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Which Sparkplugs?---'94 F150 with 302 #4458778
07/13/17 10:02 PM
07/13/17 10:02 PM
Joined: Sep 2011
Posts: 406
IL
lukejo Offline OP
lukejo  Offline OP
Joined: Sep 2011
Posts: 406
IL
Going to change them. Does it matter which brand or type? Would any make a difference over another?

Re: Which Sparkplugs?---'94 F150 with 302 [Re: lukejo] #4458806
07/13/17 10:31 PM
07/13/17 10:31 PM
Joined: Sep 2015
Posts: 5,849
Kalifornia Kollective
BrocLuno Offline
BrocLuno  Offline
Joined: Sep 2015
Posts: 5,849
Kalifornia Kollective
The most efficient plug gap from a purely ignition and flame front point of view is around 0.100" But that is not really practical in most automotive applications. So we go toward that, but never make it there. GM has run gaps of 0.050 in the past when trying to cleanly ignite mixtures that were not optimal due to early EGR implementations, etc.

The larger the spark gap, the bigger the energy requirement from the coil. So a 0.032 gap is pretty easy to jump. An 0.045" wants roughly twice the energy to jump, but works really well to ignite the mixture.

That motor has a E-Core coil that can make some spark voltage. However, the ignition is prone to spark jumping from one wire to another and causing a miss, or cross firing. So before attempting to "just change plugs", it's always a good idea to carefully examine each wire for burn or wear marks. Make sure all your loom insulators are good. OHM out the wires to make sure they are in spec, etc.

If that's all good, the next thing is helping to jump that bigger gap. Sparks jump from small surfaces or points, better than from flat or rounded surfaces. So something like NGK or Bosch fine wire platinum plugs with very small center electrodes can initiate a spark easier than a plain old plug with a fat center post.

In the old days, you used to be able to buy AC Delco plugs with the "Ring of Fire" which were little sharp ridges all around the center electrode. They sparked very easily, even though they had nominally fat center electrodes. No longer available. So look into plugs with small center electrodes - your choice on brands.

Set the gap at 0.040~0.045 and that 302 will perk up some smile But not if the wires can't get it there ...

The other thing I'd do is run a dedicated #8 ground wire with crimped and soldered lugs from the battery Neg (-) post clamp bolt to one of the coil hold down bolts, and continue it to the fire wall at one of the hood hinge bolts. This motor and ignition love new and improved grounding to make everything work better smile

That factory ground is buried behind the frame crossmember on the side of the block. So it's now 23 years old with lots of crevice corrosion and all the factory grounds are starting to corrode. It's really hard to service the OEM ground, so just add new big fat well contructed ones and all sorts of stuff will work better.

I run a dedicated ground from the battery Neg (-) pinch bolt to the alternator bracket and the whole charging system works better. The built-in voltage regulator now has a better reference ground ( 0 ) to work from, so the battery is happier and so is the ignition. You'll be amazed at how well these old ECU Fords run with a good ground system smile

Last edited by BrocLuno; 07/13/17 10:39 PM.

Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.
Re: Which Sparkplugs?---'94 F150 with 302 [Re: BrocLuno] #4458816
07/13/17 10:37 PM
07/13/17 10:37 PM
Joined: Sep 2011
Posts: 406
IL
lukejo Offline OP
lukejo  Offline OP
Joined: Sep 2011
Posts: 406
IL
Wow--thanks man!
I'm towing a mowing trailer (about 2800lbs) constantly, so looking for anything to give a little help.

Re: Which Sparkplugs?---'94 F150 with 302 [Re: lukejo] #4458820
07/13/17 10:39 PM
07/13/17 10:39 PM
Joined: Nov 2004
Posts: 1,800
SD
zrxkawboy Offline
zrxkawboy  Offline
Joined: Nov 2004
Posts: 1,800
SD
I believe in using Autolite/Motorcraft in Fords.


"Think of all the Ford owners who will someday want an automobile." John Dodge

Re: Which Sparkplugs?---'94 F150 with 302 [Re: lukejo] #4458823
07/13/17 10:43 PM
07/13/17 10:43 PM
Joined: Sep 2015
Posts: 5,849
Kalifornia Kollective
BrocLuno Offline
BrocLuno  Offline
Joined: Sep 2015
Posts: 5,849
Kalifornia Kollective
I added a bit more info.

Also look at your tire diameter. These things are not geared low enough. If your door post says 3.55 - that'll be a weak feeling truck. They struggle - a lot. So maybe 265/70R15 is about as tall as you can go w/o pulling down the motor out of it's best torque range. This is not a combo that likes tall, skinny tires. Short and fat work better smile

Then look at the water pump and the rear timing case. If they are corroded and weeping, you need to replace them. It's not a fun job, but ... While you are in there, you can put in a new timing chain. If this truck has a bazzilion miles the timing chain is stretched.

That means the cam is running retarded. The factory cam is OK, and in fact, the Speed Density EFI system will not tolerate much more cam. So no gains there. But the motor can be made to breath better with the timing restored to where it ought to be and some steel roller tip rockers with 1.7 ratio instead of the stock 1.6 ratio. It's just enough bump to be good w/o messing up the EFI smile

Last edited by BrocLuno; 07/13/17 10:53 PM.

Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.
Re: Which Sparkplugs?---'94 F150 with 302 [Re: BrocLuno] #4458857
07/13/17 11:25 PM
07/13/17 11:25 PM
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
OVERKILL Offline
OVERKILL  Offline
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
Originally Posted By: BrocLuno
I added a bit more info.

Also look at your tire diameter. These things are not geared low enough. If your door post says 3.55 - that'll be a weak feeling truck. They struggle - a lot. So maybe 265/70R15 is about as tall as you can go w/o pulling down the motor out of it's best torque range. This is not a combo that likes tall, skinny tires. Short and fat work better smile

Then look at the water pump and the rear timing case. If they are corroded and weeping, you need to replace them. It's not a fun job, but ... While you are in there, you can put in a new timing chain. If this truck has a bazzilion miles the timing chain is stretched.

That means the cam is running retarded. The factory cam is OK, and in fact, the Speed Density EFI system will not tolerate much more cam. So no gains there. But the motor can be made to breath better with the timing restored to where it ought to be and some steel roller tip rockers with 1.7 ratio instead of the stock 1.6 ratio. It's just enough bump to be good w/o messing up the EFI smile


Nailed a great deal of good points in your two posts thumbsup

I can't remember if the trucks are batch fire or sequential, but the non-HO motors were generally turds and even the HO liked a few rev's to get any grunt out of her. Non-HO engines often received the nylon geared single roller chain which as BrocLuno noted, likes to stretch and retard the camshaft timing. You can test for this by seeing how much you can move the damper back and forth (you can probably move it by hand with a bit of effort) before the rotor turns. Go one way until you see movement, then go the other direction until you see movement again to get an idea as to how much slack is there.

Is the truck 2 or 4WD? You can often pick up gears on a Mustang board for cheap (I sold a set of 3.73's a few years back that I was just trying to get rid of), and something like 4.10's if you are doing mostly in-town driving will really wake it up. I had 4.10's or 4.11's in my '88 F-250 with a 302HO swap and she worked reasonably well, even backed by a non-lockup C6.

Depending on the miles on the engine, I'd be concerned that the 1.7's would potentially raise the risk of valve float. I've used them on all my Ford smallblock builds, but these are on engines with new or newer valve springs. That said, the Crane Energizer ones can often be picked up cheap, since they are pedestal and bolt into the stock location and are often regarded (and sometimes sold as, under I believe the FMS brand) the "Cobra" rockers, as they were OEM on the '93 Cobra IIRC. The rocker swap however does mean you need to check valve cover clearance (usually required a bit of work on the baffles on the 302HO with stock covers, not sure how it is with the stamped steel truck covers) and of course installing them requires the removal of the upper intake, and will necessitate the purchase of new gaskets. Might be worth the trouble if they are already leaking though. If ordering replacement valve cover gaskets, get the ones for the '96 Explorer, they are either rubber or silicone, can't recall off-hand, and will never need to be changed again.

Regarding your original question, I'd use Motorcraft plugs straight from Ford, gapped to the factory spec, which should be .052 - .056 for your 1994. If your wires are original, now is a good time to change them, along with the cap and rotor. Use OEM parts, the grey stuff tends to be pretty good.


2018 RAM 1500 Big Horn EcoDiesel
2016 Grand Cherokee SRT
Re: Which Sparkplugs?---'94 F150 with 302 [Re: BrocLuno] #4458867
07/14/17 12:03 AM
07/14/17 12:03 AM
Joined: Dec 2016
Posts: 6,226
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 6,226
Waco, TX
Originally Posted By: BrocLuno
GM has run gaps of 0.050 in the past ...


'75-'76 Olds 455... factory spec is .080"

Avoid Bosch plugs with a center electrode flush with the center porcelain. I hate those things.

Originally Posted By: BrocLuno
... run a dedicated #8 ground wire ... This motor and ignition love new and improved grounding to make everything work better smile You'll be amazed at how well these old ECU Fords run with a good ground system smile


Very, Very true!!

Oh, BTW - the stock HO cam plays VERY well with speed density, and is really a good grind. His 1994 has a MAF, so no worries there, though. Avoid the 1.7 rockers... such a headache, those things.

It's a LOT of work to change a camshaft. In a truck, install the cam 4* advanced, since the chain will stretch close to that much after 10-20K miles anyways.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: Which Sparkplugs?---'94 F150 with 302 [Re: lukejo] #4458868
07/14/17 12:07 AM
07/14/17 12:07 AM
Joined: Jul 2009
Posts: 432
Seattle
Superflop Offline
Superflop  Offline
Joined: Jul 2009
Posts: 432
Seattle
If you want to perk up your 302. Buy 8mm plug wires i really liked the taylors personally. Get a hot coil used to use accel and flame throwers add a stout cap and rotor.. accel, msd, summit. Set your plug gap to 60-65 thousandths. I always ran autolites in my 302s (autolite 25 iirc) the added voltage will support the greater gap just fine and you will notice some extra perk. If you want to go the extra mile advance timing 2-3 degrees (this is optional and may require some dinking around with final timing, its deff not required). Dont change timing till after the rest is done.

This is tried and true and i have done it on quite a few older rigs.

Back a while ago all my off road and dd rigs were ford pickups or broncos with 302s and this was one of the first things i did. Btw also make sure your IAC is clean its a ford thing and should be cleaned every or every other air filter change. What broc said about grounds is good info i also like to ground my alternator better.

Last edited by Superflop; 07/14/17 12:21 AM.

2002 saab 9-5 2.3t wagon
2014 dodge grand caravan
Re: Which Sparkplugs?---'94 F150 with 302 [Re: zrxkawboy] #4458929
07/14/17 03:53 AM
07/14/17 03:53 AM
Joined: Jan 2011
Posts: 2,718
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,718
N.Ohio
Originally Posted By: zrxkawboy
I believe in using Autolite/Motorcraft in Fords.


My thoughts too.


The "thinking" man's friend.
Re: Which Sparkplugs?---'94 F150 with 302 [Re: lukejo] #4458961
07/14/17 06:06 AM
07/14/17 06:06 AM
Joined: Oct 2015
Posts: 2,652
Balearic Islands , Spain
FordCapriDriver Offline
FordCapriDriver  Offline
Joined: Oct 2015
Posts: 2,652
Balearic Islands , Spain
My Fords have always ran best on Motorcraft spark plugs, used Champion for quite a while but definetly runs better with Motorcraft plugs, why? No idea.
My Capri is still on points, although it has a better Bosch distributor.


1975 Ford Capri II Ghia 3000 V6, - Shell Helix HX3 20W-50 w/ 20% Rimula R4X 15W-40 HDEO.

1988 Ford Escort Mk4 Xr3i Cabrio, - Shell Rimula R4X 15W-40, w/ 30% Helix 3 20W-50.
Re: Which Sparkplugs?---'94 F150 with 302 [Re: Linctex] #4459065
07/14/17 08:18 AM
07/14/17 08:18 AM
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
OVERKILL Offline
OVERKILL  Offline
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
Originally Posted By: Linctex

Oh, BTW - the stock HO cam plays VERY well with speed density, and is really a good grind.



I wouldn't say it is a really good grind being a basic single pattern, but it was a good stock grind for the time. The Explorer cam is another one that's quite decent and has better low-end grunt than the HO cam. I always thought the "stock cam club" on the Corral was kinda neat, guys making gobs of power with cars that sounded basically stock grin


2018 RAM 1500 Big Horn EcoDiesel
2016 Grand Cherokee SRT

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