Could use help troubleshooting - Misfiring at 6200 RPM on a friend's 240sx
#1
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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.
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.
Last edited by dhyde9; 10-13-2014 at 11:09 AM.
#2
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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?
what gas is he using?
__________________
OG Racing
Your Source For Motorsports Safety Equipment
WWW.OGRACING.COM
800.934.9112
703.430.3303
info@ogracing.com
OG Racing
Your Source For Motorsports Safety Equipment
WWW.OGRACING.COM
800.934.9112
703.430.3303
info@ogracing.com
#5
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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?
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?
#6
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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?
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 .
#7
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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.
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.
Thread
Thread Starter
Forum
Replies
Last Post
bigmackloud
Miata parts for sale/trade
19
01-08-2021 11:24 AM
Zaphod
MEGAsquirt
47
10-26-2018 11:00 PM
JesseTheNoob
DIY Turbo Discussion
15
09-30-2015 02:44 PM
Mikel
MEGAsquirt
4
09-28-2015 04:46 PM