Running Lean / Running Rough

Hi all, as above

These are the right side NGKs B7EC S. Note how lean the centre 2 are !!
She started running lumpy last w end, it's as if she's stumbling / missing around 2 - 2,500 rpm. Done it before a couple of years ago, then cleared.

The centre 2 plug tops and the leads have a white powdery coating of corrosion, which I've sprayed with cleaner. Could this be causing the rough running ?

The corrosion certainly won't help

Could be the coil or amp breaking down; does it restart once it has cooled down?

Have you checked for air leaks, around the plenum or the induction hose on the plenum?

It could be any number of things, have you done anything recently before the problem started?

The injector pulse width is the same across all 4 injectors is the same across each side of the V8, so the amount of fuel should be the same and the air feed is also common, so an air leak would show up as all 8 running lean. By running lean what you mean is the carbon is burnt off the plugs due to high temp, but you can also wash the carbon off with un burnt fuel, or water getting in to the combustion chamber from a blown head gasket. Id start with a compression test. If you can get the engine to run, you could also try the trick with of touching a cable tie onto each exhaust header and see if they all melt. A non running cylinders header will be much colder than the others, so you could be looking at gasket or ignition more than fuel.

Pulled the plugs on the left bank earlier and they look similar in color to the ones on the right bank. Span her over on the starter and the left front has a spark.

Cleaned the plugs and put them back in, turned the ignition on, pressed the imobilser fob button and the fuel pump primed. Span her over and won't start !!

Put a spark plug in the right front lead, turned her over on the starter and a very strong spark.

So what's wrong ?

Will have to borrow a compression tester.

Checked 5 of the leads and all have spark. Disconnected then re connected the ECU and the birds nest of wiring and relays in the foot well in case of corrosion.

Batt was very low last night. Re charged it then tried again to start it. Fuel pump is priming and there is fuel in the pipe under pressure, but still won't fire. I'm Completly baffled as to why it won't start.

Towing it round to my garage in the morn for a compression test. Fingers XD it's not head gasket or bent valves !!

Hello Frank, yes I'm completly puzzled as well. The guys I use are pretty good, so if the compressions are ok, then I'm hoping they can diagnose whats causing it.

Hi blitz, yes, turn ignition on, press imobilser fob, then the pump primes for a few seconds, then stops ( as usual ) .

By the horrible smell of petrol as you crank the engine, or wet spark plugs if you drop one out to have a look. If you want to get technical you need a noid lamp that plugs ontop of the injector and will flash when there is a 12 volt pulse. Its worth checking for the 12 volt supply on the injector rail- if you ground one side of a test meter, and then test the injector connections, one should be at 12 volts if the ignition is on. They do tick lightly as they fire, you might be able to hear it if someone cranks the engine and you hold a screwdriver against your ear and an injector.

Quick update , Just got to the garage, pulled the plugs, but access is so tight to get a compression tester in !

No 4 pot ( right bank ) is showing 120 psi , this is the cylinder with the plug that was very white. And now my year old Halfords battery has expired.....TVRs.....don't you just Love them !

Low compression on one pot wont stop it running completely- so Id suggest you have more than one fault. To verify the gasket is gone there is a simple test a garage can do to check for exhaust gas in the cooling water, but you will need to get it firing first. Id take two steps backwards in the short term, and get a strobe on number one plug and check its firing at around 8-10' btdc at cranking speed, just to eliminate the unknowns. If the spark is good, you can always try a good squirt of easy start into the plenum, buy removing one of the blanking bolts (if you have any ) or possibly the servo take off, but put it back before you crank it over. Even if the injectors are not opening it should at least fire on easy start.