MOT fail/misfire
 

Ok where do I start?

Car has a misfire under load, I can't drive it any distance due to no MOT or tax.

Fuel is around a year old engine was rebuilt and reinstalled with 15w 40 semi synth oil (as per builders instructions). New plugs fitted as well.

Emissions are through the roof! Always passed after second test with the sports Cat in place.

Fast idle CO = 0.505, HC = 417, Lamda = 0.965
Natural Idle CO = 1.593

What do I check first? Syvecs ECU with Wideband.

I would be dumping the old fuel as it will stagnant and putting clean fuel in it as you've not used it in a while

I'm thinking of a drop of octane booster/fuel cleaner in the old fiel and run it through before topping up with clean. Only pain is I can't drive it to the petrol station so lots of cans needed!

Either drain or several bottles of octane booster and then a fresh 20l on top

I've had similar misfire issues with other cars that have been sat for a year or more.

As above dump the fuel , I'd also rebook a mot at frosts in Shoreham ;)

Hoping that I can get the misfire sorted soonish so I can get a retest for free. Only problem is I can't drive the car, otherwise it should be simple. I've also got to sort the brakes as they were a fail but only really due to lack of use.

Anybody with a Syvecs able to tell me what their wideband readings are at idle and 2500 rpm so I can see if my Lamda sensor is working?

Idle and 2500rpm should be 14.7AFR or ocscillating from around 14.3 to 14.9 if using 02 feedback.
If they are not then it will fail MOT.

If using a wideband it depends where the probe is and what exhaust is fitted.
If the probe is in the downpipe/header it should read fine. But if you have a dustbin of a tailpipe and the probe is only in the tip of the exhaust then the idle and light cruise readings are worthless.

I've calculated that a reading of 0.965 lambda is an AFR of 14.19 meaning the car is running rich. Is this likely with poor fuel? The Syvecs should be correcting the fueling based on the wideband sensor so it should be able to cope with old fuel?

Mine was miss firing when it came on boost while i was having it mapped it turned out to be a faulty plug id only fitted them the previous day stuck a new set of plugs in and it was fine

If that AFR rock solid, as 14.19AFR is fine if it is the lower level of the oscillation.

I'll get out there again today and get the readings as AFR as I think I can switch the units. My wideband is in the downpipe so should be reading correctly.

Haven't figured out how to change the units but have got some better fuel into the car and got the following readings at fast idle (2500) direct from the Syvecs Lambda fluctuating from 0.99-1.00 and at natural idle fluctuating slightly around 0.930.
The only error 'code' found was Engine coolant 1, low after warm up.

Dead coolant sensor will make it run a touch rich when warmed up.

I am going to be putting my Miltek downpipe on soon, is it worth me/can I put a wideband in? Not sure what currently have without looking and will be going aftermarket ECU eventually most probably. Thought might be good for mapping if nothing else?

What make should I get? Where from?

thanks.

Cheers Scott, I'll have to get the sensor readings from cold to see if they make sense to double check but it sounds a good and reasonably cheap fix.

SI, I got mine from JT innovations with the correct Syvecs Lead, I don't think the STD ECU can use one though.

Innovate LC-1 is a popular choice, although they seem to of now updated this to an LC-2 http://www.innovatemotorsports.com/products/MTS.php

Check out Ebay, normally a few bargains and I think some Innovate comes in from Latvia. My last sensor did and never had a problem with them myself.