1999 MG California electrical issues

[BigVic54]

I could use some help.

The PO of my 1999 MG California sport turned the wiring into spaghetti.  I'm trying to get it as close to stock as possible but I have a few issues.





1. By tracing the wires I believe this connects to the Motor Oil Temperature Sensor but I can't find the sensor.  Any ideas?





2. I was told this is the oil pressure switch and I have a wire that would seem to connect to it but somethings missing.  There is no plug.  Ideas?

3. The wiring diagram refers to a Warning Light Connector but I can't find where the wires connect.  Ideas?

Thank you in advance for your help.

[Wayne Orwig]

The sensor in front of the left cylinder that you show, is for the oil pressure light.

The (blurry photo) connector that you show, appears to be the oil temp sensor for a 15M ECU. (small computer under the left side cover). That sensor is screwed into the right cylinder head. Follow the fins around to the inside, from the intake manifold.

The only warning light connector I am familiar with was on the P8 ECU, which was a LARGE computer under the rear seat, which I don't think you have.

[pehayes]

I think the answer is hidden in that blurry picture.  I think I am interpreting the frame angles correctly, so we are looking at the left cylinder valve cover.  If this were a 98, there would be an oil mist temperature sensor right in the middle of that interior face of the valve cover (surrounded by a continuous oil weeping     )  Since we don't see that temp sensor, then the upgraded later version uses a metal temperature sensor in the right side cylinder head as Wayne has described and your computer would thus be the later 15M.  BTW, the sensor in the right head is a weak, plastic device.  Be careful.  Search on the forum for a discussion to replace that with a more-stout brass version.

Yes, the diagnostic light is probably the one in the battery compartment for the P8 computer (which you don't have).  Can you post a scan of your wiring diagram or a url reference if you got it online?

Patrick Hayes
Fremont CA

[BigVic54]

This is the wiring diagram I'm using.  The warning light I mentioned is #44.

Regarding the blurry picture, (I apologize if I'm injuring anyone's vision), there is no sensor that isn't plugged anywhere on the engine.  I've been looking for days and nada.  Do I have to remove something to access it?

[pehayes]

Anything in the interior-facing wall of your right cylinder that looks like this?





Patrick Hayes
Fremont CA

[BigVic54]

Anything in the interior-facing wall of your right cylinder that looks like this?





Patrick Hayes
Fremont CA

No, nothing on either piston.

[pehayes]

Houston, we have a problem.  The computer needs to know engine temperature in order to modulate fuel mixture via injection.  If you don't  have a mist sensor in the left valve cover or metal sensor in the right head, then I have no idea where your computer is getting a signal.  It is possible someone replaced the right side cylinder  head with the wrong model and just left the connector dangling.  I'm not sure which way the sensor operates.  It is either telling the computer that the motor is stone cold or that it is fully hot.  I'm not sure how well it would run in either circumstance.

Patrick Hayes
Fremont CA

[BigVic54]

The bike runs fine without this being attached.

I crabbed the frame to replace the shift return spring and decided to check the wires that were hanging everywhere. 2 went to the horns that were missing. 2 went to the diagnostic light that I apparently don't have. 1 goes to the oil switch that won't connect.  The last one, based on the wiring, should go to the oil temp sensor that I can't find.

Based on a visual inspection the heads match.

I'm tempted to reassemble and forget about it.

[rodekyll]

Gotta find the sensor.  Like they said -- it's essential to the efi.  Give us a wide shot of the inside of the cylinder cleavage, with an emphasis to the right like Pete did.  Also of the valve covers.  Those are the two places the sensor could be.  SOmeone might spot it.  Also, it can't be any farther than the length of that connecting cable.  So your search field is self-limiting.  You might be missing it tucked up close to the DX throttle body.

[fotoguzzi]

the diagnostic light should be under the left sidecover on a '99..  it's a small red LED, should have a sub harness that plugs into the main in the battery area..

Is there a chance the right barrel was replaced with an older version w/o the temp sensor?
is it an EV, Bassa or Jackal?

[BigVic54]

the diagnostic light should be under the left sidecover on a '99..  it's a small red LED, should have a sub harness that plugs into the main in the battery area..

Is there a chance the right barrel was replaced with an older version w/o the temp sensor?
is it an EV, Bassa or Jackal?

Yes, you're right about the diagnostic light.  I just saw that in a parts diagram. Unfortunately, it seems to be unavailable.

If the right barrel was replaced it must have been a long time ago as both barrels look to be the same age.

[fotoguzzi]

the connector looks wrong but could it be for electric fuel tap? do you have a manual tap?

[Wayne Orwig]

We need to know WHAT ECU you have.

Do you have the LARGE computer under the rear seat, or do you have the SMALL computer under the left side cover?

That connector to me implies that you have the smaller 15M, under the left side cover. That means that you should have the sensor in the right head as pehayes shows.

Any chance that the motor was swapped or something odd?

 

[Kiwi_Roy]

If you don't have a location for the oil temperature sensor perhaps bolt a thermistor to a valve cover screw, it may not be quite as hot but very close.

I would make a small aluminum block and JB Weld the sensor inside it.

[BigVic54]

First, I'd like to thank everyone who has tried to help.

I identified the plug by the wire colors and their position on the ECM.  Violet to #22 & Brown/Black to #7.  My wiring diagram tells me its a Motor Oil Temperature Sensor.  I have stretched the wire and searched within its limits and haven't found a plug.

Regarding the ECM, here is a picture:





I took pictures of the barrels:

















Unless you can see something I can't there is nothing there.

Again, thank you for your help.

[bmc5733946]

Either the engine has been changed or the computer has been changed.  It looks like a swap has been made some where along the line, possibly only the top end.  Time to start checking correlation of engine number vs VIN number.  I don't have that information but I'm sure someone here does.  Post your numbers from block and headstock and let the committee evaluate for you.

Brian

[rodekyll]

I'm thinking it's simpler than that.  I think for some reason this '99 had a valve cover temp sensor and the valve cover was replaced.  Is the plug the same for either the head-mounted or valve cover-mounted sensor?  It could be as easy as replacing the cover.

[fotoguzzi]

I'm thinking it's simpler than that.  I think for some reason this '99 had a valve cover temp sensor and the valve cover was replaced.  Is the plug the same for either the head-mounted or valve cover-mounted sensor?  It could be as easy as replacing the cover.

that sounds logical !

[BigVic54]

If the engine runs without this being connevted should I worry about it?

[rodekyll]

It serves an essential function to the fueling.  Without it the computer can't tell if the engine is warm or cold and so it runs rich all the time.  That's hard on everything, and also on your wallet.

[Wayne Orwig]

If the engine runs without this being connevted should I worry about it?

I think the engine, or at least the right head, has been changed. There should be a sensor just under the rubber vent line on the right head. Or at least the missing fins where the sensor screws in.
The valve cover sensor has a different connector. So the harness, does not match the engine.

The computer probably falls back to an over rich condition. Are the spark plugs horribly black. It likely gets horrible gas mileage. And the extra fuel will keep the cylinders rinsed clean of lube and will likely wear the rings fast. About like running with the choke on all the time.

I would at least get a valve cover sensor and find a way yo mount it, as Kiwi Roy pointed out. (the original in the cover mount sucked BTW.

[Wayne Orwig]

I'm thinking it's simpler than that.  I think for some reason this '99 had a valve cover temp sensor and the valve cover was replaced.  Is the plug the same for either the head-mounted or valve cover-mounted sensor?  It could be as easy as replacing the cover.

The connectors are very different.
And the 15M which he has, always had the sensor in the right head as far as I know. Though the head and valve cover sensors had the same values, I'm pretty sure, so likely could be swapped.

[Kiwi_Roy]

I have a few equivalent thermistors, if you send me a PM with your address I will send you one.

It's a bare thermistor so you will have to figure out how to mount it, perhaps a block of aluminum
under a bolt or jammed between a couple of fins.

[Wayne Orwig]

I have a few equivalent thermistors, if you send me a PM with your address I will send you one.

It's a bare thermistor so you will have to figure out how to mount it, perhaps a block of aluminum
under a bolt or jammed between a couple of fins.

I was wondering about jamming one into the fins on the rear side of the head out of the wind somehow.

Worse case you could use a switch and a couple of resistors, like a choke lever, manual on and off. Yuck.
 

[rodekyll]

The connectors are very different.
And the 15M which he has, always had the sensor in the right head as far as I know. Though the head and valve cover sensors had the same values, I'm pretty sure, so likely could be swapped.

That settles that, then.   

So with the 15M sensor location, what is it actually sensing?  It seems that the sort of reading you'd get from the head would be really different than what you'd get from the mist in the valve cover.  If it's looking at actual head temperature, then couldn't a ring thermocouple on a head stud or the spark plug do the same job?

[Kiwi_Roy]

Yes it could except the ECU doesn't have a thermocouple input.
The later VIIs have the sensor in the barrel, it just measures the metal temperature, that's why I say jamb a block of aluminum between a couple if the fins.
The thermistors are readily available for a few cents but of course they don't have the mating plug.

http://www.dpguzzi.com/efiman.pdf
They still used the same thermistors as the P8 ( see chart page 12)

[Wayne Orwig]

So with the 15M sensor location, what is it actually sensing?  It seems that the sort of reading you'd get from the head would be really different than what you'd get from the mist in the valve cover.  If it's looking at actual head temperature, then couldn't a ring thermocouple on a head stud or the spark plug do the same job?

There is a reason that some people would put a switch on the old P8 sensor, and switch in a plain resistor. The valve cover location would never really see the full engine temp, so it would run cold and the ECU would spray in more fuel and get lousy gas mileage.
I'm not sure it did a lot though.

[BigVic54]

Would it be possible to remove the oil pressure switch and put the temperature sensor there?

[pehayes]

Would it be possible to remove the oil pressure switch and put the temperature sensor there?

No.  The passage for the oil pressure feed is a dead end at the switch.  It detects pressure in the system.  At that point, there is no 'circulation' of oil or of heat except over a very long period of time.  Besides, you NEED the pressure detection to save your motor.

Search for a way to put a sensor on engine metal, preferably head metal.  I don't know if the sensor values are the same but in VW days we used to put a special spark plug washer which had leads to a temperature gauge.  Like this:



Maybe Wayne can comment on the actual values.
Patrick Hayes
Fremont CA

[rodekyll]

That's the type of ring sensor we used to use on VW's.  It's what I was thinking of when I asked about ring sensors.  We called it a thermocouple.  Wrong name?