Page 160 of 2009 Performance Parts by Ford Racing Performance Parts

always remember always disconnect the efi tech tips troubleto shootingbattery before doing any wiring on your vehicle efi system tips efi system tips electrical grounds electrical grounds always remember to disconnect the battery before doing any wiring on your vehicle!of most electrical problems is poor grounds the single leading cause ideally the ground for the fuel injection system should connect grounds the single leading cause of most electrical problems is poor directly to the battery at the negative post using the steel chassis or engine block as a ground can create excessive resistance causing the powertrain control ideally the ground for the fuel injection system should connect directly to the battery at the negative post using the steel chassis or engine block as a ground can create excessive resistance causing the powertrain control module pcm to function improperly module pcm to function improperly an example of how a high ground or connection resistance can have very serious effects is as an example of how a high ground or connection this particular case applies toisa 2005 mustang gt but can to a 2005 mustang gt to any electron resistance can have very serious effects as follows this particular case applies easily be extended but can easily be extended to any electronically controlled ford ford vehicle:the case wherethe case wheremaf sensoris reading v due to a controlled vehicle consider consider a pcm is reading a a pcm signal of 4.1 a maf sensor signal of 4 high ground or connection resistance when it should really be reading 4.3 v this equates to a difference in measured air mass of 13 that is the maf v this equates a high ground or connection resistance when it should really be reading 4.3 will be telling the pcm that there is 13 less air entering the engine than there really is let s say this happens at wot where air/fuel ratio is critical not difference in measured air mass of 13 i.e the maf will be telling the pcm that there is 1 only to performance but also to engine durability the result is that the actual air/fuel ratio can go from a safe 12.5:1 to a potentially damaging 14.1:1 just from a 0.2 v change in the maf return signal entering the engine than there really is lets say this happens at wot where air/fuel ratio is only to performance but also to engine durability the result is that the actual air/fuel ratio ca safe 12.5:1 to a it is absolutely critical that all electrical just from a solid and that the in the maf return signa all pcm sensors not just the maf are affected in a similar fashion so potentially damaging 14.1:1 connections are 0.2 v change grounds are reliable the potential penalty for a bad ground can range from strange drivability issues that are difficult to diagnose all the way to a damaged engine as in the above example all pcm sensors not just the maf are affected in a similar fashion so it is absolutely critical all resistance tests should be done with the ignition key in the off position having voltage going through the system can return a false reading of excessive can range from strange drivability issues that are difficult to diagnose all the way to a damage resistance additionally it is possible to have a ground that tests ok when the engine is cold but not when the engine is hot heat increases resistance so in the possible these tests should be performed on a warm engine whenabove example electrical connections are solid and that the grounds are reliable the potential penalty for a b all resistance tests 5.0l mustang use a volt/ohm meter to check the resistance position having voltage go to test for an adequate ground circuit in the efi system for a 1986 to 1993should be done with the ignition key in the off of the following circuits the system can return a false reading of excessive resistance additionally it is possible to ha · to verify a proper ground to the pcm check the resistance from pin 40 and pin 60 directly to thewarm enginethe battery resistance should be so these tests should be performed on a negative side of when possible no greater than 0.2 ohms · to verify a proper ground to the main pcm harness check the resistance from the maf sensor at pin `b directly to the negative side of the battery to resistance should be no greater than 0.2 ohms test for an adequate ground circuit in the efi system for a 1986 to 1993 5.0l mustang use ohm meter resistance the resistance of the following sensor tps · to verify a proper ground to the engine harness check theto check from the black wire at the throttle positioncircuits directly to the negative side of the battery resistance should be no greater than 0.3 ohms note that while 0.2 ohms or less is desirable a resistance as high as 0.5 ohms is considered acceptable greater than 0.5 ohms is excessive and could than 0.2 ohms to the negative side of the battery resistance should be no greater result in drivability concerns ground that tests ok when the engine is cold but not when the engine is hot heat increases · · to verify a proper ground to the pcm check the resistance from pin 40 and pin 60 to verify a proper ground to the main pcm harness check the resistance from the sensor at pin `b directly to the negative be checked at the throttle position a weak ground connection can also cause the pcm s internal reference voltage regulator to function incorrectly this canside of the battery resistance should be sensor tps by checking voltage between the black groundthanand the orange reference voltage wire with the key on this voltage signal should be wire 0.2 ohms somewhere between 4.7 v and 5.3 v general tips · whenever possible the pcm should be mounted inside the vehicle to protect it from water damage the pcm should also be mounted with the electrical connectors at the bottom to avoid trapping water some pcm s on newer model cars are mounted under the hood but they are sealed against moisture and designed to operate in such an environment when in doubt mount the pcm inside the vehicle 158 techline 800 ford788 notlegalforsaleoruseonpollution-controlledmotorvehicles directreplacementpart seepages3-9forimportantsafety,emissionsandwarrantyinformation.

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