CoPs not firing when bolted down

madjak · Postby **madjak** » Wed Oct 29, 2014 10:02 am

Basically over three nights trying to get my engine firing I was seeing strange random behaviour. The engine wouldnt run for more than 5 seconds spluttering and then stalling. It turns out that when the cops are bolted to the head they missfire. If the are just sitting there the engine runs fine. Also, when the engine is running, if I push down on a cop by hand that cylinder will stop firing.

The model cops I'm using is one of the genuine toyota models recommend. Pushing them down must be shorting them against the plug or something.

Anyone had this before? What else could cause it? Bad earthing maybe?

manga_blue · Postby **manga_blue** » Wed Oct 29, 2014 1:44 pm

Check for oil pooling in the bottom of the plug wells?

madjak · Postby **madjak** » Wed Oct 29, 2014 2:48 pm

I dont think its and issue as the end of the plug is dry. Pressing them down 5mm causes the cop to stop firing... release them and the engine runs fine again.

plohl · Postby **plohl** » Wed Oct 29, 2014 3:05 pm

Is it all of them? how are they wired? I wonder if it's a dodgy connection...

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madjak · Postby **madjak** » Wed Oct 29, 2014 3:38 pm

plohl wrote:Is it all of them? how are they wired? I wonder if it's a dodgy connection...

Yeah it's any of them. As soon as they are unbolted and just sitting there the engine runs great. Push down on any and that cylinder will miss, lift it back up and it will run. It's like it's shorting at out the bottom and not getting the electrical signal through the plug but I can't see how that can happen with the rubber boot around it and the top of the plug being ceramic.

Unless the top of the cop is earthing somewhere on the head. I'll have another look at it tonight when I'm home as it was too late last night to spend time figuring it out. I figure with that many people running cops these sort of issues would have been encountered before but I can't find anything online.

I read your post about the cops issues you were having and it all sounds a bit related. I have also found people saying they had to run capacitors etc but I thought that was all for stock ecus and not standalones.

My wiring is pretty simple. Power and ground to all cops, and a separate signal wire to each. Earth goes to my fuse box, power from the relay, signals to the ECU.

For now I'll put a lock nut underneath the cops to hold them at the required height as well as one on top to stop them bouncing out.

plohl · Postby **plohl** » Wed Oct 29, 2014 3:53 pm

How are you bolting them down?

My issues was the COPs. A mate and I bought cheap ones... we ended up going through 9 of them between us. I bought a set of genuine toyota ones and never had another problem with them.

I wired up both of the systems and we used capacitors in the COPs loom. I haven't ran without a capacitor, so not sure how need it is. I can't remember what size we used. Miataturbo had all the info, I just ordered them from RS components.

If you get a chance, post up a picture of how you're mounting them.

bartmanftw · Postby **bartmanftw** » Wed Oct 29, 2014 4:05 pm

Capacitor isn't needed. Both COP looms I've wired up don't include a cap and they work fine. It would only be useful for stopping noise going back into the rest of the electrical system.
It sounds like something is shorting to ground or disconnecting when you push down on them.

madjak · Postby **madjak** » Wed Oct 29, 2014 4:30 pm

I'm using the omgpham cop bracket. They are also the genuine toyota cops and I think they are they ones that end with #15 but I'd have to confirm when I get home.

The bracket is held down on the head via the standard head chrome bolts, then little nylocks hold down the cops. I tighten the nylocks till I see the rubber start to deflect and then stop. The nuts would have around 5mm of thread out the top. If I wind the nut to just below the top of the thread, the cop will fire fine, but the cops are fairly loose.

I'll take a photo of my setup when I get home tonight but it's all pretty simple. I've used thick wires for ground and power, and only slightly thinner for the signal. I really don't think it's wiring related though given the behavior of misfiring when I press on them.

I might try wrapping the threaded studs on the cop bracket with insulating tape, and put insulated washers before the nylock. Down inside the head I can't imagine anything that could short given the insulated nose on the cop. I could pull a plug out and see if I can press it into the cop whilst it is firing and see if the sparking stops or not.

I'm very surprised no-one has seen this before.

plohl · Postby **plohl** » Wed Oct 29, 2014 4:59 pm

I know that cop bracket really well... You don't need to tighten them down that much. You only need two threads showing above the nylock (~2mm) to secure them. It is highly unlikely the nylock, and/or the cops will move.

I might try this out on a mates car and see if I can get it to do the same.

madjak · Postby **madjak** » Wed Oct 29, 2014 5:55 pm

I pretty much tightened them until I saw some deflection in the base rubber seals. I could wiggle the cops still but only a bit. On my cops the seals are around 6mm thick and fall off the cops very easily so I'm wondering if they are the correct seals for the cops. The seal has a little lip on the outer edge on one face that looks like it should sit over the cops but it doesn't.

I figured they needed to be tight enough not to let dirt fall down into the plugs. Maybe I need a packer/washer to lift the cops up 5mm.

I'll take some photos of the cops where the engine misfires, and where it runs fine. also of the seals to make sure I haven't got something wrong.

edit: Spelling

irwin83r · Postby **irwin83r** » Wed Nov 05, 2014 10:07 pm

check the distance of the electrode/connector in the CoP and how far down the plug is... perhaps when you press them down your pushing them over the spark plug electrode/connector and onto the ceramic insulator of the plug.
the connection inside the lead/CoP is often a spring steel ring that can be over stretched to pop over the larger ceramic diameter

plohl · Postby **plohl** » Thu Nov 06, 2014 10:38 am

^ good info man. Never thought about that. Cheers :beer:

madjak · Postby **madjak** » Mon Nov 10, 2014 1:55 pm

plohl wrote:^ good info man. Never thought about that. Cheers

It's most likely something like that. My cops have a spring with the end of the wire that cuts across the middle of the spring spiral. So I'm not sure how it could push too far down the plug unless its slipping to one side. I haven't looked at since installing a small spacer as I've had no issues and have been too busy getting the car ready for last weekend.

The engine ran great without any issues both days. Certainly a lot quicker than my 1.6!