Hi everyone,

I'm going to try to list all things I'm seeing out of the normal & not omit anything that might help diagnose what's wrong.

1) After code reader clear, Seeing U0151, U0121 (I saw ABS and airbag lights ON as well last time truck was running/driving), and P0231 (Fuel pump relay - circuit low)
2) First time turning turn to ON after sitting 24 hours the yellow dash lights dim and pulsing (like something pulling too much current?) before going solid/bright.
3) No sound from low pressure fuel pump on first try and successive tries turning the ignition from OFF to ON
4) No crank

Both batteries are fully charged. When I jump the starter solenoid to 12V by air filter it cranks over fast/strong but doesn't start.

I'm tempted just to think it's the fuel pump relay but feel the problem might be deeper than that.

Please help!

 

Fuel pump relay won't cause a no crank. Does the lock icon in the dash stay lit? What year truck?

 

The lock is weird also. I have two keys. Both do the same thing. After being solid or slowly flashing for a short period most of the time the lock goes away indicating everything is fine but sometimes it flashes fast (have never had a problem with either key in the past). Trying it today the lock went away and never vetoed the key.

I've read that if the fuel system isn't pressurized it can cause a no-crank?

It's a 2008.

 

The lock light should come on for a short sequence when ignition is turned on and then go out. If the light flashes or stays on it indicates a problem with the pats system. It may think it is being stolen and won't start for that reason. I've never heard of a no crank with low fuel pump pressure.

Just a thought. Have you checked the inertia switch for the fuel pump? Make sure it isn't tripped.

Edit to add: Disconnect battery and touch the positive cable to ground for a few seconds (this discharges any voltage holding memory in components). Then wait another minute or so and reconnect the battery. See what happens then.

 

So many things "broke" at once listed below. These are things that have always worked fine (no issues) but now are:

No prime of fuel switching ignition from OFF to ON (subsequently engine won't start when I connect starter solenoid to 12V)
Airbag light**
ABS light**
Reverse proximity sensor/warning**
Cruise control**
No-crank in key start position

** = Last time it actually started and I drove it

I did check the fuel cutoff switch.. assuming it's the red tab under the passenger side removable panel. I tried sliding it out (toward engine bay) then slid it back toward passenger seat. Didn't make any difference.

 

Well, there is a smart module under the passenger kick panel. Check those connections. Also there is a wiring harness connector above the emergency brake pedal assy that has caused other owners problems in the past. It should be clipped to the parking brake mechanism. I can't tell you exactly where it is as I've never had any issues but others have had issues when applying the parking brake and during the release it will jar the connector and cause some of the symptoms you describe. Start there, find that connector and wiggle it around to see if those lights go out and the fuel pump runs. Without seeing what you have I don't know where else to send you.

 

Thanks. I've been studying the service manual and will check connectors and voltages at key places to try to get to the bottom of what's going on. I'll report back once I do or reach a dead-end. Currently the truck broke down at a golf course parking lot and I'm having it towed home in a few hours.

 

I can get 99% of my information and diagnostic aid from Alldatadiy.com The subscription on your truck would be around $20.00 but it's worth every penny. You can look up and print out the data and instructions you need and take to the truck to do your repairs. Sometimes navigating through the site is a little frustrating but it's worth the effort.

 

The plot thickens. With another attempt to start the engine with jumper wire to the alternator it actually started and I drove it back home. Now in addition to everything else I can add these two to the list of malfunctioning items:

1) Speedometer doesn't work
2) The display on the climate control is extremely dim.

 

Have you checked the plug by the parking brake yet? FWIW, it sounds like it's going to be one common issue and possibly a ground. It would be wise to get a OBDII adapter and a copy of Forscan to do some diagnostics. Normally bcm issues won't turn on a check engine light so you may have codes set that you can't get to without a good reader. Most readers that you see will only read pcm or engine codes and not body or other control modules.

 

I have an ODB2 reader.. got the three codes I listed in the original post. I also paid for Forscan back when I bought the truck to program a second key so I'll try that.

Yesterday after getting the truck home I did wiggle that connector a little bit like you suggested and had some luck with engine cranking over using the key so I think that could be the whole problem.

I'll go mess with it some more in a couple hours and report back.

 

I've attached the Forscan log file. Lots of "circuit open", "circuit low", "lost communication", etc.

Any insight anyone can offer is appreciated.

 

Some of those may have been created during testing. Clear all codes and check again. Codes that are permanent will reappear. It looks to me like you lost communication with the instrument cluster and that's probably a lot of your issues. Did you take the connector at the brake pedal apart and clean the contacts? If not that's the first thing I would do. Next check the connections at the PCM. Make sure there is no corrosion on any of the pins. They should be clean but they are also in a place that can get water.

You have so many issues that when you find the one area of damage to wire you probably will correct 99% of those issues.

You posted that the truck would crank once you jiggled the wiring harness at the brake pedal. Start there, take the connector apart, clean the pins, and use diaelectric grease to protect them. Next look at a possible ground issue. Think back real hard. Is there anything you had done to the truck in a short time before all this started happening? Did you clean a battery cable, replace a part that might have accidently disconnected a connector? Let us know what is happening.

 

All I observe near the e-brake is a wiring harness covered with a piece of plastic so the e-brake lever (or foot) doesn't strike the harness.

Looking under the steering column there are two large delphi connectors, one of which seems to be relevant to the instrument cluster (IC). When I disconnect/reconnect it the tach needle bounces against the zero-stop for a few seconds and sounds like a cash counting machine.

On the passenger side by door I also found a connector that reboots the IC. As many connectors as I disconnected/reconnected nothing made a bit of difference.

The start/crank works completely at random. Sometimes when holding the key in start it will crank after a number of seconds. Sometimes it will crank right away then stop cranking while key being held, etc.

I want to check voltage/ground at the fuel cutoff switch next which I can access easily. Still examining wiring schematic to see where to go next.

Here's relative order of events:

1) I ran out of fuel about 200 feet from gas station. Started truck again, it stalled, etc. Put about 5gal of fuel in it and was able to start it and drive it home. Truck worked fine but perhaps sucked some air into fuel line requiring me to bleed the line?
2) Truck sat for 4 days and during which time it rained a few times (we go for months without rain here in Las Vegas)
3) Next time I started it, it cranked, paused, cranked again without releasing key from start position but it did start. Struck me as odd.
4) I drove it to my destination and along the way I noticed it was complaining about the brake system, ABS light was on and so was airbag... also odd.
5) When I got to destination I turned truck off and immediately tried starting it again.. no crank, no beuno.

 

I will look under the dash of my '06 F550 tomorrow and see what I can see. That harness near the pedal doesn't get struck but it does take vibration when you use the brake and then release it. That jolt has caused quite a few problems for others. Did you check the PCM connectors at the firewall?