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OBS 7.3 Experts Please Step In - Rebuilt Fuel System - Rough Idle

Tech Tim

Tech Tim

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May 19, 2020
Member Number
168
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1,041
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Wet side of WA
Finished up doing a fuel system redo on my 1997 OBS F350 7.3 Powerstroke.

It starts up and idles smooth for the first 8-10 seconds, then goes into a rough idle. It runs strong off idle, though maybe seems a little light on power at highway speeds.



This truck has 375K on the ticker and last spring it started running really poorly, it has been down on power and mileage for a couple years and has been a great truck, so I figured it was time to redo the fuel system.

List of parts replaced:
Bostec reman HPOP - Stock
IPR - Not Ford
Pure Performance Injectors & cups - Rebuild, balanced versions, but not juiced
Dorman valve cover gaskets & harnesses - Yeah, yeah, everybody is telling me to go genie Ford.
Ford ICP sensor - Originally had an aftermarket ICP, just replaced with Ford ICP - Checked the plug, I have 5 volts.
Ford EBP sensor & cleaned the EBP tube out.
New Ford CPS Cam sensor - Gray one
New fuel pump - Aftermarket
New glow plugs
Diesel Tech of Chattanooga IDM w/ the increased voltage and current
Full of fresh oil & new oil filter
New fuel filter
New coolant
New batteries

Took it out for a drive today, put 50 miles on it on back country roads and varying speeds and then out to the highway and did some long hill climbs, both with the OD on and off revving it to 2500-3000 rpms making sure all the air is out of the system.

I'm not a diesel engine guy, this is the first one I've really dug into besides a few Mercedes OM617s, so this has been a huge learning curve for me.

My old school code reader throws three codes:
P0603 - Makes sense, we had the battery disconnected to change them and to recharge/condition them.
P1280 - ICP pressure out of range - LOW
P1282 - ICP Higher than desired

My reader isn't letting me delete the codes, so I don't know if those are old.

I figure I need a better way to read codes and to monitor whats going on.


For those TLDR types - I have two questions:
1) Any Ideas what the problem is? What more to check, tests to run etc?

2) Any recommendations on a wifi OBD reader and app to monitor whats going on with this engine.
 
Interesting that you got both high pressure and low current codes for the ICP, makes me think the ICP is bad, or the pigtail is bad. P1280 is the code you get when you run the truck with the ICP unplugged.

DTC P1280 indicates injector control signal circuit out of range low.
Possible causes:
-- biased ICP sensor/PCM
-- open ICP sensor circuit
-- short to SIG RTN or PWR GND on ICP sensor circuit
-- open in VREF circuit




I like TrikeKid 's idea of running it w/o the ICP to see what it does. It could be an issue with the wiring for the ICP, your aftermarket IPR, or it could just be that theres still air in the fuel or oil system. When i changed my injectors it took, IIRC, about a week to get all the air purged out of the fuel & oil systems so it would start quickly and idle smoothly. Or it could be shitty old fuel.
 
I think you need to run it longer as well. If air is ingested in oil, you basically have to run it, let it sit, run it and let it sit, repeat, before the air is gone.

Also too soon to tell if you think those codes are old. Could be a bad injector. Or injectors. The oil and fluid they use for testing injectors is not the same as we use in the trucks in real life.
 
I use Torque Pro and a OBD2 bluetooth dongle to display what I need on my 2002 7.3. I can see it on my Android phone on in dash Android radio. I an not sure if it will work on the OBS. It is a great tool to have to see live data and check / clear codes.
 
TrikeKid said:
What's it do if you start it with the ICP unplugged?
Click to expand...

iirc it runs worse. I've done so much testing I don't remember every detail, but pretty sure that was the case. Then I read that you only use genie Ford ICPs, so I picked one of those up from the local dealer and installed that over the weekend.


reptillikus said:
Interesting that you got both high pressure and low current codes for the ICP, makes me think the ICP is bad, or the pigtail is bad. P1280 is the code you get when you run the truck with the ICP unplugged.

DTC P1280 indicates injector control signal circuit out of range low.
Possible causes:
-- biased ICP sensor/PCM
-- open ICP sensor circuit
-- short to SIG RTN or PWR GND on ICP sensor circuit
-- open in VREF circuit




I like TrikeKid 's idea of running it w/o the ICP to see what it does. It could be an issue with the wiring for the ICP, your aftermarket IPR, or it could just be that theres still air in the fuel or oil system. When i changed my injectors it took, IIRC, about a week to get all the air purged out of the fuel & oil systems so it would start quickly and idle smoothly. Or it could be shitty old fuel.
Click to expand...

I'll unplug the ICP and start test that again tonight.

I check the ICP plug with a multi-meter and got 5 volts off one of the terminals. That's what everything I could find says you have to have.

The first time out with the aftermarket ICP, I put 8-10 miles on it last weekend. Changed to the Ford ICP this weekend.

Yesterday is when I went out and put 50 miles on it and once it got warmed up, I really pushed it hard up some long climbs etc. Burned over a 1/4 tank of fuel.

I could get out and drive it some more, but so far it hasn't changed at all.

The fuel is a year old, but it was fresh, has conditioner in it and has been in a dry garage this whole time, so I doubt it's the fuel. Plus it really runs great once you are off idle, not like bad fuel at all.
 
RustyC said:
It would be very beneficial to know what the fuel pressure is during this time.
Click to expand...

I've got a 4K PSI gauge, just need to get a hose made up and I can check fuel pressure.

RustyC said:
I use Torque Pro and a OBD2 bluetooth dongle to display what I need on my 2002 7.3. I can see it on my Android phone on in dash Android radio. I an not sure if it will work on the OBS. It is a great tool to have to see live data and check / clear codes.
Click to expand...

I've got a OBDII wifi dongle on order, it'll be here Wednesday. Getting the Forscan app, it'll work with my iPhone.
 
TrikeKid said:
If it runs smoothly at start up it's not air bound. Do you still have your stock IDM? Might be worth trying, it sure sounds like it's losing a couple injectors when it starts running bad
Click to expand...

Stock IDM was going out, couldn't get it started at all after the injector & HPOP swap. It might've been the problem all along, but at 375K, it was time for injectors and HPOP anyway.
 
Tech Tim said:
Finished up doing a fuel system redo on my 1997 OBS F350 7.3 Powerstroke.

It starts up and idles smooth for the first 8-10 seconds, then goes into a rough idle. It runs strong off idle, though maybe seems a little light on power at highway speeds.



This truck has 375K on the ticker and last spring it started running really poorly, it has been down on power and mileage for a couple years and has been a great truck, so I figured it was time to redo the fuel system.

List of parts replaced:
Bostec reman HPOP - Stock
IPR - Not Ford
Pure Performance Injectors & cups - Rebuild, balanced versions, but not juiced
Dorman valve cover gaskets & harnesses - Yeah, yeah, everybody is telling me to go genie Ford.
Ford ICP sensor - Originally had an aftermarket ICP, just replaced with Ford ICP - Checked the plug, I have 5 volts.
Ford EBP sensor & cleaned the EBP tube out.
New Ford CPS Cam sensor - Gray one
New fuel pump - Aftermarket
New glow plugs
Diesel Tech of Chattanooga IDM w/ the increased voltage and current
Full of fresh oil & new oil filter
New fuel filter
New coolant
New batteries

Took it out for a drive today, put 50 miles on it on back country roads and varying speeds and then out to the highway and did some long hill climbs, both with the OD on and off revving it to 2500-3000 rpms making sure all the air is out of the system.

I'm not a diesel engine guy, this is the first one I've really dug into besides a few Mercedes OM617s, so this has been a huge learning curve for me.

My old school code reader throws three codes:
P0603 - Makes sense, we had the battery disconnected to change them and to recharge/condition them.
P1280 - ICP pressure out of range - LOW
P1282 - ICP Higher than desired

My reader isn't letting me delete the codes, so I don't know if those are old.

I figure I need a better way to read codes and to monitor whats going on.


For those TLDR types - I have two questions:
1) Any Ideas what the problem is? What more to check, tests to run etc?

2) Any recommendations on a wifi OBD reader and app to monitor whats going on with this engine.
Click to expand...
Injector orings if the ICP sensor/wiring is good.

Was the fuel filter black, sooty?
 
Injector oring is a possibility, but I think the problem is related to the ICP/IPR.


TrikeKid said:
If it runs smoothly at start up it's not air bound. Do you still have your stock IDM? Might be worth trying, it sure sounds like it's losing a couple injectors when it starts running bad
Click to expand...
Typically they suddenly jump to that rough idle when the CEL turns on for the ICP. It's assuming injection pressure values at that point. You could do a buzz test to see if all the injectors are working, but I doubt it's an IDM issue, John (Diesel Tech) knows what he's doing.

It's true the Dorman UVCH and gaskets are kinda junky but if you had a bad connection at an injector I think it would act differently.

A scan tool would be nice to see what the ICP and IPR values are at idle, and what they are after the CEL pops and the idle suddenly changes.
 
RustyC said:
40-70 psi is spec. 0-100 psi gauge is best.
Click to expand...

Sorry, fuel pressure.... I was thinking HPOP oil pressure.

Will look into testing fuel pressure, thanks.


reptillikus said:
Injector oring is a possibility, but I think the problem is related to the ICP/IPR.



Typically they suddenly jump to that rough idle when the CEL turns on for the ICP. It's assuming injection pressure values at that point. You could do a buzz test to see if all the injectors are working, but I doubt it's an IDM issue, John (Diesel Tech) knows what he's doing.

It's true the Dorman UVCH and gaskets are kinda junky but if you had a bad connection at an injector I think it would act differently.

A scan tool would be nice to see what the ICP and IPR values are at idle, and what they are after the CEL pops and the idle suddenly changes.
Click to expand...

They say the Forscan app can do a buzz test, so I'll get that done once the dongle shows up.

Any scan tool that is better than another for the Ford 7.3?

I'll probably order up the Ford valve cover gaskets anyway. After reading all the horror stories of the Dorman gaskets, I don't want to take any chances. I should've read deeper about Ford vs. aftermarket parts before starting this project, I hate buying stuff twice.


CarterKraft said:
Injector orings if the ICP sensor/wiring is good.

Was the fuel filter black, sooty?
Click to expand...

Would it run good at higher RPMs if the injector o-rings are bad?

Fuel filter looked normal when I replaced it.
 
Tech Tim said:
Sorry, fuel pressure.... I was thinking HPOP oil pressure.

Will look into testing fuel pressure, thanks.




They say the Forscan app can do a buzz test, so I'll get that done once the dongle shows up.

Any scan tool that is better than another for the Ford 7.3?

I'll probably order up the Ford valve cover gaskets anyway. After reading all the horror stories of the Dorman gaskets, I don't want to take any chances. I should've read deeper about Ford vs. aftermarket parts before starting this project, I hate buying stuff twice.




Would it run good at higher RPMs if the injector o-rings are bad?

Fuel filter looked normal when I replaced it.
Click to expand...

I am playing catch up honestly.
If ICP % is going over 65% power will go down but smooth isn't a problem.
Any time the ICP pressure varies from the calculated fuel tables injector timing is fucked and injection quantity gets wrecked.
You need to take some data logs, ICP pressure and %,
I think 06h3 killed a engine with Dorman VC gaskets, that's off memory... Did you change VC gaskets?

We need some DATA to help this along.
 
CarterKraft said:
I am playing catch up honestly.
If ICP % is going over 65% power will go down but smooth isn't a problem.
Any time the ICP pressure varies from the calculated fuel tables injector timing is fucked and injection quantity gets wrecked.
You need to take some data logs, ICP pressure and %,
I think 06h3 killed a engine with Dorman VC gaskets, that's off memory... Did you change VC gaskets?
Click to expand...

Yes, installed Dorman gaskets. Will be ordering Ford VC gaskets this week.

CarterKraft said:
We need some DATA to help this along.
Click to expand...

Will post data as soon as the OBDII dongle shows up.

What data do people want to see? I'll make a list and grab all that is requested.
 
Wait, if youre going to buy new Motorcraft gaskets, upgrade to the Superduty stuff.

The Suyperduty 7.3 uses a better gasket with one plug instead of two. The UVCH is a better design as well, and you only need one per head. Of course youll need to buy the connector to splice into your harness.


SD valve cover gasket with UVCH:
897272541.jpg


New connector spliced into my harness:
918897471.jpg


Its not too bad to do really, and the design is better. When i did the conversion on mine it was cheaper to do the upgrade than use the original parts, so it was a no-brainer.
 
reptillikus said:
Wait, if youre going to buy new Motorcraft gaskets, upgrade to the Superduty stuff.

The Suyperduty 7.3 uses a better gasket with one plug instead of two. The UVCH is a better design as well, and you only need one per head. Of course youll need to buy the connector to splice into your harness.


SD valve cover gasket with UVCH:
897272541.jpg


New connector spliced into my harness:
918897471.jpg


Its not too bad to do really, and the design is better. When i did the conversion on mine it was cheaper to do the upgrade than use the original parts, so it was a no-brainer.
Click to expand...

Will look into that.

Have been contemplating getting a whole new engine harness just to eliminate any issues from that.
 
Tech Tim said:
Will look into that.

Have been contemplating getting a whole new engine harness just to eliminate any issues from that.
Click to expand...
Nothing to add except if you want to try a different idm I have one I can ship out to you to try. I can't use it on my International.
 
Tech Tim said:
IPR - Not Ford
Click to expand...
First thing I would do is replace the IPR with a Ford one. These engines do not like aftermarket IPRs. I had a similar rough running issue a few months ago and rebuilt my OEM Ford IPR and it went away. The IPR duty cycle before was maxing out and after cleaning and rebuilding it, it was back to a normal range so it will be good to know the duty cycle and pressures once you get something to read the live data.

The engine harness does degrade over time so it is worth budgeting for at a later time but I don't think its your issue right now.

Has the low pressure pump ever been replaced? It is fairly cheap and can be replaced with the engine in the truck as it is behind the balancer. I have read a few people having issues with their oil/fuel system and a new pump fixed their problem.

I use a Bafx Products OBD2 bluetooth reader and TorquePro app but I have an Android phone.
 
Brian1 said:
First thing I would do is replace the IPR with a Ford one. These engines do not like aftermarket IPRs. I had a similar rough running issue a few months ago and rebuilt my OEM Ford IPR and it went away. The IPR duty cycle before was maxing out and after cleaning and rebuilding it, it was back to a normal range so it will be good to know the duty cycle and pressures once you get something to read the live data.
Click to expand...

Will be getting a Ford IPR.

Brian1 said:
The engine harness does degrade over time so it is worth budgeting for at a later time but I don't think its your issue right now.
Click to expand...

Definitely in the plans.


Brian1 said:
Has the low pressure pump ever been replaced? It is fairly cheap and can be replaced with the engine in the truck as it is behind the balancer. I have read a few people having issues with their oil/fuel system and a new pump fixed their problem.
Click to expand...

I haven't replaced the low pressure pump. Would that cause a rough idle issue?


Brian1 said:
I use a Bafx Products OBD2 bluetooth reader and TorquePro app but I have an Android phone.
Click to expand...

That's what I ordered.
 
Gotta thank all of you who are helping with info and suggestions. :beer::beer:

With 375K on the clock, this is really the first time I've tore into this engine. We got this truck back in 2000 with 69K on it and in the past 300k & 23 years, it has been "little" maintenance stuff. I think the tally over the years is alternator x4, water pump x2, starter x3-4, a fuel pump, two sets of batteries, one heater core, two vacuum pumps, brakes 3 or 4 times and 4 sets of tires.

The wife has tried to get me to buy a new or newer truck in the last couple years, but this one has been so good for so long, it's like a family member. So I'll just keep it and keep at it.
 
Last edited:
CarterKraft said:
I am playing catch up honestly.
If ICP % is going over 65% power will go down but smooth isn't a problem.
Any time the ICP pressure varies from the calculated fuel tables injector timing is fucked and injection quantity gets wrecked.
You need to take some data logs, ICP pressure and %,
I think 06h3 killed a engine with Dorman VC gaskets, that's off memory... Did you change VC gaskets?

We need some DATA to help this along.
Click to expand...
Yep, it stuck an injector open
 
Tech Tim said:
I haven't replaced the low pressure pump. Would that cause a rough idle issue?
Click to expand...
Yes as it wouldnt supply the HPOP with enough oil to do its job with the injectors. Bad LPOP symptoms of rough idle, no starts, stalling, poor fuel economy, loss of power, no power. Nearing 400k I would consider replacing it, however, replace the IPR first, drive it for a while to keep getting the air out of the lines and start looking at the live data. If it still isn't running right I would consider replacing it. Its around $100 and a few hour job.
 
Dont buy anything else until you get some PID montioring capability. Throwing parts at a 7.3 is like playing wacka mole.

This is a good example of basics of this system, and how to interpret the pids.

 
Levigarrett76 said:
Dont buy anything else until you get some PID montioring capability. Throwing parts at a 7.3 is like playing wacka mole.

This is a good example of basics of this system, and how to interpret the pids.

Click to expand...


I'm impatiently waiting for the wifi dongle to show. It's one of those Prime one-day shipping things that is now three days late. :mad3:

Thanks for the vid, will check it out.
 
Im cancelling my prime this year when its up for renewal, not worth having anymore with the pathetic shipping times, and dumbass fedex drivers.

After watching your video, it sure does sound alot like the issues wes was having there around 1:00 mark in his video, his wound up being ipr as youll see.
I agree with these guys, ipr is crucial to make her run, only motorcraft, yes its expensive.

I would still wait on dong:mr-t:
 
It normally crank that much before starting? My 97 7.3L starts much quicker.
 
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