Could use help troubleshooting - Misfiring at 6200 RPM on a friend's 240sx - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-12-2014, 05:00 PM   #1
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Default Could use help troubleshooting - Misfiring at 6200 RPM on a friend's 240sx

My friend has completed an SR20 swap in his '90 240sx.

He used a new wiring harness made by Wiring Specialties and an MSPNP2.

So far, he has replaced the Plugs, Coil Packs, Injectors, Fuel Pump, TPS, Knock Sensor, - basically every single sensor except for the CAS.

Attached is a datalog meant to capture the issue. Around 6000 RPM the car begins to misfire. It got a lot better when he replaced the TPS, but it still happens. The car still builds boost and RPMs, but it just misfires horribly.

Also, I've attached the tune file. It is the base tune that came with the ECU, with merely a couple of VE runs on it.




Stock 370cc Injectors
Red Top SR20DET
Stock Turbo
Stock Wastegate
MSPNP2, MAF Delete
LC2
ISIS 255 Fuel Pump
93 Octane Pump Gasoline

Please let me know if you have any questions and thanks for the help in advance.
Attached Files
File Type: msq 2014-09-18_18.43.21.msq (96.0 KB, 47 views)
File Type: msl 2014-09-18_17.52.23.msl (1.07 MB, 37 views)

Last edited by dhyde9; 10-13-2014 at 12:09 PM.
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Old 10-13-2014, 11:55 AM   #2
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I'm not a tuner so i'm not going to try and fix the car. but i do know you'll need to provide more information. Like.

what gas is he using?
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Old 10-13-2014, 12:10 PM   #3
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Originally Posted by OGRacing View Post
I'm not a tuner so i'm not going to try and fix the car. but i do know you'll need to provide more information. Like.

what gas is he using?
Thread updated. Is there anything else you can think of that could be possibly necessary?
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Old 10-13-2014, 12:37 PM   #4
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Noise in your MAP signal is triggering a MAP based fuel cut. Increase your MAPdot threshold -- you can probably just bring it to 999 kPa/s as you're using TPS based AE.
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Old 10-13-2014, 12:37 PM   #5
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The main problem I'm seeing is a MAPdot driven decel fuel cut. Try increasing the MAPdot threshold, or setting Decel Fuel Amount to 100%.

On what I believe to be an unrelated note, your battery voltage is all over the place. Any chance you've got a bad ground? Does the car have a wire tuck?
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Old 10-13-2014, 01:35 PM   #6
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Originally Posted by Matt Cramer View Post
The main problem I'm seeing is a MAPdot driven decel fuel cut. Try increasing the MAPdot threshold, or setting Decel Fuel Amount to 100%.

On what I believe to be an unrelated note, your battery voltage is all over the place. Any chance you've got a bad ground? Does the car have a wire tuck?

It does not have a wire tuck, but it does have a remanufactured swap harness. I don't know everything about the car, but it would not surprise me if it had a grounding issue. I'll pass that along and we will check it out.

Otherwise, how did you guys determine that it was MAPdot fuel cut causing the issue? That would not have occurred to me since it was using TPS AE. The first thing I checked was the over boost protection because that is exactly what it felt like. So that makes a lot of sense to me no .
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Old 10-14-2014, 07:23 PM   #7
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Well, it actually looks like the grounding issue may, at least in part, be the cause. MAPdot was corrected but the misfire still happened. I took a look at it after Mr. Cramer pointed it out, and it looks like the battery voltage is hitting it's low (11.0v) at the same point that the misfire happens.

He is going to go over his grounds, and hope that the harness isn't a part of the issue.

For anyone else reading this who may have questions, this article on DIYAutoTune.com was very useful for me to understand the MAPdot issue.
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Old 10-15-2014, 10:35 AM   #8
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MAPdot decel shows up as the "Bit 8" or "MAP DE" indicator light in MegaLogViewer. D you have a fresh log with the issues we mentioned corrected? Hitting the space bar when the misfire happens will also help us focus on the points where you're having trouble.
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Old 10-15-2014, 10:41 AM   #9
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It wouldn't hurt to have the alternator checked out to ensure the voltage regulator is OK. A battery check is a good obvious thing to rule out too.
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Old 10-15-2014, 11:06 AM   #10
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Quote:
Originally Posted by Matt Cramer View Post
MAPdot decel shows up as the "Bit 8" or "MAP DE" indicator light in MegaLogViewer. D you have a fresh log with the issues we mentioned corrected? Hitting the space bar when the misfire happens will also help us focus on the points where you're having trouble.
Yeah, I realized that as soon as I opened the data log. I do have another, but he is going to go over his harness and get back to me. If he still has issues I'll log again and mark it as needed.

Thanks for the advice fellas.
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