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Ok so for the past while I have noticed that I have to run higher and higher octane gas to keep her from pinging. I just don’t get it; I now have to run 92 octane. It’s getting to be summer and I’m concerned to run nitrous through her this year.

If you have any idea why I’d love your suggestions.

P.S. Other than that, she runs great; I put new Zex plugs in and a new fuel filter. Cap rotor and wires where replaced last year.

You may already know this but stated for the record just in case. Detonation of unburned exhaust gases and/or pre-ignition of the fuel mixture are two conditions that are associated with types of pinging/knocking. They can occur because of too-high cylinder temps, too-low octane, incorrectly advanced ignition timing setting (pre-ignition), or some combo of these. Higher octane fuel helps to both prevent pre-ignition of the fuel mixture as it comes under compression in the cylinder, and resist unwanted detonation of unburned exhaust gases. Lower octane fuel will more easily ignite under heat and compression. When this happens, 2 conditions can occur.

• 1. The engine "knocks" because too-early combustion (pre-ignition) is acting too soon against the internal engine parts, out of proper sequence/position with the piston stroke.
  
  2. The engine "pings" because too-high cyl temps can cause unburned exhaust gases to detonate.

A few things to check, which can contribute to pre-ignition or detonation of the fuel mixture...

• 1. Check timing and adjust if it's advanced too much.
  
  2. Check the condition and connections of EGR vacuum hoses.
  
  3. Check the EGR valve for proper operation. The EGR valve functions to help moderate cyl. temps by recirculating relatively cooler exhaust gases into the engine.
  
  4. Engine deposits. How many miles on the engine? Pre-ignition and/or unwanted detonation can be caused by build-up of internal deposits that absorb heat and contribute to an unwanted increase in cyl. temps, a potential prob on higher mileage engines. BG44K Fuel Additive is a reputable product for adding to a tank of gas once a year or so to help remove such build up in the fuel delivery system and cylinders. I've been very satisfied with it.

Since you describe the problem as "pinging" and progressively needing higher octane fuel over time, I'd tend to lean a bit toward a build up of heat-absorbing engine deposits that need to be reduced/removed, but all of the above would be worth checking. Dunno if any of this helps ya but it's food for thought. Post back w/any questions or when you determine the fix...

SPeaking of which, are the block/head in the MX3 aluminium or iron?

Iron block, aluminum head, if my memory doesnt fail me. Cant go out and look, I sold the car to my nephew, who continues to wreck it and wreck it and wreck it.....

I agree with neutral that you probably have a buildup of deposits in the cylinder, effectively pushing compression up, requiring the higher octane. Problem is, youre going to have to find out what is causing the buildup, then fix that problem, then remove the buildup itself. Too much fuel will cause carbon buildup, which could be caused by a bad O2 sensor, bad airflow sensor, leaky injector, etc. You are going to have to do some investigating to find the culprit.

Make sure your plugs arent too 'hot' of a rating either. What is your timing set at? I couldnt go past 14-16 btdc without getting pinging in my sohc 1.6. It got much worse in warm weather.

So the EGR system checks out (according to the shop manual).
So what could cause the build up that you speak of, and what is that product you mentioned and how does it work? Do i need to be concerned with it cloging my egr system if i have too much build up when it losens and tries to exit the engine? Also, has anybody ever gone to a shop and used their engine cleaning procedures?

Thanx very much for the replies so far!

sounds sorta like a timing problem, check your ignition timing and if that isnt it try adding a SAFC, just adjust your air fuel till it stops pinging

Thanks jschrauwen for the comment. Most of us are pretty cautious when it comes to using any additive to anything, but for the right situation and with some homework and a reputable product, it's sometimes necessary & beneficial. Internal combustion is kind of a fascinating subject too when considering that we run our cars by creating billions of controlled explosions and still have fairly trouble free engines for many years. Sorry for the long post. Blame the Guiness.

by BEERDDWR: So what could cause the build up that you speak of

Especially on higher mileage engines, it's normal for some accumulation of varnish and carbon deposits from fuel & fuel mixture delivery as well as from the combustion process. Not surprising when considering:

*Each ignition of the cyl fuel mixt. is an explosion generating enormous heat and pressure.

*Gasoline burns pretty completely but not 100% clean.

*We put ~twelve TONS of fuel thru the motor every 100K miles. E.g. 100,000 miles @25mpg = 4000 U.S. Gal. X 5.85Lbs (per Gal) = 23,400 Lbs. of gas being pumped through the engine. That's a hella lotta gas. Looking at it as Lbs, it's easier to see how some super tiny portion of that gas could end up as normal byproducts accumulating in the engine over time.

*We don't just run 12 tons of fuel thru the motor, we internally explode the stuff more than one-third of a billion times per cylinder per 100K miles. That pressure & heat of all those explosions naturally creates byproducts. Each cyl ignites 360,000,000 (three-hundred-sixty-million) times over the course of 100K miles. For simplicity sake on the #s, figure that based on 100,000 miles/50mph = 2000hrs, and @3000rpm each cyl fires 180,000 times/hr... X 2000hrs = 360,000,000 explosions in each cylinder per 100K miles.

Ok, this was just a goofy exercise but done to make the point that internal accumulation of deposits aren't really unexpected when considering what our engine actually deals with from years of driving.

what is that product you mentioned and how does it work?

BG 44K. Comes in a small can, added to 1 tank of gas each year/12-15K miles, is alcohol-free & gently dissolves deposits without harming the engine internals. It's expensive @$20 USD and reportedly not available unless you are a certified repair shop. I've a shop near me that's also a parts store. Have never seen this stuff anywhere else. My longtime mech friend there puts a can in the gas tank when they do a shop tuneup & he uses it in his own vehicles annually. They also put out 30-50 cans of BG 44K every two weeks for retail sale & the stuff is always gone in days. lol, I buy 3 cans each yr myself. Now I'm NOT saying this to start an argument (please) but personally, as the stuff worked the first time (100K+ miles on the motor) I noticed lasting improvement in throttle response during the second half of my tank of gas. I've heard that a bottle of Chevron Techron additive is very good stuff if my annual fix of BG 44K wasn't available.

Do i need to be concerned with it cloging my egr system if i have too much build up when it losens and tries to exit the engine?

Nope. It doesn't loosen the deposits to travel as chunks thru your motor. It very slowly surface-dissolves them a tiny layer at a time to exit as part of the exhaust gases.

Also, has anybody ever gone to a shop and used their engine cleaning procedures?

I haven't but that may refer to the "Seafoam" procedure. Do a seafoam search on the BB and you'll find many posts on it. Also, can't find it now but thought I remembered a description of the procedure being in my 95 shop manual which means it would be in the online manual too...

i would really try seafoam. it also removed the deposits that could cause pinging due to escessive carbon on the pistons and combustion chamber. i have recently used seafoam in my bp mx-3 and left it in there for 24 hrs and i have to say that it works very well. noticable improvement and no more pinging.

-john

pardon my ignorance, what is this seafoam you are speaking of?