Hey everyone,

I have a 1999 F-150 4.2L V6 with an interesting issue. The previous owner claimed they replaced the TPS, MAF, Fuel Pump, Air & Fuel filters, and the IAC.

What happens is, only after she's at a good operating temperature and has been driving a bit, it'll randomly not accelerate. If I press on the gas, like 40% or so, the RPMs will drop and the engine will act like it wants to stall. If I'm real easy on the gas, like 5% throttle, it'll slowly accelerate. When it happens the symptoms will only last about a minute and then it accelerates fine again. I did throw it in neutral once during an episode and try to rev the engine and it wouldn't rev, same symptom. No Check Engine light appears when it happens. The truck does have an always on ABS light and the cruise control doesn't work. Outside of that she idles beautifully, even during an episode, and has plenty of power most of the time.

This issue reminds me of an old Mazda MX-3 I used to have a long time ago, where the MAF would randomly fall off the intake pipe at times. The symptoms are identical to what I experienced then. But I don't know the v6 F-150 well enough to know if these symptoms are the same for both vehicles. Could it be the that the MAF is randomly sending bad readings at times?

 

Cruise control not working comes from (I believe, if not only...) the center high mount brake light being out. Oh, that cruise control switch on the master cylinder, if it hasn’t been fixed via recall as well.

I’d just get that ABS code scanned. I’m pretty sure the engine computer gets input from that system, so I wouldn’t ignore it.

 

Any idea what could be causing my random issue though? It's frustrating because nothing makes any sense from my search. One thing I noticed, when I'm sitting in park during an episode, when I put the pedal to the floor and the engine goes to die and I release, I'll hear a backfire out the intake like a (POP) just before it returns to a normal idle.

 

Alright! So problem is fixed. Hooked up the computer, received a P0113 code, replaced the Intake Air Temperature sensor and she runs great now! Thanks everyone.

 

So I'm back! The problem isn't fixed but it is no longer giving a P0113 code.I replaced the PCM and ran into a PATS issue so I ended up investing in a Autel MK808. I've been going through all the sensor readings for hours and everything for the most point was looking normal. No new codes, nothing crazy. After looking through and through, obsessing over it. I noticed the Knock Sensor reading sitting at "1034". When I lightly revved the engine, no change. Just sits at 1034. If I punched the throttle it might drop to like 34 or something for a brief second but almost immediately return to a reading of 1034. I was curious and I hooked my computer up to my buddies 01 F150 4.6L and his Knock Sensor reading at idle read "8" and if he slowly revved, the reading slowly climbed. For example it hit around 55 at 2500rpms. His readings are no where like mine.

So I'm thinking it's an issue with the knock sensor. My biggest wonder is if a malfunctioning knock sensor could cause random issue I'm having with hesitation and acceleration?

Thanks in advance!

 

Check your EGR system. I'm thinking you have a faulty EGR valve itself.

 

I monitored the EGR sensor values and they were all within the norm, could it still be faulty but maintain good readings?

 

it is possible. what codes does your system show present? have you checked for any codes stored? that will help narrow this down. I would be looking for a P040x number if it is in the EGR system.

 

it's a new PCM, it hasn't thrown any codes yet but the issue persists. Prior to the new PCM the only code that was ever present was a P0113 for the IAT.

 

Thinking about your engine, 4.2, have you checked the cam synchronizer? They can be finicky as they get older, and can cause a major stumble.