chrisaw0811

Hello everyone, i have a 2000 mustang 3.8L Roush Edition and it has a high RPM misfire which happens at exactly 4,000 RPM's. I have done lots of things lately to try and fix it but nothing seems to work. I appreciate any help. Thanks.

List of things I have done recently:
-Oil and filter change
-Cleaned Intake
-Changed Fuel filter
-Changed Spark plugs
-Changed Spark plug wires
-Cleaned MAF
-Changed Bank 1 Sensor 2 O2 Sensor
-New EGR valve
-New Battery
-Cleaned IAC Valve

crysalis_01

Have you checked to see if the car is throwing any codes? If so what are they?

NeoTokyo

Could be the coil pack, replace it with a MotorCraft coil pack or a Borg Warner with a lifetime warranty.

RyansQuick6

Sounds like a basic coil pack failure. No clue why you replaced all that emission equipment though.

chrisaw0811

Is there any way to check coil pack? And the reason i replaced the EGR is b/c mine was faulty. It stayed open at all times. I had a P0141 which is Bank 1 Sensor 2 o2 sensor heater circuit fault. I replaced that O2 sensor. I also had a P0401 which was EGR insufficient flow detected. I cleared the codes after i replaced those two parts and now i don't have any codes. Thanks for the replies.

chrisaw0811

It also seems to run very rich.

RyansQuick6

Sounds like a bunch of symptoms related to a bad coil, or dirty MAF or IAC.

A code doesn't always mean the sensor is broken, it means the sensor is detecting an issue. What brand of O2 sensors did you use, the bosch ones are the absolute worst. Motorcrafts are the best thing to put in, haven't seen any issues with them so far.

gyea

Yep its the coil pack for the 60$ for a new one why bother testing it since you replaced so much allready. Now im pretty sure (but i am a bit rusty) your spark gets more voltage with higher RPMS 4000rpm and above maybe the magic voltage that causes a gap/crack to be bridged somewhere in or around your coil pack

One more thing tho are you 100% sure it is a misfire and not your torque converter shuddering I got tricked for a little while also... At around 3000rpm and above was a vibration (similar to a misfire) just food for thought

LilRoush

And to add to all that, you're probably running rich b/c it's typical with the Roush cat back on the V6.

NeoTokyo

Dont buy a cheap Coil pack.

First Best: Buy a new MotorCraft unit
Next Best: Buy one with a lifetime warranty like a Borg Warner (I have one, works great.)