Sports Cat problem

Hi all, I have a MKIV TT JZA80. My machine is wicked as all you MKIV owners know. I have had the car 12 years and had no problems with it until now. I have made small standard mods to the engine over the years and it was going great until I removed the two cats and replaced them with a decat pipe that I had. Also I had an exhaust manufacturer add a 200 sports cat on the downpipe to get me through the MOT hassle. Car sounds awesome, but when I accelerate using full boost, it is back firing, popping and running really badly. Initially, I thought that it was the missing temperature probe, as that had been cut off, so I replaced that and just tucked in the cabin, as it does not reach the hole on the new exhuast, and the old bracket was beyond rusty.

Does anyone have any ideas what has happened to my lovely machine?

Cheers.. Fil

Sounds like it maybe a spark plug/coil pack/coil pack clips problem?

What boost pressure is the car now running? has it increased since you removed the cats?

I have just noticed that my Gizzmo is showing 16, when I turn on, when it used to say 1, so I think that someone may have been dicking around with it. I will have a look in the morning and see if that is the problem. Cheers for your ideas.

Sorry all, a vaccuum pipe had fallen off. Fixed it now.

Sorry all, a vaccuum pipe had fallen off. Fixed it now.

Glad it was an easy fix lol

No, I have broken something. when it is boosting, it starts to boost ok, then as the pressure gets to around 10psi, it feels like it is misfiring / juddering on the boost. It accelarates fine up to 5k revs, so I think that it must be a boost problem.

Does anyone have any ideas what I could have broken, by not having the vaccuum pipe to the wastegate accuator attached? I have also got my Gizzmo in 'Open' mode, so it is using the ECU and wastegate as standard, and it is still doing the same thing.

5000 revs is about where the second tubby should kick in mate. So could be a problem in there (hope not though). Or you could have a split hose/leaky hose somewhere.

Personally, (I'm no expert though) I'd try replacing all of the vac pipes and see if that solves it, as sometimes leaks/splits can be hard to find, plus then you know 100% that all the hoses are good.

After that, if the problem persists, I'd start looking on the turbo side of things. If you boost well up to 5k and then nothing more happens, I'd guess something isnt right with the No2 Turbo.

As I said though, I'm no expert, and someone will probably come slap me and tell me to shut up soon

It sounds like a misfire under boost. Is it possible you're running higher boost now? This will show up a weak coil pack, or old coil pack clips that are breaking up.

Yes, ok thanks. I will change all of the vaccuum pipes, see how I get on there. I don't think the problem is a weak coil pack, as it was running perfectly before the vaccuum pipe fell off the accuator, unless of course it has damaged the coil pack / clips, or since removing the two cats and replacing with a sports cat, that has shown up the weak coil pack. What do you think to that?

I am thinking that I have damaged something, due to the vaccuum pipe falling off, so if anyone has any ideas what I could have damaged, that would be a great help also.

I don't think the problem is a weak coil pack, as it was running perfectly before the vaccuum pipe fell off the accuator, unless of course it has damaged the coil pack / clips, or since removing the two cats and replacing with a sports cat, that has shown up the weak coil pack. What do you think to that?

I am thinking that I have damaged something, due to the vaccuum pipe falling off, so if anyone has any ideas what I could have damaged, that would be a great help also.

I'm thinking that removing two cats and replacing them with one high flow one will increase your boost, and show up a weak coil pack Do you have a boost gauge?

-Ian

Yeah, the gizzmo shows the boost pressure

Sorry to hijack, but what sports cat did you fit? It replaces the orignal 1st cat and you are not running the original 2nd cat and you did pass through MOT without emission issues?

Yeah, the gizzmo shows the boost pressure

Sooooooo what was it before the exhaust work and what is it now...?

Answering Bodilix6: It was a manufacturer of hand made exhausts, so it wasn't a particular make, but I know that it was a 200 whatever. They told me that I can pass the MOT, as long as I have a cat, which is why I went this route rather than a straight through. Not been there yet, because I only just had the MOT before doing the exhaust, so I bl**dy hope it passes next year.

Ian C: I didn't really take much notice of the boost pressure before I had the exhaust fitted, but I noticed around 14.5ish when I did look. The problem is that the boost went up to at least 19, but that was because the accuator vaccuum pipe fell off I guess. Now that I have put it back on, it faulters at around 12, which is why I think that I have broken something. I am going to try the new vaccuum pipes method to remove that theory (cheaper option first), then I will do the coil packs if that doesn't work.

I don't think you'll have broken anything, at least nothing expensive. You'd know if you'd lunched the engine in some way it'd be like a bag of nails even at idle. Turbo failure doesn't manifest as low boost, it's either none, a hideous noise, or a cloud of burning oil smoke out the back.

It might be that the freer-flowing exhaust system caused increased boost pressure, and this increased pressure blew the hose off the actuator, and the even higher pressure then blew another hose off or split a worn/old hose somewhere. Use the throttle to hold boost at say 10psi and see if it's smooth or if it still fluctuates. It's tricky but possible especially in a higher gear.

Also, put up a pic of the hose that you're talking about. There are many hoses in that engine bay, and more than a couple of actuators

Regarding the lower boost; that sounds about right to me as well.

When I had only the 1st cat (OEM) mounted, my boost was around there. No cats with a bit RR or in my case a cat with a hole through it, results in the wanten 1-1,2 bar depending on gear, outside dem and so on.

After mounting a 200 cell cat, you might see that change and need a boost controller to push it up higher. But keep an eye on EGTs as that can become an issue whith more back pressure.

Placement of the cat can also affect boost as well as EGTs

Sorry, I didn't notice that we had gone to page 2

Ian C: it was deffo the wastegate accuator, as this is where I fitted my gizzmo boost controller and hadn't clamped it on properly and I had read and read to make sure that I had the correct pipe.

I am going to change all of the vaccuum hoses and I have ordered yellow jacket coil packs to put on. I have also ordered Iridium spark plugs to put in while I am doing that.

Does anyone have an ideal plug gap for my Supe?

IIRC 0.7mm or 0.9mm mate. Depending on the plugs.

Thanks listy35

All fixed now that I have changed all of the vaccuum tubes and I have put 'YellowJacket' coil packs on with iridium spark plugs. Thanks all for the information and ideas.

On removing the plugs, bugger of a job because they were so tight, I have found that two of them were covered in oil. Is this anything to worry about?

listy35: You can't set the gap on iridium spark plugs for future reference.