I have a '97 GT with 182K on it. It has been the best car I ever owned with little to no mechanical trouble (other than typical intake replacement). I have run 87 octane since day one and it use to not have detonation troubles. Now I have noticed detonation from moderate to heavy load which as increased probably in the last 40K miles or so. If there has been no work done, and timing has never been changed, what has physically moved? Is it possible that the timing chains have stretched enough to let the crank position sensor show more advance before the camshaft sensor gets its pickup signal? I know this would be small, but what else would have changed. Power feels like it is there, but cannot use it because detonation rolls in.
1997 GT Detonation
- Thread starter ryanhemi
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I've got a 97GT with 154k miles. From about 60k miles, it started developing some detonation just as you described and I delt with it for a very long time. It was worse, depending on the weather but sounded SCARY if you layed into 3rd gear getting on the highway. 
One thing that helped mine a lot was cleaning the MAF. Simply use some spray electronics cleaner (such as from Radio shack) and spray it directly through the MAF. This will clean any oil or other debris, that could be causing a false reading and fix a resulting lean condition. This helped a whole lot, but didn't completely fix my car....
Last summer, I ran a bunch of E20 and E30 because it was cheaper than regular 87 gas, got pretty much the same mileage and was a fun experiment. Of course, the higher octane fixed the pinging problem, but when I started running 87 octane again, the ping never came back. I am guessing the extra ethanol did a nice job of cleaning the injectors and any carbon build up I had. Since then, I haven't heard any detonation at all! You may not have ethanol available, but you could probably accomplish the same result with those fuel system cleaners in a bottle.
So in short: Clean the MAF and run some injector cleaner and it should clear right up.
One thing that helped mine a lot was cleaning the MAF. Simply use some spray electronics cleaner (such as from Radio shack) and spray it directly through the MAF. This will clean any oil or other debris, that could be causing a false reading and fix a resulting lean condition. This helped a whole lot, but didn't completely fix my car....
Last summer, I ran a bunch of E20 and E30 because it was cheaper than regular 87 gas, got pretty much the same mileage and was a fun experiment. Of course, the higher octane fixed the pinging problem, but when I started running 87 octane again, the ping never came back. I am guessing the extra ethanol did a nice job of cleaning the injectors and any carbon build up I had. Since then, I haven't heard any detonation at all! You may not have ethanol available, but you could probably accomplish the same result with those fuel system cleaners in a bottle.
So in short: Clean the MAF and run some injector cleaner and it should clear right up.
forum155pl
New Member
It is true that a malfunctioning EGR system can cause detonation, but not in this case. If the EGR system were malfunctioning, the detonation would be present at light to moderate loads as opposed to heavy loads as the OP described above.
Introducing these exhaust gasses gives the air charge more detonation resistance and allows for more aggressive timing. The EGR only allows circulation at light to moderate loads, and this allows for more timing, improves mileage and reduces NOx emissions. So when the system malfunctions, you may get worse mileage, and detonation in the light to moderate loads where the EGR would otherwise be functioning.
Introducing these exhaust gasses gives the air charge more detonation resistance and allows for more aggressive timing. The EGR only allows circulation at light to moderate loads, and this allows for more timing, improves mileage and reduces NOx emissions. So when the system malfunctions, you may get worse mileage, and detonation in the light to moderate loads where the EGR would otherwise be functioning.
All right, bought some of the Seafoam product, one for the tank and one to work in "vacu...venously" and it already has some improvement. Carbon accumulation and clogged injectors are starting to look like the cause here. I will continue this "diet" and look forward to more improvements. Thanks for the recommendations. This Seafoam product seems like good stuff...any drawbacks? Wonder if it deactivates your Catalysts if you use too much?
40th GT
New Member
I remember reading the bottle and seeing 'safe for o2 sensors/catalytic converters'. Look out for that.
+2 on the MAF cleaning.
Flghtmstr1
Member
It can foul your plugs, so I would recommend replacing them after you're done with the Seafoam treatment.