N43 High Pressure Fuel Pump

[Emir Ballard]

08F450, Died while idling, cranks but won't restart. FRP builds to 215 psi, Fuse 74 blown. Pump wiring shorted - chaffed. Pin 2 to ground - 1.7 ohms, pin 4 to ground - 4.2 ohms. TSB 07-26-02 says if one of the wires is shorted then just replace the pump. I'm good with that, but what if both are shorted? TSB states that the pumps are not being damaged.

One of the guys I work with had one a while back that was chaffed on both wires, hotline said put just the gasket in. Truck died on test drive and guess what.....Cab comes back off for HPP....work twice....pay once.....

What would you do???? I've got it apart now, and both solenoids measure proper specs - 2.7 ohms on one and 2.6 ohms on the other. According to PPT ME this is in spec - (1.5-8 ohms). I'm just worried I'm gonna have to pull it apart again to do the pump, but only get paid for it once!

Kind of a difficult decision to make eh? For me finding a chaffed wire is usually enough as I like to find the actual problem. It is when you start reading things like this from any source the seeds of doubt are planted. Then the fun begins because the clock will screw us all any time we have to re-trace our steps. Personally I don't see how grounding any of those circuits is going to damage the pump. I HAVE had (and got beaten up by) a bad pump that acted just like the gasket harness chaffing symptoms. A faulty PCV or VCV OR a shorted circuit can do some strange things AND not leave a DTC.

I've done several with no problems. I think I read somewhere that whoever manufactures the pumps was worried about the solenoid being grounded and the pump run at full pressure causing damage to the pump. After inspecting several pumps they said it didn't cause damage. That's just what I hear. Removing the cab isn't that bad the second time around-unless you put new bolts in like you're supposed to.

if you put heat to the bolts and a little pressure on the cab(start lifting) you can usually get them out with a ..... half inch impact ssshhhhhhh don't tell anyone. don't use the impact on the front two....i don't know why, but i haven't had any luck with those, start them by hand and then use the 3/8 cordless to finish 'em off. if they do spin, bend a 22mm wrench at a 45 degree angle and you can easily hold the top after removing the headlamps. Heat the loctite on the new ones and run 'em all in with the impact. occasionally one spins coming out, but they're all easy to get to..

Well...gasket in, 20 mile test drive good to go....guys looking at trading it off already. Go to my box to see what got drug in over the weekend, next in que - 2008 F550, died while driving, cranks but won't start.....hmmmm sounds familiar - pull codes, do tests and wouldn't you know it.....here we go again!

Come on now Josh give my full story... before the "updated" harness" were available to me I put a pump cover gasket in... after 2 test drives of about 15 miles total, truck died and no restart... had to go back in and do the pump itself, I think more the dealer being in an audit situation was what made them tell me too bad your doing it again and not getting paid for it... but really I was seeing I was hourly at the time. ANd how about the pump cover gasket I am currently doing? It is the updated gasket with the wire covering and it chafed just to the one side of the covering where the covering stopped... that is awesome...

I have a question about removing the cabs. So far I have done quite a few cab offs and overall had pretty good luck thanks to all of my resarch tools I felt very confident even the first time. Although, I have reached a new level of concern after leaving work yesterday>>>>> I have an Armored truck( machine gun on top) F-550 originally in my bay. I am lucky because the nearby Military base will be sending a bunch of these over, I suspect I will get good at these. QUESTION? There is NO possible way to remove this body due to obvious reasons as well as weight of the body. Can you actually put on the harness in question without removing the cab? I have one on the hook with the symptoms. My guess is they should be using an E-Series for this vehicle,but had to use a F-Series due to weight load. Does anyone have any ideas? Thanks

Guess the body does not come off, even if it did it would be too heavy for most lifts. It was a long journey working from the front as I removed just about everything and then a little more to access. The turbo just squeezed by the body to remove. It was an accurate diagnosis for the pump harness as the TSB suggests. We are very lucky as technicians to have such resources available to aid in our diagnosis. This one had just the slightest wear on the yellow wire in which explains the intermitt no-start and lack of power. It only took me approx. 32 hours to do the job. If you ask for any suggestions on this type of repair for this vehicle? I recommend avoiding the opportunity.

I got a last-minute call to look at this vehicle this afternoon so I stuck my face in it for a few minutes but had to go. I'll get another shot at it tomorrow, so I'd like to be armed with some better testing.

The shop had already replaced the high pressure fuel pump, low pressure fuel pressure sensor as well as the high pressure sensor on the back of the manifold. All of these seem to work correctly - when the vehicle is running the high pressure sensor sits at 17 to 19 MPa, while the low pressure sensor sits around 65 psi. Pulling the fuel pump control module fuse drains the low pressure side almost immediately and then the high pressure side tapers off until the vehicle stalls and it reads near zero.

It seems to me that this is just a regulation problem - that the fuel pressure regulator on the front of the high pressure pump is not relieving pressure at all. What I didn't determine immediately was whether this is done with pulse with modulation at 12 volts or something else.

Yes - I have continuity (and about 7 ohms, iirc) across the control circuit for the regulator solenoid.If there is an open, it is inside the PCM.I suspect there is a timing issue with the drive cam, but I haven't found the SI for installing the cam and follower.

Look at the pressure sensor and regulator connectors and check the pin fit, if it had the recall done the connectors may have been damaged by the technician man handling them during the repair. I can't remember if these are the codes that set when that happens though - That's all I've got - sorry.

Good Morning Jeff,You are on the right track. Check the PCM and verify everything is installed correctly. If that is all good then check your timing.The last one I saw had a stretched timing chain.Respectfully,Chad

I pulled the pump and verified that everything was moving around as required. With the pump installed, a 12 volt signal to the control solenoid will drain all the pressure while it's running. Made me suspect the pcm, I think I'm correct and looking at this waveform:

Took the timing cover off and verified that all of the timing marks were properly aligned and that the HPFP drive cam was oriented correctly. (Something like 9 hours of unpaid labor for the tech that did the original install.)No change.Replaced the ECM.Fixed.I was correct in that the low ref should have been a flat ground, not a current modulating waveform as was suggested above.

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