Detonation under boost!?!

Danzajax

Registered User
My car was running great when i parked it for 2 days. When i started it back up it loped a little and then ran normal. I noticed when i went beyond atmospheric pressure it started to miss and what i eventually decided was pre-ignition. The fuel in the tank was fresh 92 when i parked it. The car went from running good to **** pretty much over night. The odd part though is its only under boost that it has the problems.

Any sugguestions? Its not too hot here (Minneapolis) right now and it definately not much different than 2 days ago. Im currently driving around trying to run the fuel out of it (out of a suspecion that maybe something has happened to the fuel.)

(3 weeks ago i replaced my wireset and plugs, 2 Weeks ago my Ignition mod went, last week my window was smahed out and my radio was stolen, and now this :mad: )

Any help would be appreciated. (As im an intern here with almost no friends out here and very much in trouble if my car is DOA)
:confused:

-=dan=-
 
Check your wires again. You might think it's knocking but it just mayt be a loose plug wire.

Jeff
 
ill try that, i had a shop go over it while it was in for the Ignition module. Woudlnt a loose plug wire show up under all pressures, not just when entering boost?

-=dan=-
 
your problem sounds like a bad plug or wire , but my 89 has colder plugs and colder thermostat and good exhaust and i can run regular gas and it wont ping , my all stock 90 pings on regular gas
 
Danzajax said:
ill try that, i had a shop go over it while it was in for the Ignition module. Woudlnt a loose plug wire show up under all pressures, not just when entering boost?

-=dan=-

Not always, but if it's the slightest bit loose then it takes a lot more energy under boost than NA mode.

Jeff
 
NA mode? I believe the amount of energy coming from the coil was the same no matter the intake pressure. Anyways, I just jack the car up and check the plug wires from underneath. After your done, dont let the car down too fast, thats how I cracked my windshield.
 
2 spark plugs fire at the same time and they don't have the same amount of energy, the one on the compression stroke gets most of the energy nd the other (waste spark) gets the least. Yes the system compensates for load just like most electronic ignition systems. Not because it's smart, but because "It's the laaaaaaw of the west" I and many other people have posted how it works so I am not going to rehash it again.
Just know that it takes more energy to jump the gap when the cylinder pressure is higher than when cyl pressure is low.

Na mode is when the engine is running under the "0" on your boost/vacuum gauge. It's not a switch that makes or anything but the computer has set values that it goes by based on load and RPM and other factors.

Jeff
 
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I put the stock plugs from Motocraft and A motocraft brand wireset in (a damn pain in the *** to find in minnesota). I checked the gap going in (when i put them in about a month ago), but what should i set it at (i went by the parts counter suggestion). All plugs got a light coat of anti-seize and the boots had plug boot grease.

Ps.

My girlfriends trans blew and i pulled it out. Anyone know where i can get a 700r4 (700 = 700lbs of gm crap) rebuilt on the cheep(er)? Most people are quoting 900 or so (and one shop 1200 for a bench rebuild!!!!) So if anyone knows of a good trans shop in the Minneappolis/St. Paul Area please let me know.

-dan
 
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Its become apparent, it wasnt detonation (or if it was it finally did the motor in) at 120k MI my Titanium Frost 92 Supercoupe was consumed by the Headgasket monster. Getting estimates now. Looks like ill be getting a different car. This was my favorite car hands down. It just finally floating belly up in the blue oval pool.

:( :( :(
-=dan=-
 
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