Sigma 150 missfire at low revs

[DRH]

Hi Chaps

Experiencing a misfire at low revs, looking at many posts that suggest this was a problem with the 150, ideas so far ECU, Lambda, TBS, Map sensor.

Any help would be very much appreciated

[Domus]

 

From my experience of the 150 I would look at the lambda first. 

After that a new TPS loom, the wires cook and play havoc with the idle settings. Mine is now cable tied away from coolant hose. 

 

Good luck 

[ChrisC]

Have you got the basic right first?  

Balanced TB's, at the correct idle and the TPS set at 1.03v.   If not then that's where to start first. 

Mine needed checking/resetting about once a year.   

 

[DRH]

Hi Chris

Was it you that posted help on this subject back in 2014

[Domus]

 

I set mine to 1.04v

 

Will it make much difference?

[ChrisC]

Yes, in 2014 I converted a 2011 125 to 150 against the trend.  When my car was new the 150 kit was the upgrade, so that's why I went for it.  I did hours of reading on here and knew the pit falls of the 150 kit.   The kit was fitted by a caterham specialist, but drove like a pig when I got it back.  Once I set it up according to my posts the car was transformed.   When I sold it, last year I had comments on how smooth it drove, better than 140 examples potential buyers had test driven at caterham.  I would say it drove better than my 360R, which is my only regret about the change.  

As for 1.03 vs 1.04, it all depends on the throttle site the ECU is using.  The ECU seems to idle at 0 throttle site, and wants to pull away at 1.  Set to low you will try and pull away when the ECU is trying to idle the engine and you get hesitation at low speed.   Too high and the idle is poor, and you get problems when you're off throttle.    Without the MBE lead you just can't tell.

More than happy to check and tweak 150s for anyone local, I still have the syncronometer, and MBE lead.

[huwp]

If the misfire occurs once the engine is up to temperature my experience (currently on my third) would suggest the lambda sensor.

[ChrisC]

You can always test that, get the car up to temperature.  Then switch off, wait a few seconds, then start again, you then have the lambda sensor warm up time (90 second I thing) before the ECU uses it.  Mine tended to be rich during that period.  Obviously with the lead it's very simple to check the running status of the lambda sensor. 

[DRH]

Disconnected the Lambda sensor and problem solved, wasted my time changing the ignition coil and spark plugs today, but all a learning curve.I understand now how the problem didn't exist at high revs because the lambda doesn't do anything at that rev range only on lower cruising and idle speeds.

Looking for the best lambda replacement if anyone has any advice or part number.

Thanks for the advice Chris C & huwp

[diggerman]

 

For the record I have a 150 that I built in 2010 and has now done 24,000 miles. The original mapping was a problem. When new the car wouldn't start at all. Caterham re-mapped it and it ran rough. Subsequently in the first 6 months they re-mapped twice more and each was a vast improvement. The final version has been brilliant ever since.

The lambda seems to have a life of about 10,000 miles. When they fails, engine running becomes rough and hesitant, particularly at low and medium revs. The fault doesn't appear in the first 90 secs from start up as the ECU isolates the lambda for that period. To get home you can unplug the lambda and the problem goes away, but don't leave it like that as you will damage the cat. I have also found the wiring to the lambda to be fragile and open to being damaged by rubbing on the underside of the cill. I have resolved that problem by enclosing the wiring in split 1/4 inch rubber tubing and sealing wires  and plug with insulating tape.

The 150 seems to be hard on plugs. I had a plug failure that produced a misfire that I hastily, and wrongly diagnosed as lambda failure. The symptoms are similar so I suggest that you keep a good set of used plugs and try these before investing in a new lambda.

Finally I have to say my 150 is an absolute joy to drive. It has loads of power and torque, and the sound track with over-run pops and bangs is just amazing. It has taken me and 'er on many a long tour inc France, Switzerland, Spain, IOM and just recently, Ireland. The lambda is the only item that  occasionally fails, so I carry a spare.

It seems a shame that Caterham didn't persist with the 159, but the few that exist must surely be destined to be collectable rarities.

Peter 

 

[DRH]

Spent the afternoon with Chris from the Essex7's who kindly offered to set up my Sigma 150bhp engine after me posting that it was spluttering badly at lower revs and thank you all for the advice it was the lambda sensor that had gone.

Anyway, Chris was quiet amazing, his knowledge of the sigma 150 was to say the least expansive, I was treated to a wonderful crash course on my cars inner being. Chris showed me how to balance the TB's(throttle bodies) and set the TBS(throttle body sensor) all aided by an MBE lead and a syncronometer all through computer software what an afternoon.

I'm over the moon the education was priceless the car is running like never before the throttle response is so smooth now, but more than that is Chris offering his time and knowledge to me I just can't thank him enough and just shows what a great spirit exists in the Lotus7 club me being a new member.

I feel I am qualified to change spark plugs if anyone needs help, other skills available soon.

 

[SM25T]

Usually get the part number from the etching on the original .... then search on line.