cracked exhaust manifold pipes/headercar will not go fast revs high but No speed ?Cause?

ANSWER : In order of priority, if you have a cracked exhaust manifold (leaking carbon monoxide), that actually has to be fixed first or at least coincident with the repair(s) to the engine/transmission. The principal danger from exhaust leaks (carbon monoxide) is NOT death from acute exposure but rather long term tissue damage from chronic low level exposure. Way more people die from chronic, day to day CO exposure than from the kind of acute exposure you read about in the newspaper. So, basically, so as not to damage your health be sure to get the exhaust leak fixed at the same time the acceleration is resolved.

If your vehicle won’t go over 30 miles per hour, it is possible the PCM has forced the transmission to operate in limp mode. Forced limp mode operation can occur if, as an example, there is a fault with the input and output speed sensors on the transmission, or the kickdown switch. There are probably downloadable OBD-II trouble codes that will help the Mechanic hone in on the trouble area. You might try checking the transmission fluid level and condition. If the fluid level is low and/or burnt, that might be related to the problem. To rule limp mode in or out (without a code scanner) sometimes you can disconnect the negative battery cable for a 1 minute to reset the PCM and then see if the transmission shifts normally until it enters limp mode again. There are other possibilities for what you are describing though including faults in the fuel, ignition, air induction systems, and even the possibility of a severely restricted exhaust system. What I would suggest is diagnose the engine/transmission issue first, but again, once that is restored, the car is unsafe (unhealthy) to drive unless and until the exhaust leak is also repaired. Please let us know how we can best assist you.

ANSWER : Hi. We will be happy to assist you with your 2003 Infiniti M45. I believe it would be best to replace the cracked exhaust manifold. Your vehicle has two exhaust manifolds. It’s likely that the one you replaced cracked before the other and now the second manifold is cracked and leaking, which is the noise you are hearing. Replacing the second manifold should resolve your problem. Have the condition of both exhaust manifold gaskets checked as well. If you want to have this verified, a certified technician from YourMechanic can come to your car’s location to diagnose the noise you are making.

ANSWER : Hi There,
It sounds like you are describing the symptoms of a failing throttle position sensor. The throttle position sensor monitors the throttle position of the throttle plate inside the throttle body in relation to your foot position on the gas pedal. Based upon the inputs from the sensor reading your foot’s position on the pedal, the ECU then makes the direction to supply more or less fuel to the motor. When this sensor is not working properly, this can cause intermittent responses when pressing the gas pedal. I would suggest having a professional from Your Mechanic come to you home to diagnose and inspect your vehicle.

ANSWER : The trouble with small exhaust leaks is that they always turn into large exhaust leaks. The hot gas leaking past the gasket will eventually burn up the gasket making the leak worse. If not corrected, it will also burn the surface of the exhaust manifold. It rarely goes so far as to burn the cylinder head, but that can happen in extreme cases. To make matters even more complicated. having an exhaust leak also allows air to enter the exhaust stream and messes with the oxygen sensor reading. Mixture too lean trouble codes will follow as the system shifts rich to try to correct. So, if you want to keep this truck, you need to get this fixed. I’m not sure I buy the line about the head being warped enough to prevent the manifold from fitting, maybe you should get a second opinion on this. You can have this done by contacting Your Mechanic. They will send a technician to your home or office to check out your exhaust leak and let you know what can be done about it.

ANSWER : A damaged exhaust manifold does not affect engine oil consumption. Of serious concern though is the possibility that the cracked manifold is leaking exhaust gas (including poisonous carbon monoxide) into the passenger cabin, typically through the firewall and vents. If the manifold is leaking exhaust gas, I do not recommend driving the car because carbon monoxide is really, really bad for the body. Most deaths and injury from carbon monoxide are NOT from the acute incidents of poisoning deaths that you read about in the newspaper. Rather, the vast majority of mortality and morbidity due to CO poisoning is due to long term exposure to low levels such as driving a car with an exhaust leak under the hood. CO exposure is very bad for body tissues and again the problem is these sub-lethal, but chronic exposures that people do not think about. Most people think the problem with CO is the acute incidents and don’t give adequate consideration to the well documented negative health impact of the sub-lethal chronic exposures so get the cracked manifold repaired right away for the sake of your health!! If you want to schedule that, simply contact YourMechanic via the website inquiry form or telephone the YourMechanic toll free number. With regard to engine oil, you should add enough oil to bring the level to the full mark on the dipstick. Monitor your oil consumption. If the engine is using a lot, you might benefit from replacement of the valve stem oil seals and/or you may have oil leak(s) that can and should be fixed. Please let us know if you have any additional concerns.

ANSWER : Hi John. It’s quite possible that the source of your Infinity issues is something simple (like an O2 sensor) or major (such as a catalytic converter that is worn out). The best way to pinpoint the precise source of the issues is to have a professional mobile mechanic complete a car is slow to accelerate inspection, so they can accurately determine what’s causing the symptom and recommend the repair that should resolve the problem’s you’re experiencing.

ANSWER : Hi there. If the vehicle has sat for an extended period of time, it is likely that multiple components; internal and external have ’frozen’ or have lost lubricity and are literally stuck. The clutch and transmission specifically can be negatively impacted due to lack of motion since it’s a hydraulic system, meaning it depends on consistent flow of fluid to maintain pressure in the system to work correctly. The brake pedal is also a hydraulic system – which is most likely why you’re having issues with this system. In regards to the helicopter sound, it is likely an exhaust manifold or exhaust pipe connection below the manifold that has cracked. However, since the Mitsubishi mechanics that apparently use stock exhaust manifolds on their "three times HP engines" said that’s impossible, maybe it’s best to take your car to them and have them put their skills to work to resolve your cars issues. To be honest, fixing the clutch, brake pedal and other systems that are stuck is going to be difficult and probably very expensive, so you might want to contact some other mechanics to get some estimates about repair costs before you get too deep into this project. Best of luck.

ANSWER : Hello – most likely, this is an exhaust leak between the exhaust manifold, and the cross-over pipe. Removing the cross-over pipe will be the required process to replace the leaking gasket if this is the source. i recommend a engine noise inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, confirm this diagnosis, and give you an accurate assessment of damage and cost estimate for repairs.