Feul/ Timing Guru's, need help with detonation!


Founding Member
Aug 26, 2002
Waldorf, MD
OK, this is a fairly long one. Last year I went to the dyno. Initially we set timing at 10 for base pull. Then went to 15. Made like 20-25 more hp until 4K RPM's, then detonation. Ended turning the timing down to 11.

Every now and then I would get some light detonation with smoke when really getting on the gas, around 4K RPM's. OK, figured maybe I needed 24# injectors because evedentally I was running lean.

I NEVER use cheap gas and before the injectors the FP was set at 44 lbs. wide open.

Just put in 24# injectors. Turned FP down to 41lbs. wide open, drove to a buddy's place who has a meter to reset the TPS (had the intake, TB, ect. torn apart to polish when I did the injectors) and it seemed fine. No more detonation. Set the TPS at .98, then on the way home, one of the times I got on the gas hard, detonation--right at 4 grand!

What the hell? Anyone got any ideas? Is that a bad setting for the TPS, or is it just coincidence. Is my FP way off with the new injectors? Could the balancer be off, giving me wrong timing indications? I hope not, cause I am hoping to be able to turn the timing back up to get those extra ponies back! Could my MSD 6al be messing up? What should I look for to check? The only thing I can think at this point is my cam is degreed wrong, and I am really hoping that is NOT it!

It does not happen all the time, the car pulls REAL strong (probably good for mid-high 12's based on mods and dyno results), I don't even use good gas at cheap stations either. Only Exxon, Shell, or Sunoco 93 or up octane. The car does not run hot, and is going back to the dyno on Oct 12th. Very good cooling system mods. There is more done than what is in the sig, it won't let me add any more though.

Any help would be appreciated! :nice:
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honestly, i think you're just not getting enough fuel... with my stock ECU, i would ping with 87 octane at 8 degrees BTDC... now considering the car was made to run 87 octane at 10 degrees, that's kinda ridiculous...

if i ran 93 octane i could get away with 15 degrees, but i have less airflow mods than you do... (mac cai, headers, prochamber, flowmasters)

after purchasing an a/f ratio meter, i noticed that at WOT i would go deathly lean with the stock ECU, so when i hooked up my tweecer, i considerably increased my fuel flow at WOT... and right now i run 87 octane at 15 degrees with no problem... :banana:
24s at 41 psi should not be lean with your car. Thats exactly what I run on my car and make 292 rwhp.

Check your plug wires, your distributor cap, your coil and MSD box. Check all wires. Try to unplug the MSD and use the stock ignition for a run. Thats how I found my Crane ignition had gone bad on me.

If all of those are fine try running a spark plug thats 1 range colder than what you are using now.

15* sounds like a lot of timing for cast iron heads. Hope you can get it worked out.
heres a suggestion.

try to start it up, and take it down the road when the engine is still cold. observe for detonation at all rpms.

does it only ping when it gets hot? (the engine, not the air temp)

if so I would change out your ECT (engine coolant temp sensor) its pretty easy and cheap (12-17 bucks) and your car probably needs a new one anyway. MY ECT went bad after doing a water pump change. I guess I left it dry too long and it went to hell. have you changed out your water pump or done any cooling system work lately? The ECT is pretty important. the computer uses it to determine how much spark to remove at WOT. the difference is quite a bit of timing removed when at operating temp. the timing stored in the computer is in the form of a table. the computer looks up what timing to fire the engine at by plotting (kind of like a graph) on the X axis is RPMs and on the Y axis is Load (computed by the MAF sensor) the computer takes the number it looks up (say you are at 4000 rpm and it looks up for full load, the number it finds in the table says 25) it takes that number and then says "what is the engine temp" it reads the engine temp (say you are at full temp) and it looks up another number.. the computer says "ok, this says to remove 6 degrees of timing from that previous number I looked up (25) and that number (19) will be the timing I add on top of the initial timing (which you have now set at 11) anyways if the sensor is reading bad and the computer thinks it is cold, it is entirely possible that the computer will add too much timing, especially if the pinging is associated with a certain RPM and higher.

I would think it was something else if it was like you were pinging no matter what if you just went to wide open throttle. The way you describe the problem though it seems like you can go WOT and it wont ping until you climb to 4000rpms.

like I said. just a suggestion.

change your ACT while you are at it. it costs about the same and the car prolly needs it too.
Hmmmm, all excellent suggestions I had not thought of. Check the ECT, ACT (what is this one, can't remember), and the air/ feul ratio. The air/ feul ratio will be checked and sdjusted on the dyno, but if I can get it done before-hand that would be nice.

Have not had to do any work to the coolant system. Edelbrock water pump, FMS aluminum radiator, police pkg. fan clutch, and 160 thermostat are all fine.

Could the 160 therm. be doing it too with still having the stock computer settings?

When we had the timeing at 15 that was just a starting point. We went down a tick from there until we figured out 14 was ok. I will also take the car out tomorow and see if it pings when cold. Have not noticed.

Thanks guys, will let you know what happens. :nice:
UPDATE< problem solved!!!

Modulistic, you the man!

Replaced the ECT sensor and all the detonation went away! Then went to a buddy's shop and played with his timing light to see if I could squeez any more timing out of it now.

Put it up to 15, serious pinging. Turned it down to 13, minor pinging, then remembered my adjustable FP regulator (duh!) and ended up jacking the FP to 46 wide open (instead of the 41 wide open).

Was able to turn the timing back up to 15 with no problems, and the car feels like I dumped a bunch of steroids into the tank!

Drives much better, no pinging, definately feels like it pulls harder.

Thanks alot for the suggestions! :nice: :hail2: