Ignition Timing

I know that this topic has been covered a long time ago, but I figured I'd start a new post to educate some of the newbies.

Our X has always gotten crappy gas mileage, IMO. That is, for an X that is pretty well maintained and driven lightly almost all of the time. Usually mpg has hovered near 14-15. Checked the timing the other day (which you would figure the factory would get right), and it was set to the specs for a 2000 (15 BTDC). But I have a 2001 (spec is 10 BTDC). Changed the timing and magically, last two tanks have gotten 17-18 mpg, and increased power. We never had any knocking or other things that indicated the timing was off, so I never checked it, but I recommend that everyone else does now.

For a how to on the procedure from another board click here

This may be a little off topic but when I drove an '01 I would get 15 MPG with premium gas and when I became enlightened that only 87 octane was needed I switched and went up to 17 MPG. I didn't do anything differently like driving slower, etc. I'm only getting 15 MPG on my '02 and I use Amoco ultimate "gold" for the S/C. I know gas has been discussed before on '00 & '01...anyway did you* use the cheap stuff all the time?

[ 01-30-2002: Message edited by: LOCHS 2 ]

Always the cheap stuff, and no knocking/preignition, just bad mpg (until the timing was fixed

Knocking/pinging usually occurs only if the timing is *too* advanced for the grade of gasoline used. Advancing the timing will often improve performance or mpg as long as pinging does not occur under load.
Some ECU's have knock sensors and will alter the timing to prevent damage due to a low octane tank of gas. Don't know if the X has this system.

dave and xtoy - on regular

ok, i have some stupid questions here. how does timing thing work? how do i check?

It's not a stupid question. Timing has to do with the exact moment the spark ignites the air/fuel mixture. Consider how a four cycle gasoline engine works. It takes time for the combustion process to take place. Why does it matter?
If you fire the spark too soon, the piston is still moving up in the cylinder. Fire too late and the piston is already moving down the cylinder. Remember that the combustion takes time. So at idle you may want to fire the spark about 10 degrees of crankshaft rotation before the piston reaches the top of it's travel. (TDC - top dead center) That gives the air/fuel mixture time to burn(explode) and push the piston down the cylinder.
Simple enuf. But consider this - the combustion takes the same time but if you want to go faster, the engine has to turn faster. So as the engine speed increases(RPM's on the tachometer) the ignition system has to fire the spark sooner to give good power and economy.
How do you measure timing? You use a timing light. It's like a strobe that fires with the spark of number one cylinder. You aim the light at reference (degree) marks on the crankshaft pulley and a pointer and make adjustments if needed.

dave and xtoy - out of *time*

Yes it does. Unfortunately, it's in a stupid spot. It's under the intake manifold and I don't think you can get at it without removing the intake. Oh well, hopefully you never have to replace it. As far as I know, all modern engines, meaning computer controlled, have a knock sensor. Because computer controlled engines are capable of controlling fuel and spark for optimum efficiency they also have to have a way to know where optimum is. Older mechanical/vacuum controlled spark advance methods obviously didn't require one.

Great explanation of timing by the way!

So, the whole sensor thing brings out the possibility that the factory set the timing correctly on my X, and the computer, over time, could have retarded (yes that's the word people) the timing to the state I found it in. Or could the ECU accomplish this sort of thing?
Or maybe the timing guy on the line in Smyrna had a bit of a hangover and wasn't paying much attention on the day my X was born?

kandacarlson -
Your timing probably drifted slowly due to parts wear. In addition, the NissanGorilla may have had too much moonshine the day he set your motor.
FWIW, setting the timing an additional two to four degrees advanced can improve performance/economy over the stock setting. OK, it may not work on *every* vehicle. But there are enuf positive reports that indicate that it may be worth a try.

dave and xtoy - gotta try it on mine someday

On a number of engines that I worked on over the years, many were found to have the degree marks on the crank pully (vibration damper) off by as much as 8 degrees. This was with american manufacturers,dont know if the foreign ones have the same problem. I will have to check my 01 tomorrow to see how accurate it is.
Not the first time this board has caused me to go out to check stuff. Curiosity is sometimes a good thing.

There's a how-to for adjusting your timing on the xterra4x4.com board.

Brent

Or you could buy the Haynes Nissan Xterra/Frontier/Pathfinder Manual.
That way you can do 90% of the maintainence you'll need over then next few years.

OffroadX, or anyone else interested,

The direct link to the timing instructions is in the first post of this thread. Keep in mind that the instructions are for a 2000 (15 degrees BTDC). So if you have an '01 or an '02, check under the hood for the sticker that specifies your timing.

kandacarlson:

ok, I did the check on my 2000 and found it to be 5 degrees advanced. I want to change that, but how the heck did you get to the distributer nut to loosen it? What did you use? I got a ratchet that flexes at two points, but still can't get to the sucker.

anyone has it for 2001 X??

Craftsman and others make a "distributor" wrench. It is an oddly bent box end wrench available at most stores.

Try it from the side with no extensions. Or a real long phillips screwdriver

My timing was off from the factory as well. It is adjusted 4 degrees advanced @14 for a 2001. It seems to perform better with the advance. Much more than the 4 degrees and it will knock under load.

Charlie

I tried this adjustment as well for my 2001. But when I bumped the timing to 14 BTDC (my original setting was right on @ 10 BTDC), the engine ran a little on the rough side, and my transmission would down shift late. I also noticed that when starting it up first thing on a cold morning, again the transmission was late, this time up shifting to 4th. The next day I bumped it down to 12 BTDC, and it seems to run much better, and with a little extra response when you hit the gas to boot!

[ 02-10-2002: Message edited by: Sean ]

The trans won't shift into OD when it's cold. If I drove a lot at sea level I would probably adjust the base down, but I'm usually at or above the 5k foot level most of the time. The truck just seems to run better set a bit higher. I've been getting about 17 mpg with the settings this way. Not sure about the altitude making a difference, but whenever I make a trip to So Cali it's like driving a hot-rod!. Low altitude, the ultimate power mod

Charlie