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I have a 1997 f250 7.3 I bought a couple weeks ago. Very strong truck and has already been on two 300 mile trips since I’ve had it with no issues. I went out to start it today and fired it up which the wait to start light worked fine at the time. Idled for about a minute then shut off. Thought it was weird but started right back up then did the same thing. Now the wait to start light won’t come on and it just cranks strong but won’t start at all. I checked the fuses more than once and swapped pcm relay with horn relay to make sure it worked. Checked for 12v at red/light green wire on GPR which had 12.24v so now I’m just at a loss. I’m hoping pcm isn’t fried. Is there anything I’m missing? I need to get this truck running again ASAP so any info is appreciated thank you.
 

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Did you unplug the fuel bowl heater? There should be a 30amp fuse it tripped too if I'm not mistaken.
 

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Red,

Get FORScan and a compatible code/PID reader. In the mean time... Check the valve cover plugs/sockets for melted looking wires. It would be a good idea to use an ohm meter to check for shorts open circuits in the glow plug and injector circuits. Other things to look for - when you crank the engine do you see the RPM gauge twitch? If no then there could be problems with the CPS sensor (critical to the operation of the engine). I just read another post where a (shorted?) EBP sensor interfered with the PCM operation. You could unplug the EBP and see if the truck starts. Others have mentioned the ICP sensor as being a problem (if you disconnect ICP, the pcm will use preprogrammed ICP values to run the truck - won't run great but it will run).

Cj
 

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Also... Check fuses 22, 8 and 9 in the fuse box that lives under the hood. Fuse #8 is the IDM, fuse #9 is power for the PCM, and #22 supplies power to the PCM power relay. This was a reply I made in the second link.
 

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Discussion Starter #5
Did you unplug the fuel bowl heater? There should be a 30amp fuse it tripped too if I'm not mistaken.
I have not
Did you unplug the fuel bowl heater? There should be a 30amp fuse it tripped too if I'm not mistaken.
checked the fuel bowl heater yet, I’ve heard that a couple times now so I will after work. Thanks!
 

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Discussion Starter #6
Red,

Get FORScan and a compatible code/PID reader. In the mean time... Check the valve cover plugs/sockets for melted looking wires. It would be a good idea to use an ohm meter to check for shorts open circuits in the glow plug and injector circuits. Other things to look for - when you crank the engine do you see the RPM gauge twitch? If no then there could be problems with the CPS sensor (critical to the operation of the engine). I just read another post where a (shorted?) EBP sensor interfered with the PCM operation. You could unplug the EBP and see if the truck starts. Others have mentioned the ICP sensor as being a problem (if you disconnect ICP, the pcm will use preprogrammed ICP values to run the truck - won't run great but it will run).

Cj
Yea I forgot to mention when the check engine light came on my regular craftsman code reader kept failing connection and wouldn’t hook up so I’m trying to get ahold of my buddy’s snap on solice code reader but the rpm twitch I’m not sure of, I’ll have to check that out in the morning as well when I get home from work. Thanks I’ll let y’all know what I find out!
 

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Discussion Starter #7
Also... Check fuses 22, 8 and 9 in the fuse box that lives under the hood. Fuse #8 is the IDM, fuse #9 is power for the PCM, and #22 supplies power to the PCM power relay. This was a reply I made in the second link.
As far as fuses go I’ve pulled all of them twice and they all looked good. Swapped relays with the horn relay to test them and they worked properly so I’m not sure. Someone also mentioned crank sensor to me. Have you ever heard of the crank sensor causing all of these issues though?
 

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Red,

The CPS is a long shot... that is why I asked about if the tach was twitching while you were cranking. It does sound PCM related - perhaps there is a short somewhere in your wiring that takes the PCM down with it, but doesn't blow the fuse. Could be one of the PCM's self generated "reference voltages" being shorted that cause the PCM to drop out.

Cj
 

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Discussion Starter #9
Red,

The CPS is a long shot... that is why I asked about if the tach was twitching while you were cranking. It does sound PCM related - perhaps there is a short somewhere in your wiring that takes the PCM down with it, but doesn't blow the fuse. Could be one of the PCM's self generated "reference voltages" being shorted that cause the PCM to drop out.

Cj
Yea I’m really hoping it’s simple just difficult to find. I’m just not wanting to fork the money out for a pcm lol I work on Diesel engines for a living but it’s the big Cummins you see in semis. This is the first 7.3 I’ve owned so I’m just pretty new to it and trying to learn what I can.
 

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Welcome to the 7.3 club :). I have a v504 cummins sitting in my driveway. And, yes it does run and well. Just need to find something to stick it in and figure out how to add a turbo to it. Back to the current topic... I also remember reading about a bad Baro sensor causing problems, but I think that was more of rough operation than a no start condition. Fortunately with the older 7.3 there are really not that many sensors to dig through.

Cj
 

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Welcome to the 7.3 club :). I have a v504 cummins sitting in my driveway. And, yes it does run and well. Just need to find something to stick it in and figure out how to add a turbo to it. Back to the current topic... I also remember reading about a bad Baro sensor causing problems, but I think that was more of rough operation than a no start condition. Fortunately with the older 7.3 there are really not that many sensors to dig through.

Cj
Haha that’s awesome! Yea my dream truck has been an OBS 7.3 but now I got one and can’t keep it running for more than a few weeks lol but when I get to work on it some more in the morning I’ll keep you updated on what I find out or if I have some more questions!
 

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Any luck with the truck? I have no idea what I want to do with the engine yet.. maybe a really big go kart..
A really big go cart or maybe a rat rod of some sort! I got the truck running great but honestly not sure what it was. I came hone from work and for the hell of decided to start it. It fired right up and idled for about an hour then I drove it around and it’s been perfect ever since. I’m wondering if when I was pulling fuses and messing with wires if there was a short or something that I wiggled right but that would just mean it’s going to happen again. I just hope it shows itself soon so I can figure out exactly what it is. If it happens again I’ll post what I find for sure though.
 

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Red,

Good to hear that you are up and running. It would probably still be worth while to get FORScan and a dongle. You can do a search around the forums to find out what others use. I think it is SBluke that has made a number of recommendations on the reader.

Cj
 
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