5.2 f355 fogging out and almost stalling multiple times!

Referring to my post #19 .
Get a cheap $10 infra red temp sensor .
I had the same with my new to me 348 ( simpler 2.7 ) after a engine out belt service . Intermittent bank shutdown. Always the same side 1-4 .
Sometimes just a flashing “ slow down light “ , sometimes the light was on but no symptoms, sometimes light on and a bank shut down .
Sometimes a bank shut down and no light .

No particular reason or pattern . Some days nothing , some weeks nothing then some days 2-3 times . Sometimes engine off and restart would fix it .

I never bothered parts throwing . Obviously the ignition / coil packs or the CAT sensor s and there little ECU s by the rear suspension pillars were “ in the frame “ .
I did swap over the ignition packs , / coil pack etc the issue did not move banks so concluded those were ok .
Swapped the CAT ECUs and again made no difference so concluded they both were ok .


I Infra red gunned the exhaust and manifold s as far as could sensibility when hot and running with the CAT slow down light on but not a the shut off stage .

Here is what I found .
One bank the effected 1-4 was a lot cooler than the good bank and it’s CAT was cooler …..one cylinder area of the header / manifold was cooler than the other 3 . Conclusion. That cylinder wasn’t firing now .

When it was running all ok all the temps on all the cylinders were identical and both CATs identical…..+ or - 10 degrees .

So is it a plug lead or plug ? ( we know it’s not the ignition module as they have been previously swapped and made no difference)

Removed the plugs to check .
Cylinder 2 looked black and fuelled up ( I run two stroke scrambler bikes ) .
To my amazement the plug caps were all loose ..that little bit that screws on the top of the plug . AND the plugs looked original.
10 yrs of previous history showed nothing on the plugs .They were original champions. These are tiny and used on Ducati bikes .

So I bought a set of iridium DEI 8 X ( the forum favourite) and a new plug socket to fit as the 348 tool kit one was too small ( bike plug size ! ) .

Ensured the caps were tight . Fitted 8 .

Hey presto .
Never ran better .
The “ stalling “ or in my case Bank shut down has never returned.

I will go further the idle is smoother and it’s low down pull from 1500 - 2000 rpm is like a train . It’s just more drivable at junctions etc .

If it wasn’t for the infra red gun …l guess i would have entered the parts throwing contest …starting with leads .

Turned out just aged a plug within a set of I think old plugs ?- 1990 s tech campions But the caps were all loose never tightened down = weak spark issues ? ?

So unburnt fuel is detected by the sensors in the CAT apparatus which eventually triggers the bank shut down . The no 2 plug failed intermittently and the loose caps with heat compromised the conductivity of probably all the plug lead extenders to plug ( s) .

 

I don't think loose terminal nuts on the spark plugs can cause any issues because there is some 50,000 volts flowing through them so some resistance through the threads, or even (theoretical) air gap or corrosion in the threads means nothing for this high voltage. DR8EIX have 5,000 ohm resistors in them, meaning a total of 10,000 ohms for the high voltage to pass while creating sparks on two plugs, and this resistance does not really reduce the spark intensity.