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Daniel Wilson
Daniel Wilson,
Category: Ford
Satisfied Customers: 5188
Experience:  Owner at DJ Wilson
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I have a 99 7.3 powerstroke that misfires at ilde and uner

Customer Question

Hi i have a 99 7.3 powerstroke that misfires at ilde and uner acceleration, no cel on.
Submitted: 1 year ago.
Category: Ford
Expert:  Daniel Wilson replied 1 year ago.
Hi my name is***** will be glad to help. If there is no check engine light, verify you have 80-90 PSI fuel pressure and if the fuel pressure is ok you likely have a short or bad connection in the Valve cover injector harness pigtails. Check the connector pins for damage and replace the valve cover gaskets and pigtails if found. Also you could have a mechanically failing injector. Do an injector test with the diagnostic software/scan tool connected. Perform a buzz/click test/cutout and contribution test. If you dont have the software it will likely only be an hours labor from a shop to have this done to isolate this. Let me know
Customer: replied 1 year ago.
Ok quick run down of what iv done so far. It came to my shop for a misfire condition. I did a cylinder balance test and found number 7 misfireing. I replace all injectors on that side and then drove it 40 miles . It was stil misfiring but now on number 3. I got another injectir from ford hoping the first one was a bad one and still get thr same misfire on contribution test. All injectors pass buzz test. Iv check fuel pressure and its good, iv replaced the injectors, the wiring, the vc gasket, and a pig tail to the gasket on the pasenger bank. I have also tried 2 idms and no change. Customer has replace furl pump, fuel filter housing and clean thr tank filters.
Customer: replied 1 year ago.
What else could cause it to misfire at idle and under load? Compresson is good also. I have a cps i was going to try right now.
Customer: replied 1 year ago.
Also misfire seems to get worse thr longer it runs, runs better cold. If you unplug drivers side complete harness tominjectors while running it killes the motor but if you do the pasenfer side the driver side bank will keep the engine runnjng but poorly. Somthing is messing with thenpassenger bank. I went through one by one unplugging eCh injecgor and thr drivers side always have more of an effdct on how the engine runs then the passenger aide does. The passenger side makes a slight difference but not much.
Customer: replied 1 year ago.
The truck has 300110 miles, looks to have the orignal hpop but icp reads 500 to 600 psi at idle. Also the drivers bank has all orignal injectors
Expert:  Daniel Wilson replied 1 year ago.
Thanks for the update. Most commonly it is harness trouble. I see you have replaced pretty much all the hardware. If fuel pressure is good then i agree that you could be getting erratic engine speed signal. Check the sensor harness too. If that checks ok, compression is good, then check and monitor the ICP pressure to see if it is in spec and the IPR. With no leaks in the high pressure rail you should see up to around 4000 PSI full pressure cranking with 12V applied to the IPR to deadhead the pump to full pressure. Let me know
Customer: replied 1 year ago.
It hit 3100 psi when cranking after 12volts to ipr. I have a new ipr, icp, and hpop, and hoses i just havnt put the in yet cus thats an expensive guess.
Customer: replied 1 year ago.
I havent given itna good run since i put in the 2nd number 3 injector yet but i wouldnt think itd misfire from only 1 injector letting air in. I also installed a new icp on the passenger head and used the ebp connector to hook up to it to watch both icps on my scan tool and they almost mirror each other, about .8 to .9 volts at idle
Expert:  Daniel Wilson replied 1 year ago.
You can install a clear hose to watch for air inline in the suction and return and see if fuel pressure is steady between idle and under a load. I will be out for the rest of the afternoon but log in late in the eves for follow ups and will reply on my next available login.
Customer: replied 1 year ago.
Can i dead head the pump with out the ford tool and can i get the air out if it has any by not driving it?
Expert:  Daniel Wilson replied 1 year ago.
12V to the IPR forces full pressure from the pump.Just be sure theres no injector o ring leaks. Block off the heads if you need to. Test one bank at a time for a difference in pressure.
Customer: replied 1 year ago.
When you first start the truck there is no Miss and then after about 20 to 30 seconds you start to feel it misfiring, the longer you let it run the worse The miss gets to a certain point. ICP pressure is reading about 460 at idle and the computer is commanding IPR at about 9 to 10% and it's reading about .8 volts I noticed if ICP reads about 700 PSI the motor runs smooth and from idle to about 1700 RPMs it seems to misfire.
Customer: replied 1 year ago.
When i drove it yesterday and full floored it the most icp pressure got to was 2560ish
Expert:  Daniel Wilson replied 1 year ago.
thanks for the update. It sounds like it is ICP pressure related. Pressure test both heads and see if there are any injector o ring leaks. since the IPR is new this is the most likely cause outside of a weak HPOP.
Customer: replied 1 year ago.
I tested both at same time and there almost mirroring but a .1 volt difference that flucuates and icp is new not the ipr
Expert:  Daniel Wilson replied 1 year ago.
IPR testing
Expert:  Daniel Wilson replied 1 year ago.
ICP voltages
Customer: replied 1 year ago.
Thanks for the specs. At idle the voltage is about .89 and reading 450ish psi from icp so i suspect a wore out pump
Expert:  Daniel Wilson replied 1 year ago.
Pleasure to help.