Jump to content
The mkiv Supra Owners Club

Misfire at higher boost


SimonR
 Share

Recommended Posts

I have a misfire problem at the moment. Can anyone help? The car is a Soarer Twin Turbo.

 

Everything is OK at 1 bar but when I raced the car at 17psi a couple of weeks ago I noticed a hesitation (which I think is a misfire) at about 4500rpm. The revs bounce around a bit and then seem to make it through and continue to climb. Gutless, though.

 

I can run higher boost OK as long as I stay in a higher gear. 3000rpm in third and there's plenty of pull. Kickdown to second and the problem starts. It actually feels as though the pull in second is weaker than the pull in third.

 

I tested this a lot last weekend and found that the situation occurred as soon as I moved from 15psi to 16psi. Fine below - problem above. Same every time, completely reproducable.

 

I have Denso Iridium IK24's gapped to 0.75->0.8mm. They have been in for about 4000 miles. I've read that misfires can be caused by not running a cold enough plug but the IK24's seem to be recommended for higher than stock boost.

 

Someone has also suggested that the spark may be being blown out. I assume that this is based on the idea of denser air having more resistance.

 

Also, the Emanage was set up by Thor for running at 1 bar. Could that be a contributing factor?

 

Any suggestions gratefuly received. Thanks.

Link to comment
Share on other sites

Guest Terry S

I doubt it is the plugs, check by swapping in a set of NGK BCPR7ES' ( they are about £1.50 per plug). Do you have an AFR gauge? If the car is too rich it could cause a miss.

Link to comment
Share on other sites

Thanks Terry. Given that Pete set up the Emanage for 1 bar, would going to 17psi cause me to run rich? I would have thought that it would cause me to go lean if anything. If you think that it does sound as though it's running rich then maybe a less restrictive air filter?

Link to comment
Share on other sites

Guest Terry S

Jake is right generally the iridiums are pregapped. Is it using the stock Fuel Pressure regualtor? I also assume it has the fuel cut removed?

Link to comment
Share on other sites

Yes, HKS FCD fitted. FPR? The Australians do a lot of work on these cars and they reckon that the stock unit is good for 400rwhp (I'm on a measly 290). Is there any kind of (simple) test I can do for this?

 

In case anyone was going to ask, the fuel pump is an uprated Skyline GTR jobbie which should be more than man enough.

Link to comment
Share on other sites

Can you get your map off your car?

If you can PM me and I'll give you my e-mail address so I can have a look at the map.

I'll need your full spec too.

Injectors, turbos, FPR (fuel pressure regulator)

 

Have you had it dyno'd and had the AFR's (Air fuel ratio) checked?

 

If the plugs have been "gapped" then they could be damaged the iridium is very sensitive.

Link to comment
Share on other sites

I wouldn't have the foggiest idea how to get the map off the Emanage. I've never logged in to it - don't even have the required cable. Thor installed and set it up for me. Thanks very much for the offer though.

 

I had it dyno'd when the Emanage and IK24's were put on (and in). AFR tuning would have been part of the Emanage setup process?

 

Perhaps it's time to try some new plugs then.

Link to comment
Share on other sites

Try some NGK 3330's (BCPR7ES's). Gap them to .7mm.

If these work you know what the problem is, if they don't I'd recommend an AFR check on a Dyno or bringing the car to Norfolk and seeing IanC. He should be able to extract your map and inspect it.

 

Also if you don't have one you need your exhaust to be modified with a standard O2 sensor bung installed. Mig of vortex is close to you and will probably be able to do this. This will allow a Wide Band 02 sensor to be fitted to check the fueling.

Link to comment
Share on other sites

Problem solved. Main man Bedlam (a member here) advised me to get NGK BKR7E plugs from http://www.sparkplugs.co.uk. £2.70 each and arrived in less than 24 hours.

 

Gapped them to .7mm on his recommendation and fitted them yesterday. 150 miles of mad driving later (got to test them thoroughly) I have found that the problem has gone. No more misfire at all, right up to 17psi.

 

The Denso Iridium IK24's that I took out looked fine. Nice greyish tan colour to the electrodes. No sign of any damage to any of them, so Chris Bewick could have been right about the spark being blown out.

 

Strangely, curing the problem hasn't been without side-effects. Common sense suggested moving the boost back from 1 bar to 17psi in small increments. I use a Blitz DSBC and it uses a percentage system (percentage of max capability I assume). Running at 49% gives me 1 bar. With the old plugs, 53% gave 1.2bar. With the new plugs I had to extend that to 56% to get the same boost. I wonder why. Any suggestions?

 

Anyway, problem solved and I might see you at Japshow next week and see if I can get into the 13's now.

 

Thanks to everyone for their help. :clap:

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. You might also be interested in our Guidelines, Privacy Policy and Terms of Use.