Trying to trace misfire with Exhaust Temps

[Mr Cerbera]

Dear all you intelligent, experienced peeps….
I am having trouble with a misfire.
I thought that the intelligent thing to do would be to test the exhaust manifold temps which would point to the HT leg needing attention.

I have done this and am more confused than when I discovered the prob.

I took her for a slow run, unstressed for about 5 mins and these were the exhaust temps…



I returned home, so about 10 mins in all, and these were the temps….



… both taken with the engine running.

Now I presume that anything over 240 is probably running well but I am amazed at the wide range in running temps.

Do you think that I have an intermittent misfire on the others ??

Any thoughts and comments would be most appreciated

[scotty_d]

I can't see the pictures due to rubbish internet, mine tend to sit on standard manifolds at warm idle around 460 degree's iirc ( could be talking ste) but I am sure it was this warm.. Hope this helps. I would say the colder cylinder will be the potential issue so try swapping ht leads round and move the problem and rule out the lead itself. A starting point I guess. Could be plugs or coil pack to if your sure it's a ignition fault.

Edited by scotty_d on Saturday 23 February 15:56

[Mr Cerbera]

Sorry Scotty,

Hope this helps

After 5 mins....

Temp	Cylinder	Cylinder	Temp
247	1	2	139
190	3	4	257
200	5	6	204
114	7	8	259

After 10 mins....

Temp	Cylinder	Cylinder	Temp
252	1	2	131
188	3	4	176
124	5	6	192
105	7	8	229

Just don't like running the motor with a misfire that's why the readings are taken after a short time.
(apart from the fact that it's illegal to run without snow tyres on )

Edited by Mr Cerbera on Saturday 23 February 16:24

[clive f]

I`d expect readings to be varied by up to 50 degrees which would be down to different mixtures, leaner being hotter, but number 7 is your lowest then numbers 3 + 2 so start there, check condition of spark plugs, ht leads etc, I`d expect anything from 170deg to 250 IMO.

I`d sort out your missfire problems, then check the throttle bodies, give it a good check over/tune up.

[aide]

If 5, 7 and 2 are not firing due to ht leads or coil packs, then I would suspect the ecu would throw an AFR fault due to the unburned fuel. And the adaptives would be adding a massive negative trim on both banks. Which would mean the other cyllinders that are firing propery will running pretty lean and hot.
If you check to see if there are AFR faults and if the adaptive maps are maxed out netagively then it might be just leads or coils.

[Tang Soo Tim]

Not sure how the temps would vary

My old trusty method was to simply pull each lead off in turn with engine running, if you pull a lead and misfire gets worse then that's a good one, if you pull a lead and misfire stays the same then bingo that's your baby

Prob telling you to suck eggs with that one so I apologise in advance

[ukkid35]

If I had to try to resolve this issue I would replace the following in this order:

Spark Plugs (probably not the culprit but who cares they're cheap) £24

HT Leads (seems like a reasonable chance they're to blame) £50

Coil Packs (if you're willing to go generic then just) £50 a pair

Injector Clean (perhaps they're not flow balanced) £??? never tried it

[Mr Cerbera]

Cheers All for all your brilliant suggestions.

Particular thanks to Aide for his mail and Tim for the "scrape me off the roof" suggestion.

Have a great weekend.
(and "Away the Lads !" to Wales )

[Tang Soo Tim]

Mr Cerbera said:

Cheers All for all your brilliant suggestions.

Particular thanks to Aide for his mail and Tim for the "scrape me off the roof" suggestion.

Have a great weekend.
(and "Away the Lads !" to Wales )

Are you saying that was a shocking idea

Worked in the old days on my strada Abarth .....although I will confess to not trying it on the Cerb yet

[Mr Cerbera]

Tang Soo Tim said:

Are you saying that was a shocking idea

Worked in the old days on my strada Abarth .....although I will confess to not trying it on the Cerb yet

Had I had hair, it would have had an erection