Detonation Weirdness

hytorksc

Registered User
Hello everyone,

i've been down this road many times with the SC's i've owned, and it seems that detonation is a common problem that has plagued the 3.8. My problem, to make a very long story short, is that i have this mysterious detonation problem that comes and goes. it's not all the time (very intermittent), and it seems to show it's nasty presence when powering up a fairly good upgrade right around 50 mph in 3rd gear, 3000 rpm. When i get on it from that speed, it's detonating like crazy until i'm doing 70 or 80 mph and just dissappears. and it happens only when it's 50 degrees outside or colder. it's as if load is really messed up when the computer reads the maf calculation for that speed. i admit to using a C&L meter with 30# calibration, but i put the stock maf back on, and guess what?? it does the same thing. i had this exact same problem with the last SC i had, and it's driving me nuts trying to get rid of the problem.

it's almost like every SC i have ever owned had this problem, and aside from disconnecting the timing plug, the problem persisted no matter what i did.

What may be happening is that i had installed a 70mm TB, and a 5% od pulley with the C&L, which will throw off all load calculations, and the only way to combat it is to use an EEC tuner. Maybe i just answered my own question-

Aside from the obvious things, any of you had experiences in getting rid of this problem?
 
WOW

I've owned 3 SC's and with the exception of my heavily modified car detonating when it's really cold outside I've never had any detonation. Nor have I ever even heard of a stock (ish) SC having detonation issues.

What octain fuel are you running in the car?
 
93 octane, always. i did notice that when i first bought this 5spd it did not have detonation issues. when i put the big TB, C&L maf, and 5% pulley on, and removed air silencer, without doing anything else to it she detonates off and on (not all the time- only when powering up fairly steep hills on a cold day). Very weird. it's almost as if the knock sensor is playing a little game with the EEC.
 
hytorksc said:
Hello everyone,

i've been down this road many times with the SC's i've owned, and it seems that detonation is a common problem that has plagued the 3.8. My problem, to make a very long story short, is that i have this mysterious detonation problem that comes and goes. it's not all the time (very intermittent), and it seems to show it's nasty presence when powering up a fairly good upgrade right around 50 mph in 3rd gear, 3000 rpm. When i get on it from that speed, it's detonating like crazy until i'm doing 70 or 80 mph and just dissappears. and it happens only when it's 50 degrees outside or colder. it's as if load is really messed up when the computer reads the maf calculation for that speed. i admit to using a C&L meter with 30# calibration, but i put the stock maf back on, and guess what?? it does the same thing. i had this exact same problem with the last SC i had, and it's driving me nuts trying to get rid of the problem.

it's almost like every SC i have ever owned had this problem, and aside from disconnecting the timing plug, the problem persisted no matter what i did.

What may be happening is that i had installed a 70mm TB, and a 5% od pulley with the C&L, which will throw off all load calculations, and the only way to combat it is to use an EEC tuner. Maybe i just answered my own question-

Aside from the obvious things, any of you had experiences in getting rid of this problem?


You just described my problem. If I let the trans shift into third early and I push the engine hard without downshifting. I will randomly get detonation/ping. I mean I can get it to happen at one intersection. But not at the next. My car is bone stock except for pulley and mufflers. I always put in 91 octane and try never to get ethanol. If I do get ethanol, this problem gets worse.

It also seems to happen more when it is cold outside and the engine isn't at full temp.

But yet when I ran it 8 times at the dragstrip where it was a cold and windy 47 degrees last month, it didn't happen once. Each time the engine was cold.
 
Detonation under partial load is usually caused by a malfunctioning EGR system or the presense of oil in the intake system. However it can also be caused by a buildup of carbon in the cylinders from running rich over time. The C&L meter does not throw off load calculations unless you have also changed injector sizes.

A faulty BAP sensor could also cause excessive ignition timing if it is reading off, but I don't know how to easily check the sensor output.

Nonetheless, I don't believe that detonation is an issue on SC's under partial load unless something is wrong in the first place. Another possible issue might be a totally inneffective IC due to varnish buildup or crap in the fins.
 
Would just changing or evacuating the oil in the IC help? also, is there something fairly inexpensive i can do to remove the carbon buildup in the cylinders (i know it's dirty in there)?

i don't have egr to worry about, but i am now very curious about that BAP sensor. that thing is probably one of the most ignored sensors on the car.
 
hytorksc said:
Would just changing or evacuating the oil in the IC help? also, is there something fairly inexpensive i can do to remove the carbon buildup in the cylinders (i know it's dirty in there)?

i don't have egr to worry about, but i am now very curious about that BAP sensor. that thing is probably one of the most ignored sensors on the car.

If you have a 5spd, you have EGR to worry about.
 
XR7 Dave said:
Detonation under partial load is usually caused by a malfunctioning EGR system or the presense of oil in the intake system. However it can also be caused by a buildup of carbon in the cylinders from running rich over time. The C&L meter does not throw off load calculations unless you have also changed injector sizes.

A faulty BAP sensor could also cause excessive ignition timing if it is reading off, but I don't know how to easily check the sensor output.

Nonetheless, I don't believe that detonation is an issue on SC's under partial load unless something is wrong in the first place. Another possible issue might be a totally inneffective IC due to varnish buildup or crap in the fins.

hytorksc,

If you want me to start my own thread, just say so.

I don't have an egr system. When you say intake system, are you talking IC, ic tubes, and intake manifold? I When I took off my IC, it looked brand new inside and there was only about 2 teaspoons in the IC tube. If it was an ineffective IC, wouldn't it happen more when it was warmer out.

I do believe I have carbon buildup. I read one of your old posts where you had a knock only when the car was cold and you attributed it to carbon on the pistons. When you had the heads off you cleaned up the carbon and noise went away. Well in my case I have knock for the first 10 minutes or so, and then it is gone, not to return until the engine is completely cold. No, I haven't put on a different oil pressure gauge to check oil pressure.

What if I used a autozone PVC valve? I was already on the car when I read you should use only ford.

BAP Sensor (Barometric Absolute Pressure) That measures altitude right?
 
90blkbrd said:
hytorksc,

If you want me to start my own thread, just say so.

I don't have an egr system. When you say intake system, are you talking IC, ic tubes, and intake manifold? I When I took off my IC, it looked brand new inside and there was only about 2 teaspoons in the IC tube. If it was an ineffective IC, wouldn't it happen more when it was warmer out.

I do believe I have carbon buildup. I read one of your old posts where you had a knock only when the car was cold and you attributed it to carbon on the pistons. When you had the heads off you cleaned up the carbon and noise went away. Well in my case I have knock for the first 10 minutes or so, and then it is gone, not to return until the engine is completely cold. No, I haven't put on a different oil pressure gauge to check oil pressure.

What if I used a autozone PVC valve? I was already on the car when I read you should use only ford.

BAP Sensor (Barometric Absolute Pressure) That measures altitude right?

I only mentioned the IC as a "possibility" not a probability. On a long hill if the IC is not getting air/cooling it could become badly heatsoaked.

In your case carbon is a likely source. Water injection is the best way to remove carbon deposits.
 
On 5spd cars the EEC adds part throttle timing in anticipation of a diluted mixture. If you have removed the EGR without a chip, then you will have excessive part throttle spark advance.

One thing you can do to help fight detonation is run cooler spark plugs and reduce engine temperatures.
 
XR7 Dave said:
I only mentioned the IC as a "possibility" not a probability. On a long hill if the IC is not getting air/cooling it could become badly heatsoaked.

In your case carbon is a likely source. Water injection is the best way to remove carbon deposits.

Sorry, I didn't think about heatsoaking of the IC.


I got the opportunity to get on it tonight. I was at near full throttle without downshifting. (pretending I was on a dyno :) )

60 degrees and not a lick of ping, sounded perfect with just the right SC wine. Just Monday night it was pinging all the time.
 
XR7Dave,

i thought '92 SC's didn't have EGR. I previously owned a '92 AOD which didn't have EGR so i thought the '92 5spd didn't either. Where is the EGR located?

Can you or someone explain in detail what EGR does relative to detonation (how it works with the EEC) or what it should do, and what type of problems occur/how to fix problems with it?
 
Mannysc-

mine used to ping but i backed off the cam sensor and now it dont ping and i can rev higher

Did you modify your cam sensor to make it adjustable? can you please tell me how you changed fuel injector timing to stop the detonation?
 
hytorksc said:
XR7Dave,

i thought '92 SC's didn't have EGR. I previously owned a '92 AOD which didn't have EGR so i thought the '92 5spd didn't either. Where is the EGR located?

Can you or someone explain in detail what EGR does relative to detonation (how it works with the EEC) or what it should do, and what type of problems occur/how to fix problems with it?

The egr adds exhaust to the intake during light loads to reduce the combustion temperatures. With reduced volatility of the mixture, more timing can be added under those conditions. If the EGR is not functioning, the added timing can cause pinging.

All 5spd SC's have EGR. It is located at the back of the inlet plenum behind the passenger valve cover.
 
thanks XR7Dave- i know i am pretty much like another blade of grass in this forum, not quite a beginner, but still learning. i hope that someday i will have the time and money to have real fun like you guys do tuning and running the big horsepower SC's. i really do appreciate your valuable input as well as the other's here. :)
 
XR7 Dave said:
The egr adds exhaust to the intake during light loads to reduce the combustion temperatures. With reduced volatility of the mixture, more timing can be added under those conditions. If the EGR is not functioning, the added timing can cause pinging.

All 5spd SC's have EGR. It is located at the back of the inlet plenum behind the passenger valve cover.
92 5 spds do not have egr at all
 
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