Tachometric Relay Question

[pslynam 1]

Hi all,

 

New to the forum here having just bought a Phase 1 205 GTi 1.6

 

Basically the car does not run at the moment. There was no spark which was fixed by a new set of HT leads. There is fuel at the rail but the injectors are not firing as the plugs are dry.

 

My question is with regards to the Tachometric relay. The relay is currently removed from the car - I have jumped pin 30 to pins 87 and 87b - so the pump is running and there is power to the injectors and the AFM etc. However I noticed from the wiring diagram in the Haynes manual that pin 9 on the ECU seems to be somehow linked to the tachometric relay - so does the relay need to be installed and working in order for the ECU to tell the injectors to fire or is the relay simply there to provide power to the pump and the other parts of the fuel injection system?

 

Also, where should I go now in terms of troubleshooting why the injectors are not firing?

 

Any help would be greatly appreciated.

[jackherer 543]

There is a small flylead connected to the distributor that supplies a pulse to the ECU that triggers injection, check the connections on that.

[Anthony 1,000]

If that was playing up though there would be no spark either, which if I'm reading Paul's post correctly, he now has.

 

As far as I know, from the relay point of view you just need to provide power to the two thick white cables (from the thick brown supply) and that should be enough AFAIK - certainly that's sufficient to get the car going with a failed relay. It sounds like you've done that.

 

The other connections on the relay from memory are a switched ignition feed, an earth, a feed from the starter solenoid and the signal from the negative side of the coil - basically what's required to switch the coil and keep it latched whilst the engine is running.

 

PS. Treat the Haynes manual wiring diagrams with a pinch of salt as whilst broadly correct, they're certainly not 100% accurate. I've scratched my head trying to work something out before only to strip the loom and discover that it wasn't actually wired how Haynes said (or indeed how you would logically have expected)!

[pslynam 1]

Thanks for the replies lads. Yes I have spark and from the above I think the fact that the tacho relay is not in the car should not stop it from starting given that I have jumped the wires that supply power to the fuel pump and injection components (AFM, injectors etc).

 

I think my next step should be to see if there is a pulse from the -ve side of the coil to pin 1 on the ECU plug (I think this is the pin 1 of the ECU is the one that receives the coil pulse??). However would I be able to test this with a multimeter - i.e. will a pulse signal from the coil to the ECU plug register as 12V on a multimeter or will the pulse be too short to register anything?

 

I was going to try the same thing with the plug that goes onto each injector - i.e. connect the multimeter between the two pins on the injector plug and see if the ECU sends a ground then I should see 12V on the multimeter or again will the pulse be too short?

 

Apologies for all the questions - very amateur mechanic here!

 

Cheers

[welshpug 1,627]

is the rev counter moving as you crank? from memory the signal goes from the coil via the tachymetric relay plug to the instrument cluster and ecu, wire 112 as mentioned.

[pslynam 1]

To be honest I don't know if the rev counter moves while cranking, I never looked. I will check this at the weekend. If the rev counter isn't moving I will refit the tachy relay and see if that causes the rev counter to move, I guess we will know for sure how the wiring is routed then.

 

Does anyone know if the pulses at the ECU plug or at the injector plugs could be measured using a simple multimeter?

[welshpug 1,627]

ive never had success with a multimeter however a power probe does work on a wasted spark coil and the injector triggers

[Telf 222 2 Cars]

Paul,

 

 

To the best of my knowledge

 

Pin 9 on the ECU - it completes the circuit to the injectors from various other components - ie the throttle switch,AFM. I think its a earth/neutral.

 

Anyways after all the issues I had recently I don't believe the injectors will fire if the circuit from the ECU pin 9 to the injectors 37,38,40,41 and to the AFM pin 18A, throttle body 18B etc isn't complete. you can trace it all on the wiring diagram.

 

If you look at the Haynes manual for testing the throttle switch it states between pin 2 and 18 expect zero throttle closed and 3 and 18 zero throttle open. That pin 18 is connected to wire 9 from the ECU and also to the injectors.

 

I therefore think it is a earth/signal return, and therefore your injectors wont fire if the circuit isn't complete.

[pslynam 1]

Cheers for all the replies, will investigate more at the weekend and report back

[Telf 222 2 Cars]

Paul,

 

there is an article on the forum- what is a Tachymetric relay - have a read of it. I'm fairly certain looking at the wiring diagrams that the information about the pin outs is incorrect, terminals 87 and 87b are the opposite to what is described.

 

This seems to bear out looking at the wiring diagrams.87b (wire 18) is common to the injectors/AFM etc and 87 (wire 76) supplies the pump.

 

Ofc the diagrams may be wrong but a simple check with a multimeter will conform or deny.

[pslynam 1]

Success! Got the car started over the weekend. After Welshpug queried whether or not the rev counter was moving when the engine was cranking I noticed that it wasn't. From the wiring diagrams it appears that the wire from the coil supplying signal to the rev counter also supplies signal to the ECU to tell it that the engine is turning over and hence fire the injectors.

 

Cleaned up the contacts on the -ve side of the coil and on the wire and also cleaned up the ground, car fired straight away. Now its misfiring badly and won't rev above 2,250rpm but haven't put everything on the spark side back together properly yet so I'm hoping that may be the cause.

 

Incidentally the car started without the tachy relay in place - I had simply jumped pin 30 of the relay socket to pins 87 and 87B to supply power to the fuel pump and fuel injection components.

[Telf 222 2 Cars]

good work,

 

87 is the fuel pump supply and 87b connects to the injectors.30 is the permi live from the battery so that would seem to make good sense.

 

I may be mistaken but I don't think you need a permi live to the pump- if its running badly it could now be overfueling? I think the tachy relay shuts the supply to the pump off once the car is self sustaining- if im wrong someone will correct me im sure.

 

(fairly sure a common fault is a continuous running pump which is caused by a sticky relay)

[welshpug 1,627]

without power to the pump you wont have any fuel pressure

[pslynam 1]

Well fromm reading up on the tachy relay I think it gives a constantt feed to the pump when the car is running. I guess any unused fuel is just sent back to the tank on the return line??

 

I've noticed that the pump doesn't prime when I switch on the ignition, it only kicks in when the starter is engaged - is this correct?

[pslynam 1]

Should have mentioned in my previous post that the tachy relay is now fitted in the car - pump doesn't prime though with ignition on, only primes when starter is engaged...

[Tom Fenton 1,526]

Some do prime others don't. As long as the pump runs as soon as you crank the engine it will work fine.

[Telf 222 2 Cars]

I knew I'd get corrected pretty quick so thanks Mei. I'm used to working on fuel pumps that only operate during start so I can never remember what my 205 does.

[WALDO 1]

Hi

 

I don't know if i need to open another thread on this topic. I opened one on Tachymetric relay - no power at the injectors etc., but kind of killed it off by suggesting bad wiring?

 

I have been away from the car for 6 weeks but have resumed work on it. I was interested to see (from welshpug) that the rev counter should move when the engine is cranking. Mine doesn't and that now makes me wonder if this is the key to the problem? Telf mentions a lot about the wiring circuit being complete. This presumably could involve the components themselves eg: the ECU? My car will fire up on 'Easystart' so the ignition side seems OK. I have cleaned the coil terminals and 'ground' without success. There must be other areas I need to consider? Auto electrics isn't my strong point. In the past i have simply replaced components.

 

Any contribution would be appreciated.

[Anthony 1,000]

If the car starts on easystart then like you say the ignition side of things is fine.

 

The tacho should flutter when cranking, but I've seen a few cars where this doesn't happen even when there's no problem - I've just put it down to a slightly lazy tacho.

 

In your case, to rule out the tachymetric relay use a length of wire to bridge the thick brown wire (constant 12v) to the two thick white wires (fuel pump and injectors) as a temporary measure. The fuel pump will run continuously and the injectors constantly powered. If the engine now starts and runs, it's likely the tachymetric relay is faulty. If it still doesn't run, it's time to dig out a multimeter and see what's what - starting with checking for 12v on the thick brown wire at the relay.

 

Jetronic ECU's are typically very reliable so I wouldn't be immediately suspecting that of fault unless you've other reasons to.

[WALDO 1]

Hi Anthony

Thanks for that. I did buy a new Tachymetric relay and tried it to no avail. I have tested the large brown wire to the Tachymetric relay socket and it appears to be permanently live. I did bypass the relay and joined what would be Pin 30 (Brown) to pins 87 (blue wire on my car car) and what would be pin 87b (white wire). The car didn't start unfortunately and I noticed that after a few minutes smoke started to come up through the engine bay . Fortunately I had my head under the bonnet so quickly disconnected one of the battery terminals. The relay etc lives under the battery. Although this is an unfortunate development I am inclined to think this may be a clue to the problem. What I can't imagine is what would cause such an event? I couldn't see exactly where the smoke was coming from. I have to guess the wiring loom? I am hoping this means something to someone? My only instinctive reaction at the moment is to try and physically follow the wiring loom to see if it is damaged anywhere but as you will know that is not easy on a 205 GTI engine. Any pointers would be appreciated

Thanks again

[Anthony 1,000]

Oh dear, never good when the smoke is released from the wires

 

I suspect that you're right in that it's a clue to the underlying problem, as what I described above is only effectively emulating the connections that the tachymetric relay makes when it is energised and thus shouldn't cause wiring or components to overheat and is something that I've done many times over the years without issue when testing or as a get me home fix.

 

Assuming the engine wasn't running or cranking over at the time then it's almost certainly wiring that's overheated from carrying too much current (probably from shorting) and melted. Not enough information to begin to guess exactly what without knowing at least where in the engine bay the smoke came from and preferably the wire(s) or connector(s) that have melted.

[Tom Fenton 1,526]

Kit available here that might help!!!!!!!

 

http://www3.telus.net/bc_triumph_registry/smoke.htm

 

[WALDO 1]

Hi again

 

I thought Tom's contribution was entertaining . The smoke (of which I suspect there is no shortage of smoke not electrics) appeared to come from somewhere between the battery and the inlet manifold. I have removed the air flow meter and will dig down until I can find something melted etc. I did disconnect the battery quickly in an attempt to minimise damage. If it is melted/shorted wires then at least it is a 'physical' problem which should have display some physical evidence? I could bypass one of either the blue or white wires separately to confirm the culprit. The suspicion of course is the wiring to the injectors AFM and temperature sensor, which I understand to be what would be pin 87b on the relay which is also the white wire. The blue wire on my car going to the pump. It is reasonable to assume that the white wire splits into three wires at some point and wondered if this could be a point of weakness? I will investigate further and report back.

 

Thanks again

[WALDO 1]

Hi again

I have dug down. I removed all the air inlet hoses, drained the radiator and removed the top right hand (as you face the car engine bay) radiator hose. The wiring arrangement is far more complicated than I had anticipated. That said in the centre and below the radiator hose is a 1/2" diameter group of 7 wires leading off towards the inlet manifold and injectors etc. These wires are in very bad shape. 2 or 3 of them have broken through and there is a lot of sheathing no longer there. I obviously made the situation worse by bypassing the relay but there must have been a problem in this area and the smoke gave me a very good idea where to look etc. My plan is to study a little about what the wires are and replace probably 3 or 4 inch sections of most of the wires. My only concern is the initial damage to the wires a symptom of a problem eg: seized injectors or likely to be age related wear and tear?

My initial appraisal of the wires is

2 X White (although they look a bit pale yellowish)

1 X Green and yellow striped

1 x Green with yellow dots every 3/4" or so

1 X Small white blue

1 X Small orange

1 X Smallish green wire

In the absence of any further advice I will carefully reconnect the wires as mentioned and take it from there.

[Telf 222 2 Cars]

Alan,

 

I've had my main loom out recently and spent a good while cleaning and inspecting the wires - particularly the ignition and injectors. The wiring to the injectors has additional fly lead type wires that are effectively soldered onto the parent wire then covered with a environmental seal. They may not be as bad as you think if these are the wires you are looking at.

 

Can you post a picture- it would help no end in identifying what's happening.

 

You may be as well buying a second hand loom (possibly). Do you have much wiring experience?