Slight rough idle 7.3
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Slight rough idle 7.3
1995 with 7.3 turbo diesel
I'll try and post a video of the tach and parameters on my otc scanner.
Basically it starts up and after 3 seconds of idling after initial start up it has a slight chug or rough idle. Then It somewhat cleans up and idles smooth.
Now there are times at a stop light, it will also have a slight rough idle. Nothing major to almost stalling but annoying because you can feel the rough idle in the seat.
New engine oil/filter
New fuel filter
Here's the deal. I've replaced the icp sensor. It seems to be working properly according to my scanner HOWEVER if I unplug it shut the truck off then restart it it will not do the chug or rough idle anymore. Seriously doubt it's a bad sensor it came directly from the ford dealer so I really don't want to get into how it could be a bad sensor out of the box.
Can someone tell me if my icp sensor psi fluctuation is normal?
Unplugged ebps no change and it operates I believe at 16 something it's not stuck at 20
Unplugged map sensor no change.
I'll try and post a video of the tach and parameters on my otc scanner.
Basically it starts up and after 3 seconds of idling after initial start up it has a slight chug or rough idle. Then It somewhat cleans up and idles smooth.
Now there are times at a stop light, it will also have a slight rough idle. Nothing major to almost stalling but annoying because you can feel the rough idle in the seat.
New engine oil/filter
New fuel filter
Here's the deal. I've replaced the icp sensor. It seems to be working properly according to my scanner HOWEVER if I unplug it shut the truck off then restart it it will not do the chug or rough idle anymore. Seriously doubt it's a bad sensor it came directly from the ford dealer so I really don't want to get into how it could be a bad sensor out of the box.
Can someone tell me if my icp sensor psi fluctuation is normal?
Unplugged ebps no change and it operates I believe at 16 something it's not stuck at 20
Unplugged map sensor no change.
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Joined: Nov 2016
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Mine use to sound like that, found I was only getting 12psi of fuel pressure at idle. I replaced the fuel pump, and bought fuel pressure regulator spring off ebay, that cleared it up.
Check your fuel pressure at the schrader valve on the fuel filter housing.
Check your fuel pressure at the schrader valve on the fuel filter housing.
Postmaster
Joined: Sep 2007
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From: Medford Oregon
Yes, it's normal for the ICP pressure to fluctuate. When the injectors fire the pressure goes down then back up. Mine does about +- 50 PSI. More concerning is the recovery time from start to normal idle pressure, seems to take awhile. Also the IPR% seems low to me, 8% to 9% at idle? On a hot engine mine is around 12% and a cold start around 19%, until the oil warms up a bit. It could be the IPR is sticking closed causing the issue, but just a guess at this point. You might try unplugging the ICP and look at the IPR% and see if it goes up to a more normal range as you did mentioned it idles good with it unplugged. If so then I would go with a bad (new) ICP sensor.
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Yes, it's normal for the ICP pressure to fluctuate. When the injectors fire the pressure goes down then back up. Mine does about +- 50 PSI. More concerning is the recovery time from start to normal idle pressure, seems to take awhile. Also the IPR% seems low to me, 8% to 9% at idle? On a hot engine mine is around 12% and a cold start around 19%, until the oil warms up a bit. It could be the IPR is sticking closed causing the issue, but just a guess at this point. You might try unplugging the ICP and look at the IPR% and see if it goes up to a more normal range as you did mentioned it idles good with it unplugged. If so then I would go with a bad (new) ICP sensor.
Can you confirm those ipr numbers please.
It defaults to like 725-750 psi when unplugged.
You really think a brand new ford icp sensor is bad out of the box? What if something else is bad cause those icp numbers?
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UPDATE
lift pump leaks fuel. I can visually see it dripping out and puddling in the lifter valley.
Is it normal for there to be so much pressure fluttering and fluctuations on the gauge?
I went ahead and ordered a lift pump (not saying it's the cause. I hope it is but it's leaking and needs to be fixed)
This is a quality liquid filled gauge we use at work to test hydraulic systems.
What about something in the fuel pressure regulator like the spring?
lift pump leaks fuel. I can visually see it dripping out and puddling in the lifter valley.
Is it normal for there to be so much pressure fluttering and fluctuations on the gauge?
I went ahead and ordered a lift pump (not saying it's the cause. I hope it is but it's leaking and needs to be fixed)
This is a quality liquid filled gauge we use at work to test hydraulic systems.
What about something in the fuel pressure regulator like the spring?
Last edited by bc18; Aug 8, 2017 at 07:27 PM. Reason: Added videos
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The mechanical pump causes such pressure fluctuations as a natural result of the mechanical pumping action. I installed an electric fuel pressure gauge fitting where the Shrader valve went and put a needle valve between the fuel bowl and the sending unit / gauge to keep the pressure fluctuations from breaking the gauge. With the needle valve I can tamp down the fuel flow and eliminate the bouncing needle.
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My numbers are similar to Hussler's.
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The mechanical pump causes such pressure fluctuations as a natural result of the mechanical pumping action. I installed an electric fuel pressure gauge fitting where the Shrader valve went and put a needle valve between the fuel bowl and the sending unit / gauge to keep the pressure fluctuations from breaking the gauge. With the needle valve I can tamp down the fuel flow and eliminate the bouncing needle.
Postmaster
Joined: Sep 2007
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From: Medford Oregon
How many miles on the truck?
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With it unplugged the PCM uses a pre programmed default value, it's guessing. I'm not saying the numbers are bad but the time it took to recover from start to idle and - up down up down on the numbers. You indicated with the ICP unplugged it does not hunt for idle? That's why I ask for the IPR percent with the ICP unplugged. It's possible the IPR itself it going bad too. You did not mention why the ICP was replaced, can only assume for the same issue at this end?
I haven't unplugged the icp and read ipr percent I will do that when I get home.
While loosening one of the fuel lines to the cyl head wrench hit the socket of the sensor and broke it.
Runs the same as before.
It's a bit low but should run OK and not cause a idle issue. Of course if the pump is leaking it's time to replace anyway. Maybe the f350 was a California truck which had a fuel dampener on the pump, an emission thing which took the pulses out a bit. The mechanical pump is really a good design and reliable but .. nothing lasts forever.
How many miles on the truck?
I haven't unplugged the icp and read ipr percent I will do that when I get home.
While loosening one of the fuel lines to the cyl head wrench hit the socket of the sensor and broke it.
Runs the same as before.
It's a bit low but should run OK and not cause a idle issue. Of course if the pump is leaking it's time to replace anyway. Maybe the f350 was a California truck which had a fuel dampener on the pump, an emission thing which took the pulses out a bit. The mechanical pump is really a good design and reliable but .. nothing lasts forever.
How many miles on the truck?
Of course so that is why I'm starting there. Now I'm curious if it's able to suck in air. And that could be causing my issue. Especially after you shut the truck off the fuel could be bleeding off or sucking air. But then I would suspect long cranking times which I'm not experiencing.
Lead Driver
Joined: Apr 2016
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From: Bahstun
the pump can leak but not suck air
when running you can dump some fuel out and check for air bubbles
There is a little hole in fuel bowl that removes air from the system and behind it is a screen that can clog up
when running you can dump some fuel out and check for air bubbles
There is a little hole in fuel bowl that removes air from the system and behind it is a screen that can clog up
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