Detonation problems: Help?

[95GTS]

For some reason I'm getting detonation in my 95 5.0. I've had the car maybe a month. It's only got a little over 78,000 miles on it. When I bought it it was bone stock except for FMS 9mm wires. It was detonating then so I since have done a tune up and added a few things: New K&N cone filter, new spark plugs Motorcraft 42C gapped at .054, new cap (brass terminals) and rotor, and new Magnaflow mufflers. Still getting detonation so we checked the timing and it's at the stock 10* (and yes that's with the spout connector pulled out). Also, this is all on 89 octane fuel and I've run 2 different types of fuel system cleaner thru it. So now what? What could be causing my detonation? The only thing we can think of right now is maybe the stock cats are, for some strange reason, getting a little backed up and causing too much back pressure which, in turn, is causing the detonation. I wouldn't think the cats would be going bad already (stock H-pipe). I plan on getting an off-road X-pipe anyways but I would like to figure out what the heck is going on with the detonation first. Any ideas?

[Dark_5.0]

Very odd, I would check the fuel filter and the regulator. Maybe its not getting enough fuel and going lean

[go4it]

Try some 92-93 octane gas

[shacar87]

Had this problem on my 87 Mustang GT. I just put an adjustable Fuel Pressure Regulator on it, bumped up the pressure a few pounds, and problem solved. I would definitly check the filter and code scan it for a weak or failing fuel pump first. This stuff was ok on mine.

[stang_racer20]

try testing or replacing the TFI. if that doesnt solve it, its gotta be gas related.

[pedley]

sorry this will not help but i was just woundering what an adj. fuel pressure regulator is worth?? i would like to invest in one but where i am in canada they cost about 200/250$ so i was thinking of getting one from the states
and agian i am sorry to jump in on u r threads
thanks

[95GTS]

Go to www.summitracing.com/ and www.jegs.com/ to get some ideas of american dollars on the prices of adjustable fuel pressure regulators. On average they run around $100-110 american. Aeromotive is a good one to go with.

I've been trying to figure out why I"m getting detonation so I don't have to run the 91 octane fuel. I hate having to pay the highest gas prices. That adds up after a while. What do ya'll think about just going to a step colder spark plug? Maybe Ford just has the incorrect plug recommended for the 94-95. If not I guess I'll just run the 91 octane and see how much higher I can take the timing from it's present 10* without getting detonation. I'll get the adj FPR later.

So, what do ya'll think about a step colder plug? I've talked to another guy that did it and it worked for him.

[shacar87]

It's worth a shot, and most people don't know this, but believe it or not, a colder spark will gain you a little bottom end (low RPM) torque. I would try to fix the problem to the point of being able to bump your timing up to 14 degrees for more power.

[SilverSN95]

I've been watching this thread since I have the same issue. My 94gt has detonation as well under WOT starting at about 3500rpm. I found that the timing was advanced to 14 degrees so I turned it back to 10. I still get the detonation but it is not as bad. I've wondered about the plugs as well. I have also noticed some damage to some of the plug wires from the previous owner. It looks like some insulation was shaved-off for whatever reason I do not know. The engine seems to always run on the cool side. I'm wondering if the previous owner put in a 180 degree thermostat.
Is it possible the bad wires and/or colder thermostat cause the detonation??? I'm going to do a full tune-up this winter while I have it stored and I don't want to start the new fun season with this annoying detonation.

Also, I'm a bit of a rookie, can someone explain this colder spark plug thing to me as well

Thanks much

[95GTS]

SilverSN95, you have a PM.

Well I put some 91 octane in the stang and it seems to have stopped the pinging for now. We'll see how long that lasts, lol.

[shacar87]

silverSN95,
I read a tech article on this in my Muscle Mustang and Fast Fords magazine. They took stock heat range plugs, and ground the prong that arches over the center electrode so the end of it was round (like a horseshoe), not square, and the end of it should extend to right in the middle of the center electrode, not over to the far side like stock.

When comparing dyno charts of before and after, with no other changes to the engine, the cut plugs netted a 20 ft/lb increase in torque just off idle! Now that 20ft/lb gradually dropped as the RPMs went up, but with NO loss of torque anywhere in the powerband when compared with the stock plug numbers. All it did was slowly dropped until about 5500 RPM, where it just matched (but never fell below) the stock plugs numbers till they stopped at 6500 RPM. And horsepower was up about 1-3 horses the whole way from start to finish!

They said about it having to do with low RPM swirl in the combustion chambers ( I don't remember exactly how they put it), that changes as the RPMs rise, and that's why the numbers drop also. They said the main factor in all this is that the cut makes the plug fire cooler, which reacts better with the low swirl.

Well, I was curious about all this, so I snooped around at the local drag strip. I found out that alot of racers do this to their plugs for that little extra! And that was everything form stockers to 10sec. rides. So I went home and tried this, next time I raced, I honestly could feel my car launching a bit harder, and it was backed up by a slight drop in my 60ft. times. Now I do this to all my rides, even my VERY lightly modified 91 Escort GT (which by the way hasn't been beat by ANY 4-banger without a turbo or nitrous yet)! If you look at the majority of the newest performance plugs on the market, they usually have a rounded or narrowed prong (the Rapidfires), or smaller electrode. Now it may be diiferent for certain setups, like 7-9000RPM motors, that i'm not sure of, but for the majority of street/strip cars, it works. Try it and see for yourself. If you have any more questions about it, just post, and I will try to answer them the best I can. Good luck!

[shacar87]

silverSN95,
Sorry, I forgot about your other questions! The wires are a possibility. Usually it's a fuel or timing problem, but your ignition system does have alot to do with it. As for the thermostat, that shouldn't be the problem. You actually will predetonate or spark-knock (ping) quicker on a warmer engine than a cooler one. Heat alone can cause the problem. That's why aluminum head motors are harder to make spark-knock, because the aluminum disperses the heat better, therefore helping it.

A good definition of spark-knock: the pinging or rattling noise sometimes heard during acceleration that indicates detonation is occurring inside the engine. Spark knock can be caused by a variety of things including using low octane fuel, over-advanced ignition timing, too much compression (often due to a buildup of carbon in the combustion chamber), by an inoperative EGR valve, and/or by too much heat. If switching to a higher octane fuel doesn't cure the problem, the cause should be investigated because prolonged or heavy knocking can damage the engine.

This might also give you a couple of ideas of what to look at. Hope this helps you out!

[SilverSN95]

I'll give the spark plug mod a try when I do my tune-up and see what happens. It looks like I should also try running the codes but I have no idea how to do that. Is there a link to this process or can someone give me a description I should be looking for fuel pump or EGR codes from what I see.

[NoSlow5.0]

If you are still having problems have your MAF sensor cleaned. This was the culpret on my 97 cougar. The Wires were gunked up and were not reading all of the air entering the motor so it was running a little too lean, this coupled with 89 octaine caused detonation. It might be worth a ty. JOn

Light Em Up!!!

[SilverSN95]

Is it safe to use carb cleaner on the MAF ??