my mom left the key in the on position overnight (not running) said she was putting the windows up and got distracted. anyhow I found it the next morning with a dead battery. I recharged the battery it seems to be fine tried to start and smelled gas real strong so I took out the plugs they were in need of replacing so I changed those out and it started but there was a miss and it was smoking bad oil burning blue smoke, also got a code 27 fuel injector problem so I started unplugging the fuel injector wiring one at a time and I found one that did not change the engine but it seemed to smooth out a little with that injector unplugged so I tested for voltage it was good hooked up a test light to the neg. side of the connector and the test light is staying on so I guess with the wire connected it is just dumping fuel all the time that's why its smoking so bad . I know the neg. should pulse like all the other connectors do but this one is on solid so I traced the wire back to the big plug in on the computer and cut the wire there and tested again same result . so my question is can the computer be bad and send a steady signal out instead of a pulse. is there any type of repair that can be done I don't understand how leaving the key on fried that part of the computer. any help would be greatly appreciated.
94 jeep grand cherokee computer bad?
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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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First check the dipstick for a strong smell of gas in the oil. If there is, change it and the filter before running the engine any more.
There will be steady power (+) to the injectors with the engine running. The computer just turns the ground (-) side on and off as required for the fuel squirt. If the internal computer driver is shorting the injector to ground, it will be on all the time. Look for a replacement (reman) PCM.
The ASD relay should have cut power to the injectors and coil when the crank position sensor saw that the engine was no longer turning, long before the PCM should have been damaged.
Also make sure that all the injectors have about the same resistance. If one has shorted, it may take out the replacement PCM also.
A jump start might have also possibly damaged the PCM.
There will be steady power (+) to the injectors with the engine running. The computer just turns the ground (-) side on and off as required for the fuel squirt. If the internal computer driver is shorting the injector to ground, it will be on all the time. Look for a replacement (reman) PCM.
The ASD relay should have cut power to the injectors and coil when the crank position sensor saw that the engine was no longer turning, long before the PCM should have been damaged.
Also make sure that all the injectors have about the same resistance. If one has shorted, it may take out the replacement PCM also.
A jump start might have also possibly damaged the PCM.
"so I traced the wire back to the big plug in on the computer and cut the wire there and tested again same result"
Did you test the wire from the injector or the wire in to the computer?
You should have a steady voltage from the injector, if not its shorten some where.
Into the computer is more difficult to measure since it will probably require a load on it.
Make sure there isnt anything bad with the injector side of the circuit and measure at the splice voltage to gound with everything connected and engine running.
It should be pulsing. If not a bad computer
Did you test the wire from the injector or the wire in to the computer?
You should have a steady voltage from the injector, if not its shorten some where.
Into the computer is more difficult to measure since it will probably require a load on it.
Make sure there isnt anything bad with the injector side of the circuit and measure at the splice voltage to gound with everything connected and engine running.
It should be pulsing. If not a bad computer
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I find that, 9 times out of 10, the problem is not the computer on a vehicle, but people replace the computer anyways because "it's the only thing left" or because they don't understand that there are a lot of other things, even in a simple system like this, that can go wrong. If there's an issue in the wiring, such as chafed insulation shorting to ground, the injector will stay open constantly. I find it particularly strange that only one injector is misbehaving and that the ignition system is still working. I'm not sure what the internal architecture is like in the computer (whether there's one drive circuit for all injectors, or individual circuits for each injector). However, in my experience with breaking electronics, overvoltages or reversed polarity kill pretty much everything, fast. I would strongly recommend not cutting any more wires. A break in a wire is a failure point waiting to happen, even if it's carefully repaired.
Blue smoke is not good. An overly rich fuel mixture tends to smoke brown or black, in my experience. It could be just that the oil has thinned out too much and you're getting blowby.
Blue smoke is not good. An overly rich fuel mixture tends to smoke brown or black, in my experience. It could be just that the oil has thinned out too much and you're getting blowby.
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