Hesitation, sputtering under load at any RPM, idles fine

[scoob8000]

Hows that for a title.

The other day I ran the tank pretty low on fuel, puttering a little bit on the way to the station.
[edit] Maybe I didn't run out of fuel, that might just be when something else started flaking out. I looked at my reciept, and it only took 12.2 gallons.. [/edit]

Even after a fill up, it still continued.

Initially I considered the sock on the pump clogged up, but I had replaced the pump/sending unit and filter less than 3k miles ago. The inside of the tank was clean.

This happens regardless of engine temp, but it is much more pronounced after 2-3 minutes of driving.

Idle is fine, no sputtering etc.

Fuel pressure looks good at idle and engine off, can't say for sure while I'm driving.

Wires look fine, cap, rotor, and wires and plugs have about 6-7k miles on them.

Cycling the ignition, I can hear both pumps running too.

Kind of reminds me of a bad TPS, but I even ran with it unplugged and no difference.

I've also run some dry gas thru the system and topped off with fuel from another station. After about another 100 miles, it seems to be getting worse.

So sorry for the long post, just pretty stumped here..

 

[scoob8000]

Update..

Today I jumped in the truck went for a ride without letting it warm up. I got about 4 miles before it started puttering and bucking. Pulled over and checked under the hood, everything was still cool to the touch.

Came back home and let it sit about an hour, then started it and let it idle until it reached operating temp. Went for the same test drive, again it was perfect until I drove about 4 miles again.

This makes no sense whatsoever. Oh, no codes are set either.

 

[Tedybear]

So in open loop computer operation all is fine. Once the computer hits closed loop operation it goes wacky?

Does from my end sound sensor related. Could be a sensor on the way out, just bad enough not to trip the CEL.

It could also be the TFI module or pickup in the disty. Both (the TFI even more so) when they start to fail, can be due to the heat build up.

Or if the O2 sensor is starting to fail? It can also create headaches. (recommended replacement of that one is about every 60,000 miles or so)

This one is going to take some digging into in order to figure it out.

S-

 

[scoob8000]

The O2 has come to mind more than once. Is it possible it's causing a lean condition but not setting a code?

Soon as the rain quits, I'm gonna unplug it and see if it makes a difference.

Is there a way to tell if it's in open or closed loop? I remember on some older GM's, you could short a few of the diagnostic connector pins to make the check engine light flash at a different rate.

I didn't give much thought to open/closed loop. Makes sense, 3-4 miles should be enough to put it in closed loop.

 

[scoob8000]

Well I unplugged the O2 and went for a drive. It acted up the whole time, but it didn't seem to do it as badly. Although it's snowing badly and I could not get on it as much as I did yesterday.

I did notice I did not get a check engine light until 4-5 minutes of driving. Assuming that's when it went to closed loop..

 

[MAKG]

It never went to closed loop with an unplugged HEGO sensor.

Unplugging that tells you nothing. It puts the PCM into limp mode. It was already in limp mode.

I will suggest you need professional help, but if you really want to go after this yourself, the ABSOLUTE FIRST THING to do is find out whether it is lean or rich or neither (inspect the spark plugs). The next thing to do is run a vacuum test.

 

[scoob8000]

It never went to closed loop with an unplugged HEGO sensor.

Unplugging that tells you nothing. It puts the PCM into limp mode. It was already in limp mode.

I will suggest you need professional help, but if you really want to go after this yourself, the ABSOLUTE FIRST THING to do is find out whether it is lean or rich or neither (inspect the spark plugs). The next thing to do is run a vacuum test.

Okay, plugged the O2 back in. Didn't know if it was possible it was misleading the PCM into leaning out the mixture but not tripping a code..

Pulled two plugs, sure fire they're indicating it's been running lean (very white).

Is it possible the PCM (or whatever ford calls the computer) making it run that lean or am I looking for a more physical problem (fuel pressure or volume)?

Wish I could hook my gauge up in a way I can see it while driving. Idle and off pressures are good.

I'll try some vacuum readings tomorrow, it's too dark out now.

 

[MAKG]

Sparkling-clean spark plugs can be a sign of coolant burning. Which two? If it's lean, it will likely detonate at high throttle. It's important to know what all six look like. You would also get very clean spark plugs from not having any fuel in those cylinders (and the engine can run -- badly -- on as few as three).

A mixture code means the HEGO sensor showed no change when the PCM commanded a change. It will never command a change in open loop.

 

[scoob8000]

Without looking at F.O. I would guess 2 & 3 (middle cylinder on either side).

Went for another test drive tonight and when I got back home I noticed a faint new sound. Almost a rattling from the area of the frame rail fuel pump. I cycled the key a few times to run the pumps and on every couple cycles the pump can be heard making an unhealthy noise.

Going out now to re-take my pressure readings and see if the pressure builds more slowly when it's making a noise..

 

[scoob8000]

Pretty sure it's the frame rail mounted pump for sure now..

I pulled the relay and jumpered the pumps to make them run with the engine off. Pressure looks fine and pump sounds fine.

Hooked the mityvac up to the pressure regulator to open it up. The pump makes all kind of funky noises when it's free flowing, but quiets down as long as I'm letting it make full pressure.

 

[scoob8000]

Update: Replaced frame mounted fuel pump, problem solved!