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NeilH

CIS Pump Relay, Yellow Crank Wire Odd Multimeter Readings?

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Hi all.

 

I posted separately about cold start issue with CIS on a 1981 Euro SC -  providing Cold Control pressures etc that all look spot on. Still needs 5+ cranks to fire from cold when left idle after 2-days or more! All other running is spot on. I have a second-hand cold start injector on it's way to me to test - and the thermo-time switch tests ok and 12V at the CSV.

However, via the pressure gauge, I can now see cold control pressure starts from 0psi and only climbs about 2-to-5 psi each crank - until finally @ 22psi "bang" it fires"!

Therefore pulled fuel pump relay and measured voltage at socket 87 on cranking - only 9.56volt. Is this too low? Battery is 12.5volt engine off. I also have no starter motor cranking issues. 

This set me off just checking through the yellow wire circuit in case of any high resistance back towards the ignition barrel. Initially disconnected the battery earth and did via a resistance check between battery + terminal and fuel pump relay socket 87. I got what I thought were the below odd results!? 

  

TESTING RESISTANCE BETWEEN PIN 87 AND BATTERY + TERMINAL (LOOKING FOR POSSIBLE POTENTIAL DROPS INITIALLY VIA RESISTANCE);

- Ignition key in OFF position = 1.6Kohms climbing to 3.6K ohms as I connect the meter - think this normally indicates a capacitor charging?!  Could I be accidentally seeing\charging the CDi? But would it need the autoheat switch to be closed in the attached circuit diagram for this to happen?

- Ignition key in Pos 1 = 63.6 ohms (don't understand this load being on the circuit)

- Ignition key in pos 2 = 8.5 ohms (again don't understand this load being on the circuit)

- Ignition key pos CRANK = 0.2 ohms  (only this reading makes sense to me!? Can see I will need to see what voltage drop this gives me when I feel confident to connect the battery again!)

I discovered an immobilizer circuit inserted between the two sides of the connector T1e (in the diagram). This had mislead me into thinking I was initially getting 8.5ohms on cranking. On removing, now get 0.2 and makes sense. But I still don't get all the other readings and would have expected the below;     

- Pos off = Open circuit

- Pos 1 = Open circuit

- Pos 2 = Open circuit

- Crank =  0ohms

I've confirmed I do get these "sensible" readings if I break apart T1e behind the ignition barrel.

Not sure if anyone else can check and confirm meter readings they get on their 1980' 3.0ltr SC or similar? Or if someone can explain if this is correct that I'm seeing? 

 

I'm really not understanding this part of the circuit if these are correct.

Also, is the hot air blower circuit (seemingly "tacked" onto the back of this yellow crank circuit) using the earth through the starter solenoid? Really can't see how it gets one otherwise.

I also noted if I pull the big 14-way engine bay\regulator panel plug, the 1.6Kohms climbing to 3.6K with the ignition off disappears! I ran out of time to investigate any further, but it should only be a single straight yellow wire to the starter solenoid?

I'm a bit confused?

Thanks for any help

Best regards,

Neil   

FuelPumpCrankCircuitbetter-edited.jpg

FuelPumpCrankCircuit.jpg

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Can't help with the other specific questions, but offer an observation on the heater blower operation.

The heater blower stops when the engine cranks, but runs with ignition on otherwise. So I would guess the relay switches to cut power from fuse 23 when powered by the cranking circuit.

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My car's in bits, so can't check any readings.

 

- Agree with SilverWT about the 'strange' connect to the blower circuit - normally the heater earths through the solenoid, except when you energise it (cranking)

- Disconnecting the 14 way connector by the engine bay also disconnects the WUR, Supp Air Valve and Thermo Valve, cold start valve & thermo switch.  By removing the earth connection to the heater blower circuit you will back feed the CDI box - pull fuse 22 while testing to disconnect blower circuit link to CDI.

- Do you have the rev limiter fitted to your car ?  If fitted, that also feeds off the FP relay (pin 86, which is linked to 30)

 

 

Watching with interest

Peter

 

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On 12/19/2019 at 8:21 AM, SilverWT said:

Can't help with the other specific questions, but offer an observation on the heater blower operation.

The heater blower stops when the engine cranks, but runs with ignition on otherwise. So I would guess the relay switches to cut power from fuse 23 when powered by the cranking circuit.

SilverWT.

Thanks for reply.

Unless I'm reading cct diagram wrong - I can't see this "odd" bit of the heater cct operating as a cut-off - am sure its a "supply" instead.

Heater relay has to be energised for hot air blower to run. The single contact of the relay looks like the only way to control the motor in turn.

The 12v to the heater relay (via fuse 22) seems to tee off the CDI 12v supply which will have to be on throughout cranking - therefore the heater relay will get 12v supply while cranking?

The heater ventilation switch that ultimately controls the heater relay - I'm sure - is cam operated off the red lever in my little Auto Heat control box by the handbrake and totally controls that lever. Bizzarely looks like the cct is for heater relay supply - can only see it working via solenoid earth. If heater relay drops out on cranking can only assume it's due to insufficient current to keep it energised at the time. Weird!

I wonder if their are mistakes in the Haynes manual diagrams I'm using - but think they're sourced from porsche anyway. I have just found errors with some numbering of the Continuation labels taking you from one page to the next as well as the location of a couple of connectors.

Done a good bit of amateur car electrics in the past, but seen nothing as weird as porsche wiring! 

 

Thanks

Neil

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On 12/19/2019 at 8:45 AM, PeterK said:

My car's in bits, so can't check any readings.

 

- Agree with SilverWT about the 'strange' connect to the blower circuit - normally the heater earths through the solenoid, except when you energise it (cranking)

- Disconnecting the 14 way connector by the engine bay also disconnects the WUR, Supp Air Valve and Thermo Valve, cold start valve & thermo switch.  By removing the earth connection to the heater blower circuit you will back feed the CDI box - pull fuse 22 while testing to disconnect blower circuit link to CDI.

- Do you have the rev limiter fitted to your car ?  If fitted, that also feeds off the FP relay (pin 86, which is linked to 30)

 

 

Watching with interest

Peter

 

Peter 

 

Thanks for reply

I think you're right that the solenoid is used to earth the heater circuit - I can't see any other way it can work.

My very odd readings at fuel pump relay pin 87 (with relay removed) seem to disappear when unplugging P14 off the regulator - well, at least the suggestion of a capacitor does with ignition key in 0 position - will need to double check pos1 2 and 3 of the key. But I realise P14 suddenly chops loads of circuits - so can assume issue towards engine starter - but pulling fuse 22 is a good call to see if that proves if it's the CDI that I'm seeing.

Will update

 

Thanks

Neil

 

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Just occurred to me - had the car 2 years only. Found heater wasn't working and yellow wire was disconnected off the switch (very same one mentioned) in the auto heat controller. Connected to simply get it working.

Cold start worsening and bad last few months. I've also just noticed through all this, the original fuel pump relay has been prised open and reglued - to clean contacts? 

Wondering if pulling yellow wire was intentional or all just a coincidence. ....

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Not sure that is the correct wiring diagram for you car if you have autoheat.

The heater control unit relay is not a single relay and has multiple connections, not just four. Likewise, the heater ventilation switch is not just a simple stand alone switch with autoheat, there are multiple connections to the black box with the dial on top that sits between the seats.

Even with the simple relay (or maybe a simplified version just for the diagram) shown, power supply to the blower is from fuse 23 to connection 30 on the relay (I can not make out the other numbers). The connections on the left switch the relay. The CDI box has two live feeds to connection 15. If the one via the blower relay is cut, the other can supply power, both feed via different positions on the ignition switch (run/crank).

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47 minutes ago, NeilH said:

Just occurred to me - had the car 2 years only. Found heater wasn't working and yellow wire was disconnected off the switch (very same one mentioned) in the auto heat controller. Connected to simply get it working.

Cold start worsening and bad last few months. I've also just noticed through all this, the original fuel pump relay has been prised open and reglued - to clean contacts? 

Wondering if pulling yellow wire was intentional or all just a coincidence. ....

Good thought, maybe worth pulling the yellow wire again to see what effect it has, if any.

Ian

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Happy new year all :-)

Had some time to look at this again over xmas and now realize I'd been "a bit" daft!

Almost everything seems correct on my yellow cranking circuit now (almost) and since then I've been confident in re-connecting the battery and fitting and trying the new Cold Start Valve\injector to FINALLY sort my cold starting issue! :-)

- I'd been trying to confirm I had no high-resistance in any connectors (ignition barrel as well) along the yellow crank wire between battery + and fuel pump relay contact 87!

- The "odd" resistances (possible loads?) I'd measured on mine came about as stupidly I'd left the yellow wire connected to the starter solenoid!

- By leaving the solenoid "in circuit" it was providing a path (backwards?) in to all sorts of other circuitsvia their earths! Hence the bizzare measurements! I know - now realise how stupid!

- After "pulling" the solenoid - all looked good and clean, expect an odd 500Mega Ohms.

- Have proved this is coming from the heater circuit and appearing between heater relay contact no. 85 and the T1a connector in the rear regulator box. The only thing in this run of the yellow cranking circuit is the Auto Heat switch! I'm not sure if it's an actual physical switch contact in the auto heat or a "transistor" - as I remember from a year ago (when I found the yellow connector unplugged) it's a small PCB. So maybe 500MOhm maybe OK - as long as not enough current is drawn to operate the heater relay in the OFF position.

- I've pulled the fuse no.22 to remove this for the moment anyway - but it proves the heater circuit does "piggy back" off the cranking circuit and uses the solenoid earth!

- Also removed my immobilizer from the same circuit as a test.

- Fitted second-hand Cold Start Injector - and BANG! All now working fine! My old injector had a thin stream jet pattern and not an atomized mist. Many dismissed this as being the "cold start" issue.

Will reconnect immobiliser and auto heat at some point - hopefully without the issue returning!

 

 

Thanks all,

Neil

        

 

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