Hopefully somebody here can give me an idea on where to look for this...

I picked up a 95 F-150. Overall in good shape, but has an intermittent miss (I suppose I could call it a stumble/hiccup, too...) I'm trying to track down. 300ci inline six motor, manual transmission. Has 95k miles. I thought it was probably the plugs at first, so I replaced those. That didn't take care of it. Given the symptoms I thought it may be a fuel filter, and replaced that which also didn't help.

What the symptoms are, is it will occasionally miss throughout driving. Sometimes when it is warm, sometimes when it is cold. Typically it is when I am light on the throttle, but not always. It almost seems like it could be the fuel pump, except for the fact that it never has any trouble starting up, and does it the same on either tank.

Any suggestions on what to check would be greatly appreciated. Thanks-

 

Did you replace wires as well?

If you suspect a fuel supply issue put a fuel pressure gauge on the schrader valve on the fuel rail and make sure its getting constant pressure. Its a low impact test.

The pumps are usually a work/don't work affair.



Next up TPI sensor on the throttle body. Not sure how much they are but its an easy swap. be sure you have a good seal behind it. My stang had a vac leak from the gasket.

Next I'd look at the TFI module on the distributor. They are temperemental garbage on Mustangs. I keep one in the glove box.

 

Yep, wires were changed as well. TPI sensor? Do you mean TPS?

Also, wouldn't the TFI cause a no start/no run situation rather than an occasional miss/stumble?

 

My 300 does the same thing, only under light throttle and its worse when warmed up. If I step on it over 1/2 way it smooths out and runs perfect and seems to have more power than usual.
I'm thinking TPS, TFI, and/or possibly PIP since my timing advance is non-functioning.

 

Sorry yup TPS

The TFI is kinda new to me. My stang has it and Ive already had a couple fail.
You're right, it was a start/no start for me. A few guys on Turboford.net have had intermittent issues with them when the engines are hot.

I was thinking of stuff in the ignition system that would cause your issues.


Check this out too if you run out of ideas:
Ford Fuel Injection 10-pin Connector Fix

 

I've had the "miss" issue on my 94 since it was new. Took it in for warranty claim when new and was told that's the way they run. WTH? Oh well. 15 years and not another problem, but it does do it's "miss" thing still. With 170K + miles on the clock, I'm leaving well enough alone. ;-)

 

Well, whether they say that is the way they are supposed to run or not..they don't all run that way.. this is the only straight six I've owned that does it...others ran smooth as silk..almost eerily smooth, actually.

Maybe I will just leave it alone if I can't find the solution soon...but, it sure is annoying...

 

My 96 developed this annoying habit at about 230,000 miles. The #5 cylinder goes lean and misses at idle. As soon as I throttle it, it goes away. I know I have a bad injector (bad wave pattern on the scope when probed, it is sticking at idle) but I haven't gotten around to replacing it. Oddly enough, it won't do it in the summer with the AC compressor engaged. At idle, the injection pulse is so short, I don't think it has time to open enough to flow fuel.

 

My miss gets quite annoying, especially in town, its killer on u joints. I'm thinking of getting a whole new distributor and seeing what it does. Maybe then my timing advance will work and I can break 12 MPG

 

The trick.....

You basically have a lean out condition at part throttle (very predominent on sticks). What I did on mine was to insert a restrictor plate inbetween the EGR valve & the manifold, reducing the ports to 3/8". Mine still past smog, was not visually detectible and really helped part throttle accel and eliminated all hesitation.

 

had the exact same problem on my 87 300 six
Turned out to be the TPS

If you want to try just disconnect it, if the TPS is bad the miss will go away (but then you will have a lag in the throttle response)

 

I have done all of the above, albeit with a warranty. None of them worked. It is smooth at idle, but misses at 55-65 mph. Above or below that speed no issue. All the smog items, all the emissions sensors, positioning sensors, etc were replaced before the truck hit 5K miles. Oh well, it's half worn out and so am I. Actually, it'll probably outlive me! I'm not fooling with it any more. It is what it is. Mine!

 

OK I would bet this is the solution!!! My dad bought a 91 300 I6 5speed new in 91. Always had a small hicup or miss under light throttle!!!

Did a complete tune-up on it and nothing helped.
Did a search on this forum and found that the EGR valve is oversized for this truck. Basically ford wanted to use the 300 as long as they could. Why not is a great motor, but due to emissions they had to increase the egr valve to the point that it would pump too much exhaust into the intake under light loads.

To see if this is your problem simply unplug the vacuum line that is going into the egr valve and plug the openings. This will keep the egr from opening.

Now you will throw a Check Engine light, once the truck gets warmed up enough to open the egr. but since the egr wont' open it will throw the light.

There are some that have made a restrictor plate of some sort to limit the flow and not throw a light.

What I did was leave it off until i had to pass an emission test then plug it back in a go.

I would bet you this is your problem. I usually leave mine unpluged and it runs better then new!!! Oh and i just put a small piece of electrical tape over the check engine light. I do pull the codes every so often to make sure there are none besides what i know is there, the egr code!!!

Oh i would get a new rotor and cap for your distributor. Get the step above the cheepest or go to ford. The cheep ones are just that... junk. but you will be suprised what you find if they haven't been replaced for a while

Best of luck let us know what you find, but i would bet this is your solution

 

Hmm..if this does seem to be the problem, do you happen to know when they increased the size? I'm thinking I could just get an EGR from one before they did this..I don't suppose you happen to know if one of these older ones would work/fit?

 

I do not know what will work. I do know that my 91 did the same thing. It would buck and miss under light throttle. Go unhook the vacuum line going to it and go for at least a 15 min drive, enough to have the egr open, your check engine light should come on. Now see if it misses/ bucks. if it doesn't then that is your problem. I would bet it runs nice and smooth

I do remember something being said about changing the egr when they switched from carb to efi, but i can't remember. I did find all this info on this forum though. Maybe a search will help ya find it, its been like 4 yrs since i found it so im not sure if its there anymore or not.