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Old 11-22-2020, 05:35 PM   #1
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Intermittent no start v10 Class C

Hello,
I have been fighting an intermittent no start condition for a while and finally had some time this weekend to do some diagnosis. Intermittently it will crank but not start.
Rv:
2003 coachman Santara
6.8L v10.
75k miles on the odometer

When it doesn't start there is no voltage to the injectors or the fuel pump and I can start it on starter fluid. I jumpered the fuel pump and verified fuel pressure when it doesn't start.

I am leaning towards a bad pcm.
Any other ideas before I drop 200-300 on a rebuilt pcm?

As part of previous maintenance/repair last year i replaced the coils and plugs as well as the fuel pump.
Any help is greatly appreciated.
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Old 11-23-2020, 12:55 AM   #2
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Inertia Switch (crash) or bad plug connection somewhere in the harness. Just one loose female connector in a multiwire plug can cause intermittent issue that is HARD to find? Have even read of loose battery connection at post causing intermittent full power loss while driving on some modern cars. I jumped a car just the other day, and lifted the NEG terminal off the battery w/o tools? Lights were bright, but just clicking the starter. Not always how we imagine, often a new experience, LOL
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Old 11-23-2020, 10:02 AM   #3
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Replace crank sensor on front of engine, check continuity from crank sensor plug to pcm.
Quote:
Originally Posted by IrelandRV View Post
Hello,
I have been fighting an intermittent no start condition for a while and finally had some time this weekend to do some diagnosis. Intermittently it will crank but not start.
Rv:
2003 coachman Santara
6.8L v10.
75k miles on the odometer

When it doesn't start there is no voltage to the injectors or the fuel pump and I can start it on starter fluid. I jumpered the fuel pump and verified fuel pressure when it doesn't start.

I am leaning towards a bad pcm.
Any other ideas before I drop 200-300 on a rebuilt pcm?

As part of previous maintenance/repair last year i replaced the coils and plugs as well as the fuel pump.
Any help is greatly appreciated.
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Old 11-23-2020, 10:06 AM   #4
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Next question, is your v10 throttle " drive by wire" or mechanical ( cable) ? If drive by wire, replace or rebuild electronic throttle body.
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Old 11-23-2020, 11:49 AM   #5
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"Starts on starting fluid" has me thinking crank position, etc are OK.

Power to injectors is not switching, if you have fuel pressure.

Go over all the connections you can find. If it is just a poor connection, you will likely move it around, and make it work if you change the PCM.

Unplug and check all those connections before you order a PCM.
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Old 11-23-2020, 02:16 PM   #6
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Ford software will not turn on injectors unless it sees the throttle plate move during key on/crank
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Old 11-24-2020, 05:07 AM   #7
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Interesting. Would it also shut off the fuel pump?
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Old 11-24-2020, 01:24 PM   #8
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No it does not
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Old 11-24-2020, 01:32 PM   #9
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Open up the main breaker / Relay compartment under the hood right behind the air filter and check the Fuel Pump 20amp fuse.
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Old 11-25-2020, 04:55 AM   #10
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Quote:
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Open up the main breaker / Relay compartment under the hood right behind the air filter and check the Fuel Pump 20amp fuse.
Thanks. I did check the fuel pump fuse and relay. Problem is intermittent so ot were working.
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Old 11-26-2020, 05:54 PM   #11
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Intermittent might well be a loose pin/ socket in a plug. or a loose fuse holder, but most likely culprit in fuel delivery issues is an INTERNMITTENT/ FAILING FUEL PUMP, and/ or restricted/ clogged FUEL FILTER. (I.e. restriction allows enough fuel at lower speed, but NOT at higher speed)
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Old 11-28-2020, 10:32 AM   #12
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IrelandRV,

Intermittent issues are by far the more difficult ones to locate.

Don't forget most of the Ford relays are the same so they can be interchanged in the case of an intermittent relay. Just swap (don't replace) relays to determine if the intermittent issue goes away.

I have heard discussed when a crank and no start happens sometimes it's the ignition switch.

I don't have a schematic handy but a lot of 12-V DC power flows through the IG switch to get power everyplace it needs to go when cranking and starting the V-10.

If you do a crank and get a no start can you immediately cycle the IG switch off/on and get it to crank then start up?

How about having someone crank for a few seconds while you tap relays and wiggle wiring harnesses. That will often expose and isolate an intermittent issue.
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Old 11-29-2020, 06:34 PM   #13
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Another fun day working on the electrical issue. Not sure if this is good or bad but now it won't start at all.
Removed and checked out pcm. Opened the pcm box looking for damaged or bulging capacitors, Move the relays around, jiggled lots of wire connections, checked all fuses in the power box for both continuity and voltage. All good. Checked pcm diode as well and appears to be good.
Still no voltage at the fuel pump and the injectors are only getting 1.3v.
I opened up the steering column to jiggle some wires next to the ignition switch. Kind of tough to see anything with the plastic covering but still won't start.
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Old 11-29-2020, 09:02 PM   #14
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IrelandRV,

You say it won't start at all. Is the no start a no crank or a crank but no start maybe due to no ignition or no fuel? You understand the difference I understand. I can't tell you how many times I heard, It won't start but yes it does crank over. Vastly different diagnostic paths to follow.
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