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2012 mustang gt new motor will not exceed 4K rpm

5K views 16 replies 12 participants last post by  AnEffinCookie 
#1 ·
Hello everyone,

I have a very strange issue and was wondering if anyone had it before.

I recently got a new motor installed from the dealer because the old one failed due to rod knock.

Once I got it, I was gentle with it and didn't rev it past 4K rpm to break it in properly. However because of this I didn't notice a major problem with it.

If I try to accelerate past 4K rpm, the motor does like a rev limit. It won't go any more and if I hold it for long enough the wrench light comes on and I have to restart the car. It does it in gear or out of gear (manual).

It's really bizarre and I have replaced the throttle body to no avail. It's at the dealer right now but they are diagnosing it. I just want to see if I can get any information to help them fix it sooner.

Thanks
 
#2 ·
Maybe your using the valet key? Probably not, but just tossing that idea out there.
 
#3 ·
The dealer should be able to figure it out. But you broke in the new engine without going over 4000 RPM?
 
#4 ·
Definitely wasn't the valet key or any MyKeys. I made sure to reset all those first.

I was being gentle for the first 500 miles, then when I decided to open her up catching up to a Ferrari, it went into limp mode. I repeated it and noticed it wouldn't go past 4000rpm.

Hoping the dealer will figure it out. I'll report what I discover. If they don't I'll be getting my hands dirty lol.
 
#6 ·
Cookie,

Any update? Enquiring minds want to know!

Firing order fouled up?

Thanks,

Chris
 
#7 ·
I would have them check to make sure your keys haven't been messed up on the ECU side. Maybe have them plug their computer into your car and check on your key statuses?
 
#10 ·
Little more background:

I had them put in a new clutch, boss oil cooler, transmission fluid flush, and break fluid flush when they put in the new engine. Also it is getting a new cat because it's rattling bad and throwing codes.

Anyway, the update I just got from the service advisor is...they don't know!!!

They had to call into higher up on the food chain to see why it's acting this way lol. As soon as I know I will report in, as this is a very strange issue.

I just want my Stang back though...Honda civics have very little smiles per gallon :(
 
#12 ·
I recently experienced a similar issue. I replaced my stock short block with one I had build and when I started it for the first time, it was misfiring and would not rev much past 4k. I thought the issue was due to it needing the crank relearn performed, but the CEL never illuminated. I reloaded the tune and the problem went away. I never had to do the crank relearn.
 
#13 ·
Good to know txcharlie

On a side note I just traded it in after I got frustrated and figured it would be better with a new car. So I got a 2017 mustang gt w/PP lol. It's great and best move I ever made.

In hindsite, that mustang was beat on heavily. The welded on cats should have been my first sign to get away from it. Anyway lesson learned and I'm rolling my new one and its awesome. I keep a close eye on the oil and everything else.

just a tip, avoid buying a used grabber blue 2012 mustang gt with a new motor, Pipes exhaust, solid grabber blue rear window covers, and with 68k miles lol.
 
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