Should the resistance be the same at both ends ?

[maston]

Hi All,
Still trying to diagnose my running faults and my question is :-
Should the resistance be the same for the coolant temperature sensor wiring at both the ecu multiplug end and the sensor end ?
The resistance at the ecu multiplug was 4300 ohms and the resistance of the wiring at the sensor connection end was 1050 ohms ?
Should this be the same and therefore could this be the problem of my running problems (it will now not even start !).
I look forward to your replies.
Regards
Ian

[Wedg1e]

It should, as long as you definitely have the right terminals. A loom in good condition would add negligible resistance (an Ohm or so at most).

[maston]

Wedg1e said:

It should, as long as you definitely have the right terminals. A loom in good condition would add negligible resistance (an Ohm or so at most).

Thanks Ian, not sure what you mean "right terminals" ? (sorry I'm a complete novice).
Also what do you think the results mean, a broken wire somewhere ?

Cheers
Ian

[Wedg1e]

maston said:

Thanks Ian, not sure what you mean "right terminals" ? (sorry I'm a complete novice).
Also what do you think the results mean, a broken wire somewhere ?

Cheers
Ian

I just meant that the readings would be wrong if you were measuring across the wrong terminals, pins, prongs, whatever you want to call them, at the ECU connector.
A broken wire would probably give you infinite resistance (open-circuit, as it's known); excessively high resistance could be caused by corrosion of the wiring or poor connection of the spring 'fingers' in the temp sensor connector - they are easily bent so if they don't have a good 'bite' on the sensor pins you might see high resistance.
Hang on while I grab my book of words...

[honestjohntoo]

maston said:

Should the resistance be the same for the coolant temperature sensor wiring at both the ecu multiplug end and the sensor end ?
The resistance at the ecu multiplug was 4300 ohms and the resistance of the wiring at the sensor connection end was 1050 ohms ?
Should this be the same and therefore could this be the problem of my running problems

I suspect from your description you are not performing the test at the sensor end correctly.

Also, it helps to know the approx temperature at which the measurements are taken so I'm assuming something about 10 deg C, which makes the measurement at the multiplug with sensor connected about right.

I wonder if you have read through this? You'll also see mention of the earth tag connections which I still dont know if you have them connected properly.

CTS Testing

Circuit

The CTS has a silicon element that changes its resistance to signal a change of temperature so the ECU can compute injector "open time"

It is connected to pin 13 and earth pins 5,16,17 and 35 of the ECU. The other (very important) earth on the black/white (BW) wire is a heavy duty ring tag on the Efi loom going to an earth stud on the engine block behind and below the LH rocker cover





Conditions as follows: Engine HOT, ECU multiplug disconnected as in A: Ignition OFF: Measure coolant temperature with thermal probe: Connect an ohmmeter as shown in B below and take a single reading. Compare it to the resistance/temperature profile below. Consider connecting the ohmmeter for only short periods, not in fear of damage, but the meter battery may cause the sensor to heat up and give an incorrect reading. Allow the engine to cool and take further readings. If the measurements match the profile within (say) 10-15%, the CTS and its connections are OK.



TEMP.......OHMS........TEMP........OHMS

-10°C...9100-9300....60°C.......500-700

0°C.......5700-5900....80°C.......300-400

20°C.....2400-2600....100°C....150-200

40°C.....1100-1300

If the readings are clearly wrong, remove the sensor for a controlled test using a pan of water and thermometer.

Suspend the sensor in the water and bring to the boil. Compare resistance readings to the profile. Variations of (say) 10 -15% are not critical but if they are obviously way off or there is a clear intermittant or distorted result then consider the test failed. Obtain a replacement unit, check it as above to verify OK, fit it into the manifold and reconnect to the Efi circuit. Reconnect the ohmmeter as in B and repeat the measurement between the ECU pin 13 and earth. If this still incorrect there is a wiring problem so check the black/slate wire (BS) and black/white wire (BW) and their connections paying particular attention to the earth stud at the rear of the engine.

more here

http://www.vintagemodelairplane.com/pages/Rover_Te...

[Wedg1e]

Who does own the copyright on those pictures?

[maston]

Wedg1e said:

I just meant that the readings would be wrong if you were measuring across the wrong terminals, pins, prongs, whatever you want to call them, at the ECU connector.
A broken wire would probably give you infinite resistance (open-circuit, as it's known); excessively high resistance could be caused by corrosion of the wiring or poor connection of the spring 'fingers' in the temp sensor connector - they are easily bent so if they don't have a good 'bite' on the sensor pins you might see high resistance.
Hang on while I grab my book of words...

Thanks for your reply, in case I didn't measure it correctly (quite likely !) I connected the multi meter to pins 13 (cts) and 5 (an earth) of the ecu multi plug, then I reconnected the multi plug and disconnected the cts and measured the wiring of the cts connector itself by insering the multi meter into each pin actually on the connector ?

Is this right ?

[Wedg1e]

maston said:

Thanks for your reply, in case I didn't measure it correctly (quite likely !) I connected the multi meter to pins 13 (cts) and 5 (an earth) of the ecu multi plug, then I reconnected the multi plug and disconnected the cts and measured the wiring of the cts connector itself by insering the multi meter into each pin actually on the connector ?

Is this right ?

Sounds about right.

Edit: you didn't mix up the thermo-time switch with the coolant sensor did you? The CTS is the smaller of the two...

[maston]

Wedg1e said:

Sounds about right.

Edit: you don't mix up the thermo-time switch with the coolant sensor did you? The CTS is the smaller of the two...

No, i double checked that, thanks anyway.
So, am I right in thinking that the cts wire or the earth wire might have a break somewhere in the loom ?

[Wedg1e]

honestjohntoo said:

Consider connecting the ohmmeter for only short periods, not in fear of damage, but the meter battery may cause the sensor to heat up and give an incorrect reading.

I doubt the 0.0324W of heat generated (by dropping 9V across 2500 Ohms, ignoring internal impedance of the meter) is going to make a blind bit of difference. You could impart more heat with your fingers.

[maston]

[quote=honestjohntoo] suspect from your description you are not performing the test at the sensor end correctly.

Also, it helps to know the approx temperature at which the measurements are taken so I'm assuming something about 10 deg C, which makes the measurement at the multiplug with sensor connected about right.

I wonder if you have read through this? You'll also see mention of the earth tag connections which I still dont know if you have them connected properly.

I tested about 2 hours ago.
Also regarding the earths they are on 2 seperate bolts on the side of the block (but not like my 390 where the earths are all on 1 bolt at the top of the block just behind the LH rocker cover ?
Thanks for your reply

[Wedg1e]

maston said:

No, i double checked that, thanks anyway.
So, am I right in thinking that the cts wire or the earth wire might have a break somewhere in the loom ?

What you could try is... strip the loom insulation and identify the wires that take the CTS signal to the ECU (usually Black/White and Black/Grey). Strip a few mm of insulation and then link the two with an offcut of wire. This kids the ECU into thinking the CTS is bloody hot
See if it'll start. If it will, remove the link wire, tape up the cuts and poke your link wire into the CTS connector. See if it'll start. If not, you have a broken or high-resistance loom.
Might sound a bit 'animal' but I grew up fixing cars at the roadside, I'm an electronics field techie and often have to dream up diagnostics techniques on-the-spot. You have to work with what you have in front of you, and if you have no spares then eliminate what you can.

[maston]

Could I also try and make a new temporary earth by bridging some wire into the cts connector and the engine block to see if it is the earth wire at fault somewhere ?

[Wedg1e]

Yes, that would be worth a try.
Quickie for you: with the ignition on and the cold start injector unplugged, if you blip the throttle (by hand) can you hear all the injectors 'tick'? If so, repeat a good few times then try to start the car. If it fires then dies you are getting fuel via the injectors so the ECU is at least doing 'something'...

Do I recall you said you thought it was overfuelling? It may be that the lack of starting now is that either the plugs are wet or fouled, in which case a good clean may be necessary or you will go round in circles.

Edited by Wedg1e on Tuesday 3rd January 00:16

[maston]

Wedg1e said:

Yes, that would be worth a try.
Quickie for you: with the ignition on and the cold start injector unplugged, if you blip the throttle (by hand) can you hear all the injectors 'tick'? If so, repeat a good few times then try to start the car. If it fires then dies you are getting fuel via the injectors so the ECU is at least doing 'something'...

Do I recall you said you thought it was overfuelling? It may be that the lack of starting now is that either the plugs are wet or fouled, in which case a good clean may be necessary or you will go round in circles.

Edited by Wedg1e on Tuesday 3rd January 00:16

Aah, firstly, yes correct it was completely over fueling when it did start (does not now at all) with plumes of black smoke etc.
Now, just tested ignition on, cold start injector unplugged and NO ticking or any noise from the injectors whatsoever !!! Ok, the battery is a bit flat but still...nothing from any of the injectors.
Also at the weekend I took all the plugs out but they were dry so I wonder if it is the ecu which is now at fault due to it not sending any signal to the injectors ?
It can't be the fuel pump as it is brand new.

[Wedg1e]

maston said:

Aah, firstly, yes correct it was completely over fueling when it did start (does not now at all) with plumes of black smoke etc.
Now, just tested ignition on, cold start injector unplugged and NO ticking or any noise from the injectors whatsoever !!! Ok, the battery is a bit flat but still...nothing from any of the injectors.
Also at the weekend I took all the plugs out but they were dry so I wonder if it is the ecu which is now at fault due to it not sending any signal to the injectors ?
It can't be the fuel pump as it is brand new.

When my ECU threw a wobbler on the way to Wedgefest ('08 or '09, I forget which) it used half a tank of fuel in 89 miles . I 'fixed' the overfuelling by unplugging half the injectors sounded like an Impreza but still did 90 (er, KPH ). A good shoeing later and normal service was resumed. However the car would actually start, unlike yours.
Maybe what I need to do is charge for providing information, then I could buy a swanky house darn sarf and spend my days fixing Wedges... Even Peter Wheeler admitted his export market was South-East England.

Edit: actually I'll be on the south coast for the next few weeks from Monday so if anyone does need a fix...

[maston]

LOL, I'll certainly be a customer, especially as I have 2 wedges that are currently f*cked !!!

Seriously though, if you or Adam Quantrill or any other wedge expert are in the essex area I have beer tokens waiting !

[Wedg1e]

If you could introduce a few capfuls of petrol to the plenum chamber that may allow it try to fire up; if it does then you at least still have sparks.
The injector 'tick' is the ECU thinking you've just floored it; it gives all the injectors a quick squirt, in the same way as the acceleration pump on a carburettor, however it doesn't know that the engine isn't running so squirts anyway!
It could be a number of things, from a really bad earth to dead coil to no 12v supply to the throttle pot unplugged to the ECU disconnected (seen it done)... but in light of the overfuelling prior to that it equally could be a major ECU fault.
Does your other wedge have the same type of injection? Might be worth an ECU swap, can't do any harm even though it's unlikely either car will run properly on the other's ECU.
Lucas matched the ECU and airflow meter in the factory, and each application also sees some component value differences between ECUs but 4CUs can be swapped for elimination of some problems. This is why buying random ECUs off Ebay is almost never a success; you may get close between two 3.5 RangeRovers or even two standard 350i's but throw in some tuning work or a doctored AFM and you can forget it.
I have over a dozen ECUs here and have worked on many more; myself and several others on PH have compared data and I'm still waiting to see two the same.

Edit: I never claimed to be an expert, I just don't like paying people to do jobs I can do myself

[adam quantrill]

More background info on this story is that the engine was running fine before clutch replacement. During this operation the engine was moved forward a number of inches (probably 6 or so) but nothing disconected. So I started suspecting the loom had been damaged slightly leading to high readings at the ECU end. Usually this procedure is fine but our looms are getting older and more brittle as the years pass.

As the CTS is 'floating' with respect to the block it's fairly likely that the 4300 ohm reading is off the correct multiplug connectors - get one wrong and you will get infinite ohms (barring shorts in the loom).

Rather than baring the wires I suggest sticking a pin through each one - it's much less invasive. On the other hand baring the wires will reveal the dreaded tarnished copper if there is any. Then short out the temp sensor at the ECU end, which bypasses the wiring fault, for a quick test.

If this has proved the fault (it might still be elsewhere) then proceed by testig each wire individually from the ECU to the temp sensor, and re-wire these as necessary.

[honestjohntoo]

maston said:

The resistance at the ecu multiplug was 4300 ohms and the resistance of the wiring at the sensor connection end was 1050 ohms

I think a PO may have wired a 10,000 ohm resistor into the sensor connector to cure engine surging, and the measurement taken was not 1050 ohm but 10,500 ohms, when measured from the open end of the sensor loom.

Rover SD1 Efi System Hunting or Surging is when the engine idle speed rises and falls usually immediately after starting and more often when the engine is quite cold. This annoying condition is generally fixed by putting a 10,000 ohm resistor across the Coolant Temperature Sensor (CTS) terminals, soldered neatly and safely to the wires inside its connector shroud.

This resistor trick first emerged in a post production Technical Bulletin, around 1986-8 to correct a characteristic that manifested itself during the warranty periods, requiring dealership intervention when the customer reported the phenomenon.

The whole nine yards is here:

http://www.vintagemodelairplane.com/pages/Snippets...