Dear List,

Recently, I had to have the engine replaced in my Ford F-150 after possible trash entered the fuel injector causing it to stick open and the main rod was bent.
Since the repairs, I have noticed hesitation (I don't know how to better describe it than saying, how an engine might act with water in the fuel). The garage I took it to, replaced the fuel filter and bled some of the fuel from it to reveal almost a chocolate milk like fluid. I ran 3 - 4 more tanks through and the problem still exsisted.
Yesterday, I replace the fuel filter myself, AND bled the entire tank until the (fuel) pump would not pump any more.
This morning, the problem still remains.

What next???

 

I think the fuel tank needs to be dropped. If your fuel looks like chocolate milk, You might have a bunch of crud in it.

 

Actually, I don't think I'll have to go to that extreme just yet. I would have agreed with you if the gas I drained yesterday would have looked the same as the previous "chocolate milk," but more like slightly muddy water.

The gas tank was completely pumped out and the gas was clear of any sediment. Fresh gas was replaced, and that gas pumped out with the same results (clear).

I have purchased some fuel system cleaner as I have tried the fuel injector cleaners before without much success.

I'll try to remember to let you know how it works. I know I'll let you know if it doesn't! : )

Thanks,

 

Help me understand why today I press on the gas and it resulted in a slight hesitation in it's acceleration....RPMs just completely dropped and then increased again. I have tried fuel cleaner before as well, but it seems to just return acting the same way....Same problem!!!!!
And recommendations?

 

Well, as bad as it might sound, I believe I am about to take Podunks advice about dropping the gas tank.
I added a bottle of the Prestone Complete Fuel System Cleaner into a full tank of gas and still can not tell much diffrence.
The problem occurs most when stopping, rounding curves and at acceleration after sitting still (like trying to pull out into traffic!).
The only thing I can figure is (like Podunk said) there is still sediment in the tank that needs to be flushed out. That and possibly changing the O2 sensor.
I'll let ya' know.

 

The symptoms you describe sounds just like a camshaft position sensor or a crankshaft position sensor going bad. Is your check engine light on? If so, have your truck scanned at Autozone, Pep Boys, or Advance Auto and ask them to scan your trucks to see if it has any diagnostic trouble codes.

Or it could be a simple plug or wire thats loose or gone bad.

 

Peacemaker,

Would any of these problems happen intermittantly during driving. Or, would they occur all the time?
I would think electrical would be a constantly occurring problem. I have no ideas about the Cam and/or Crankshafts.

 

Well, my mom's old durango would shake and hesitate as soon as you started it up. Rpm's would dip down real low, and then shoot back up. After it ran awhile, it would run somewhat smoother. But it would always come back when I drove down the road a piece.

Sensors can act funny, as there are alot of variables/info that they relay back to the trucks computer. "I would definatley say it was an intermittant problem". I Finally got a check engine light and it was the cam shaft position sensor.

Edit/Quick note: The check engine light would only come on when it would act up. But when it cleared up, the CEL went back out.

 

Peacemaker,

Ok, I'm sold. Tomorrow, I will be near an Advanced Auto and a Auto Zone. I will have one or the other check it for me.
I have to add that the "check engine" light has been on for a long time even before I had the engine re-built. Everyone just kept telling me it was nothing more than an emissions sensor (or something). Since the truck didn't run any differently arfter the light came on, they said ... "I wouldn't worry about it."
With this being a new onset of problems, just so happened to be after I had the engine re-built, I'll need to have that checked before I drop the tank.

Thanks for your input!

 

Good luck.

 

Hey Guys,

Ok, I went to Auto Zone yesterday and had them put the truck ('97 F-150 4.2L, V-6, 2 WD) on the little handheld computer (whatever that thing is called). It gave 6 problems, 2 were repeats (total=4). The EGR Valve needed to be cleaned, O2 sensor bad, and can't remember the other 2.

Yesterday, I removed the EGR valve and cleaned it with Carburator cleaner and a battery cleaner brush (male end) which worked perfectly, I might add.

HOWEVER, since the '97, and probably other models, have 4 - O2 sensors, I didn't know which (exact) one to replace.

This morning, I called Auto Zone back to find out if they would know which one, and was told to take it to the "Ford place" and they could tell me exactly which one is "bad."

In the meantime, the salesman I spoke with brought up an interesting point.
Since the computer may not have reset after the re-build (which I thought it should have) I could be getting a false reading from their handheld.
His suggestion was to remove the battery cable for 15 - 20 mins. When and/or if the check engine light comes on again, he will recheck it and clear the codes, which wasn't done yesterday.

At this point, are there any suggestions for ya'll?

'Preciate it!

 

Bad 02 sensors will cause hesitation. I think that's what the matter with mine. When they go bad they read rich all the time which causes hesitation. Except mine only does it at idle on a cold start for about 10-15 seconds then it clears up.

When an 02 sensor goes bad, it's almost always the upstream sensors closest to the exhaust manifolds. Not the one's further back on the exhaust. Advance Auto has Bosch OEM replacements for about 45 to 50 bucks. Be sure to tell them you want the upstream sensors.

 

Peacemaker,

Mine actually say the following; P1151 - Lack of HO2S21 Switch - Sensor Indicates Lean." Mine runs better when idling in Park, intermittant hesitations during driving.
What do you make of that?

Thanks!

BTW, What is the proper name for that little computer they hook up under the dash to get these readouts?

 

A vacuum leak will cause a lean condition. So will a dirty MAF sensor. Do a search on "cleaning MAF sensor" and "vacuum leak" and see what turns up. But I still wouldn't rule out a bad 02 sensor or two.

The name for the computer they hook up underneath the dash is "Diagnostic Trouble Code reader/analyser. Or "DTC" reader.

 

If you had that much crud in your tank the little sock that is on the bottom of the fuel pump is plugged. It would also cause lean codes because your just not getting the fuel to the engine. Check the fuel pressure, I bet its low. Sounds to me like somebody stuck some sugar in your tank. Drop the tank and clean it out and get a new fuel pump sock if it is replaceable.