Voltage problem, need help, affects engine
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New User
Joined: Dec 2004
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Voltage problem, need help, affects engine
I have a 89 f250 with the 5.0L engine. When I first start the truck the volt gauge reads low like 10volts, but the truck runs fine and the tach needle reads a steady reading. There is no hesitation at low rpms, in any gear, and the voltage at the battery is 14volts. As the truck warms up the voltage gauge reads lower almost down to 8 volts. This is when the truck starts to hesitate/mis at low rpm. It will buck sometimes.
I've checked the voltage with the engine running at the battery 14v, at the stater relay 14v, at the coil 14v when this condition occurs. Also the tach gauge is fluctuating a couple hundred rpms. The tach gauge will not hold a steady line at idle, and it fluctuates when I rev the engine. This condition has gone on for a few days and the truck has always started right up, so the battery is being properly charged. I have no idea what's going on. When the volt gauge reads 10 or higher it runs perfect no complaints but once it drops to 8 or so the truck runs like crap. How is this affecting the engine? Any help would be greatly appreciated as this is my daily driver.
I've checked the voltage with the engine running at the battery 14v, at the stater relay 14v, at the coil 14v when this condition occurs. Also the tach gauge is fluctuating a couple hundred rpms. The tach gauge will not hold a steady line at idle, and it fluctuates when I rev the engine. This condition has gone on for a few days and the truck has always started right up, so the battery is being properly charged. I have no idea what's going on. When the volt gauge reads 10 or higher it runs perfect no complaints but once it drops to 8 or so the truck runs like crap. How is this affecting the engine? Any help would be greatly appreciated as this is my daily driver.
Elder User
Joined: Sep 2004
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Your engine and/or chassis grounds are probably bad. Check the two ring-shank connectors tied to a stud right in front of the battery. Check the PCM ground on the driver's side of the firewall (near the hood hinge). Check the high-connection to the frame and to the block.
If you have a dual-terminal replacement battery, you can buy a GM-style side terminal ground cable, and run a second connection from currently unused side ground terminal over to one of the bolts holding the alternator to the block.
The ground path for the coil runs from the coil negative lead, to the TFI module, to the distributor body, to the engine block, through the battery negative cable to the negative terminal on the battery. The ground path for the PCM runs from the PCM to the firewall, thence through the body to the front of the car, thence through the little pigtail to the stud on the radiator support and over to the battery. There is a secondary path through the body mounts to the frame and via the intermediate frame ground/clamp to the high-current negative battery connector.
If you have a dual-terminal replacement battery, you can buy a GM-style side terminal ground cable, and run a second connection from currently unused side ground terminal over to one of the bolts holding the alternator to the block.
The ground path for the coil runs from the coil negative lead, to the TFI module, to the distributor body, to the engine block, through the battery negative cable to the negative terminal on the battery. The ground path for the PCM runs from the PCM to the firewall, thence through the body to the front of the car, thence through the little pigtail to the stud on the radiator support and over to the battery. There is a secondary path through the body mounts to the frame and via the intermediate frame ground/clamp to the high-current negative battery connector.
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great info, I will go through all the grounds tomorrow. As additional info.......when I first turn the ignition on, the volt meter only reads 8 volts, it moves up to 10v once the engine is running, then back down as the engine warms up. Next time I will post in the electrical forum, thanks for the tip.
