Engine cut off up 75 mph


Funpilote

GT Owner
Jan 7, 2015
10
Hi everybody,

I am mecanic in french riviera and i work sometime on GT's .A friend of mine own a fresh 05 with 4500 miles ,this car is full stock
When i drive this car in freeway the engine cut off whithout hesitation and i must switch off ignition and on to run engine with gear engaged !
When the engine go down like no more fuel , brake and abs ligths go on, but all gages work normaly, i can see the vacumm boost gage move when i press accelrator pedal. This occur only when i drive in constant speed more than 65 miles No rattle or power loss when i use with full acceleration in low speed condition. I check lot of things ; battery connectors, inertia cut off switch , fuel pump relay (2), fuses.
Does anybody get an idea? thank you
Marc
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,176
Hi Funpilote! Thanks for posting and sorry you are having trouble. Your english is a lot better than my French!

I will assume that you literally mean that the engine shuts down and you must cycle the key to get it to come back to life. If this is correct, you problem is almost certainly electrical and not fuel related at all. So, you can stop look for fuel problems in my opinion. (Exception: You can be losing electrical power to the fuel modules but the fact that you have to cycle the key is an indicator that it is a major system-wide electrical issue.) I think the electrical system is interrupting power. I would advise to start checking (removing, cleaning, re-attaching) primary electrical connections. Start up front at the battery itself. Check the ground cable's attachment to the GT chassis (remove, lightly sand/clean) and re-attach. You may even consider to add a secondary ground strap - either temporarily or permanently. (The ground to chassis has been a known weakness on some GTs.) While up-front, also check the fuse junction box near the front bonnet latch assembly. Make sure everything is tight. Make sure that that the relays are seated well and there is no corrosion.

At the back of the car, check the electrical connection at the alternator - just behind the driver. Make sure it is tight and free of corrosion. With the rear pan/diffuser removed, you can check the connection on the starter. (Be careful as this connection is always 12v. If you want to remove/clean it, disconnect the battery up-front first.) With the alternator connection and this starter connection, you are also looking for the possibility that something is shorting the connections. Back at the starter, high heat sometimes high heat melts the plastic connector. Inspect this area carefully.

With all of these areas inspected and cleaned, I would look at the primary fuse box at the floorboard where the passenger's feet are. Remove the cover and make sure the cover has not been smashed and make sure all fuses and electrical connections are tight.

Finally (and least likely culprit), inspect the rear part of the front right passenger side wheel liner. The fuel pump modules are located behind the rear part of this liner. You want to make sure no damage to the liner in that area that could have harmed the modules.

Best of luck and please tell us what you find!!
 

Funpilote

GT Owner
Jan 7, 2015
10
Thanks for your reply nota4re, I also mean that is not a fuel problem, i checked the two fuel pump by remove the two relays at idle one by one until engine stall. Must be a micro electric break somewhere, but i must find where it is. Curiously, this occur at stable speed like a freeway
Marc
Sorry for my flat language!
 
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Funpilote

GT Owner
Jan 7, 2015
10
I think, i found the problem! This car is full stock excluding the tires, because factory good-year was 13 year old and rear are 60 % used, I changed for a new michelin pilot sport cup 2, but there is not lot of choice regarding dimensions ; factory 235/45 X18 and 315/40 X19 are not available anymore in Europe without exotic Asian brand. I put a 245 /40X18 in front and 325/30 X19 at rear. Original ratio between front and rear is 1,098 (9,8%) and now the ratio is 1,038 (3,8%) this bring the car in Limp go home mode, i tried the car until engine shut down, and the engine come back below 50 mph. Also the speedo is 10 mph up wrong.
I know than a SCT tuner can correct and calibrate the speedo, does this recalibration affect ABS signal too?
Thank for reply
 
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fjpikul

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Jan 4, 2006
11,475
Belleville, IL
You should look at the very long tire thread here. Bridgestones are the tire of choice.
 

fjpikul

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Jan 4, 2006
11,475
Belleville, IL
Usually limp mode only happens when the engine temp goes very high (over 240 degrees F). You need to check and change the coolant and make sure there are no air bubbles in the system. While you are doing that, you should change the clutch cloud which is often overlooked.
 

TO AWSUM

Ford GT Owner
Mark II Lifetime
Jul 4, 2007
1,506
Niceville FL
Usually limp mode only happens when the engine temp goes very high (over 240 degrees F). You need to check and change the coolant and make sure there are no air bubbles in the system. While you are doing that, you should change the clutch cloud which is often overlooked.

Mine went into limp mode because the battery amps got too low. If my memory serves me, I believe the old battery amps were around 250amps. The car would start, but would only run in limp mode. Changed the battery and everything was fine again.
 

Funpilote

GT Owner
Jan 7, 2015
10
And, concerning the SCT tuner, anyone get knowledge, regarding calibration when height tire has been change?
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,176
Incorrect tire sizes is NOT your problem.
 

Funpilote

GT Owner
Jan 7, 2015
10
I changed the battery, clean and check terminals, this didn't correct the problem....
 

Funpilote

GT Owner
Jan 7, 2015
10
And do not forget than when the car come in Limp mode ,the ABS and brake ligth go "on" ....
 

Funpilote

GT Owner
Jan 7, 2015
10
Today, i swap the four wheels from another GT with Stock wheels and tire, go for a long road test in fact to be sure ; no limp go home problem anymore ! It was realy incorrect tires size who enter limp mode.
 
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2112

Blue/white 06'
Mark II Lifetime
How can all of the rest of us with non-stock tires drive without going into limp mode?

Edit, just read in the other thread about the Wagon Wheels used up front.
 
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GT101

*UK Support*
Supporting Vendor
Jan 20, 2010
380
Colchester, Essex, UK
This actually happened to the European Press Car back in 2005 - some journalists from Denmark had the car on track and got through the rear tyres. They thought it was only fair to replace them but couldn’t get the right size. Fitted some lower profile rears and then the car went into limp home mode. When they brought it back they were relieved to find out it was just the tyre size that caused the problem. They thought they’d done some other damage


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