Stuttering 2010 Sigma 150

[Moggie]

Apologies for those on Facebook who may have already read this, but thought I'd post here for some further input.

I had major problems with the car Saturday; picked her up from S&C after a nose job, and after 20 mins she started violently bunny hopping on the motorway. Pulled in and couldn't restart her. The battery was playing up before and since it had been unused for 6 weeks thought this was the cause.

Replaced the battery and on I went. Same problem and just got worse, only difference I now had the battery to restart it. It was like the throttle didn't work until it got to high revs and then it was fine. At anything under 5000rpm it just choked and spluttered. Oddly I could maintain a constant rpm when out of gear, although the rpm kept dropping on idle and it cut out a few times.  Fuel was very low when I picked it up, however I filled her up and the problems persisted.  If I turned the engine off and waited a few minutes, it would be fine for a minute or two before the problem returned.

I didn’t have any problems (battery aside) before she sat idle for 6 weeks, and I expect she was outside a lot, but that’s no different to home.

Really appreciate any advice as to what may be causing this.

Cheers, James.

[Jonathan Kay]

Replaced the battery

Brand new?

Unlikely to be battery if that's a new one and because it happened while running. But measure battery voltage at rest, while cranking and at 3,000 rpm. 

Then measure battery voltage when the problem recurs.

Recovery after a pause could be fuel starvation from an air lock, but running OK at high engine speed is against that. Check by removing the filler cap when it happens: does the running improve and do you hear an inwards whoosh?

Check connections on feed to ECU and all earths for that and the engine: disconnect, clean, inspect and reconnect.

If those don't show anything I think you're into checking the throttle position sensor and wiring. Visual inspection and wiggle the connections while we're waiting for the experts on diagnosing that.

Jonathan

 

 

[Moggie]

Battery is brand new.  I will check and clean connections.  My only hesitation with TPS is that it seems ok when out of gear.  The problem occurs at low-mid rpm in any gear.

[Jonathan Kay]

Oxygen sensor as another possibility? I'm not sure but I think it was recently suggested that you could disconnect that for diagnostic purposes. Check the archives.

Jonathan

[revilla]

Yes I would go with Jonathan's suggestion above. Certainly worth a try at least.

At lower throttle settings the ECU will be using the lambda sensor to trim the mixture and if it's getting silly readings it could well drive the mixture fully rich or fully lean. At high throttle setting it ignores the lambda sensor because for optimum power and also for cylinder cooling purposes it will actually want to run the engine a bit rich where a narrow band lambda sensor is of no use, so it will just run off the base map and run happily again.

Certainly the K Series ECUs will also drop back to the base map if the lambda sensor is unplugged. Yours may well do the same. If you unplug it and it runs better you should be able to sort the problem properly by replacing it.

Don't just unplug it and leave it unplugged though, you don't want to inadvertently leave the engine running lean as the igher combustion temperatures may do damage and it would be unlikely to get through an MOT like that too.

[martyn]

I had very similar symptoms on my sigma 150.  Spluttering and cutting out at anything less than 3/4 throttle.  Switching off for 5 minutes would resolve it temporarily.  Turns out it was simply the spark plugs. They were completely black - replacing them fixed everything.

Sounds like yours may be something else by the fact that you couldn't restart the car after pulling in.  That sounds like an intermittent electrical problem like a faulty connection.

Probably worth checking the spark plugs anyway just because everything else sounds so similar to my problem.

Do you have easimap and the diagnostics cable?

[Moggie]

Thanks, spark plugs are worth a check.  The battery was low before these problems therefore its failure to restart I don't believe is connected to the running problems.  The battery would have needed changing regardless.

I don't have easimap or the diagnostics cable.

[ChrisC]

I have the cable you need, where are you based?

TPS and Lambda are good shouts.

The TPS is very sensitive on the 150 and to get a clean running car must be spot on.   If its out and you are light on the throttle the ECU could be trying to kill the power, causing the kangaroo. 

The Lambda probe is known to cause problems, but I thought the ECU didn't use the signal for the first few seconds before its up to temp.    Not sure what the ECU would do if its open circuit however.    

You can just swap random parts, or find out what the ECU thinks is going on, which I would recommend.    If you local willing to help

Chris.

[ChrisC]

Also know to fail are the MAP sensors, although no longer used to detect engine load on the 150, they are still fitted and open to the atmosphere.    The opening is upright, and can get water in, which will cause all sorts of problems. 

[Moggie]

I'm in Epsom, Surrey, so sadly not local, thank you for the offer though. Sounds like the cable could be rather handy purchase for future diagnostics.  Is is difficult to get set up?

If the ECU doesn't use the lambda sensor until it's up to temperature, this could explain why the problems didn't start until 20 mins into the journey and only got worse from there.

[ChrisC]

When I say warmed up, the sensor takes about 30 seconds to warm up before lambda information is fed to the ECU.   That said, I know the lambda information is not closed loop, so its only a modifier within a specific range, it wont correct a mapping problem, and I am not sure what effect engine temp has on the map. 

For me 20 mins in, sounds like something failed or slipped, and there is a long list to check, which is why I have the lead.

It was about £100 +Vat from SBD (local to you I think), and the software was a download from their site.    All I needed to do with my 2011 car was plug it in (connector behind rubber bung on knee panel) and plug it into my laptop (USB) and it all worked.  So it was simple to setup. 

I use mine every 6 months or so to ensure the 150 is in tune (TPS set correctly).   It tends to need a little tweak once a year.   When its spot on, it will pull clean in 5th from 950 rpm, when not it tends to have hesitation and starts to be come a pig to drive over speed humps when it gets even further off.

I think its essential to have access to one, and a syncrnometer for the TB's

[paul richards]

Yes I think synchronometer and ECU lead are very good to have if you have a 150 Sigma. I know of 3 Sigmas that displayed the symptoms you have described and in each case the lambda sensor was the culprit. 

[Jonathan Kay]

Very interesting.

Is there consensus that it's OK to disconnect an oxygen sensor for a short time for diagnosis?

Jonathan

[ChrisC]

I think disconnecting wont tell you anything.   The error will different, i.e. "Open Circuit", not "Invalid Signal".   What the ECU does it the specific instances may be different, which may mask the the diagnostic process.     I.e. it runs different when its disconnected anyway, regardless of the sensor being faulty.

I agree with Paul, its not like the sensors have a good reputation, so its a good shout.   A genuine Bosch part is going to cost somewhere in the region of £70 - £90 (more for Ford branding).   There are cheaper options out there.  

But my method would be to have the ECU tell you the problem, then replace the sensor as needed, I know this adds £100ish to the eventual cost of repair, but this is to get the tools for the Job.   If you purchase the oxygen sensor, and its not that, then you would have spent the money anyway, and I bet you can sell the lead a few years down the line if you want some of your money back. 

[John Vine]

I'd agree that Easimap plus a diagnostic cable is the way to go.

But your symptoms do suggest a lambda fault, so while you're waiting for the cable, it's worth doing some basic checks of the lambda sensor.  The connector and wiring are both very exposed and prone to damage, so is everything dry and clean, with undamaged wires?  Also, is the sensor itself clear of sooty deposits? 

And if you have a multimeter, you could check the voltages etc on each of the sensor wires.  There's some useful info in post #40 here (it relates to a Duratec R400, but I'm assuming your lambda is the same, and that your ECU has the same pin-outs).

Edits:

I forgot to add that there's a newly published register of tools and equipment available for loan to members. You'll see from that list that I have a OBD-II MBE diagnostic cable for loan.  Unfortunately, I'm abroad at the moment so it won't be available for at least three weeks.  But let me know if it's of use.

Also, here are some useful tips for testing a lambda sensor.

JV

[martyn]

Disconnecting the lambda for diagnostic purposes won’t cause any damage.  When no lambda sensor is present, the ECU reverts to its default map (or rather it uses the same map it always does, but just doesn't attempt to modulate the fuelling).  It runs in this state during the 30 second warmup timer, and during wide throttle openings.

On my car, the base map is actually pretty close to optimal.  To the point that there is no discernible difference between having the lambda connected or not.

The SBD cable is a good investment if you're going to attempt to fix faults yourself.  Certainly better than randomly replacing sensors.  The easimap software also gives you a very good insight into what’s happening inside the engine and ECU.

 

[Moggie]

Thank you all, you've been really helpful.  Lots of reading to do and things to check now.  I will definitely order the cable.  Thanks again!

[Jonathan Kay]

Thanks.

Any offers to lend these when needed?

Jonathan

[martyn]

Good call.. I've added the SBD cable to the equipment thread.

[John Vine]

Thanks, Martyn -- that makes two!  If you email Shaun (details here), he'll add it to the register.

JV

[diggerman]

Am also a 150SV owner. Its the lambda sensor. Can almost guarantee it!

Your cars age is the same age as mine and your symptoms the same as I experienced last summer. The sensor has a part number printed on it and these can be found on-line for about £25. They are also easy to replace.

if you do replace, suggest you look at the wiring, which in standard form rubs against the underside of the floor and can get damaged. I wrapped mine in a short piece of split 1/4 inch rubber hose and clipped it to the floor.

 

peter

[brianmurray325hotmail.com]

i would check your throttle cable if free to move in its sleeve in it sheath and not frayed. it can give some strange symptoms if it is sticking ever so slightly