My '93 with the 351 has has this long-standing little annoyance. Whenever it rains for an extended period of time(or even just high humidity), the motor runs noticeably worse, and gets a hesitation right around 1500rpm. After an hour or so of driving, it goes away, I presume the heat dries things out. In dry weather, the motor runs fine.

The fact that the poor performance goes away after a while means that it's not a plugged or wet air filter, and that it runs fine when it's dry means the fuel filter isn't the issue either.

My guess would be the plug wires. They're stock Motorcraft 8mm gray ones. I can't tell exactly how long they've been there (128k on the clock) but it looks like quite a while. The coil is definetly the original, as the bolt on it's clamp is rusted to hell, it's never been touched.

I read (I think) on FSB about a fairly simple upgrade using a MSD coil, a set of the Ford Racing wires, and a new cap and rotor. It also mentioned advancing the timing a couple degrees if you want to run premium. I'm always skeptical about MPG claims, but several members there claimed a 1+ MPG increase over stock. Since I was planning on replacing the wires anyway (and I've always heard to replace the cap and rotor when you do that), I might as well break a few extra bucks and get a new coil. I might play with the timing and premium in the spring, too cold for me now to be fiddling with that. Though I have also heard of hotter coils burning up the stock electrical box. Any truth to this?

Any thoughts about the hesitation or the upgrade? It seems to be a decent benefit for a fairly low cost, particularly if the wires on there need to be replaced anyway.

 

Look at the Crane PS-91 coil. It's an exact plug-in/bolt on replacement for your stocker. I'm not convinced that improved ignitions offer much on a near stock vehicle in perfect operating condition but as the engine wears and looses a bit of performance, a hotter spark may (or may not) restore some combustion efficiency. FWIW on 300s and 302s the techies at Crane recommend the PS-91 in conjunction with their Hi-6S inductive ignition rather than the Hi-6 CD for improved fuel economy; never asked them about 351s.

 

Not to be a jerk, but this has been covred about 5 times in the past month here. Look around some and you will find all you need to know.

Check this thread, post #3 for the link to a good ignition uograde.

 

Hi RA warrior. I have a 2001 xlt with 5.4l in it and that is what my truck would do after the snow. I put my actron scanner on it and got a code reading of po301 # 1 cyl. misfiring. after replacing plug, cop. I accidently hit the connector for the fuel injector and it fell off! This was my problem!

 

I've pulled codes whenever it happens, hoping something will show up, but it never throws any (just the 111-system okay code). No stored ones either, I cleared it after I fixed the O2 sensor issue.

I'd imagine what goes for the 302's also goes for the 351's, the motors share about everything.

I'll probably poke around the Jeg's website and see what they have for this motor. Always had good experiences with them in the past. Autozone is fine for picking up a gallon of washer fluid but they really bend you over on "specialty" items, as in anything that isn't poured into your car.

 

I forgot the link to the thread in my earlier post. Once again, post #3 has the link to the ignition upgrade, but you should read the whole thread.

https://www.f150online.com/forums/sh...d.php?t=314772

 

I can't speak first hand for the 351, but my 302 got great improvements from ignition upgrades. My around town mileage went up about 1.5 mpg and I can get 15+ if I don't drive it hard.

I did the full Jacobs system with box, coil, and wires. Along with that I opened up gaps and such per their recommendations.

Figure 15% or so of your fuel cost at todays gas prices. You'll probably save $75-80 between oil changes.

I will say that I've now fried two boxes, but Jacobs backs them with replacement for a minimal handling fee if anything. I've heard of just about every box that is common getting killed at some point.

But in the long run, mine was free, as the mileage improvements more than paid for it already. Power improvements weren't huge, but I could notice more low end torque, better idle, and less torque converter unlocking under load. With the 351 torque curve being so much different than the 302, it's hard to say if you would notice the same improvements.

 

That FSB article is where I first saw the bit about adding a hotter coil and adjusting the timing a bit.

How much is an aftermarket box, and how's the installation? Is it just a "plug and play" sorta deal or does it require something more? I don't want to have to be fixing and replacing parts down the road for a paltry gain.

I looked around for the PS-91, and can't find it anywhere. All the sites google turned up gave me the 404 error(outdated link)

Upon looking around the common stores (jeg's, rockauto, ect) it seems just about every ignition manufacturer has a coil for this motor. Some say they're for the 302, while others say compatible with 302/351. I can get a coil, wireset, and cap/rotor for about $100.

Is there any difference in material? Some coils/caps tout having stainless for long life, whereas others say brass conducts better and gives better performance. Does it really matter?

 

I went to the Accel coil, and it was worth every penny. the MSD unit they are talking about is prolly as good if not better.

 

Skip the box. There really is not point in doing it.

STick with brass wherever you can.

Like the link says, run cheap copper Autolites. No need for platinum plugs.

100 bucks is about what I payed for everything when I did it.

 

You can get boxes from a little over $100 up to several hundred dollars, depending on what all you want. Some have rev limiters, nitrous control plug ins, and timing control plug ins, others don't. Many throw multiple sparks up to a certain RPM, and virtually all will throw a fatter spark with more energy.

Most big name boxes have adapters so you don't need to splice anything. My Jacobs triggers off the stock coil, so it can be switched back quickly and is easy to install.

When I got all my stuff from Jacobs it wasn't cheap, almost $400. But everything is very well backed, with a no questions asked return policy, lifetime warranty on the wires, no questions asked replacement on the box if it fails, etc. The coil is rated at 65,000 volts, and their support and service was excellent.

But as I said, in the long run it was free. The MPG improvement paid for it, and I'd do it again.