No Voltage At The Injectors With The Ignition On Or Whilst Engine Cran

[WALDO 1]

Hi and Merry Christmas

NO VOLTAGE AT THE INJECTORS WITH THE IGNITION ON OR WHILST ENGINE CRANKING OVER

It is my intention to open a new forum topic even though this is not an uncommon problem because I don't feel that that anyone has fully got to the bottom of this one? I hope that I am wrong and I have missed something?

Phase 1 1987 CTI doesn't start unless Easystart is used then fires until the ethanol (or whatever is in it) expires. It is pretty much a phase one car (although on the cusp) and has the Tachymetric relay unfortunately (for ease of access for testing) situated under the battery etc. I have had the car for over 25 years and this is first time it has had starting problems other than for obvious reasons.

Fuel pump etc. etc. are all working. There have been no modifications made to the car.

I have changed the Tachymetric relay with a new one but it didn't make any difference.

I am fairly convinced that this has something to do with the Tachy relay setup.

I am no auto electrician for sure and I am trying to understand the 'mechanics' of the 7 pin relay which I see (at the time of writing) as two 4 pin relays sharing an earth? .

I have studied the relay pins and wiring and from reading the other forums I was of the view that the injector 'rail' voltage supply would come from the Tachy relay as I can't see where else the missing 12V voltage would come from (having studied all the wiring diagrams and all). Having read about other people shorting out the three centre pin sockets to temporarily get the engine to run I take this to be connecting the lIve (positve) input to the fuel pump and injection rail (injectors) supports this idea?

What I don't yet know is does the relay need to be energised in order to allow the through flow (continuity) of the 12v voltage(?) ..... and if so (and I accept that is an if) could the relay need a 'control signal' for example from the starter motor solenoid before the much needed power to the injectors is provided?

Thank you in anticipation of any contributions to this problem and because I have owned this car for so long I may be able to contribute something back.

[DamirGTI 342]

See if this helps : http://www.205gtidrivers.com/articles.html/_/articles-guides/engine-related/what-is-the-tachymetric-relay-r98

 

 

D

[WALDO 1]

Hi

 

Thanks for that link. I had read it before although not till late on because I already knew what a tachymetric relay was. When I did read it I would have to say it is a very comprehensive and useful article and it consolidated everything that my other research had led me to understand .Its title is slightly misleading (in its modesty) in that it goes way beyond simply telling you what a tachymetric relay is. What I don't understand is whether both pins 87 and 87b (the power to injectors etc and the power to the fuel pump) need to be energised before providing that missing power? When I tested the pins on both tachymetric relays (the original and the replacement) there was 0 ohms resstnce between them and the 12v power 'pin' leading me to believe they are of the open switch variety. They would have to be really otherwise they would be on all the time unless something was taking away their 'grounding' etc. It seems at the moment that the fuel pump (load pin) is being energised but the injectors etc (load pin) isn't? At least that is the symptom? Also if the injectors etc. pin needs to be energised - what component provides that 'control' power? I suggested the starter motor solenoid because it appears to be connected (from the wiring diagrams) to the tachymetric relay but I can't understand why? I wondered if this energising was part of a fuel shut off/safety mechanism but again can't readily see why that would involve the starter motor solenoid? This may be relevant or a red herring? What I am sure of is that the lack of power to the injectors etc is the only thing from stopping the car starting and running.

 

Thanks again for your input and i hope you enjoy the festive break.

[DamirGTI 342]

Backprobe the relay connector (relay must be connected) with an multimeter probe on the pin 87 , check if theres battery voltage present whilst cranking .

The relay uses starter motor voltage for an 'pre energizing' phase , afterwards when the engine starts it then uses pulse signal from the ignition .

 

Can check the starter signal also , it's pin 50 - should read 10 to 12V when the starter kicks in .

Also , pin 15 (ignition supply) - 10 to 12V with the ignition ON , and pin 1 (coil signal) - check for continuity between the pin and coil negative terminal .

 

D

[WALDO 1]

Hi again and happy new year

 

 

I think that the ignition side of things- coil etc., are OK. I am now thinking that there is a high resistance on the injection circuit and wondered if this could be caused by a failed component such as the Supplementary Air Device or simply bad wiring the car being 2 years old and all. I say this because I have been unable to bypass the Tachy relay?

 

Thanks and regards.

[WALDO 1]

Sorry 28 years Old.

[WALDO 1]

Hi again

 

The problem in this case transpired to be a damaged wire between the tachymetric relay socket and the injectors. Suspected to to be the white wire which runs from what would be pin 87b to the injectors. The damage to the wire was hidden under the AFM meter and radiator right hand top hose. Repair and reconnection of this wire (and its immediate neighbours) corrected the problem. The Tachymetric relay survived the ordeal without need for replacement. The damaged wire appears to caused by wear and tear - heat - water and oil and vibration etc?

 

 

Regards