Hi everyone, seeing if anyone has any words of wisdom when it comes to my problem.

I have a 99 F-150 5.4L with a recently installed FQR engine. I have put about 7000 kms on the engine but have recently experienced a problem. My problem is only experienced when I park outside overnight and only recently since the temperatures dip to around the freezing mark. The truck starts just fine and fires right away however after about a minute of high idle, the truck's idle goes from normal to almost a stall, then back to normal, then stall again and so on, it feels like the fuel is cut off for a split second. After about 3-4 minutes then truck acts normal again. If I try and drive right after I start it and not let it warm up it has stalled on me a few times.

Yesterday the CEL finally came on and I pulled only code P0320. I don't think its the crank sensor as it was replaced with the engine. However you never know.

Any ideas fellas?

Thanks in advance

 

http://engine-codes.com/p0320_ford.html

Is the battery good?

 

Yes, battery is new Optima, no issues with charging system.

 

Yea Optima's are and have been problematic. So bad, its a bad choice when choosing a replacement battery. It's a Johnson Control battery whom supply many, such as Walmart, for one (Everstart). The best and most economical choice in battery's is the Diehard (Platinum series only). A more expensive route, but you actually get what you pay for is the Odyssey Battery.

So with a Meter, check the battery and charging circuit. Check the battery after it's been sitting for a time (overnight). See what that battery's doing after start and running when ignition problems occur. If in question, have the battery "Load checked". A defective battery can result in many different issues, PCM related.

Crank sensors, = I haven't heard of crank sensor ever just "acting up" or causing this issue. It's possible, however, - a bad crank sensor will always forward a "no-start" situation vs failing slowly or reeking havoc.

1. I would look at the harness first. Look here, -above the AC accumulator. The harness drops or dips here. At times to the extent where it contacts the top of the accumulator, peels the foil insulation from the wires (harness) enough to reek havoc with the ignition circuits, = magnetic disturbance. Or it bares the wires completely and may sever one or two as time goes on.

2. I'd have to inspect the IAC as well. Clean it.

3. Maintenance sensors, such as the MAF SHOULD be cleaned by hand with that model. ALWAYS disconnect the battery.

 

I have seen it before on a ford. It was a 2000 4.0L ranger. It would do it at the weirdest times too. It never did throw a code but would do similar things to what the OP is describing.

I am leaning towards the crank sensor myself. There is a magnet in the crank sensor and once your engine warms up the metal and magnet expand which helps to send the signal to the pcm to give it the spark at the right times. This would explain your exact symptoms. It does explain your problem.

I would check your battery voltage first like described though. Easy and free to diagnose.

 

Oh yea, huh, - I believe it for sure, just never came across that one as ending at a Crank Sensor problem. It says that's a possibility in the link SubSkip provided as well.

 

Sorry its been awhile, checked charging system, shows normal when it acts up. Voltage drops only .1 when the idle drops. Cleaned MAF, changed O2 sensors just in case they were reading wrong. Today the truck started fine (-11degrees), drove fine for about 7-8 minutes, then it stalled about 5 times when driving, always restarted with no problem. Then it drives fine after a few more minutes. I'm stumped, no CEL, no codes. Any other ideas??

 

Did you change the crank sensor?

 

No I didn't yet, I did install a new one with the new engine though. I might do it again however, just a pain in the *** to do. Think thats the culprit?

 

I kind of doubt it since you already replaced it not long ago, and it does run into money
throwing parts at these things.

 

I'm leaning towards idle air now, but would it stall under tip in or only at idle? But I would think there would be a CEL if it was toast???

 

Not usually. Unless there's a problem with the circuit. That's usually not the case.

 

Just another note to add, I'm noticing that when I start the truck in the cold, the high idle only runs momentarly, then tries to run at regular idle. The only thing that baffles me is that I was under the impression that the IAC only operates under idle. I stall out or have rpm drops when driving with acceleration. I hate throwing parts at a truck based on a guess, just want to be resonably certain that I am on the right track. Any input is appreciated though guys

 

The IAC shouldn't affect anything if you have your foot on the go pedal, you have a cable-operated throttle. However, a bad TPS might screw things up.

 

Well not that I was ignoring your input glc, but I installed a IAC last night, old one was diffenatley sticky, and seems to idle better when not acting up, but it didn't solve my issue