freddyuk

Yes seems to be, Fred

FredR

I take it you understand that the sender Adrian is talking about is the one for the dash panel- not the temp2 sender- gthey are different animals.

Did you get any further measuring your temp2 sender output?

freddyuk

Ah, OK, no I was half thinking so thanks for the nod. Not sure which is which when I get under the bonnet but will figure it out. Still not had chance to check but may get time next week as I'm off work looking after my kids - if they can stop killing each other or wrecking the place for a few minutes!

StratfordShark

Yes U.K. owner. I got sender from Rose Passion in France, but any OPC will supply.

Arrived today with some other parts. It measured around 1600 ohm in icy water, and 45 ohm in boiling water. Almost exactly same readings as the original, so I didn’t actually need a new one!

Wisconsin Joe

Actually, no. The temp sensor for the dash has two pins because it sends one signal to the gauge and the other signal to the warning light.

Both the dash temp sensor and the Temp II ground through the mount to the water bridge. That's why powder coating the water bridge has to be done in a way that leaves the mount point for the sensors bare metal.

And for Freddy:
An 'external ground' is simply a good ground point. The sensors carry current from ground on the water bridge, through the variable resistance of the sensor to the computer or dash.
You can get a good resistance check by putting one probe from the meter on the pin on the sensor and the other probe any where you can get a good ground (hint: the water bridge itself is one, and it's right there).

FredR

Joe,

Thank you for correcting my comment- have been working on my LH/EZK harness recently and it slipped my mind that mine [being a digi dash model] is somewhat different thus my comment is not applicable to the pre digi dash models that do not have the same level of sophistication. Thus I presume that the sender in question has an analogue channel and a switched contact for the alarm.

The [potential] problem about grounding on powder coated bridges applies to both items just the same [FYI].

Wisconsin Joe

Yes. Variable resistance for the gauge and 'on/off' for the light.
Different sizes so it's harder (not impossible) to put them on wrong.

I was unaware that the digital dashes were different.
Haven't we taught each other the differences between older/less old cars before?

FredR

​​​​​Probably!
As I can fathom the digi dash must have a built in trip amplifier to detect an alarm value and they seem to use a separate discrete earth directly wired to the panel. However the digi dash oil pressure sender still has two discrete channels-one analogue and one alarm with a discrete earth cable thrown in dor good measure. Ironically I could not my oil pressure sender out despite new cables and reverted to an earlier two pin oil pressure sender to get it to work correctly.
Logic is not always readily apparent with these cars!!

freddyuk

Hi all,

I managed to get an hour on this yesterday and measured across one pin to the water bridge (@FredR - I don’t know how to locate and test the LH EZ, passenger footwell near the fuse box?) and after 10-15 mins of idle on a freezing wet british summer day I saw a reading of 480 ish ohms, decreasing as the coolant temp increased - something is working, and if I pull off/put back not he plug it changes the engine sound. Are the readings likely to be close to what you posted from the WSM?

Is it best to remove and test in a jug of water with a thermometer for more accurate measurement?

It’s pointing to being something else, I’m guessing so what would be the next thing to look at?

Thank you all for all your help, as ever!

FredR

The computers are usually mounted on a common frame bolted to the inner wall of the body just in front of the passenger door at foot level. There should be a carpeted cover with a foam pad underneath held in place with a black thumb screw or whatever they are called.

You can tell which computer is which by the labelling- for ignition you will see the letters "EZF" on the casing and for fuel injection "LH" somewhere in the part number descriptors. The plug terminal layout is depicted on the wiring diagram for your model year attached below- one row of terminals has two extra pin slots so easy to figure out. The plug terminal numbers for the two temp2 channels are 23 for the EZF plug and 2 for the EZF. The earth pin for EZF is 12 and for LH is 5 if yours is same as in my WSM.

Resistance drops with temperature and at 80C should have a value of 400 ohms or less. The computers are programmed in steps as per the list I posted earlier. Once the computer registers 80C the engine is fully warmed up as the computer is concerned- If the resistance value is higher than 400 ohms it will add unnecessary fuel. When you measure the resistance values on the computer plugs they should be same as they are on top of the sender.

Trust you haave a decent digital multi meter- some of the cheaper ones can be bit erratic- suggest you check over a known resistance value if you can

freddyuk

Thanks Fred, I may be able to check this today after work.

If it's fine what would you recommend looking at next? Air intake temp sensor?

FredR

I am not familiar with the air intake sensor function on your model but presumably it does the same thing on your car as it does on mine and presumably drives the auxiliary electric fan on your car upon shutdown as and when the switch is triggered. Assuming that is correct it will have nothing to do with fuelling at all.

I think I need refreshing as to your problem which is an over fuelling problem if I remember correctly. Have you checked the condition of the plugs recently- presumably they are showing up as sooty. A wideband O2 sensor is a useful tool but I assume you do not have such kit. Knowing the AFR and the operating point helps diagnosis a lot. Too much fuel pressure will cause over fuelling. The fuel pressure regulator and the dampers are referenced to the vacuum inside the plenum. If by any chance the vacuum lines are compromised and see atmospheric pressure the reference point will be wrong for all but full throttle operation and the lower the engine speed the more the error will be. The fuel pressure regulator is the main problem but the dampers will not work correctly if they are compromised so make sure they are all present and correct.

What condition is your MAF in? MAF problems tend to under read air flow and that causes a lean condition. If you have not done so you might consider sending your MAF to Mike at JDSPorsche.com for a calibration check. I think he is in the Maidstone area- if you are close by you could pop in but as I recall you are in Devon- still the Royal Mail are operating and reasonable. The wiring loom into the MAF can [will?] be in poor condition so given that measures resistance in the hot wire I suppose excessive resistance in the wiring could change the reading but I am not sure how that translates in terms of false high or false low.

Given that you have the LH/EZ system you do not have a warm up regulator to worry about. Fuel injectors tend to clog up and thus reduce flow leaving a lean condition so that is not likely to be the problem. A partially blocked air filter will not show as a immediate problem or cause over fuelling- just a loss of power - cannot think of anything else at the moment.

freddyuk

Quick update: I have run out of brain power and talent, but fortunately found a local indy that knows 928s and can have a look at this for me so when I get some info in the next few weeks I'll post it here to help those in future. Thanks though everyone who has contributed here and given me further insight into how these beasts work.

John Speake

Braunton Engineering

freddyuk

No, I spoke to them recently and their 928 guys are all gone, this is Oaktree in East Devon