dhyde9

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.

OGRacing

iTrader: (1)

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?

dhyde9

Thread updated. Is there anything else you can think of that could be possibly necessary?

Ben

iTrader: (33)

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.

Matt Cramer

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?

dhyde9

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 .

dhyde9

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.

Matt Cramer

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.

Ryephile

iTrader: (1)

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.

dhyde9

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.