Alright, this is a bit annoying... Ive done searches, but not sure where to start.

I have a 1999 F150, 4.6 4X4

Under hard acceleration, I have an extremely heavy miss. Miss would probably be a bad way to describe it.... it simply cuts out completely.

The tach doesn't drop or go wonkey when this happens, nor do any of the lights cut out. There is NO check engine light displayed, and no codes pulled from the computer. Its literally like you shut the motor off for a split second.
This has happened several times in the three months I've owned it. It needs a passengers side exhaust manifold (common leaky manifold issue) and every ONCE in a while it chugs slightly at idle. It always recovers on its own in a couple of seconds without me touching a thing. Otherwise, it runs fine other than maybe a slight hesitation while accelerating to highway speeds under moderate throttle. the fuel filter was replaces just prior to me buying it. This seems to be a very intermittent problem. Sometimes I can floor it and it will get up and go, no cut out, other times it will cut out until you get your foot out of it. Very strange It looks like it had a recent tune up, and I cant find any vac leaks or lose wiring anywhere.

One other strange occurrence was when I was idling in a car wash, the truck suddenly died like I cut off the key. It re-started immediately without issue.

Any ideas where to begin? Its obviously something strange, because it has yet to throw a check engine light at me. Does anybody have a suggestion?

 

You don't say what the RPMs are when you experience this "miss". Are you possibly hitting the rev limit? What you're describing (a miss under hard acceleration) sounds very much to me like what happens when you hit the rev limit. I believe both fuel and spark are cut off when that happens, but as soon as the RPMs drop enough both are restored, which bumps you back up to the limit again and the cycle repeats.

I think your factory set rev limit is somewhere around 5400 RPM.

As to the other problems, I don't have any brilliant thoughts.

- Jack

 

LOL no, definitely NOT hitting the rev limiter. Not even like it. It cuts out and back in, and back out and back in rapidly, but its a complete power cut off and back in. the happens anywhere between 2K and 3500 RPMs.

When you hit the rev limiter, the truck would stop pulling, like you said until the revs (or speed in the case of fords) drops. You are talking about a speed limiter. If you sit and bounce the truck off the REV limiter in neutral, sure, it could be sort of like what I'm seeing.


BUT before we confuse this any further, it is NOT bouncing off the rev limiter. The truc cuts out hard, and back in rapidly. Its a complete loss of power, like the engine completely shut off.

I did a wiggle test in the driveway last night trying to see if something was loose in the harness, and nothing made the truck stall or hiccup.

 

I'm sorry, but what you are describing sounds like hitting the rev limit, not the speed limit. The only thing that doesn't add up is the RPMs where you say this is happening. It should not be as low as 2-3.5K.

But, I DO know that some trucks with programmers installed had the rev limit set too low, around 4k. If you have a programmer, you should be able to raise the rev limit, but I would not set it above 5600, because the torque converter starts to balloon above 5400.

I've hit the rev limit with the gas pedal pushed all the way to the floor in my truck in the mid-80 mph range while passing someone. The transmission had not shifted up since I was at WOT and the RPMs hit my 5600 limit. And, as you described above, the power cut off and then back on, very rapidly, and completely, over and over until I backed off on the accelerator some, then the truck continued to accelerate normally when the transmission upshifted. The power cut off, when it happens, is complete, because fuel and spark are both cut off.

The speed limiter in my model year truck was factory set at 99 mph. I raised that to 110, and have never hit it.

So, I think your rev limit is set way too low from what you describe. If you cannot adjust it with a programmer yourself, you could take it to a dealership for a PCM flash, which would probably take care of it.

- Jack

 

Could be a fuel filter only letting enough to run at lower RPM, If it old , change it. I have seen this problem. Does this happen when its cold , hot or anytime?

 

crank sensor?? How old is the Fuel filter? One bad load of gas can clog it.

 

If the motor is cutting out at some random times, your losing electrical power that is vibration sensitive.
This shuts down PCM processing, spark and fuel injection same as if the ignition key were turned off and on very quickly..
A lack of fuel would not cut off abruptly, all cylinders in such a fashion.
Check out fuse seating, PCM relay seating and the crank sensor plugup.
The crank senor is the reference point for the whole operation. If it fails everything stops.
When there is a loss of electrical power, no codes are possible, to be set when the PCM is not processing and monitors are out of power.
There is another possible cause that gets rather complex.
That can be a faulty coil with shorted turns.
It can send 'trash' back to the PCM that can cause it to stop processing then recover processing again because the crank is still turning during the momentary loss to regain the reference for timing.
The only way to find this kind of problem is with a Scanner to look at the misfire monitors for one cylinder with a high count.
This type of issue does not set a code.
Good luck. Hope you find it.

 

I see what you are saying, JackandJanet. I really don't think that its hitting a rev limiter though, it doesn't feel like that. For ref, My only other vehicle I've owned with a 4.6 was a Ford Thunderbird, and I hit the rev limiter a few times with that. This is definitely not the same. Not only that, but this happens at really any speed. I could be accelerating from a stop hard enough.

Revbiker, The fuel filter was supposedly replaced shortly before I bought the truck not to fix any issue, but as preventative maint. I looked under the truck last night, and its shiny and new.

Now that crank sensor MAY be a possibility. Bluegrass Nailed it. Its like I;m loosing electrical power completely, and thats why I'm not getting a CEL. Thats why I performed a wiggle test on all the wire harness I could get ahold of while the motor was running. Not a single hiccup in the way it ran. I did NOT however, inspect the crank sensor or the wiring to it.

Where it looks like that sensor IS, it would make sense that if something was screwed up there, it COULD be affected by a stream of water from a car wash/underbody flush.
Would that cause the symptoms I'm seeing?

 

Shaihullud, I'm not saying the problem is definitely the rev limit. And, if the crank sensor is the culprit, then I hope you can confirm it is and correct the cause.

But, you keep mentioning vehicle "speed" in your description of the problem and I'll say this again: "The rev limit is not dependent on, or a function of vehicle speed." You could hit the rev limit at ANY speed, if your commanded gear state was low enough and you push hard enough on the accelerator. The only thing the rev limiter acts to halt is an ENGINE overspeed. (Actually, I think it's protecting the transmission torque converter.)

Hitting the rev limit does not set a CEL.

I suppose you could test this without hurting anything by putting the truck into neutral and then stepping on the accelerator smoothly and steadily while watching the tachometer rise until you hit the rev limiter. I'd do this with the truck fully warmed up. And, if you can go above 5000 RPM without experiencing the "cut out", then I'll withdraw my thinking it's the rev limiter. But, by doing this, you'll know exactly where your rev limit is set.

If anyone else here feels my thinking is muddy on this, don't be afraid to offer your own opinions. I'm discounting the fuel filter, RevBiker, because a partially clogged fuel filter generally limits the maximum engine speed, not by cutting it off, but by acting like you have stopped trying to accelerate. The open loop control of air/fuel ratio would attempt to keep things in balance and the engine should still run, just not react to the offer of increased fuel which is not there.

I really have no opinion about the crank sensor or a faulty coil pack, except they both seem somewhat complicated reasons. I generally try to check the easy ones first.

- Jack

 

I'll put it this way. The likelihood of it being the rev limiter was somehow set wrong from the factory or that it was somehow modified is extremely unlikely. I mentioned speed only in the context that I've ran up on speed and rev limiters in MANY cars before, and this is NOT the same.

How in the heck would it be a rev limiter problem if it happens in a range, and NOT at a specific RPM? If it was the rev limiter, it would cut at the SAME spot no matter what, and it would be CONSISTENT. This happens anywhere between 2-2500RPMS, and intermittently. Sometimes it happens sometimes it doesn't. Unless somehow the rev limiter is changing itself to random settings, which I think is generally impossible.

This happens hot OR cold.

And btw, revving it in neutral and revving it while the vehicle is in Drive will net two separate results as far as where the rev limiter is on a later model ford.

 

I would start w/easy 1st. check all the fuses and relay's are tight in their sockets, I would change the CKP Sensor, ( i've seen these cause cut outs on Volvo's when they start to go bad) You could keep driving until whatever is causing the problem breaks down. The think that bothers me is the RPM doesn't drop when this happens, which makes me think its fuel delivery or I hate to say this----Rev limiter------ Good luck, may be time to take to a dealer??

 

OK, I have no dog in this fight. Just offering my opinion, which is probably worth exactly what you're paying for it.

Hope you get your problem solved. I see it as a safety issue, since a cut out during a passing maneuver could be, shall we say, unpleasant?

Let us know what you find.

- Jack

 

Will do guys. and yeah... "unpleasant" is one way to put it LOL "completely angering" is another hahah!


I did tap and wiggle around the fuses and relays under the hood while doing my wiggle test, i might just pull them and make sure I spray each one with some contact cleaner along with their sockets.

I have a question.... if it WAS the crank sensor, wouldn't I see the tach go nuts or at least "flick" when this happens? I would expect that to happen if for some reason i lost main power, but im not sure if it would act that way if it was just the crank pos sensor.
I'm going to try to wiggle the harness down there after I get home, and check all teh fuses/relays for contact.

 

I'll throw out a shot in the dark. Check your air intake system for debris, Where the air box connects to the fender well and inside that whole passage. If there are leaves or paper in there it might be just fine until you romp on it causing something to be sucked up and choke off the air.

But like I said.......a shot in the dark.

 

And while you are checking the intake, make sure it isn't leaking between the flow sensor and the throttle body.

I had a loose connection on my son's 1989 Escort way back. Upon acceleration, the engine would rock and it would leak causing the engine to miss. Probably not your problem but may be worth checking.