91whitelariat

I have a 4.9l I6 with about 243000 miles, and only gettin about 11-12 mpg. I was looking at some upgrades to help it and i was wondering, if i get an ignition upgrade but no timing bump will it do anything. Any other ways to help greatly apreciatted... thanks.

00gstang

New ignition components are always good. You probably won't gain any HP with just new wires/plugs/cap/rotor (unless you advance the timing). But your truck will definitely run better and get better gas mileage. If you advance the timing be sure to keep it in the 14-16^ range and use higher octane gas to prevent detonation (or else you could blow the engine).

93f-1504x4

where's ymeski on this one? he'll chime in soon no doubt

ymeski56

The amount of advance your engine will tolerate w/ 87 octane many times depends on the overall health of the engine, including the efficiency of the coolant system & amount of deposits on the combustion chamber surfaces. I've run 16 BTDC for four years now w/ 87 octane. Although, compression PSI does not have to be great, just relatively balances.

I only run 89 octane when I haul my motorcycle to Oregon. Over 700 miles @ 80 mph, non-stop. Don't have to really, I just do, for the added quenching effect.

A steady diet of hi octane will guarantee combustion chamber deposits in a low compression engine.

If you do advance timing, Motorcraft stock copper cores are actually engineered to fail prior to piston damage occurrence.


when you increase your gap after doing the ignition upgrade, you trade a higher temperature, more intense spark, for a less temperature generating, but larger exposed spark kernel. This in itself is helpful for allowing more advance.

Use of double plats, won't allow as much advance safely or otherwise as they require more resistance to be overcome to initiate spark to begin w/, & store heat rather than disperse it once generated. This is how they "self clean"! Personally, if a situation is occurring that would normally cause a stock plug to foul, I'd like to know & deal w/ the problem. Rather than the plug self clean, masking the problem. Especially if it costs me higher cylinder temps to accomplish it.

I also run a 180F thermostat & add a bottle of Water wetter to the coolant, which is 1/2 antifreeze & 1/2 "distilled" water to eliminate scale build up within the block cooling ports.

Engine oil sludge build up is not conducive either.

00gstang

you are one of the lucky one's who does not get engine ping with low grade octane and advanced timing. however, many people HAVE to run 89-91 with advanced timing because their engines aren't up to par. Personally I don't think it's worth the risk just for a few ponys on a truck that wasn't built to race.

But to the poster- it would be beneficial for you to do a full tune up!

ymeski56

My truck wouldn't run at 12 BTDC w/o ping, got 9 mpg, & would only do 65 mph downhill w/ a tail wind, when I got it 5 yrs. ago. There are certain minor procedures & mods required to run at 16 BTDC w/ 87 octane trouble free. Many of which I mentioned.

The whole point is to never reach the ping temp threshold. One you reach that point it's very difficult to reduce temp below that point. While the added quench effect of 89 octane is good insurance, your better off reducing advance than running 91 octane.

Most everybody can handle 14 BTDC w/ stock copper cores, especially w/ a bottle of Water Wetter added to the coolant system.

16 BTDC however, requires a little more effort in prep & having the rest of your ducks in a row. Less than adequate maintenance it the biggest reason further advance w/o ping occurs. Also, a continual high octane diet, resulting in combustion chamber deposits, prior to attempting further advancement. "Seafoam" is your best friend to rectify this problem!

91whitelariat

so, what should i do...i am getting paid next tuesday. I want to do something but dont want to spend too much. What should i get or do and what brands? I have a small skip, but its not like a plug, its not at a certain cycle its just random.

ymeski56

http://fullsizebronco.com/forum/show...ht=timing+bump
MSD 48K volt low ohm coil, brass cap & rotor, Taylor thunderbolt low resistance wires, Stock Motorcraft Nic Plated copper cores.

Get your increased gap dialed in first, then you can deal w/ any further advance if you want. Any further advance from 10 BTDC will be an improvement. As I mentioned earlier, 14 BTDC is almost always within reason.

What is your stock gap?

I would start w/ Seafoam!
https://www.f150forum.com/f33/how-se...-1991-a-31505/

ymeski56

87 octane is not "low grade"! Many stations only carry 87 & 91 octane. 89 is made available via a mixing pump that draws from both tanks.

Octane is added for the purpose of controlled delay the moment of ignition specifically for higher compression engines, to maximize use of that compression. 87 Octane actually has the best overall combustive properties.

Read this: http://www.jcmmachine.com/detonation_preignition.htm

91whitelariat

So how much will those supplies cost? I just did seafoam a few weeks ago, worked good, smoked like crazy and when i changed the oil it was very dirty. It had only been 3000 miles since last change too. But i was thinking about 12 btdc...will that help some? Its a pretty old engine and i dont wanna kill it.