I have a 2004 5.4L that worked fine one day, but would not start the next. It turns over and is very close to starting, but won't catch. I have done some basic diagnostics to make sure the battery is good, the fuel pump is working, and that it is getting an ignition signal at the COP. I have checked all of the fuses and relays to make sure they look good. The only thing that does not check out according to the manual I have is that I get no voltage at the Camshaft position sensor, or the crankshaft position sensor with the ignition on. The manual says I am supposed to see battery voltage. This makes me think it is the PCM. Does anyone have any ideas?
Same thing with a friend of mine and we replaced the Crqankshaft Posittion Sensor. Bought the new one at Checker Auto Parts.
Only tough part is the belt had to be removed to get to the bolt holding it in place.
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Disconnect the PCM and the Crankshaft position sensor. Measure the resistance of the Crankshaft position sensor positive circuit and negative circuit. It should be less than 5 ohms. If not the circuit is open. If that checks out let me know and I will send you the complete test procedure.
I have verified that the sensors are ok (camshaft and crankshaft). The problem I see is at both of those sensors and the MAF sensor I get no power supply from the wiring harness with the ignition on. Is there a way to check the PCM to verify it is working properly?
Check for battery voltage (ign switch to RUN) at the RED wire at the MAF. If missing, check fuse F18 in the underhood fusebox (15A).
In addition to the MAF, F18 supplies the PCM, fuel pump relay, fuel injectors, and IAC. The cam and crank sensors are supplied from within the PCM, possibly from this same 12V line. The EVTM does not give that detail.
I checked the #18 fuse to make sure it was ok. I even replaced it with another to be absolutely sure. No problems there.
I have not measured the resistance of any of the circuits connecting the sensors to the PCM. Since the power problems are occuring on several of the sensors, I didn't think it was an open circuit. I will check that this weekend though.
Thanks for the ideas, please keep them coming, I'm sure one of them will identify the problem.
you might want to start by checking all fuses in the box under the hood on the drivers side ther are many fuses related to the computer and engine managment system, also in that box are relays, fuel pump, computer power etc. get yore owners manuel and star checkin fuses and relays coomon to the engine system.
In case anyone is interested, it turned out to be the IAC valve on my truck. I was surprised that it woud cause the truck to work one day and not the next. I thought something like that would show some signs of a problem first.
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