Misfire fault code & Rovergauge

[taylormj4]

Hi there,
Been having some slight poor running with the Chimaera, sounded like it was running rich. Put Rovergauge on expecting to find a lambda fault or a temp input giving false readings but nothing obvious and no fault codes.

The evens lambda sensor was reading richer than the odd lambda but not hitting the peg so mixture should be correct.

Wondering now if it is actually an electical fault.

What is needed to trigger the misfire fault code ? How does the ECU pick this up ?

[blitzracing]

The only way the ECU can pick this up is when enough unburnt mixture goes into the the exhaust to change the lambda readings- unburnt mixture reads as lean, but its got to be a really bad misfire- and you tend to get the short term trim showing high addition of fuel on the side of the V8 thats failing. The ECU appears to recognise the misfire from the wrong lambda readings, as The ECU is not smart enough to pick up the fractional RPM drop with a misfire- only the later GEMS system can do this by measuring the flywheel trigger teeth speed between firing stroke.

[taylormj4]

I guess I'll just be removing the plugs one by one to find the wet one then !

[blitzracing]

If you are lucky you might pick up a difference in temperature between the exhaust headers- Put a dab of water (as in a damp patch) on each one, then start the engine for 30 or so seconds from cold- if ones not firing it will dry out slower then the rest. The problem is with short headers is the heat transfers quickly between the branches to you loose the temp difference pretty quickly. Another method is to try and melt a cable tie on each header on a hot engine, and see which one does not melt so well.

[taylormj4]

blitzracing said:

If you are lucky you might pick up a difference in temperature between the exhaust headers- Put a dab of water (as in a damp patch) on each one, then start the engine for 30 or so seconds from cold- if ones not firing it will dry out slower then the rest. The problem is with short headers is the heat transfers quickly between the branches to you loose the temp difference pretty quickly. Another method is to try and melt a cable tie on each header on a hot engine, and see which one does not melt so well.

Thanks Mark, some interesting techniques there.

Quick update:
Noticed that the misfire got worse with wet weather driving so started to suspect ignition components. Found somewhere away from street lights one night and looked over the HT leads and was amazed to find a blue glow arcing between the lead from the coil and the top radiator hose, which the lead was resting against. Now this is a rubber hose, beyond the part where the metal pipe lies inside the hose, which was quite surprising. There is also a very very slight denting in the top of the hose where presumably the arc has been flowing for some time. The arcing was actually coming from multiple points along the lead over a distance of a few centimetres.

I am guessing that the heat from the hose has degraded the insulation.

So looks like new HT leads requried.
So next question is the age old one on whether to fit standard of super-dooper ones/race leads.

I have the thermal socks fitted and no extenders. Does that make any difference as to whether I need the resistive leads or not ?

Cheers, Matt

[blitzracing]

Race leads are not super duper, the last thing you want as "low resistance" leads can cause issues with the tacho, and other electronics in the car. Just get some decent OEM ones (I like Bosch)

[taylormj4]

Hi Mark,
Thanks for that. I presume you should be able to run the HT leads up against the engine (earthed metalwork) like the plenum etc without them discharging through the insulation. The breakdown is presumably just something that happens with age and heat damage.
Thanks.

[blitzracing]

You should have a number of plastic clips to hold the leads apart , and in a certain order mounted on the rocker covers- you can see it on this layout for the Range Rover. This stops crossfiring between the leads.

[taylormj4]

Thanks Mark,
I have recently fitted some extra clips to keep the leads apart but where they run between the coil and the plenum to the dizzy, they are bunched up due to the limited space. Have you run yours a different way ?

There are other places where I have had to secure the lead to something to prevent the thermal socks touching the manifolds (as I am using these in place of the extenders). Have been concerned that the proximity of the earthed engine parts could cause field intensification that would breakdown the insulation. The leads are supposed to be insulated to a suitable level but I have had micro-shocks off leads before, which suggests the insulation isn't always as high as it should be !

Do you have a link for those Bosch leads. I can't find any from a Bosch leads from TVR suppliers. I have found ones for Range Rover and DIscovery but not sure if those lead lengths would be correct.

Thanks.

[blitzracing]

I agree the TVR hardware makes routing the leads correctly more difficult- but you need to try avoiding bunching the leads together if you can- its not just leakage to ground thats an issue, the leads act as ariels, and can put enough power into adjacent leads to introduce enough power to make other plugs fire when they should not- hence the name cross firing. I think all the leads from a standard Range Rover classic kit will fit apart from the king lead to the coil- that will be wrong, so you will need to get one on its own from a local motor shop.



http://www.ebay.co.uk/itm/LAND-ROVER-Range-Rover-I...

[taylormj4]

You're right. Not thought of that before. The impulse current flowing in one wire will induce an opposite emf in any lines run in parallel with it. I suppose this only matters if a spark plug fires early in the induction stroke, which would give the effect of massive advance and could cause pinking. If it fires after the main fire or during the exhaust stroke there wouldn't be anything to ignite would there ?

There's a Lucas set including the King lead fro under £20 here. Any good ?
http://www.dingocroft.co.uk/acatalog/Plugs-p2.html...

Or these from Bosch for vehicles "factory fitted with resistive leads"
http://www.ebay.co.uk/itm/LAND-ROVER-Range-Rover-I...

[blitzracing]

Not had a problem myself with Lucas leads in the past- but I gather there are a lot of poor quality parts now badged as Lucas, so I would not target the cheapest. In terms of the resistive leads- they are just fine as long as you dont have resistive plugs, and plug extenders at the same time, thats asking a bit much of the coil output. Ive have run resistive leads and plugs at the same time without problems, but one resistive item in the spark path is enough to keep the ignition spikes under control.

[taylormj4]

blitzracing said:

Not had a problem myself with Lucas leads in the past- but I gather there are a lot of poor quality parts now badged as Lucas, so I would not target the cheapest. In terms of the resistive leads- they are just fine as long as you dont have resistive plugs, and plug extenders at the same time, thats asking a bit much of the coil output. Ive have run resistive leads and plugs at the same time without problems, but one resistive item in the spark path is enough to keep the ignition spikes under control.

Thanks Mark,
When you say the lead in the standard kit will be wrong, do you mean the length ?

As for resistance in the spark path - extenders removed and plugs are standard fit so presume will not be resistive ?

[blitzracing]

Sorry- cant help with the king lead lenght- my coil is not in the same place as the TVR. As for resistive plugs they have an R in the part number like BPR6ES- so no R, no resistance

[taylormj4]

Thanks Mark,
Have ordered a set of Bosch. Was tempted with some from Rachtech that have 8mm insulation (presumably giving better electrical insulation from breakdown) but they don't specify the manufacturer so left it. I don't think the engine bay temperatures do these leads favours over time, even though they are allegedly good for 200deg C.

If it's not the length, what is it that's wrong with the standard RR king lead then please (ie your earlier comment) ?

Regarding the lead clips, I only have one set of clips mounted on the rockers on each side. Should there be more?
The other ones I have are floating ones that I have added.
There certainly weren't enough when I bought the car to keep the leads away from everything, particularly the ones from the rearmost cylinders.

Anyone got photos of a well-routed set of leads on a Chimaera ?

Edited by taylormj4 on Sunday 25th January 00:18

[blitzracing]

The insulation thickness you need depends on the peak HT voltage the lead is likely to experience before the plug fires and stops the voltage rising any further. This voltage does vary with conditions inside the combustion chamber at any point- but typically for the RV8 its around 5-10kv, so you dont need 40 kvs worth of insulation. The term race leads really should quantify very high compressions, turbo charging, nitro or alternative fuels that push the plug firing voltage much higher.

The connectors should be correct on the Range Rover king lead- but I dont know the length.

[taylormj4]

Car misfiring worse this evening. Stopped in an unlit road area to have a look and there were sparks jumping everywhere, between leads (even where clipped apart), from leads to pipes and other cabling !
These leads have really broken down now.
I hope the postman brings my new ones quickly !
Wish I could get a video of it, its pretty spectacular but too dark to come out I suspect.

[taylormj4]

New Bosch HT leads came yesterday so fitted them today. A little bit shorter than the Lucas ones I removed.

Another difference I noted was that the Bosch ones have longer rubber boots at the spark plug end than the Lucas ones, which makes them harder to bend upwards away from the manifolds. The Lucas leads also had angled boots at the spark plug end, which helped.

The old Lucas leads literally fell apart. I only managed to remove 2 of the 8 leads without the spark plug end of the lead falling apart (lead pulled off the metal connector). They are probably 2 or 3 years old but that was still a bit surprising. Guess it's the heat.

Re-routed the leads around the coil area and clipped them apart better.

The engine is now running better than ever, with no mis-firing at all. Even when the Lucas leads were new, there was the very occasional single isolated misfire.

Regarding the spark plugs, these are NGK ones with the code B7ECS. Does this mean that they are not resistive then Mark ? You said they usually put an "R" on the end ? If so, I have non-resistive plugs and no extenders (replaced by the thermal socks). Is this OK because I still have resistive leads or am I now collapsing the spark to early? Seems to be running better than ever.

[blitzracing]

You have the required resistance in just the leads- it should be as good as it gets. Im not sure why TVR went for the plug type you have, they seem to run a bit cold and sooty in my book,(are yours jet black?) so you could try the stock BP6ES for general use. Neither type is resistive.

[EGB]

Try lifting the bonnet in a dark garage. With engine running and reving up and down cross firing can/hope be seen if leads are have poor insulation. HT lead in particular. Need clean gap adjusted plugs also.