Re:Bit of help needed here

I've had some issues with the my Jimny (M13A) running roughly which, I thought I'd got to the bottom of, but...

(Previous history... I'd had engine warning caption repeatedly coming on last year, so changed the top oxy sensor which cured for a while, but eventually light started coming back on, then it struggled through emmissions at MOT last year so I changed the CAT and bottom sensor and also the rear sections of exhaust. The engine caption has remained out ever since - and it flew through MOT in March so all seemed good there)

Just before lockdown I was getting rough running - initially this was mostly on start up from cold, it would clear with a bit of gentle revving or just driving off. With time this became more frequent and I almost didnt get home on one occasion after a long journey. I elected to change the crank and cam sensors a month or two ago at a service interval, and also changed the plugs and fitted new coil-packs .

Since then I've had no rough running... but in the past couple of weeks if I let the engine get into a situation where it labours, I've noticed a tendancy for it to momentarily run very rough and I dont mean the usual wrong-gear kind of rough - this is rather more pronounced.

Today I was cruising out of Oxford on the A40 and noticed the engine going into one of its rough moments after not changing down for a roundabout.
On the other side of the roundabout I noticed a roughness but more alarming the engine warning light was flashing. so I slowed down, a bit unsure of the situation as it was dual-carriageway with nowhere to stop - I clutched-in to see if the engine would stop but it continued running and I noticed the flashing engine caption had now gone out!

I parked up in Burford and had a look under the bonnet - no nasty niffs and nothing looked like it was melting. It was hot today but all temp readings were normal and no other warning lights came on.

I'm getting a bit exasperated now and unsure of what checks to do next. Can anyone suggest anything else above and beyond the things that I've already done?

Hi Max.
Sounds like you have a sensor going out of spec, hence the engine light.
Just trying to remember which sensors / items don't put the light on or report error codes.
If I remember correctly Coil packs and crank / cam sensors tend not to put codes or the lights on, so unlikely to be these based on this logic.
Do Lamda sensors?
If the engine lights on will it have stored the error code? My exVW saves DTC codes even if they had gone, not played with my Suzuki so unsure if it does the same.
Just trying to throw in some suggestions and offer moral support, hopefully you will get better help from the forum.
Mike

Hello Scimike

The Lamda sensors are the oxy sensors on the exhuast either side of the cat I think - those did initially put the engine caption on - but not flashing, just steady - that seems to have been fixed and Ive had no engine caption on until today - and it was flashing -allegedly more serious so I understand!

Modern cars and all their electrickery is great while theyre working ok but a pig when it all goes 'orribly wrong

It should have stored the codes assuming you have a reader? Given the cold start aspect I might think air flow sensor? Was the new cat a reputable one or a cheap ebay job?

Get a cheap Bluetooth OBD2 plugin reader and look at the error codes using your phone. There will be something stored if the MIL light came on.

Sent from my Pixel 2 XL using Tapatalk

Thank you for your suggestions Martin and Lambert,

I have got a code reader somewhere - never used it -no idea how to - but I'll work it out I'm sure - it is only a cheapie but I'll see if any codes are thrown up an report back.

The CAT was indeed an eBay job - I recall it as BM brand which someone on here directed me to and suggested was a reasonable choice.
As I say the car struggled with MOT emmissions last year but flew through it this year (March/April) with not even an advisory.

The rough running at start-up seems to have disappeared since changing the cam and crank sensors, but is now happening with the engine fully hot - usually on long runs.

UPDATE:

Ok found my OBDII Reader - its an Aldi job but got reasonable reviews and didn't break the bank - Unfortunately this reveals "NO CODES"

So I'm still a bit in the dark as to what to do next

Isn't the stored area called "pending DTC"?
Sorry it's been a long time since I plugged in a code reader. I think my CAT is BM and because a local exhaust place fitted it I can't describe it as cheap, reputable maybe, ebay possibly, as I don't know how they obtained it. :laugh:
Works fine though.
My gut feeling is Lamda based entirely on guess work. Have you anyway to check the emissions at this time, cheap Gunson gas analyser is good enough.

Yeah the "pending" thing - I couldn't find anything there either. I'll give it another try tomorrow.

It's very frustrating.
Apart from the two sensors either side of the CAT and the cam and crank sensors, is there something else that could be the cause of this?

Yes unfortunately.
Anything eldctrical-poor cable / connector etc, faulty injector or fuel pump / pressure regulator, I could keep going. These random faults are the devil's own.

I keep thinking you Lambda sensor is out and here is why:
Sons Toyota MR2 purchased by us with 12 month MOT and in the document pack a receipt for a £1K Toyota CAT just before MOT - ouch!
Next MOT car fails catastrophically with emissions, 5% co, no faults codes, and a few other things!
Car idle a little unstable, but other than this it runs fine, looks like the CAT again.
I push ahead and fit a new Lambda instead and it sorts the car out, idles perfectly and co .5%
So a new CAT can hide a failed Lambda sensor.
This is why I was interested in if you could get emissions tested. High CO with acceptable HC would suggest the same problem.

But it's just one of many possibilities.

It could be worth systematically unplugging and replugging all the engine connectors and sensors in turn to eliminate a bad or failing one. It's a bit of a task but it's also free. If you don't fancy that then you could start with the air flow sensor just after the filter box and follow the path of the air same with fuel and spark. You just have to be logical about it.

Thanks guys - any suggestions is much better than clutching at straws with this! Also helping me find these components too - the pointer to where that air-flow sensor is is very helpful

I chanced a trip over to Evesham in yesterday's heat and a bad hill to go up on the way back total (30 miles) - I was a bit worried but got back with no major rough running.

Today I have to do a much longer run to Shropshire and back (128 miles) - it was on this same route that I almost didnt get back, but that was before the crank/cam sensor change - a bit of trepidation nevertheless.