Stock Engine Detonation, New to SVTs

[5.Ohhno]

I'm almost positive now that my high RPM troubles are detonation. I had a 95 5.0 with a Vortech S-trim 10 psi, so i know the sounds of detonation.

Here is my problem. On a WOT Run, my stock 98 Cobra recently started to hesitate and "buck" lose major power from 5kRPM and up. The engine would be smooth up to that point (5Kish), then I feel the car lose all acceleration instantly, the exhaust note changes dramaticaly, and the car continues to Rev, but with no power, and this happens intermitant. At first I couldnt hear anything and thought it was those extra air butterfly valves getting stuck or somthing, but ive noticed the tell tale paint can rattle of detonation. Im new to the DOHC engines and dont know anything about them (I'm an old school push-rod guy) Since i know nothing, i was going to take it to the dealer and let them figure it out, but any help would be great before i go through that hassel.

I have replaced the fuel filter and ran an injector cleaner. No luck. Thanks. Also the car has an intermitant miss at idle, and seems to be a few mpg less. I've been through a few tanks of gas too all 91, no luck.

Thanks!

 

[Jpjr]

i know nothing about the 98's but on late model cars the computer will cut power at a prescribed rpm if an engine sensor senses overheating or other potentially damaging probs. on the 03 cobra i believe its at 3k in any gear. if you can't run the codes yourself then you would have to take it in, not sure why your check engine would not come on though if that were it?

it looks like your already running premium so the detonation wouldn't have anything to do with cheap gas. if you don't have the tools i would definitely take it in and at least check the a/f and compression.. but understandibly the dealer rips you off for this and i could understand being hesitant to do it.

i'm sure some of the other guys here can help you more..

 

[99SVTAddict]

I'm going to sound like a nobbie here, but isn't that the IMRC's? They start to gum up and won't open at the RPM like the should. I'd put money on it saying it's something to do with that.

 

[5.Ohhno]

I originaly thought that it was the IMRC's, but how random my problem is, combined with the signs of detonation, I highly doubt it. Also the rough idle leads me to believe its my plugs or wires. I checked under my hood at night with a "black out test", and found a few blue jumps or "electric Fuzz" between a few wires but thats normal. That is the next thing im going to replace though to be sure.

 

[bigpapa]

I would just head to a good dyno tunner. I had problems with knock that wasn't there and the ecu was pulling timming at hig rpm's. 1 dyno tune later and the car pulls hard all the way to redline. SCT says this is a common problem and they advise to just turn the knock sensors off.

Not sure if this is your problem but the dyno will find it.

 

[5.Ohhno]

How do i find a "good" dyno tuner?

 

[az_r2d1]

I'm almost positive now that my high RPM troubles are detonation. I had a 95 5.0 with a Vortech S-trim 10 psi, so i know the sounds of detonation.

Here is my problem. On a WOT Run, my stock 98 Cobra recently started to hesitate and "buck" lose major power from 5kRPM and up. The engine would be smooth up to that point (5Kish), then I feel the car lose all acceleration instantly, the exhaust note changes dramaticaly, and the car continues to Rev, but with no power, and this happens intermitant. At first I couldnt hear anything and thought it was those extra air butterfly valves getting stuck or somthing, but ive noticed the tell tale paint can rattle of detonation. Im new to the DOHC engines and dont know anything about them (I'm an old school push-rod guy) Since i know nothing, i was going to take it to the dealer and let them figure it out, but any help would be great before i go through that hassel.

I have replaced the fuel filter and ran an injector cleaner. No luck. Thanks. Also the car has an intermitant miss at idle, and seems to be a few mpg less. I've been through a few tanks of gas too all 91, no luck.

Thanks!

First I would have the codes read. There might be something there. Second, have the fuel pressure checked. There's so many thing that can go wrong.

 

[98svtconvert]

sorry to hear about your problem, but i am kind of happy at the same time. i am having the exact same problem and i have been banging my head against the wall trying to figure it out. i have put the car on the dyno and it didn't do it. i have changed the coil packs, O2 sensors, fuel filter, and checked all of my plugs. nothing. the only thing that i did find was that the gasket around the spark plugs, where the valve cover sits, is starting to push through. the ends of the plugs were dry, but there was a very small amount of oil around the threads. i have no idea what it is. i was going to check the imrc's but like you i went from an old 5.0 to this so i am not to familiar with them. the only time mine does it is when the engine is hot. if the engine is cool and i run it through the rpm's at wot then it won't do it. if the engine is up to temp then it will do it every time under load. i have had the ecu checked for codes and nothing came up. i am out of idea's. if you do figure it out please, please, please p.m. me or e-mail me and let me know what it was. thankyou.