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Been having some issues for a while now and thought I would check with the experts here for some answers

99 7.3 with high miles and a 6 speed manual. After driving and warmed up truck will lose power to the point that wont even hardly get up to 55 mph. Boost is definitely dropping off and runs very rough. Sometimes to the point of not idling. Usually happens worse when running at lower rpms. Like maybe loading up... many times if truck.is shut off it will restart and run fine, other times may have to sit several hours but once cooled off always runs fine. Have torque pro and have been monitoring ipr duty cycle and hpop and numbers look pretty normal. Tried today when acted unplugged icp...seemed to get better and then got worse like loading up. Hpop numbers were higher than when icp connected. My question is where do hpop readings come from with icp disconnected? I was under the impression icp was the feedback to computer for pressure reading. Do you think this is bad icp or ipr? Truck has 340k and both are original. Hpop readings hit 2800 with 35% duty cycle at a 2500 rpm...so I thought those were good. Or could bad icp be telling me hpop numbers that are incorrect? Done alot of reading on here and learned a lot but this one doesn't make sense to me...
 

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When the ICP is disconnected the PCM defaults the ICP information. If the ICP is connected, then you could have a bad ICP sensor as they can give erroneous information if they are bad. The IPR is probably more suspect to being faulty as it is controlling the oil to the injectors and with high mileage, they are usually the cause to poor running engines. Check the IPR Tin Nut for the solenoid. It could be loose, but I am thinking it is just a worn IPR.
 

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I have checked the tin nut and it is still tight. Is there a way to determine if the issue is the icp or the ipr? And further test that can be done?
 

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I have checked the tin nut and it is still tight. Is there a way to determine if the issue is the icp or the ipr? And further test that can be done?
If you have an app or software, you can run IPR duty cycle and ICP pressure while driving. If your ICP is normal, then look at getting a new IPR.

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Alright.. here is the update...installed new ipr and icp...neither made any difference...it is very strange. It will start up and sound great, but after running about 10 minutes it starts.acting like it is running on half the cylinders. Usually does and wont even restart. Let it sit for half an hour or so and it will start up and the whole process begins again. Occasionally it will stay running fine for an hour or two...I yield to your suggestions. As I watch hpop pressures when idling...they seem kinda high to me, barely off idle and pressures are already 1300 or so...almost sounds like a gas engine running real rich and choking on all the fuel....
 

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Have you checked the under valve cover harnesses? Could be that one is coming loose. Do you notice the check engine light on when you're having the problem? Does the CEL come on when you first turn the key?
 

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I believe that uvch is a possibility...just strange how it fixes itself so regularly...they had come loose years ago and I was able to rig a system together that has held for several years. Any time that was the issue before it always kept running badly until I fixed them. This seems like it is very heat related. Check engine light does come on when starting and usually goes out but have seen it on a few times but always says no codes. I was really believing that the icp and ipr was gonna fix this and just replaced them yesterday.
 

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Unless you have a PowerStroke capable scan tool, you won't be able to pull codes for an open in the injector circuits. The UVCH connectors can easily come loose enough to be affected by heat and remake the connection when things cool down. The thermal expansion rate of the plastic connectors is 6 times greater than metal.
 

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Worked on the truck some more today...took both valve covers off and checked for any signs of loose or damaged wires. Everything looked fine. In addition I checked the ohms on all the wires to the glow plugs and the injectors. Everything checks out fine with all readings close together and within spec...any other ideas? N
 

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You need to isolate which system is malfunctioning.

Start with the Fuel system and make sure you are getting a constant supply of fuel at ~51 PSI to the bowl. If you have good fuel pressure, you can pretty much rule that out. A bad fuel pump will give erratic and sporadic running.

High Pressure Oil System. You have replaced the ICP and IPR. Once you get the truck running, what is the ICP at idle and what are you getting when on the throttle? You should see 500+ at idle and roughly 2,800-3,000 on throttle. That may drop some as you hold throttle, but not below 2,400 psi.

Injector electrical. Checking the UVCH resistance is a good start. Have you or has anyone performed any splicing or wiring on the engine harness between the 42 pin connector and the UVCH connectors? The other suspect (low) is the IDM failing. I would suspect it is not that, but electrons can be finicky.

That is pretty much the three systems to validate for what you have going on. You can throw a CPS at it, but it doesn't sound like a CPS issue. Heat could be causing the CPS to fault out though.
 

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Thanks for the reply! I have tried to check all the things u mentioned.

Fuel system
I did put a new fuel pump
On it this summer. It was holding almost 60psi but that was measured at the output of the pump when driving under load. I have to get adapters to check it at the bowl. Does have a new fuel filter and in dropped the tank and cleaned the two small screens and tank is clean.

Oil system.
As mentioned I did replace the icp and ipr. Numbers look fine to me. About 500 psi when idling, over 2600 when driving. Duty cycle changes never goes over about 60%. The one thing I do notice is when it acts up...it looks to me like the pressure is high...like 850 or 900 psi

Wiring
Checked harnesses and no sign anyone has ever been in them or done any repairs. I have owned truck for 15 years and my best friends parents bought it new. So no secrets as to what has been done.

Personally...I am beginning to suspect things like idm....wouldn't think that would "repair" itself as fast as this does. Was also considering a new cps... the one on there was replaced over 10 years ago by one from napa but it has never acted up like this till now. I wouldn't think that would keep being as intermittent as this either but I am considering anything....
 

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I would put in a OEM CPS. They can be effected by heat. Usually they just die, but they can be effected by heat and then work again. Pretty cheap and easy swap.

If you can borrow A IDM from another truck, you can swap it out as well. Then you can eliminate it. Again, I don't feel it is the issue, but don't rule it out.
 

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I will try an OEM CPS in the next day or so. As far as the idm...how interchangeable are they? What years or options make a difference?
 

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IDM's 99-03 for the 7.3 are all the same.

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IDM's 99-03 for the 7.3 are all the same.

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You can actually use an IDM from 94-97 trucks as well. They're marked IDM-100, the later ones are marked IDM-110 or IDM-120 for 99 and up.


You might want to check continuity in the injector circuits from the heads to the IDM. Also a possibility that the harness is chafing on the driver's side valve cover. Easy fix with some electrical tape. Check the underside near the 42 pin connector.
 

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I inspected the wire harness next to drivers side valve cover and dont see any sign of abrasion there. I did put a new Ford dark grey cps on it today and no change. I was watching the hpop and ipr duty cycle numbers very close. When truck first started and was running good the hpop is 550 and ipr is 12.9%.... at it runs longer and starts to chug and run worse especially when I try to rev it the numbers both go up...like 650 and 17%. When it gets even worse...they will be 900 and 20%.... the truck had been plugged in all morning and engine oil temp started at about 80 and was at 120 when acting the worse. Is computer trying to raise pressure to spray more fuel and cool the engine off or something? Someone mentioned a manifold temp sensor in the intake spider that might cause it to think the engine is warmer than it is. I cant find a reading on it put did try unplugging it to send it to default and that didnt do anything. I havent been able to get my hands on an idm yet...still looking for one I can borrow and not have to spent a bunch more money till I can determine that is the real problem.
 

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Your Injector pulse width units appear to be smaller than the standard micro seconds ( I don't recall right now what the "u" symbol stands), but I think your reading is equivalent to 2.68 microseconds, which isn't excessive.

You can unplug certain sensors (such as EOT) which will cause the PCM to use default settings, and see how that affects the problem.

How long has it been since you changed your oil? The 7.3L can be sensitive to oil condition. Maybe you're getting oil aeration.

Both IPR duty cycle and ICP normally go up together. I don't think your readings are out of range.
 

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Someone mentioned a manifold temp sensor in the intake spider that might cause it to think the engine is warmer than it is. I cant find a reading on it put did try unplugging it to send it to default and that didnt do anything. .
That is the Intake Air Heater (IAH), it is not a sensor, but a heating element that energizes via the IAH Relay (forward of the GPR Relay) and most likely will not come on as it needs several inputs, including the parking brake to be set. Most people remove them and plug the hole as they block air flow and are usually never energized.
 
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