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Loss Of Power-13' Shelby.


Kayz

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Well this is really perplexing me. At first I thought it was some sort of heat soak issue, therefore made a post about it.

 

The car behaves exactly the same way, ALL the time. ie, I would take her out, drive for 5-7 minutes to warm up, give it and it will go like a rocket like its supposed to. But after around the 15-20 minute mark of driving, theres a huge difference in power. I mean at all gears. The car just wont climb in rpms like its supposed to, feels like the supercharger aint working or something. At 1st gear, no tire chirp nothing, just climbs slowly.... I chked all the gauges, boost, afr, etc looks all good. No check engine light, no funny smells from anywhere.

 

Does anyone here have ideas as to what possible things could be wrong here?

 

thanks a lot , I am really depressed for the past month now =/

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Well this is really perplexing me. At first I thought it was some sort of heat soak issue, therefore made a post about it.

 

The car behaves exactly the same way, ALL the time. ie, I would take her out, drive for 5-7 minutes to warm up, give it and it will go like a rocket like its supposed to. But after around the 15-20 minute mark of driving, theres a huge difference in power. I mean at all gears. The car just wont climb in rpms like its supposed to, feels like the supercharger aint working or something. At 1st gear, no tire chirp nothing, just climbs slowly.... I chked all the gauges, boost, afr, etc looks all good. No check engine light, no funny smells from anywhere.

 

Does anyone here have ideas as to what possible things could be wrong here?

 

thanks a lot , I am really depressed for the past month now =/

 

Does your boost gauge show the same boost from cool to hot?

 

 

Phill

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Just curious. What's limp mode andwhat causes it

 

Limp Home Mode is the failsafe program in the PCM that allows you to get your car to a dealer/repair shop if you have a catastrophic failure of a input sensor.

 

 

It is a very rich AFR program and the car runs like crap, sometimes barely at all.

 

 

 

Phill

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Limp mode is a self defense mechanism that rev limits the engine and disables the supercharger (I think it is both and maybe more) to prevent engine damage while still allowing the vehicle to be driven. It should be accompanied by a check engine light

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From the 2014 Factory Service Manual.
Failure Mode Effects Management (FMEM)

The FMEM is an alternate system strategy in the PCM designed to maintain engine operation if one or more sensor inputs fail.

When a sensor input is determined to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value for the incorrect input and continues to monitor the suspect sensor input. If the suspect sensor begins to operate within limits, the PCM returns to the normal engine operational strategy.

 

This is interesting, I don't know if it applies to our cars but it was in the Mustang section.

 

Fail-Safe Cooling Strategy

Note: Not all vehicles with a cylinder head temperature (CHT) sensor have the fail-safe cooling strategy.

The fail-safe cooling strategy is only activated by the PCM when an overheating condition has been identified. This strategy provides engine temperature control when the cylinder head temperature exceeds certain limits. The cylinder head temperature is measured by the CHT sensor. For additional information about the CHT sensor, refer to Engine Control Components in this section.

A cooling system failure, such as low coolant or coolant loss, could cause an overheating condition. As a result, damage to major engine components could occur. Along with a CHT sensor, the fail-safe cooling strategy is used to prevent damage by allowing air cooling of the engine. This strategy allows the vehicle to be driven safely for a short time with some loss of performance when an overheat condition exists.

Engine temperature is controlled by alternating the number of disabled fuel injectors, allowing all cylinders to cool. When the fuel injectors are disabled, the respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power.

A wide open throttle (WOT) delay is incorporated if the cylinder head temperature is exceeded during WOT operation. At WOT, the injectors function for a limited amount of time allowing the customer to complete a passing maneuver.

Before injectors are disabled, the fail-safe cooling strategy alerts the customer to a cooling system problem by moving the IPC temperature gauge to the H (hot) zone and setting DTC P1285. Depending on the vehicle, other indicators such as an audible chime or warning lamp, can be used to alert the customer of fail-safe cooling. If overheating continues, the strategy begins to disable the fuel injectors, DTC P1299 is stored in the PCM memory, and a malfunction indicator lamp (MIL) illuminates. If the overheating condition continues and a critical temperature is reached, all fuel injectors are turned OFF and the engine is disabled.

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Have you replaced the fuel in the tank since this started?

 

The guys that fill gas stations are not infallible, putting 85 octane on the 91-93 nipple can happen. Or contaminates in the fuel from faulty tanks. Once the car is hot and it detects knock from low octane it can pull timing, boost, all kinds of things. It happened to me once buying from a crappy sinclair station but it triggered lights in my case. Once I replaced the fuel, never happened again. If so, I wouldn't be getting on it hard unless you want a new window on the side of your block :-)

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As said before, no chk engine light and my rpms are not limited, I can still get to redline, but slowly. The boost guage read 4/5 psi on WOT during this today. Do you guys think this could be the supercharger pump and yet no chk engine light is turning up? Could be signs of the clutch going? ( I don't smell anything ever). The DTC thing u mentioned means I shud take it to the dealers...but honestly where I live u cant trust them at all before atleast having the basic knowledge of the issue at hand so you don't get conned .

thanks again for chiming in guy.

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As said before, no chk engine light and my rpms are not limited, I can still get to redline, but slowly. The boost guage read 4/5 psi on WOT during this today. Do you guys think this could be the supercharger pump and yet no chk engine light is turning up? Could be signs of the clutch going? ( I don't smell anything ever). The DTC thing u mentioned means I shud take it to the dealers...but honestly where I live u cant trust them at all before atleast having the basic knowledge of the issue at hand so you don't get conned .

thanks again for chiming in guy.

 

I asked what your boost gauge showed because I don't have a vacuum reading from the engine so I'm using the boost gauge in place of one. The low boost reading is telling.

 

This sounds like it could be a plugged/restricted exhaust.

 

 

Phill

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it could easily be something associated with the heat exchanger for the supercharger.....if supercharger discharger is too high (such as an issue with that system) timing would be pulled but probably without any codes indicated. With the 13 you may be able to display your IAT2s.....check and see how high they are...I think timing is pulled over 125 or so. but definitely make sure your pump is pushing coolant thru the system by a visual check.

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It might also be associated with the By-Pass Valve on the supercharger. If is defective or not functioning correctly, it could cause low or no boost.

 

The SC bypass vacuum actuator mounted on the SC :

  • controls the bypass valve inside the supercharger. The bypass valve allows the high pressure air at the outlet of the supercharger to vent back into the inlet of the supercharger, equalizing the pressure.
Supercharger Bypass (SCB) System

The SCB system allows the high pressure air at the outlet of the supercharger to vent back into the inlet of the supercharger, equalizing the pressure. This eliminates the boost (increased pressure that the supercharger produces) for times when supercharger function is undesirable. The system uses a vacuum bypass actuator, which controls the bypass valve inside the supercharger. The system normally operates with engine vacuum applied to the upper port of the vacuum bypass actuator, while the lower port references the air pressure in the clean air tube to cancel out any pressure difference in the intake air system. The actuator is set to open (bypassing the supercharger) during high vacuum engine conditions. As the throttle is opened and engine vacuum decreases, the actuator closes to allow the supercharger to pressurize the air in the manifold.

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thx a lot for all the info guys ill be laying it down when I take her to the dealer. I think I found out the issue tho.

Took her out just now. Everything great, car at full throttle getting 12psi . after exactly 19 minutes of driving, at full throttle it wont go above 5 psi, in ALL gears, 1 - 5. so basically the boost , after driving for 20 minutes, goes from being a healthy 12 psi to 5 psi. EVERYTIME. day or night. 20 minutes .

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thx a lot for all the info guys ill be laying it down when I take her to the dealer. I think I found out the issue tho.

Took her out just now. Everything great, car at full throttle getting 12psi . after exactly 19 minutes of driving, at full throttle it wont go above 5 psi, in ALL gears, 1 - 5. so basically the boost , after driving for 20 minutes, goes from being a healthy 12 psi to 5 psi. EVERYTIME. day or night. 20 minutes .

 

Yep, that's why I say plugged/restricted exhaust. When the CAT's heat up they're plugging the outgoing gasses.

 

By-pass valve would be my second guess but there's no reason it should work fine cold and get worse as it gets hot.

 

I've seen your symptoms on a Naturally Aspirated (NA) car before and you get a very low vacuum reading when you give it gas. I've never diagnosed the same thing on a SC car so I may be way off.

 

 

Phill

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Oh yeah, check the blower drive belt for slippage too. You might see black dust around the pulley.

 

 

Phill

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UPDATE:

Was told today that my intercooler pump was faulty was "causing intake temps tto rise and PCM to pull timing, cut boost and command a richer fuel mixture" . Weird thing is my AFR never showed me running rich in during the whole ordeal, nor any chk engine light popped up. Regardless they are ordering the pump since none in stock. Will update once they install it. Thanks for looking into this case fellow Shelby lovers.

 

 

Much love.

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glad you found it...makes sense. The computer is only sensing a hotter discarge from the supercharger into the engine, which could be a result of many things. So it is reacting acordingly, by pulling timing, and in your case, limiting the pressure somewhat. The fix is easy, and you should be good very soon. After you get it back, visually verify that the flow thru the tank is good, and that all the air was removed from the system.

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  • 5 months later...
  • 2 weeks later...

same issue again yesterday, PSI barely breaks 10 at any rpm. Vac gauge stays around 20 at idle. leaking vacuum hose maybe?

 

Not very likely with 20" Hg at idle. Typical vacuum reading should be 17"-20" at idle. If you had a significant leak, you'd see it in a lower reading and you're at the top of the scale.

 

You could have a small leak but that wouldn't cause a driveabliity issue, just a idle issue (as *most* vacuum leaks do). That's why I was thinking more along the lines of false (unmetered) air or more so, fuel starvation.

 

I'm thinking fuel starvatoin because you say it happens when you're coming out of a particular corner. I'm guessing that is where your lateral G force is going to be pushing gas away from your pick-up. Is it the tightest corner on the course by chance?

 

 

 

Phill

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Not very likely with 20" Hg at idle. Typical vacuum reading should be 17"-20" at idle. If you had a significant leak, you'd see it in a lower reading and you're at the top of the scale.

 

You could have a small leak but that wouldn't cause a driveabliity issue, just a idle issue (as *most* vacuum leaks do). That's why I was thinking more along the lines of false (unmetered) air or more so, fuel starvation.

 

I'm thinking fuel starvatoin because you say it happens when you're coming out of a particular corner. I'm guessing that is where your lateral G force is going to be pushing gas away from your pick-up. Is it the tightest corner on the course by chance?

 

 

not on corners, happens on straights, highway driving, every where. I wonder if a bad batch of gas could cause the issue?

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not on corners, happens on straights, highway driving, every where. I wonder if a bad batch of gas could cause the issue?

 

Not likely. Bad gas would happen all the time, not just in one particular RPM range/band.

 

 

Phill

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