All parts were replaced with known good parts. It will die EVERY time at the same MPH, give or take a couple MPH. It feels like a MPH limiter kicks in. It does not matter when you drive the car, how hot the car is, it does what it does without fail every time. Im sure its something simple that we have over looked ,but its giving us hell. *LOL* We have taken the car to around 78-80 MPH in 4th and 5th gear and still does it. He is not a kid that dogs the crap out of his car. He is 48 years old and likes his 240, BUT he is getting to the point that he is ready to give up on it.

 

bad ecu . . or are you completely sure the ecu is stock.. dumb question but its an idea.

 

Look under the car and make sure all of the sensors are plugged in on the transmission.

 

see, the part that makes this weird is the "about 80" if it was speed related, then it would be a set mph every single time.
It is obviously not rpm related.

It might sound funny, but go over a bridge, see exactly what mph it does it on the up side of the hill and then again on the down side of the hill.

meanwhile, I'd check out the relays for the fuel pump and the ECU...
does the ecu keep power when the motor shuts off.... if it does you'll get the oil pressure light and the check engine light and all of that...
that will help narrow it down to were we are looking...

 

that wouldn't matter... you could un plug all of the sensors and be just fine... all there is, is reverse, 4th gear, 5th gear and speed sensor. the 4th and 5th gear sensors are for the 4th and 5th gear limiters. reverse just turns on the lights and the speed sensor just gives a speedometer reading, the ecu only wants to know when the speedlimiter is, it doesn't care how fast the car is moving for anything else...

i know this because my car runs just fine and all of the sensors on my car were ripped off in a rather recent unintentional, interstate drifting incident....

 

is it auto or manual?

 

Its manual. I talked to him last night and like I said he does not get on his car hard, BUT yesterday he told me he got on it hard from a stop and it cut out way before 80 mph. I dont know what to say about the car now. Maybe he should just take it in and let them mess with it. This car is cursed.........

 

It's prolly just something loose somewhere. I had this happen before on a car I worked on, whenever you shifted hard into any gear it would start running like shit, or whenever you hit 55. I'm thinking 80mph is that harmonic sweet spot that something keeps coming loose possibly. Check all of your connections for your fuel injectors, grounds, and ignition. BE VERY CAREFUL but you can try jacking it up and taking it to 80 (slowly) and checking for anything under the hood. Worth a shot.

 

my old coupe kept randomly dieing like this.it came out to be the coil pack was bad...i would be driving and it would just die so i would pop the clutch and get it going again...

they are only like $40 at auto parts store

 

yeah, didn't think of that....worth looking at, it could do it.