CTS fault???

[dapinky]

Hi guys (yes, this is aimed at the gurus who can read, compare and understand the things that I am simply able to (sometimes!!!) capture)

As per the title, but here is the story.

When I went to Castle Combe it fired up and ran without a noticeable issue (but maybe someone else who was there within earshot whilst I was driving could comment?). But on the Saturday it seemed to idle quite high, no matter what position I put the 'service mode' switch into.... no worries, it seemed to drive okay.

However, on the way home it seemed to be running far too rich (exhaust was/is black) and using more petrol than expected.

It went into the garage until I had time to look at it, which was today.

I set up the laptop to elanscan (W11, using Bluetooth link- connected straight away) and got it talking to the car.

Immediately saw that the CTS says that it was -38C in my (seemed quite warm to me) garage..... so I started it up, and it settled to an idle of about 1350RPM, with black exhaust.

I know that you all want to see a scan log from cold to fans cutting in, then going off again - so thats what I did....... except I didn't!

I forgot to "start logging" and only realised when I went to save the log

Obviously, at that point, it would take ages to let it cool down to start again, so I noted that the CTS read 28C(IIRC), even thought he engine was clearly hotter than that.

I then did a short log from that point to fans cutting in, and off again - which is what I add to this post.

From what I can see, the engine is running rich, at far too high an idle, at low temperature...... and the O2 sensor cannot cope very well, or is working very hard to do so.

When comparing to Raw temperature (which seems okayish to me) I come to the conclusion that the CTS is knackered!

I know I can get the resistance figures, but I need to allow the engine to cool down first...... it says to me that the CTS is doing something, as the range went from -38 to +28 - could it be wiring, or is it the sensor??

I have got a new sensor somewhere, but as I am meant to be off to a car show tomorrow, I will probably prefer to worry about it next week - the show is local enough, at about 5 miles away.

What say the experts????

cts.zip

[muley]

For a 5 mile trip, I'd probably drive the car "as is"

BUT, if I had another Elan I could borrow one from, I'd probably swap it out and drive without checking.

I did have a CTS fail once and the symptoms were very obvious ..

[dapinky]

This is my thoughts at the moment - I can see little point in borrowing more parts from the other car though, as I have a new unit in the garage (I've dug it out of the crate, and it's sitting on the bench!)

My issue is that, to get to the CTS I have to remove the CAS..... so I'll have to look for the new 'O' rings...... and then set the timing.... (even if I mark it up first).....

.... then the old CTS may not come straight out...... and the new one may or may not leak......and then it will all be sorted!

The reality is that the job could take 10 minutes, tops, or it could drag on for many hours if things don't go right first time.

So, as it is running, I think I should have looked at it last week, but I didn't, so maybe leave it until next week.

[chrism]

Hi dapinky I've compared your 'more-odd' EScan parameters in black with my SE in blue. (Imo it doesn't matter if it's not from absolute cold as long as it's stationary...)

Certainly your engine speed is high, but then your a:f ratio is correspondingly low - and these we'd expect to be related. Oxygen sensor seems to be 'struggling' and I'd expect this, too, given the other results. It's not really getting up to temp for ages - and this might be due to the heat of the exhaust gases rather than the heater current. (Btw the red 'ignition' light does go out doesn't it??)

CTS?- imo not absolutely convinced. Your engine temp graph seems normal in the circumstances - but I'm happy to be corrected

I've got a spare O2 sensor if you'd like to try it (which'll only cost postage rather than purchase) - but I think I'd try O2 sensor subst. rather than CTS in the first instance.

Spark advance does seem a bit 'iffy' tho' and, perhaps, that might be another issue - but from your scans it doesn't seem to be directly related to the more obvious fuel guzzling issue. (However if you're renewing CTS you could perhaps clean + adjust the CAS I've heard it's quite easily done...))

Hope this helps in the first instance. I'd be interested in further comments, tho'...(Btw great to see you kneeling in abeyance before the yellow S2 at CCombe wish I'd taken a pic )

[chrism]

Actually, sorry...yes...I can't imagine why I thought your coolant temp was normal. Lookong at your EScan in blue it obviously isn't...

So yes, CTS it is then I reckon...the engine thinks it's cold and is demanding more fuel.

Why isn't the O2 sensor getting up to temp tho'? I wonder if it's been struggling in the past and now your CTS problem has flagged it up as well?

[dapinky]

Chris,

To reiterate and clarify - the ES low temp result is completely at odds with the actual ambient temperature, gauge temperature, and fan switch..... it was about 22C in the garage when ES said the car was -38C..... and when the fans cut in, the gauge was at the usual 3/4 with ES saying 28.6C (so it appears to think it's about 60-80 deg C lower than it should be).

Thanks for your thoughts..... I have a new CTS on the bench, and (clearly) the ES plot shows it reading low.....

....... and thank you for your offer of a Lambda sensor - but I also have one of those in the crate I got the CTS from, so can grab it if required.....

..... I am hopeful that the 'obscure' readings will clear once the ECU stops thinking it needs to chuck an extra bucket of fuel into the engine every revolution, and that no damage will happen to the O2 sensor - but if I change the CTS and then get similar readings, I will look at the new ES trace for what the Air/Fuel ratio is settling at, and likewise the idle - but as it was all fine before, I hope that just a CTS will sort it (but with my luck, probably not!).

[dapinky]

I had a bit of a brainwave - which may work for today....

..... if I simply take the plug off the installed CTS and plug the new one into the socket, and then secure the unit somewhere suitable......

.... if the ambient temp is 20c, then the CTS will tell the ECU that the engine is 20c and fuel accordingly......... far from ideal, but a lot better than telling the ECU that it's -38c!

This will get me where I need to go, and I'll sort it next week......

(I even had a look for a 200 ohm resister to plug into the socket, but couldn't find my box of bits last night.)

[chrism]

Yep a good simple way of finding out for sure, cable tie it for that short journey and EScan it to see about the O2 sensor and spark advance...done...

Spanner it in properly later.

[KenS]

Might need to tape the additional CTS to the cooling hose to get its temperature up a bit, looks like the plots think its at around 27degC and still overfueling. I think the odd O2 sensor plot is just because the ECU is overfueling in response to that low temperature, hopefully it is fine. Interesting to see plots of real cases! Good luck.

[alan e]

Can you plug the new CTS in put it in a bowl and then fill it with hot water watch the reading on ES change without moving the car.

[Simon_P]

Didn't open elanscan symptoms described = 99% CTS

If it causes problems unplug it and drive in limp mode

[dapinky]

Well, I didn't do anything this morning because I was running late..... it was raining on and off during the show, and I decided that getting the plug off the CTS wasn't easy to reach, so I just drove home as it was.....

.... terrible overfueling, and the petrol gauge looks like someone is syphoning my tank for the last 5 miles.

So, it's back in the garagem and I'll do the CTS change this week - I've got a new one, which is a Standard TX3T part, which should be the same as the Elan, as it is for the Isuzu..... if it doesn't read right (although the resistance at ambient (18c) looked right according to the Wikilec numbers), then I have one fitted to my spare engine which I can rob, or even take the one from the blue car - so I'm confident that I can sort it easily.... and if the overfueling has buggered up the O2 sensor I've got a spare one of those somewhere.

Still, at least there is a plan of action.

[muley]

Well, it's a relatively easy fix.

MY minor concern is the thought of the extra unburnt fuel sloshing down the bores and washing the oil away

but I'm probably overthinking it

[dapinky]

Well, it's a relatively easy fix.

MY minor concern is the thought of the extra unburnt fuel sloshing down the bores and washing the oil away

but I'm probably overthinking it

That is something I hadn't considered, but will have to worry about if and when it causes an issue.... too late to do a lot about it now - and the CTS is scheduled for swapping on Thursday. (I'm not going to be driving it before then)

[roj]

Hi Dapinky.

Did you resolve this issue in the end? I too have an Elan guzzling fuel, spitting out black smoke/liquid of the exhaust. Reading this forum and watching multiple YouTube videos point me in the direction of the CTS sensor. It had a new one installed last year but the car has not seen many miles. Did a continuity test on the harness and all good. Likewise checked the voltage coming through and showed 5V. So my reckoning is the harness is okay. I’m thinking hooking up ElanScan and taking some readings.

Just wondered if you had discovered the ‘silver bullet’ to stop the over fuelling and black soot issue.

Cheers,

Rog.

[dapinky]

I ought to have added the finalisation......

.... yes, it is sorted!

Changing the CTS sorted out the terrible overfueling straight away - but it took a few drives to spit all the black crap out of the exhaust.

Elanscan now records a realistic temperature and not the very cold (negative) numbers which the failed one showed.

[roj]

Great. Thanks for coming back to me. The car has only had a 20 minute run since being put back together, new injectors, etc so fingers crossed, it needs more running. MOT expires tomorrow but goes in on Monday so will be interesting to see emissions, etc. Will defo hook up to ElanScan and check the readings to still make sure I’m not in the negative temp figures.

Out of interest, do you know or recall how many journeys it took to clean out?

[dapinky]

Out of interest, do you know or recall how many journeys it took to clean out?

Only a couple of good runs (30 minutes plus) - the gasses were clear pretty much straight away, but the carbon deposits were still in the pipework..... and ended up on the garage workbench!