So like many this winter, I had an intermittent crank no start issue. Thought it to be fuel related, based on low fuel pressure readings.

Now all new - battery, iac, cam sensor, fuel pump, fuel filter, fuel pressure regulator, air filter. Cleaned maf, temp sensor and throttle body. Engine starts, but I don't know if the problem is solved.

Fuel pressure is 40 with key on, falls to 35 on start-up, (which seems ok) but then after a few seconds, the pressure drops to 26 where it seems to want to stay. Hitting throttle hard makes it fall to about 20. I can't find any leaks in the fuel lines. Truck seems to run fine while driving.

To me, this doesn't seem good. Engine is not throwing any codes, but the ST fuel trim is running 0 to +3, and as high as +9 on occasion.

Does the consistent drop to 26 sound normal? Should I dig more into it, or just forget about it since truck seems to be running fine?

 

Too low.

Also, wrong direction. When you open the throttle, it has to come up.

 

I agree. Not good readings. You might want to verify that your gauge is working properly. If it is, then you still have a problem.

 

Thanks for the replies.

yeah.... I agree the problem isn't solved based on the readings-thought I might be chasing ghosts, which I do from time to time. Fuel pressure gauge is new, but I'll confirm that it's accurate.

Even though my manual says that the relay is in the power distribution box in engine, and there is one there, I pulled the radio and I found another fuel related relay there as well. Both relays click when ignition is switched to run position. I'm guessing one is for the initial power-up and one is for the pcm control. I guess I could put new ones in, but I don't like just throwing parts at a problem, especially on this old truck. After pulling out the relay in putting it back in, I was able to get the pressure to climb on a hard acceleration. Gradual acceleration keeps the pressure constant, with a slight drop when the pedal is released and the rpm drop to idle.

The fuel pump assembly I put in was a new carter from a chain auto parts store, and the manufacture claims it is tested.

I can hear a slight misfire going on at idle. Nothing is coding, but I have an actron 9580 and it has some diagnostic tests on it. A test $41 id 12 returned a HI status, and A test $56 ID 00 also returned a HI status-but I have no idea what these tests are.

I'm wondering if the injectors could be leaking? They are original with 130K miles on them. Any thoughts?

 

So I left the fuel pressure gauge on overnight. Pressure dropped to 0. Does this mean anything?

 

I believe there is a tsb on 5.4 injectors concerning a leakdown issue. Does your truck blow black in start up? It could be leaking fuel into the cylinder basically flooding a cylinder over night

 

What year?

 

This is a 99 F350 5.4L engine with about 135K miles. Plugs and coils were replaced Jan '13 about 8k miles ago.

It does not blow black on start up-exhaust is clear on start up.

 

Another clue

This mornings running drop coincides with fuel system status changing from open to closed.

On cold start up the morning, with code reader attached

Fuel pressure was at 0; key on engine off - rose to 35
Engine idle 32psi; fuel system "open", exhaust clear
idle for about 2 mins (46 deg coolant temp at startup)
Fuel system status switched to "clsd" Fuel pressure drop to 26; white puffing exhaust starts coming out of exhaust.

Now I have to try to figure out what the difference between "open" and "clsd" fuel system status means.

 

This is kind of interesting symptoms. What happens in open loop is that the computer is using the "default" fuel trim for a "cold" engine. As the engine warms up and goes into closed loop, the computer uses the signal from the O2 sensor behind the cat to set the injector pulse width to regulate the amount of fuel. A couple of things to look at: Fuel trim during closed loop and open loop conditions. The signal from the rear o2 sensors. An injector balance test to see if one or more injectors may be sticking. Also since you mentioned a fuel pump replacement, I would look at the long term fuel trim numbers to see if they are looking normal now.

 

It uses the O2 sensor BEFORE that cat. Depending on which level of OBD calibration is present, it may or may not have any O2 sensors after the cat(s).

 

Thanks for the info. I've been doing some reading and I think I'm getting an understanding of how the system operates. The open/clsd make sense. Luckily for me I only have 2 O2 sensors before the cat, no sensors after it.

I put in new relays for the under the dash and power dist. box in engine just so I could feel good about throwing more parts at the problem.


Now a "new" development......

Noticed that I had a P0230 code sitting in my reader. What's a P0230 code you may ask? Per my scanner, it says fuel pressure voltage problem with just 1 recommend fix - replace the pcm. My haynes manual does not define one for Gas engines, but lists fuel pump relay driver fault for a diesel. Yesterday I chose just to focus on the "relay" portion of these suggestions.

When I was previously messing around with the relay box under the dash on Thursday, I did cycle the key with the relay out in an attempt to determine which of the relays in the box pertained to the fuel. So I am hoping that I temporarily caused the code. MIL never illuminated btw.

But based on the pressure drop when the pcm's in charge, I'm not too hopeful.

I reset the code and now I need to drive a little to get beyond the P1000 code. I'm hoping that p0230 doesn't come back, but in my mind, it is looking to me like one of my problems could be the power being supplied by the pcm. Whether that's wiring or the pcm itself remains to be seen.

Regarding the ST fuel trim - when it is open, it reads 99.4 on both banks. Once closed it fluctuates from 0 to +3.

On LT fuel trim, I believe they are sitting around -2ish. I don't know if they are meaningful at this point, because the truck has not been driven much at all since this problem started back in early feb. I replaced battery and ford had the truck and did some "diagnosis" (everything OK) so I don't know exactly how much data is in the "LT" memory.

On the injector front, on the few I could see, I noted #2 has dirt/dust stuck to half of it - like fluid was running down one side of the yellow "cap" making it moist so dirt would stick to it...hmmmm.

Looks like I'll be doing some wire tracing in the near future.

 

That's fine. In open-loop mode, the ST trim is "undefined".


That's also fine. No vacuum leaks, that's for certain.

 

Update:

Been running the truck at 26 psi for some time now with no problems. No really, really hot days, so I haven't experienced any vapor lock.

Strange thing is that I recently ran into a friend that was experienced the exact same situation this past winter with an older Chevy 2500. Now I'm wondering if the issue was more a (frozen) water-in-fuel issue (ethanol) than a fuel pressure issue... Friend's fix was a new truck.