris]

Result! Sorry it didn't cross my mind sooner though - kind of obvious after the event.

....so I forget which tacho you have now Chris...did you have one of my new type ones? ..or are you happy with what you have?

John, Chris is right - the small chap is fine as it's only dissipating about 50mW

[chris.richard]

I have the tacho that you modified a couple of years ago - Mark 1? - It seems to be fine, so I'm happy to stick with it. And the binnacle is all bolted in for the final time (Yeah, right! :rolleyes: ) If it comes out again, I'm going to put Rivnuts on the binnacle so I just stick a bolt up from below rather than pi**ing about with washers and nuts.

[CorseChris]

Ah, OK...lost track. As long as you are happy with that one then no need to change it. The main issue with the old style electronics is a lack of linearity but some are better than others.

If you do go for captive fixings....I prefer those captive nut plate types for fibreglass - no way they will ever come loose the way Rivnuts can. Wee bit pricey (40p each I think) but worth every penny for awkward locations.

[rutthenut]

If you do go for captive fixings....I prefer those captive nut plate types for fibreglass - no way they will ever come loose the way Rivnuts can.

Totally agree with you there. Much more secure than rivnuts. Also much, much better than usng self-tappers into fibreglass (such as for inner door panels). Also agree that they could be cheaper.

As well as fixing the captive nut to the back of a panel (i.e. inside the binnacle) it can sometimes be possible to run the small bolt through from the back, maybe with a locknut, to create a 'captive stud' which can help fitting some parts. Mind you, it can be more tricky to fit the nut in some locations than a simple screw/bolt.

I've used these to fix my dash binnacle in place, and would you believe that a couple of the screws have come loose over the years!
(yep, driver has a screw loose too)

Cheers,
J.R.

[rutthenut]

No, the former is fine - the one you want is M1K , just over half way down the page.
I soldered mine in between the black +12v feed to the alternator light and the brown tacho signal input, but it could equally well, and probably more easily go on the yellow/black +12v instrument power feed

OK, I'll get one of these - really expensive, eh? A whole nine pence (plus p+p) ;)

http://www.maplin.co.uk/module.aspx?TabID=1&ModuleNo=-9400&doy=3m1

Then I guess I really should do some work on the car this coming weekend...

[CorseChris]

That'll do the job John.

[Chris J]

I have the tacho that you modified a couple of years ago - Mark 1? - It seems to be fine, so I'm happy to stick with it. And the binnacle is all bolted in for the final time (Yeah, right! :rolleyes: ) If it comes out again, I'm going to put Rivnuts on the binnacle so I just stick a bolt up from below rather than pi**ing about with washers and nuts.

Chris

I thought...(you know what thought did?) that once the binnacle was fastened down, that was it. If you need access after that, it was just a case of pulling the facia (with everything in place) away from the binnacle. Or do you need greater access than that would give you for this particular job?

I'd planned to cut one great big hole in the front of the binnacle, rather than one hole for each guage/switch, leaving the facia to do that job. I believe that Chris S. and probably lots of others have done it that way.

So you reckon a quick(ish) release fastening system for the binnicle to dash would be a good idea too?

Sorry if I've hi-jacked this thread, a bit.

[Swamprat33]

Hi Chris, what are these rivnut/plate things and where can I get some.

cheers

Tim

[CorseChris]

Chris J - quite right - I cut a humungous hole in the binnacle and the dash panel complete comes out the front no bother (other than a bit of a fiddle with the speedo cable). Binnacle itself is attached to the dash with about 10 M4 nuts & bolts (nylocks of course...).

Tim, got them from DT. http://www.demon-tweeks.co.uk/products/ProductDetail.asp?cls=MSPORT&pcode=R/PLN29671AM4 seem to have gone up a bit...... I like the ones with floating nuts (Ooh Err). I usually run a tap down them before use as they can be a bit tight otherwise.

[Chris J]

Thanks for that link Chris.

They're the type to have, are'nt they?

I ought to reckon up how many I need (+ a few more) and order them now, while it's fresh in my mind?

[CorseChris]

They do seem to have gone up a lot since I last bought some. Over £1 for an M4 floating nut version. You'll need some tiny pop rivets or the like to attach them as well. DT never seem to have many in stock and typically have to order them in so order early! I used quite a lot of them on my car. Door panels, headlamp pod inner covers, instrument panel of course, dash attachment to car, heater eyeball vents, rear spoiler, front louver panels. Anywhere that needed a decent thread fitting into fibreglass or thin sheet basically.

I think Merlin do them as well but their website isn't showing a picture of them. http://www.merlinmotorsport.com/index.php?cPath=1695_1696

[strat6v]

Being tightfisted i made my own. I had a load of rivnuts already, some clean steel banding, around 12 mm wide from packs of bricks. Drilled them then squashed the rivnuts in. i reckon i'd have paid around a £100.00. not a bad saving. :)

[rutthenut]

Grumpy Bates (GB Engineering) made some of these up in the past, pretty good quality too. He may consider creating another batch or ten if asked - but that would of course depend on what price he wants to charge...

J.R.

[CorseChris]

Being tightfisted i made my own. I had a load of rivnuts already, some clean steel banding, around 12 mm wide from packs of bricks. Drilled them then squashed the rivnuts in. i reckon i'd have paid around a £100.00. not a bad saving. :)

Used to do a similar trick with rivnuts and plate myself...but I'm getting lazy these days!

[Chris J]

Grumpy Bates (GB Engineering) made some of these up in the past, pretty good quality too. He may consider creating another batch or ten if asked - but that would of course depend on what price he wants to charge...

J.R.

I think I've got some of the GB type lying around.

There's a very good local fastener supplier to me. I'll ask if they're available, what price they are and what quantities they come in.

[Sando]

Being tightfisted i made my own. :)

:D :D So did I, but being even more thrifty ;) I just glassed in some M5 Nylocs :) (Greased a bolt to hold in place while it sets) and like Chris cut out all of the holes to make one big opening. Makes getting behind the clocks for access a whole lot easier.
Been on and off about 5 times now since it was originally and they have held perfectly so far.

And sort of back towards the original thread, they'll be undone again very soon to get my Tacho out to send you for the V6 mod Chris :) :)
chers
Rob