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Would a spark plug still soot up in injector kaput?


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I'm conscious that my posts are probably too long before I get to the question so this time, it's in the title! ?. I've put it here because I am looking for any suggestions...

The supporting evidence is listed below.

New build top hatted 4.6 with Megasquirt running Niges base 4.6 map. PWM valve not hooked up installed in a 110 with ZF Autobox.

The engine was "run" as per recommendations to bed the cam in - >2000rpm for 20mins.

Running NGK BPR6ES plugs, gapped to 1mm.

Tubular manifolds to Longlife system.

It did a couple of hundred of smooth miles, generally less than 3000rpm.

On Thursday, on the way to work, I had to sit in traffic for 20mins. Temp wise, the fans kept it "normal" but when I eventually got moving it seemed to be running on 7... (When cold, it used to start like that but clear within a few secs). Only now, it hasn't and although it still pulls well, it has a vibration that seems to show it's still not running on all 8.

Attempts to diagnose:

1. Checked that all injectors are getting power with a NOID light.

2. Checked all plug leads are delivering a healthy spark.

3. Compression test - all at 11 to 12 Bar.

4. Changed the plugs for new NGK BPR6ES, gap set to 1mm. (The old ones were all sooty / white, looked normal but maybe a bit rich).

It had a slight "chuff" from No.3 exhaust manifold so replaced the gasket..

I am now stumped. It's still doing it. I've pulled the new plugs and they are all getting sooty so I assume they are seeing fuel..... But, could it be that one of the injectors isn't working?

Any other thoughts would be gratefully appreciated before I pull the thing to bits again. (I'm not too bright but I try!!)

Many thanks,


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It could be, I had one fail on me recently, but OPEN...... that wasn't good for the cylinder wall I guess.

Not on my V8, but on my Audi, but it is the same type of injector, Bosch.

Symptom was a big misfire and unbelievable stench from the exhaust pipe of hot vapourised unburnt petrol, made me eyes bleed :P

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If all of the plugs are equally sooty then at least they are all firing. over fuelling and sooty plugs is one thing, the misfire is another. Is the temperature sender correct? does it 'think' it's cold?

Is there a snorkel or pre cleaner fitted? Is there a squashed / blocked bit of exhaust? Bad plug leads / coil packs might just be breaking down at certain loads?

If it's a regular misfire then I suggest to pull the ht leads until you can at least identify the culprit. A slightly sticking valve / lifter might not show up in the compression test at cranking speeds but might when it's running.

Can you post a picture of the plugs?

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There is a snorkel into the original TDi filter which has been relocated. The hose to the snorkel is new and clear.

I've plugged it in to the laptop and the water temp is correct on the screen.

Although it doesn't mean they are good, all of the lifters, rockers and the can were new.

Oil changed to Valvoline last week after initial run-in.

I've pulled each injector plug when it's running (apart from the git under the plenum intake) and can hear an effect...

I'll pull individual plug leads and see if I can figure out which cylinder is playing up.

That's interesting on the coil packs / leads. I've got spare of both so will swap each one at a time and see if it makes any difference.

I'll report back tomorrow hopefully, currently had to go in a little work trip.

Many thanks Jamie & Bowie.


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  • 3 weeks later...

Bit of an update:

I swapped a spare coil pack onto the engine and that made no difference...

I then ordered a set of second hand injectors but having read a bit online, have come to the conclusion it is pointless slinging them in without at least getting them refurbished and then came to the conclusion that I may be as well buying the Bosch Gen II Injectors which are a direct fit and have a better spray setup (4 hole as opposed to the standard 1).

I took the injectors off last night and they all look grey / dry apart from one which looks wet and almost oily so I'm hoping that its duff. (I may send them away to get an opinion on them just out of curiosity...).

I was sure that Nige had done a section on injectors / refurb etc but can't find it. I've seen the other thread about testing them at home and dont really have the kit.

Can anyone point me in a good direction for new Bosch Gen II Injectors or have any other recommendations / suggestions?

Thanks, Donald

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  • 2 weeks later...

Eight, brand new injectors duly arrived and have made sod all difference....

I've pulled the leads off one by one while it is running and can't figure out which cylinders are not working... I can understand the comments about spark plug gaps now - When I pulled the leads off, it was like there was a Van der Graaf generator going off under the bonnet...

I even began to wonder if it is my imagination but when driving it, you can feel an uneven, rpm related throb.. and although it seems reasonably powerful, I expect more from a 4.6...

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Maybe stick a timing light on it and see if the strong spark you have is disappearing under certain conditions. Maybe a megasquirt problem? No chance of it 'falling off' a base map? No chance of the ecu getting unshielded signals from something? Clutching at straws here. By now the engine will be run in a bit and maybe ready for more than a base map? It might just be the time to stick it on a dyno with someone who really knows megasquirt and baseline values with your setup to get a map together. Would probably be really good fun too. I'd be keen to hear how you go.

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