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Powerstrokeless
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71 Posts
Discussion Starter #1
I need some help with a 97 7.3 that was brought to me by another shop with a no run condition. After much testing we have determined that the electrical system has been shorted out either by crossing battery cables or something else. We had to replace the PCM and IDM to get the truck to even run. Now it will start but idles very irradically, sometimes it idles decent with only a hiccup like a bad signal from the cam sensor sometimes it cycles between nearly dying and then back up to around 800 rpms and then bounces back and forth between the two. The truck will rev up if you pump the throttle from full throttle to complete idle but will not hold any rpm. If you floor the throttle there is little to no response at all the truck just stays in the irradic idle. In addition to the PCM and IDM we have replaced the CPS and the UVC harnesses. The pcm that we have gotton is from a 94 and is not OBDII capable so I cannot retrieve any codes or check any sensors with Autoenginuity. I am at a loss of where to go next and do not like throwing parts at something trying to fix it.
 

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Registered
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682 Posts
I would start with updating the comp so you can retrieve codes. You already know that it was bad so replacing it with a new comp for that year is a legitimate charge. Without live data and codes you are just tossing parts.

Also this is this might get more response in the obs section. Maybe someone will move it for you.
 

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Powerstrokeless
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71 Posts
Discussion Starter #3
The problem is we have already replaced the PCM with on from Swamp's and this customer is on a tight budget. I am just not sure what if any effect on idle the TPS has. There seems to be a problem with it since I have to cycle it from full on to full off to get any response from the motor.
 

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Busted Knuckles
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2,456 Posts
Have you checked anything related to the HPO system, icp sensor, tin nut on the back of the ipr? Try unplugging the icp sensor and starting the truck with it unplugged, make sure there is no oil in it.
 

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Powerstrokeless
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71 Posts
Discussion Starter #5
Just realized I had a brain fart and remembered how to link AE to a non obd II truck. I will get readings from various sensors and go from there.
 

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Powerstrokeless
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71 Posts
Discussion Starter #6
New update. Switched the truck back to a 97 ecm so I could get AE to work with it. Started the truck and it had the same symptoms. Checked all sensors, ICP is jumping all over the place. Unplugged the ICP sensor and it changed nothing. Ran a comtribution test and noticed that while the computer was running the test the truck ran great, It would even rev and hold RPM with the throttle. As soon as the test timed out it went back to running like crap. I then ran the Key on engine running test and the cleared up and ran perfectly. I shut the truck off and restarted it it still ran and drove great. We let the truck set for around an hour and then started it to back it out of the shop and it is back to running rough with flashing WTS light and check engine light. Plug AE back up and run the KOER test and it smooths right out. There are no stored codes in the truck and it actually says it fails the KOER test but does not give a reason. I am really stumped now as I do not know what about the KOER makes the truck clear up it is like it clears the codes in the PCM or something. Has anyone seen anything like this before?
 

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5,373 Posts
Just a WAG, but if it doesn't respond to the go-pedal, that's the part I'd suspect. Either the idle switch is stuck (or is opening/closing intermittently) or the pedal rheostat is just not responding. "Elephant in the room" check would be to verify good connections at the pedal.
 

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Powerstrokeless
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71 Posts
Discussion Starter #8
The pedal responds fine after you run the KOER test. The truck runs great and continues to run great. It can even be shut off and restarted as long as it does not sit for more than 45 minutes to an hour. When the key is first turned to on the odometer lights up then goes out when it returns back on the wts light is flashing and #2 relay in the fuse box is clicking. I am thinking that it has to be something temp related but I am not sure.
 

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Old But Sexy
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1,945 Posts
I would look for bare wires.. I had a shorted wire on my dads excursion and did the same things..Move the harness's around and go from there..
 
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