Sigma Oil Pressure Gauge

[Chris Perry]

Dear All,

I once more call upon the wisdom of blatchat for enlightenment!

Whilst blatting this morning my 2010 S3 1.6 Sigma engine momentarily cut out then came back to life with the oil pressure gauge reading 8 bar.

I pulled over and stopped the engine, looked for leaks and checked the oil level. All was in order so i restarted the car but then the oil pressure gauge read only 1 bar at idle and did not increase with revs.

Fearing doom i called the AA who confirmed there was nothing wrong with the engine's oil pressure and that it was either a faulty gauge, sender until or wiring.

I 11 miles drove home but as well as the oil pressure gauge only reading 1 bar and in the red, the rev counter occasionally spiked at 5000 revs even though i was only cruising at 40 mph where 2000 revs is the norm.

I think the culprit could be the gauges as my temperature gauge also under reads. I have heard other owners remark that the gauges Caterham fit could be better.

Is there a direct replacement for the caterham electrical oil pressure guage or is it a fairly simple job to wire a Stack or Racetech guage on to the current Caterham plug which goes on to the gauge?

Or could it be the oil pressure sender that has gone?

I dont really want to fit a mechanical oil pressure gauge.

Thanks in advance for any ideas.

Chris Perry

 

 

 

[Jonathan Kay]

Is there a direct replacement for the caterham electrical oil pressure guage or is it a fairly simple job to wire a Stack or Racetech guage on to the current Caterham plug which goes on to the gauge?

Or could it be the oil pressure sender that has gone?

I dont really want to fit a mechanical oil pressure gauge.

It could be the sender or the gauge that is at fault. (Or just possibly something else but that's unlikely.) It's quite easy to do the initial diagnostic tests: do you have a multimeter?

From what I can tell electrical senders are more unreliable than electrical gauges. And you can make them more reliable by mounting them with a small length of hose to the aperture.

To use another type of gauge you need two things to be compatible: the diameter and the resistance range. Wiring is simple.

If it is the gauge that is at fault then it's probably repairable.

Jonathan

 

[Jonathan Kay]

Whilst blatting this morning my 2010 S3 1.6 Sigma engine momentarily cut out then came back to life...

... but as well as the oil pressure gauge only reading 1 bar and in the red, the rev counter occasionally spiked at 5000 revs even though i was only cruising at 40 mph where 2000 revs is the norm.

Not sure what's happening here. Can you reproduce the fault? Any recent work done?

More when you tell us if you have a multimeter... 

Jonathan

[Chris Perry]

Hello Jonathan,

Thanks for the replies.

Yes i have a multimeter. But not sure what to do with it. Do i check the connections for continuity of the sender connections?

I believe all the gauges are linked, so if one plays up it may cause a fault on another one. I checked all the fuses and they are ok.

Thanks for your help.

Chris Perry

 

[Jonathan Kay]

I believe all the gauges are linked, so if one plays up it may cause a fault on another one. I checked all the fuses and they are ok.

Yes, they probably share a common feed (and fuse) and a common earth. That earth has been known to play up. Probably best to locate it (let us know if you can't), disconnect, clean and reconnect. Then check continuity from the earth lead of one of the instruments to chassis earth.

Yes i have a multimeter. But not sure what to do with it. Do i check the connections for continuity of the sender connections?

I'd start by checking some background points. What's the voltage across the battery terminals at:

1. Rest?
2. Minimum during starting?
3. 3,000 rpm... and how constant is it?

Initial tests on the gauge:

1. Release it from the dashboard.
2. Identify the wires and the terminals on the back. How many are there? The wiring diagram and the wire colours will help.
3. With it connected and the ignition on check the voltage between the power terminal and the earth terminal. 

The sender varies the resistance seen by the gauge. Initial test on the sender:

1. Identify the wire(s) and terminal(s). How many are there?
2. Disconnect the wire(s). 
3. Measure the resistance between the terminals with the engine off, at idle and at 3,000 rpm. You'll probably need to set the meter to a range of 0 to 1000 Ω.

Jonathan

[Dorset AR]

Check the wheel speed sensor earth, this can be the culprit when it comes to erratic gauge action. There has been a modification issued by CC and I know Roger Ashelford has completed the work on his car. 

The electric OP sender on a Sigma is an arse to get but a box spanner (size escapes me) works although be prepared to lose a little skin! The sender is located about a quarter of the way up the engine on the left hand side, above the filter and slightly back towards the bell housing. 

They tend to be quite reliable as they don't get covered in crap and water like a K series one can. I suspect the wheel speed sensor earth is your first port of call. The additional earth loom from CC is £1.98 plus postage. 

[John Vine]

Check the wheel speed sensor earth, this can be the culprit when it comes to erratic gauge action.

That's certainly true of the speedo, but does it also affect the OP gauge?

JV

[Chris Perry]

Dear All,

Thank you for your replies. It is very much appreciated.

I have ordered a new gauge and sender unit from Caterham. I agree, the gauge looks a lot easier to replace than the sender unit!

I checked the wheel speed sensor and the wire is intact and the speedo reads ok.

With any luck it will be the gauge and i will let you know how i get on with it.

Regards,

Chris Perry

 

[Chris Perry]

Dear All,

My electrical issues still confound me.

I changed the oil pressure sender and sub-loom to the main loom. I have 5 bar of oil pressure. Result!

However. The rev counter needle keeps jumping.

I have checked all the earths, engine block to chassis, under the dash board near the wiper motor and front passengers side near the front lights. All are ok and sound ok when i check the continuity with a multi meter.

I have also tried a new rev counter itself and also changed my battery cut off switch but the rev counter needle still jumps.

The connections on to the alternator look ok, but i have not had the unit tested.

Any ideas what it could be.

Im am going to check the earth onto the back of the gauge and also may investigate the wheel speed sensor earth.

Any other ideas would be appreciated?

Regards,

Chris Perry

[Jonathan Kay]

The rev counter needle keeps jumping.

Dropping to zero and recovering by itself or something else?

I have also tried a new rev counter itself and also changed my battery cut off switch but the rev counter needle still jumps.

Please confirm: both rev counters show the same problem? And that's when the swapping is done at the connector on the rev counter itself?

Jonathan

[ChrisC]

From memory, I think the rev counter provides the power to the rest on the instruments, and also the ECU provides the engine speed signal to instruments.   The connections to the pressure sensor and the ECU are on the engine loom, and the instruments are on the chassis loom.     If you have a working oil pressure and temperature gauge now I would check the connection between the engine loom and chassis loom are clean and good (three plugs located above the gearbox), and the earth on the rev counter is good compared to the engine block (not just the chassis). 

[Chris Perry]

Hello Jonathan,

Thanks for the reply.

The second gauge was brand new from caterham. I swapped them by removing the gauge from the dashboard and un-plugging the gauge.

Both old and new gauges do exactly the same thing.

The car idles at about 1000 rpm. But the needle will start to jump to about 3000 to 4000 rpm even though there is no change in the engine revs and then drop back to 1000 rpm. Like it is being revved.

The revs do not drop to 0 rpm.

Thanks for your help.

Regards,

Chris Perry

 

 

[Jonathan Kay]

See ChrisC's post just above: I'd also be looking for intermittent loss of continuity and would start with those connectors + the one you've been plugging and unplugging.

Jonathan

[Chris Perry]

Hello Chris C and Jonathan,

I have checked the three plugs between the chassis and engine looms and they look ok. The pins are all straight and the plugs clean.

I have rigged up a long wire so i can check the continuity of the earth from the rev counter plug to the earth on the engine.

There are a lot of wires on the back of the rev counter.

Am i correct in saying that the green and green and white wires would be something to do with the earth to the gauge?

Thanks for your continued help!

Regards,

Chris Perry

[Jonathan Kay]

Do the connector and wires to the rev counter match this?:

Jonathan

[Chris Perry]

Hello Jonathan,

Yes that is the wiring diagram in my build manual.

Is the ground (earth) G79?

Excuse my ignorance when it comes to electrical stuff and being able to read circuit diagrams. I understand hacksaws and hitting things with hammers much better.

And im not ruling them out soon!

Regards,

Chris Perry

[Jonathan Kay]

Yes that is the wiring diagram in my build manual.

But does it match the actual car?

Jonathan

[Chris Perry]

Hello Jonathan,

Yes i think it matches the car.

Regards,

Chris Perry

[Jonathan Kay]

I really don't like the way they now do the diagrams, but we did decode one in the recent resistor saga. I'll have a go.

Jonathan

 

[Dorset AR]

Absolutely standard behaviour on a Sigma car. 

Both of mine have done it on tick over, a 2010 car and now my 2016 car. 

 

[ChrisC]

B37 is the tacho earth, G79 is the power (joined to G74 from the instrument fuse).   Check the earth continuity between B37 and the earth on the engine loom (two eyelets BY12 / 13 / 14  and  BY 15 / 48 / 49 / 51.   The two eyelets are separate earths in the engine loom, both need to be good.

I agree the occasional flick from the rev counter seems normal at tickover for a sigma, but I was able to greatly reduce the occurrence of this on my car by improving the earth connection between the looms and engine and chassis. 

[Chris Perry]

Hello Jonathan and ChrisC,

This morning i checked the rev counter plug earth and engine loom earths and all were ok.

I had my engine upgraded from 125 to 140 bhp about two years ago and still have the old 125 bhp MBE ECU.

In desperation i swapped the 140 bhp ecu for the 125 bhp ecu and the rev counter gauge stopped bouncing. I think i have an ecu problem. A eureka moment!

Thank you both for your help over the last few weeks. I can feel another upgrade coming on.

Regards,

Chris Perry

[Dorset AR]

From what I've learnt and been told by a man very much in the know - the chances of ECU failure or issue are incredibly remote but I'm glad you've tracked it to where you have. 

 Guess your next move is to get your ECU to CC to have it checked and flashed with the latest map. 

[aerobod - near CYYC]

As there has been an ECU change and a difference in behaviour between the two ECUs, I would check that the 'Tacho Setup' in Easimap for the map you are currently using is showing an appropriate 'Tacho Duty Cycle' value for the new ECU (assuming the 'Tacho pulses per Cycle' are correct as the tach is normally showing the correct rev value). 75% is the norm. Also, depending on the current ECU vs the old one, there may be some signal output voltage level differences that may require a pullup or pulldown resistor to get the correct voltage level at the tach. When I switched from the standard 992 ECU to a 9A4, I needed to put a 1K pullup resistor on the speedo feed.