Backfire

[andy_coops]

This car doesn’t like me. More spluttering today and then a backfire and flames out of the exhaust. Stuttering and not running nice at all and a 90 mile drive home from Caffeine & Machine ahead. Everything’s been changed for new so any ideas?

 

[Coops Mk1]

Crank position sensor

 

[andy_coops]

Crank position sensor

Thanks chap. I need the loom too, yes? Tried to find a guide to fitting it as I’m not taking it somewhere to join some wires - I need to do this stuff myself.

Could it be anything else that I could change while I’m at it? Plugs, leads, coil pack and injectors are all brand new. It coughed slightly about 15 miles before it died. Changed from 5th to 4th and as I accelerated it apparently spat a bloody great flame out, scared the crap out of my mate behind and then died. Coasted to a stop and it fired up again. Ran rough as f**k for the last few miles to C&M.

Drove home without missing a beat.

 

[Coops Mk1]

Yeah there is a repair loom and newer blue connector sensor too which I've just ordered for my car, but I diagnosed a similar issue by just swapping on a known working sensor to prove.

 

[andy_coops]

Checked and it’s the blue sensor with the new loom. Can barely get a finger to it - joy.

 

[MRBILLYUK]

How olds your lambda sensors?
https://www.ebay.co.uk/itm/303441549650

 

[MrBlonde]

What about the timing,could be out?

 

[andy_coops]

How olds your lambda sensors?
https://www.ebay.co.uk/itm/303441549650

Not sure - running a decat anyway

 

[andy_coops]

What about the timing,could be out?

Belts etc. done last year by Gary Spooner and I went back to double check timing after she ran 167 at SRR (175 the session before).

I’m getting the car scanned today to see what it throws up. Hopefully something simple.

 

[MRBILLYUK]

Not sure - running a decat anyway

There are 2 lambda sensors. 1 precat 1 post cat. Even if you're running a decat you still have the pre cat sensor, the important 1 that checks the emissions and alters the fuel/oxygen mixture accordingly . Bosch recommend changing them every 90k miles.
Seems like you've thrown the parts canon at your car except the lambda sensor.

 

[andy_coops]

There are 2 lambda sensors. 1 precat 1 post cat. Even if you're running a decat you still have the pre cat sensor, the important 1 that checks the emissions and alters the fuel/oxygen mixture accordingly . Bosch recommend changing them every 90k miles.
Seems like you've thrown the parts canon at your car except the lambda sensor.

Thanks. Plugs and injectors changed last summer. Coilpack and leads end of last year after another misfiring issue. Thought it had resolved it as I’ve done a couple of long journeys without issue since.

 

[Mbeau]

Should be able to tell on live data if the lambda is working correctly. They normally cause EML to come on eventually too, although I have replaced quite a few that have not.

If it's never had lambda sensors replaced definitely worth doing with genuine Bosch ones. What is your fuel economy like? If bad that is often indicative of bad lambda as they tend to run rich.

 

[andy_coops]

Just had the car scanned and this was the result. Coil pack was new from RPD a few months ago.

 

[Pegasaurus Rex]

View attachment 1533587

Just had the car scanned and this was the result. Coil pack was new from RPD a few months ago.

Did you have historical codes removed previously? I plugged mine into my RS tuner for the first time last week and had several old stored codes, which I removed. Best to clear then recheck in my experience

 

[andy_coops]

Did you have historical codes removed previously? I plugged mine into my RS tuner for the first time last week and had several old stored codes, which I removed. Best to clear then recheck in my experience

Yep. Cleared and then restarted and no codes at all 🤦‍♀️

 

[andy_coops]

Should be able to tell on live data if the lambda is working correctly. They normally cause EML to come on eventually too, although I have replaced quite a few that have not.

If it's never had lambda sensors replaced definitely worth doing with genuine Bosch ones. What is your fuel economy like? If bad that is often indicative of bad lambda as they tend to run rich.

Using the dash display it’s averaging 38. Was lower before I had the dephaser service done last year when plugs and injectors were changed - genuine items.

 

[Pegasaurus Rex]

Yep. Cleared and then restarted and no codes at all 🤦‍♀️

Well that’s good news I guess, have you run the car and then plugged in for diagnostics again? Like others have said live data is probably what’s needed

 

[andy_coops]

Well that’s good news I guess, have you run the car and then plugged in for diagnostics again? Like others have said live data is probably what’s needed

Yep. No codes at all. Having a disliking French cars day today 😂

 

[Pegasaurus Rex]

Yep. No codes at all. Having a disliking French cars day today 😂

They are s**t mate, we all know that. Just gluten for punishment

 

[andy_coops]

They are s**t mate, we all know that. Just gluten for punishment

To be fair I’ve only had a couple of f**kit moment with this one. The 02 Laguna I ran as a company car 20 years ago was about a thousand times worse.

 

[botfch]

Look at the live data coming from the sensors.

Lambda should alternate between .2v and .8v every few seconds iirc.

 

[andy_coops]

Dyno session booked to try and diagnose what’s wrong. Less than the cost of another coilpack to figured sensible to find out what exactly is wrong before firing more parts at it.

 

[Louis]

Check all the wiring too for anything obvious

 

[Touring_Rob]

Have you changed the cps yet?

If the car ran badly, misfiring and then later ran fine again it's incredibly likely to be an electrical fault.

Also keep in mind that some faults can create other fault codes. It's unlikely both coil pack circuits have failed for example.

Has it done the same again or is it running normally now?

 

[Greeny.]

One of my old cars did exactly this when one of the injectors was on its way out, it was intermittently working for a week or so then totally died.

 

[andy_coops]

Have you changed the cps yet?

If the car ran badly, misfiring and then later ran fine again it's incredibly likely to be an electrical fault.

Also keep in mind that some faults can create other fault codes. It's unlikely both coil pack circuits have failed for example.

Has it done the same again or is it running normally now?

I’ve put the parts cannon away for now...booked in for a diagnostic run at a local dyno on Friday to try and determine what’s not working. Drove it a few miles yesterday without any obvious issue but I’m honestly driving it like Miss Daisy until it’s sorted!

 

[Touring_Rob]

One of my old cars did exactly this when one of the injectors was on its way out, it was intermittently working for a week or so then totally died.

Yea thats also really common - one of my injectors started to fail and initially the car ran super rich before developing a miss at idle. With a decat you might not spot it until it was really bad and the MPG computer likely wouldn't spot it either, it anything it might display a higher MPG as the lambda would make the other cylinders leaner to try and compensate and most trip computers look at the injector duty and make an assumption over fuel used.

My lambda also failed and that made the car run lumpy (but not missfire), and after half a mile it just ignored the lambda and ran normally.

The injector didn't throw an EML until it got really bad but the lambda did.

 

[andy_coops]

I’ve had no misfiring at idle at all. Usual lumpiness but nothing else. The symptoms are hesitation under acceleration above 4k then what I’m sure would be termed a misfire as it splutters to the point of cutting out. Get engine and stop lights but in truth the 2 times it’s happened I’ve been more focused on stopping safely than watching the dash lol.

It then restarts, acts like a t**t for a couple of miles then runs normally. Backfire was a new one and reasonably comical as it made my mate cack himself - flame the first time and less noise and a puff of black smoke the second.

Going to see what the dyno run tells me on Friday before changing anything else.

 

[Touring_Rob]

I’ve had no misfiring at idle at all. Usual lumpiness but nothing else. The symptoms are hesitation under acceleration above 4k then what I’m sure would be termed a misfire as it splutters to the point of cutting out. Get engine and stop lights but in truth the 2 times it’s happened I’ve been more focused on stopping safely than watching the dash lol.

It then restarts, acts like a t**t for a couple of miles then runs normally. Backfire was a new one and reasonably comical as it made my mate cack himself - flame the first time and less noise and a puff of black smoke the second.

Going to see what the dyno run tells me on Friday before changing anything else.

Sounds like a good plan - however all of that was fairly similar to my failing primary lambda. Took a long time for the fault to be logged.

Good luck

 

[andy_coops]

Sounds like a good plan - however all of that was fairly similar to my failing primary lambda. Took a long time for the fault to be logged.

Good luck

Thanks chap. The place I’ve booked has a decent reputation so fingers crossed that we’ll get to the bottom of it.

 

[botfch]

Can always swap the lambda’s around if you get bored before Friday to check.

 

[andy_coops]

Results from the diagnostic today. They recommended cleaning the VVT solenoid and checking timing. Screenshot of their findings below.

I popped into my local garage (who ran the basic diagnostic Monday) as I had to catch up with the owner on another matter and he asked if he could have a quick look. Within a minute he’d found that when wiggling the plug into the coilpack as pictured the car cut out immediately. He pulled back the cover and the centre wire appears secure but wiggling causes an immediate cutout, wiggle again and she fired up so that’s our starting point. I’m going to find a replacement plug and we’ll see if this cures anything.

Dyno centre feel that lambda sensors are fine as they gave readings. They suggested electrical could be an issue too.

 

[Louis]

Check all the wiring too for anything obvious

🥵😂

Glad you've hopefully found the cause!

 

[andy_coops]

If anyone has that plug and a foot or so of the wiring from it, please let me know. Ta.

 

[andy_coops]

🥵😂

Glad you've hopefully found the cause!

Hope so bud. To be fair I don’t even know where to start with wiring but they picked up on the loom that runs under the throttle body close to the block and that the insulation is a bad crap. Another fix needed.

 

[Greeny.]

Glad its getting there, you should have checked ALL the wiring

 

[Touring_Rob]

if the 25% is accurate thats a massive trim value

 

[andy_coops]

if the 25% is accurate thats a massive trim value

That’s what they said. They are 99.9% sure the o2 sensors are working too. We’re going to try that plug with the wobbly connection and see what that does but on shorter trips I haven’t had any issues - first time was after driving 70 miles without issues and last time slightly more than that. Bloody odd.