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Discussion Starter #1
Quick question - can a mostly clogged EGR pathway cause detonation? I've never had any EGR codes. I ask because I found the passageway into the plenum after the EGR valve to be 80% clogged with crap today as I was cleaning parts. I was getting bad detonation in 3rd gear before I cleaned my MAF, then it went away until summer came around; now I get a bit of it occasionally - but very faint - when the engine is hot under the same circumstances. MAF is clean.

On a side note, would clearing that EGR port out help my economy in any way? :D
 

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Are you 100% certain it is detonation? Pull the octane plug and drive it around. Sometimes being certain of something that may not be correct will make you chase a problem in the wrong direction. If the slightly retarded timing helps atleast you know for sure your car is in fact detonating.

It might help you eek out a bit more MPGs.
 

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Discussion Starter #4
I'm pretty sure it's detonation... It's the same sound I was getting before I cleaned my MAF sensor last year. It only happens with my foot on the pedal in 3rd gear to the point where it's on the brink of dropping back into 2nd. The EGR question stems from the fact that the service manual said it was supposed to bring combustion temps down a bit. Are you sure my 97 has an octane plug? I thought they did away with all that in 96... As far as coolant, I flushed it not too long ago but I do know the car was neglected by its first owner(s).
 

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I am not positive, I apologize if I gave you crap info.
 

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Discussion Starter #6
No, it's not a problem... I appreciate your desire to lend a helping hand.
 

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You may find that it helps economy a tiny bit. If you aren't getting any EGR codes, then it is still flowing at least as much as it is commanded (within some threshold), so the results won't be night and day. But unless your DPFE sensor isn't measuring EGR flow accurately, then it's unlikely to help your detonation issue.
 

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Okay, so if I understand all this correctly, it's not likely that having cleaned out that passageway will cure my leftover detonation, but it's possible. Hopefully it does though - I don't know what else could be causing it. I'm putting in a 180 t-stat too which I hope will help.
 

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In old tech engines, lack of EGR would cause denotation (the recirc lowers combustion temperatures) but if that was the case here, it should be throwing codes. I'd check the DPFE.

Bob
 

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When I bought my 95 T-Bird used it ran bad and the windows didn't work. Fixed the windows and replaced the MAF. Ran great but still had egr codes. Replaced the DPFE (old style it was bad) cleaned egr ports in intake (they were clogged). After that had new egr codes. I didn't finish fixing the egr sys untill the trans started leaking. Egr valve was siezed and the feed tube was clogged.
I told that story to say that for the year I drove it (about 500-600 miles a weak) I never had detonation or low power. And that was with the the entire egr sys shafted.
I just had a LS in the shop with your problem. The air filter was installed wrong and a bee got into the MAF. Cleaned the sensor installed a new filter. Car runs like new.
This might not be your problem but hope this helps.
 

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Discussion Starter #12
I'm having Lonnie write me a 93 tune in addition to my stepping down to a 180 degree thermostat - which I'm hoping kicks this detonation issue in the can for good. Like I said, it's nowhere near as bad as it was when the MAF was dirty and it only happens once or twice a week, but when it shows up it's just enough to drive me nuts.
 

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My GF's 96 Cougar 4.6 has horrible detonation in the summer under light throttle, low RPM. I had her put BP 93 in it, and I still had to pull the octane plug to eliminate 90% of it!

With 89 octane, it rattled really bad after shifting into 2nd and 3rd at low RPM. It can usually get by on 87 octane in the winter.

The MAF and EGR ports are clean, and no codes. Temps are normal. Regular copper Autolites. Can I swap my new 1995 MAF on there, or will it throw a code immediately?

Thanks,
Al
 

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Discussion Starter #14
How are the plugs and wires?
 

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My GF's 96 Cougar 4.6 has horrible detonation in the summer under light throttle, low RPM. I had her put BP 93 in it, and I still had to pull the octane plug to eliminate 90% of it!

With 89 octane, it rattled really bad after shifting into 2nd and 3rd at low RPM. It can usually get by on 87 octane in the winter.

The MAF and EGR ports are clean, and no codes. Temps are normal. Regular copper Autolites. Can I swap my new 1995 MAF on there, or will it throw a code immediately?

Thanks,
Al
You can't use a 94/95 MAF on a 96/97. I agree to check the ignition system for problems.
 

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Plugs are 6 mo old, and Motorcraft wires and coil packs are a few years old.

A bad plug wire or coil pack would make the car cut out, which it doesnt do. Used to though, and so did mine!

This appears to be related to the air/fuel mixture in some way, and/or air temp. Happens every summer.

Al
 

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Discussion Starter #17 (Edited)
I'm going to go out on a limb and suggest the things I'd suspect or try next - IAT sensor, injectors or fuel filter possibly clogged? Try a can of Sea Foam? Running lean would easily cause detonation, of which all the previous could be a contributor towards. I'm also thinking a bit about the coolant system - if the engine runs too hot it would be more likely to show signs of detonation. Have you flushed the coolant system recently?
 

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It could be carbon buildup. I'll try a can of Seafoam. When I replaced the intake manifold with a Dorman over the winter, there was some major carbon in the ports on the pass. side, I cleaned down in as far as I could. Also replaced the injector o-rings.

The temp doesnt run hot on the gauge, but it could probably stand fresh coolant.

Dont suppose the IAT from my '95 is compatible with the '96, just to check?

Thanks,
Al
 

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Discussion Starter #19
No, the IAT sensor from a 95 won't work in a 96.
 

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The Seafoam worked! Didnt ping a lick on 93 octane. Now she is back on 89 octane, with the octane plug back in, with just a slight hint of pinging. I plan on running another can thru.

Al
 
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