Big misfire on offside bank

[Chim Chim Cheree]

Guys, tricky one I'm hoping you can give some ideas on...

The car will now not fire on any of the offside bank. Plenty of fuel and sparks. Problem started smaller, but progressed very quickly.

On Thursday drove to work. 5 miles, 26 traffic lights(!), lots of slow driving. Engine started and ran fine.
Thurs eve on the return after about 15 mins/ 2-3 miles slight misfire started whilst waiting at lights. Engine warm enough for fans by now. Cleared with a blip of the throttle. Ran fine, but did it again whilst parking up. Turned engine off whilst still a bit lumpy.
Friday morn. Started fine and ran sweet to work. No problem.
Friday eve, again started missing after about same time, at lights. Cleared when moving off and ran fine for 200yds - to next lights. Now started missing again, and didn't clear - even with some revs. Stopped (left engine running) to check leads, etc. Nothing obviously wrong. Continued to limp remaining 2 miles stedily getting/sounding worse. Observed symptoms:
. Sounds now like a dumper truck
. clouds of smoke from exhaust starting off from lights
. smoke smells strongly of unburned petrol
. engine getting progressively 'laboured' and unresponsive to throttle
. parked up with it barely running

Next day (didn't drive to work!) removed plugs all 8 black but healthy. Plenty of petrol present.
Oil (dipstick, oil filler, breather) smell strongly of petrol.
No sign of mayo in oil cap or oil on plugs or in water.

Turned over engine to purge flooded cylinders. Left plugs out for 24 hrs to let cylinders vent.

Next day, replaced plugs and started it. Fired on nearside 4 (4 hot manifold branches 'immediately'), but not on offside 4 (4 cold manifold branches)

I have a few ideas, and what I see now could be secondary symptom caused by running on misfire with flooding cylinders?

Any ideas guys, very gratefully received

ETA: should have said by now, sorry, late '98 450. All standard - no mods.

Cheers
Jon

Edited by Chim Chim Cheree on Thursday 25th August 23:31

[Alexdaredevilz]

Head gasket?

[carsy]

If you are sure you have got fuel to the offside bank, it must be spark. I would check all leads and see what sparks you have and quality of spark. I would have thought ignition amp or coil.

[Simon says]

Faulty Lambda probe on that bank that is running rough possibly,each Lambda probe trims 4 cylinders either offside or nearside,you may find that the cause of the failure is the pre-cat in the manifold as shot forward and sheared off the tip of the sensor remove the sensors and swap left to right to try to move the condition to the other bank as said if the sensor is damaged by the cat the damage will be obvious this would explain the smell and the fact it's over-fuelling/misfiring on 1 bank

[Chim Chim Cheree]

Alex, please don't say that. I wanna hear something else... Actually that's my fear, but head gasket on all 4 cylinders at the same time?

Carsy, lots of fuel. And quite sure of spark. Whilst it was running (on the 'next day') I pulled 2 plugs on o/s and heard the ticking of the spark doing its thing. Coil and amp new - 1500 miles. Could be, but why on offside 4 only and not nearside 4?

Simon, ok. Lambda broke, reading high oxygen, over fueling and flooding spark... Hope so. Is it likely that a lambda could fail a bit and then come back several times, like symptoms?

Other observations when I ran it 'next day':
. with plugs out engine turned over ok and smooth on starter
. with plugs in, and firing on 4 only, a definite 'quiet clatter' sound from o/s bank. Not very loud, but loud enough to have not been there before - or I'd have noticed

Thanks for the ideas! All good stuff to check. I intend to put on my old coil/amp and test. Didn't try yet because that's not likely to account for 4 firing and 4 not, right? I don't have much experience, but doesn't sound right.

I don't relish replacing head gasket in the street, so I do hope it's not that.
After coil/amp replace what should i check next? Compression test, or is there something else it could likely be?

Thanks again, your time is much appreciated

[nuttyfruitbat]

check wiring going to lambda sensor,where ir goes down near alternator mine had worn through and was earthing out,need to look under wires as looks fine from above.

[FlipFlopGriff]

Similar to what happended on the Griff. Ran Ok then one bank died and no power, misfiring and loads of fuel coming out the exhaust. Switch off and all OK again. ECU was swapped and problem solved so probably an intermittent connection. Could you borrow one to try?
FFG

[Chim Chim Cheree]

Cheers Pauls.

This evening and/or tomorrow I shall mostly be looking at various wires, firstly. I'll check ignition before I really panic more about head gasket...

[mikial]

I would check the ECU terminals first. Just disconnect and remove, if possible crack open the unit and check no residue, if you feel cheeky remove the chip ( take a picture first to ascertain the position of the chip )Carefully replace chip , . Spray some electrical contact fluid on the forty point connector and refit .

Also this : http://www.rv8r.co.uk/home.html might be of help.

Good luck.

Edited by mikial on Friday 26th August 16:47

[blitzracing]

There are some simple things you can try. Firstly unplug the lambda sensor from the failing side, then do an ECU reset (unplug and replug the ECU). Next time you start the engine, the lambda signal will be missing, so the lambda circuits are not activated. This has 2 effects, the first being that the ECU will run on the fuel map only, and it should run perfectly well this way. The lambdas are only there to make small corrections. It also stops the lambda detecting un burnt mixture as a lean mixture. This is a problem if you have an HT misfire on one side, as the ECU keeps putting in more fuel to try and get the lambda voltage up, but it cant because its unused oxygen its measuring, and this stays high when the mixture is not burning. If the engine will better with the probe disconnected the try and isolate the HT fault. It may be as simple as seeing which plug is cooler if you run the car for 30 -40 seconds on a cold engine and then touch each plug to feel how warm it is.

As for head gaskets, pull the fuel pump relay out or unplug the injectors, then crank the engine over and listen to the cranking cycle whilst holding the throttle wide open. It should be even if the compression is even across all 8 pots, but if one side or chamber is bad, the compression will be low, so the engine / starter will speed up on the low compression cylinder. This leads to an uneven cycle you can hear.

Edited by blitzracing on Friday 26th August 17:41

[Chim Chim Cheree]

It's been thundering and raining since yesterday morning. I made use of this time today by watching old episodes of Top Gear. I had a brief window of blue sky between 18:30 and 19:30 before it started thundering again.

I used that time wisely. Perhaps the gods of Hammond, May and Clarkson smiled upon me.

• * It's now firing on 8 ! :-) ***

albeit with copious smoke and not too smooth yet. Ok, possibly 7 1/2, but that's better than 4. Oil needs a change too!

So not head gasket. Phew.
I followed various advice from all of you - so thank you all for your ideas. Disconnected Lambdas, unplugged ECU, confirmed spark (weak!) at one plug, swapped back to old coil, etc. Something somewhere has started to work.
My guess so far is ECU connectors and coil - though one offside plug lead gave me a shock when I touched it so perhaps even HT shorting.
Anyway root cause is electrical or ignition, so it can be tracked down by a man with a spanner standing in the street, and not gasket or valves, which can't really...

Thundering again now so I'm off to worship at the altar of TG to give thanks.
And thanks again for your help.
To those of you that I know - our paths will cross again I'm sure. Next time you pop over to the Nurburgring give me a shout - I live only 3 hours away now :-). Paul, either of those Grifs would suit it well :-)