Unplugged ICP....no start

van.diesel · Aug 8, 2019

If your van doesn't start with the ICP unplugged -- is that a sign of a good ICP?

I just replaced the ICP (OEM) in my 1996 e350. The old ICP started up great while it was unplugged. The new ICP won't start up at all unplugged. Is that a sign of a good ICP or is there something wrong with the new part?

jleedog · Aug 8, 2019

Un plugged ICP would not be the reason for a no start. You may have introduced some air in the rail when you changed it out, which may account for the no start problem. Others that are smarter than me will chime in soon with more help.

klhansen · Aug 8, 2019

How is the pigtail that plugs into the ICP sensor? You may have shorted it out or otherwise damaged it when you changed the sensor. A partial short (high resistance) may be sending a false signal to the PCM, causing it to tell the IPR to dump pressure.

van.diesel · Aug 8, 2019

The pigtail is in good shape, I've been careful not to damage it. Could the issue be the IPR?

klhansen · Aug 8, 2019

Was (is) there oil in the connector. That could affect the signal as well. Try shooting some contact cleaner in there if there's oil. But with the ICP disconnected, it CAN'T be the ICP at fault. jleedog's comment about air in the system is valid. But even with air, it should eventually start with enough cranking.
It's possible the IPR is the issue. Is the tin nut holding the coil on tight?

Does it start and run good with everything plugged in? If so, I wouldn't mess with it.

Other than a no-start with ICP unplugged, what issue are you having?

van.diesel · Aug 10, 2019

The connector is clean, no trace of oil. The tin nut is solid on there. It runs great when the ICP is plugged in. The biggest issue I've been having is the van sputters without going into idle -- only on hot starts. I have to rev the engine 3 times to 3500 rpms to get it going. After that, it idles pretty consistently.

On cold starts the van starts right up. Every now and again I'll lose compression on the road. That lasts a few minutes before returning back to normal. I replaced the CPS and ICP, both OEM. Oddly, the van started up with very little sputtering with the original ICP after I greased the connector with dielectric grease.

I had someone tell me it could be the crankshaft sensor.

dieseldogtom · Jan 13, 2020

Thought you said you changed the CPS? And I can't think of how that would be relate to unplugging the ICP Sensor.

Colin7.3 · Dec 12, 2022

I’m having a similar problem that mine won’t start with it unplugged or plugged in I just replaced new starter, solenoid, glow plug solenoid, icp sensor oil level is full and fuel bowl is full, also battery’s are charged. I’m getting black smoke out the pipe with it wanting to start but won’t, my thoughts are bad idm or ipr , btw the tin nut is right on the ipr. Someone please help

jleedog · Dec 13, 2022

How good are your batteries? You might not be cranking fast enough. Have you tried with a jump cable to a good vehicle? You might consider starting a new thread to get more help from our group.

bork · Dec 15, 2022

What your outside temperature? Fuel pump is humming for 1st 20 seconds or so when key first turned on? What year is your rig?

Colin7.3 · Dec 28, 2022

Yes there is humming and it’s a 1996

bork · Dec 29, 2022

I could be wrong but I thought pre 99 had mechanical fuel pumps. I don't know what is humming, unless it has been converted. Probably need to find out a way to get a pressure gauge on the fuel system somewhere to verify pressure. IIRC the coil in the bottom of the engine fuel filter will cause a no-start if burned out. I think it will blow a fuse. Do a search on it. If I were you I would watch a bunch of no start OBS pre 99 diagnostic videos. I don't see where you tried a CPS. (classic symptom ,if you have a tach, is tach fails to show reading) https://www.youtube.com/results?search_query=1996+psd+7.3+no+start

On edit: IIRC it was poster "sixiron" that was stranded & found a 50 amp fuse blown, feeds filter heater & PCM. He unplugged wire to filter heater & replaced fuse & it started. (but it might show a CEL on dash ) There might be a resister kit to plug in to make CEL go out, if you want to forget about heater. Not sure how essential that heater is? Riffraff has helped me a bunch when I've got into a jam. A call couldn't hurt. Ford - Riffraff Diesel Inc

parabolst · Jun 26, 2025

I am having the similar issue with the icp unplugged no start. So with everything plugged in it starts and runs i can drive it about a mile then it will start in on its issues. So if im doing 55mph it's OK but if I let off throttle to keep speed under that light throttle it will start bucking. If I give it more than part throttle it will accelerate fine no bucking. If I come to a stop it will start bucking/sputtering under light acceleration but ok once I give it lots of throttle. Before all this started happening if the icp came unplugged it would sound like it was cammed and have really touchy throttle, and start fine. But now this issue has arrived if I unplug icp while running, it will do a rev up once then go back to what sounds like a normal idle but no acceleration at all. Like full throttle won't go over 10 15mph. If I try to start with icp unplugged it will just crank no start with oil pressure gage bouncing around midway up. Plug it back in and it will fire right up and drive except for the bucking at slight throttle or slight acceleration. With full throttle or decent acceleration it will act fine even on a grade. But with slight throttle like trying to maintain speed it bucks.

dieseldogtom · Jun 28, 2025

OK....I don't want to deep dive into ICP/PCM/IPR...BUT......

I'm reading post about unplugged ICP Sensor and " driving around"...

I thought the unplugging of the ICP was STRICTLY a "see if it will start" and idle type thing?

IE: When unplugged, the PCM will (recognize) it's not getting a PROPER signal from the ICP & send a default signal to the IPR? to "CAUSE" it to operate in a manner that will produce (500+p.s.i.?) into the oil gallery in the heads required to properly operate the injectors? AT IDLE condition?

OK...So engine can START & it hopefully answers or helps in diagnostic of a faulty ICP Sensor. BUT....

I did NOT think the vehicle could be DRIVEN without a continuous signal from a ICP??

IF the ICP is unplugged, how is the PCM going to (instruct) the IPR what to do to create the proper oil pressures for all the varying load conditions of driving???

Either I STILL don't understand how these things work together or ?

Well you tell me....

Can/ SHOULD you actually drive around with your ICP unplugged???

Is it different for older 7.3's (OBS)??

Mine is a 2003 Van if that makes a difference.???????

EDIT: OK...Maybe I misread parabolic post. Maybe he's NOT driving with it unplugged...
My request for some clarification stands.
WORKING ICP must be plugged in to drive, Right?
Unplugging ICP is STRICTLY a means of bypassing a Possibly bad ICP for diagnostic purposes to allow PCM to default a signal to (IPR???) that allows vehicle to start (AND IDLE) if all else is OK?

Unplugged ICP....no start

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