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95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 304K miles
985 Posts
Get a Motorad Fail-Safe (192-195 deg) factory temp thermostat so the computer can function in Closed Loop and you can maximize your mileage and life of the engine and also when it fails it fails in the open position so you don't overheat and possibly ruin your engine. Just my "Opinion"...

1988 Ford Bronco 351w, c6, auto locking hubs, manual transfer case, 3inch lift, 33s
5 Posts
Discussion Starter #22
I also noticed that 4 of the 8 intake holes on the manifold are more black, would this have anything to do with mpg? I'm just assuming that means it's running more rich on those cylinders?

Premium Member
1992 Bronco 351 V8 5.8
11 Posts
Yo Jay,
Check Engine Light (CEL) comes on when the electronic engine control system is not working properly. The check engine warning indicator comes on briefly when the ignition switch lock cylinder is turned to ON, and should turn off when the engine starts. If the check engine warning indicator does not come on when the ignition switch lock cylinder is turned to ON or if it comes on while the vehicle is moving, the system is malfunctioning
If the CEL does not light up at all when starting it; then suspect that bulb is burnt-out or loose, socket was damaged by PO or shop, etc. or someone removed it, which does happen, unfortunately.

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
Code Reader..... - 80-96 Ford Bronco - Ford Bronco Zone Early Bronco Classic FullSize Broncos
A helper is good to assist in reading Codes; best is to take a cell fone vid and replay it.
Some basics;
Visual Check
1.Inspect the air cleaner and inlet ducting.
2.Check all engine vacuum hoses for damage, leaks, cracks, blockage, proper routing, etc.
3.Check EEC system wiring harness for proper connections, bent or broken pins, corrosion, loose wires, proper routing, etc.
4.Check the Powertrain Control Module (PCM), sensors and actuators for physical damage; IAC, TPS I see was replaced, etc.5.Check the engine coolant for proper level and mixture.
6.Check the transmission fluid level and quality. See E4OD Fluid Condition Check Below)
7.Make all necessary repairs before continuing
8. Check headlights

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears including Reverse.

Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Turn off all accessories; radio, lights, A/C, heater, blower, fans, etc. (close driver's door)
Then turn off engine and wait 10 seconds.
Do KOEO test First

You should see 2 digit code (s) if any
Post Code(s) here according to:

Following applies to California, etc.
TSB: 96-10-7
very minimal mpg loss.

99-26-9 for 91 F250 Revised

Fuel Saving Tipso
I have always factored in any cost to improve MPG in the overall $ "savings".
Reduce weight of the Bronco and tools, accessories and ... passengers; driver's get a pass; also, grille guards, side steps, etc.
Ensure that brakes are not dragging
Driving style/ light foot - Foot on Pedal too much while accelerating and high speed driving over speed limit
proper tire pressure - Under inflated tires Increase rolling resistance 1-2 mpg;
Dirty air filter Causes excessively rich fuel/air mixture 2.0 mpg;
Worn spark plugs Cause inefficient combustion, wasted fuel 2.0 mpg;
Worn O2 sensor Unable to detect and adjust air/fuel mixture 3 mpg (not it your year);
Dirty or substandard engine oil Increases internal engine friction 0.4 mpg;
Loose gas cap Allows fuel to evaporate 2.0 mpg
Potential loss in fuel economy if all of the above were neglected 11.4 mpg
Add them all up and you get yaris mpg. Lol

Check Timing
Try Sixlitre Tune-Up @ ignition upgrade and timing bump (no 56K)

One more low mpg perp could be, it's common for Fuel Pressure Regulator (FPR) diaphragm to fail, allowing high pressure gas to leak into it's vacuum line, which then dumps straight into the intake plenum. This can flood the engine, and if allowed to continue, it can wash the rings out & damage the bearings. To check it, simply disconnect the vacuum line with the engine idling & inspect for the presence or any aroma of gas.
It may take a few seconds for the FPR to fill with gas and begin spitting it out the FPR's engine vacuum nipple.

Also, any Smoke from tailpipe?
Black exhaust smoke is an indication of rich fuel condition. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition."

Blue/Gray Smoke:
PCV System: A stuck closed PCV valve will cause excessive crankcase pressure resulting in blue/gray smoke.
Oil burning in the combustion chamber. Pull a few spark plugs & ck iaw Spark Plug Diagnostic Chart
spark plug fault diagnosis
Oil Deposits Symptoms: Oily coating caused by poor oil control. Oil is leaking past worn valve guides or piston rings into the combustion chamber. Causes hard starting and misfiring.
by ASE Study Guide

& more Items that Cost $:
tune-up. plugs - pull and check/re-gap, replace if nec, same for plug wires (check for insulation cracks, and resistance (more on this later), distributor cap and rotor
brake parts - always $ WELL SPENT
I use Ford Motorcraft parts via AMAZON; they are VG at delvy and esp pricing; I bought a $150.00 DPFE Sensor (not incl. sales tax) for $50.00 with free shipping and no state sales tax; same for the IAC sensor.
Some buy from a Ford pn on-line or local parts stores that list the Ford PN, but the ads show the PN as a reference only and the supplier may be a company off-shore. other than a Ford supplier.

High Quality Motorcraft TFI Ignition Coil Attributes
Source: by SeattleFSB (Seattle FSB) @ MSD 8227 coil problems
Many Bronco owners shop for an ignition coil by looking for the highest voltage available. But I venture to say that there is much more to look for in achieving both a quality ignition system and saving money in the long run.
For clarification, it takes approximately 10-14,000 volts to initiate the spark across the OEM spark plug gap. After the initial arc, the voltage required to sustain the arc is much less and drops off significantly. So while you may have a 48,000v coil you can't actually get that across the plug. The extra power becomes reserve voltage which compensates for worn plugs, increasing resistance in wires and carbon fouling. This increased stress can require an additional 1-5000 volts.
Fact is a higher voltage coil does not work any better, it just lasts longer due to having a higher reserve reducing heat. You cannot push more than 20,000 volts across a spark plug without bad things happening. If you were to try you would see arcing down the side of the plug, across carbon buildups at the electrode end and out any weak points in the wire insulation and connections.
The bottom line is the ideal coil output required for normal applications is about 30,000 volts. So no, your coil does not need to be 48,000v for proper ignition. The benefit would be in having enough reserve to compensate for high resistance due to a worn or altered ignition system.
This is why the Sixlitre Tune recommends a 48,000v coil and larger spark plug wires – to compensate for a substantial increase in resistance from larger than specified spark plug gaps. You are adding resistance as the spark attempts to reach ground. This in turn causes the plug wires to break down and decreases the service life of the rotor, distributor cap, spark plugs and increases the chance of spark scatter within the Distributor Cap.
Think about it, you are setting your spark plugs at a maximum gap even before wear. The higher voltage coil does not reduce stress and wear on your ignition system; it only compensates within a larger margin and then ultimately becomes dependent upon the quality of construction for survival. When opening up your spark plug gap from factory specifications you must be prepared to check your secondary ignition system annually, as opposed to about 40,000 miles with a stock vehicle, or risk performance decreases down the road.
With that being said, IMHO the Motorcraft DG470 TFI Coil is one of the most dependable 48,000v TFI Coils on the market. This is largely due to the quality in design, testing and construction. I have personally had many dependability issues with other imported TFI Coils, such as MSD. Where a Motorcraft Coil has lasted 15 years, I have went through three MSD coils in five years. Your purchase of a TFI Coil should not be totally dependent upon the voltage, but strong consideration should also be made regarding the contruction attributes listed below:

Motorcraft TFI Ignition Coil Attributes
Insulation - Multiple coats on the primary and secondary windings to ensure no internal arcing
Radio-Frequency Interference (RFI) Suppression - Minimize electronic noise
Magnets - Hold strength for the coil to maintain proper energy output
Steel - Used in the lamination stack to ensure a consistent magnetic field needed to develop the required voltage
Coil Housing - Engineered to withstand extremes in temperature without cracking

Low Quality TFI Ignition Coil Potential Issues
Rough Running Engine or Misfires - Causing Check Engine Light
Fuel Economy and Power Decrease – Costs money and performance
Radio Frequency Interference – Affects radio, EEC, sensors, cell phone
Pre-Ignition and Detonation – Can cause engine damage
Weak Voltage Output – Can cause increase tailpipe emissions..."

For future mods;
Project M.P.G. in a Centurion 460; miesk5 Note, Results are Comparable to Tests in other Ford Engines
Source: by @
FOUR WHEELER Magazine's Project M.P.G.
Some use this information while others write that the results are not achievable.

COLD air intake - insulate air intake from grille entry area to throttle body.
Air Tube & Box Insulation pics in a 94 5.0; Ken used Reflectix Insulation, avail @ Lowes. etc. ST16025 - 16" x 25 feet. miesk5 Note; Ken installed the K&N® & removed the cold air intake tube that runs to the top of the radiator; but he could have installed the intake tube section later.

Source: by Ken B (Kenny's 94)

Here's the 1988 Bronco Dealer Brochure, part 1 by Ford via member sneal @ 1988 Bronco Dealer Brochure part 1... site upgrade rules...
1988 Bronco Dealer Brochure, part 2 by Ford via member sneal @ 1988 Bronco Dealer Brochure part 2... site upgrade rules...

For any Bronco questions or to chat about it's planned modifications or build, it's better to post each seperately in Noobie Bronco Tech Questions. Flame free zone. This will get more attention and you can build up your post count to get into other sections such as Bronco and Ford Parts/Accessories (75 posts required to participate due to scammers who preyed on our members).

To save you time and for better responses, please fill out your Bronco info with location, year, engine size, transmission type, transfer case type (manual or electric shift), locking hub type (automatic or manual) info & major mods such as a Lift, etc. .
Bronco info is now able to be put under your user name.
Click your profile button in the top right and go to account settings.

On that first page, named Account Details, scroll down to "Vehicle Info" and type in up to 100 characters.

Now you can simply enter your information in the text editor and click save.

Our Forum FAQs includes for example, How To Upload Images To Posts, How to Use Search and more tips!

➡ See Baba Looey's Favorite FSB Links (lots and lots of tech links) including, "how do I get the tailgate glass to...", etc.

Find time to Participate and VOTE in our next Full-Size of the Month (soon to change to Quarter) Contest and later in the year, Full-Size of the Year Contest @ Voting
You will get ideas by those competing.
That is all really good info. what is the best tire pressure for 31's? better to have it on the high end rather the lower end like you said?

95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 304K miles
985 Posts
You can run 40-45 psi without any problems. That's where I run mine at and they are wearing great, but that is highway and around town driving only.

(edited) Moved edit to new post #26 to clear things up. Hopefully!!!!:geek:

Premium Member
4,025 Posts
That is all really good info. what is the best tire pressure for 31's? better to have it on the high end rather the lower end like you said?
every tire has the recommended maximum PSI molded into the tire. i usually inflate tires to ~5 PSI less than maximum.

you want it properly inflated, no high or low.


95 5.8L MAF XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Man hubs, KYB Quads, 31x10.5x15, 304K miles
985 Posts
I will add this info as mind stimulation for all interested!!!! I hope ya'll enjoy..

The more air pressure you run in a tire the lower the rolling resistance should be (Theoretically) up to a Specific pressure (Safety wise). The narrower the rim that a Specific size Radial tire is mounted on the less pressure that setup will require to have the tread in perfect contact with the road or in other words flat across the tread with equal pressure along it's face and the longest wearing tread life. If that same size Radial tire is mounted on a wider rim it will require more air pressure to accomplish the same Flat Tread pattern and Tread wear. Radial tires are much less susceptible to Over inflation wear than the Bias-Ply tires of the past because the tires are designed to handle higher pressures and retain their shape better but as stated above if they are mounted on a narrower than specified rim they will wear just like an over inflated tire would because for that size rim they are over inflated at stock pressures. For our vehicles the, tire sizes and rim widths we use it is a trial and error thing where you have to measure your tread depths and monitor them to see if your tires are wearing flat across the face (perfect pressure) or if the edges are wearing more than the center (under inflated) or if the center is wearing more than the edges (over inflated). The pressure numbers called out on the sticker on the door are for stock rim sizes and stock tire sizes and they are also "ALWAYS" less than the "IDEAL" pressures you should run. Your tires will "Almost Always" last longer and perform/handle better when inflated to higher pressures, those pressure recommendations are there to keep people from complaining that the ride is too hard to make it feel more like a Cadillac or Lincoln of days gone bye. That's why there was the Firestone tire Debacle years ago because Ford recommended to low of an Air pressure for the tires on the vehicle and hence the rollover problem, but Firestone got the blame unfortunately for them.
I am a Mechanical Engineer so this is one of my pet peeves and I can go even deeper into this tire pressure thing but I hope this helps. This is my "Opinion" and "Findings" from a lot of years of experience so you can Believe it or Not! So let the Flames Begin.
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