What Are My Plugs Trying To Tell Me?

[Guest timswait]

My engine isn't too happy at the minute. Nothing serious, but it just doesn't quite sound right, is sometimes a little reluctant to pick up and sometimes misfires under load on the motorway. The plug leads are a year old and resistace is consistent and within limits, the plugs have about 2000 miles on them, I've just replaced the dizzy cap and rotor arm which were looking tired, which has helped, but not complety eliminated the symtoms. I have a feeling it might be a tad lean, it was only 0.6% CO at the MOT, which is within limits (0.5-1.5%), but on the low side. Anyway I decided to have a look at the plugs and check the compression. Compression's fine (150-170 PSI on all cylinders), but I can't make up my mind on the plugs. They're black round the outside, which I thought indicated too rich, but the tips look a bit overheated, like it's too lean. No 2 cylinder had heavier deposits than the others, but the deposits were the right sort of grey colour. I took a photo of No 4 plug, what do you reckon?

[Guest Tim Norman]

Sounds lean to me

[miikae]

Hi , if you are running a pair of twin choke carbs then they are in need of the mixture setting up as you appear to have all the symptoms of out of tune carbs . An easy job to sort out yourself if you have got the gear .

 

Mike

[Guest timswait]

Should have said, it's an EFi Pinto. I'll fiddle about with the mixture screw when I get it back on the road. Been timing 20-50mph in 2nd and 3rd gears, so hopefully I'll see an improvement.

[Guest john]

Most Haynes manuals now show a guide to plug colour and deposits.

It sounds on the weak side to me, but I would want to know why plug 2 is different. Have you got a leaky manifold gasket near that cylinder ? ( lets more air in , so even weaker ) or is it blacking up with oil ? ( stem seal or piston ring gaps aligned ).

[Guest timswait]

I was going off the photos in the Haynes manual, the thing is it doesn't look quite like any of them! I did spray some WD40 all around the manifold to try to detect leaks, and didn't hear any change in running of the engine at idle, I guess it's also possible it's the injector on No2.

[Guest chris brown]

It looks lean to me as well Tim. Screw in (clockwise) the air bypass screw (alan key) situated in the mass air unit about 1 turn and try again. If you have a friendly MOT station near get them to put it on the 4 gas then adjust the CO to around 2 to 2.5 or even higher easy to turn down for MOT. I run mine around 3.5.

[Guest timswait]

Turned it half a turn richer and it's made it run much better. Couldn't really tell much difference by going richer still until it got to 2 turns when it started running worse. Thinking about getting a lambda sensor so I can set it properly, would also be useful if I ever do get round to fitting a Zetec!

[Guest ballin]

a wideband sensor and guage will set you back around £2-300 just so you are aware

[Guest STEVE OXON]

Turned it half a turn richer and it's made it run much better. Couldn't really tell much difference by going richer still until it got to 2 turns when it started running worse. Thinking about getting a lambda sensor so I can set it properly, would also be useful if I ever do get round to fitting a Zetec!

 

 

 

that would be quite correct, if you turn half turn richer and it runs better,then mixture is better.go too far ie richer still and it would be too rich!

steve

[Guest timswait]

The problem is there's quite a long way (ie between 0.5 and 2 turns from where it was) when I'm not really sure which way to turn it!

[Guest john]

Then stick at the 0.5 turn position. Any richer and you are wasting fuel.

[Grim]

Tim,

 

i have a feeling that your car isn't running quite right, perhaps more than just a simple ignition problem. I'd say it's unlikely that it would be the same problem that i had, but it has certain similarities: the loud farty exhaust note (exactly how mine used to be, rather than sporty), plugs complaining (i'd eat a set every 5000 miles), and the fact i was around the same speed as you on the ring when my car wasn't running right. Before we left on our trip, i made it a little richer which improved things, but not a great deal.

 

Were these the plugs i gave you? If so, they were fairly new, a few months maybe, with no significant deposits on the insulating ceramic, but plenty of soot on the edges of the plug. The crusty white deposits do puzzle me tho. The plugs we changed off your car were much the same mind, possibly ever crustier (i couldn't get my car to run with them in when i had a serious misfire problem).

 

What i'd suggest is to have a side by side performance comparison (which is entirely differant from a race, officer) and see if there is any difference. Send me a message, and we can meet up sometime. I'm free pretty much every evening this week.

[Guest timswait]

I know what you mean, but it is running much better since changed dizzy cap and rotor arm and adjusted mixture, sounds better too and returned slightly better fuel economy on the drive from Kent to Sheffield, and it's not mis-fired at all. I've a feeling I might have a slight air leak on the trunking between the MAF sensor and the plenum. I used the same type of trunking as a filler neck and it leaked pretty badly where it joined to the tank, so I reckon the piece I'm using on the MAF sensor is probably leaking as well. I've sealed the filler neck with the gunge you gave me, have to wait til tomorrow to see if it's done the job, I'll seal the MAF to pleanum chamber with some silicon and see if that makes a difference.