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Discussion Starter · #1 ·
The last couple of months, my car has felt absolutely flat. I've been running the rotofab 93 Cortex tune with premium gas (from several different and reputable sources). The torque down low AND the power up top seem to be about 15-20% reduced using my ass to measure. I understand that a dyno is the only true measure, but I've had the car for 4 years, and feel like a pretty good judge of my vehicle at this point.

The oil is fresh, I've cleaned the MAF, throttle body, and gave the intake filter a cleaning and recharge. The engine idles well and sounds good, but there is just no snap to it.

I'm about to make my normal commute of about 100 miles (80% highway) and am wondering what parameters I should log/record with my cortex that might be helpful. Are there trims I should record prior to setting out and then do another battery reset?

Edit, for reference, my mileage has been averaging 19.9 with 80% highway @70. It was about 17.5 in the winter on the 87 tune prior to the cleanings and recharge etc.

Any help is, as always, greatly appreciated!
 

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Discussion Starter · #3 ·
Stock exhaust all the way back
 

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Yea my first thought was partially plugged cats. How many miles on the car? Any slightly rotten egg smell to the exhaust? Original plugs and wires also?
 

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Discussion Starter · #5 ·
Exhaust smell seems normal, original plugs and wires on the car...44k. In the winter I was having some chirp from the engine at idle, but that is gone now. I checked the belts at that time and the balance of the idlers and pulleys and they were all true, as much as i could tell by hand anyway.
 

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I can't imagine a plugged cat at 44,000 miles and your plugs should be fine too. Hm.
Scan for knock retard on a WOT run and see what it shows.
 

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Also scan for timing advance as well as commanded air fuel if you're able to, all during a WOT run.
 

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Discussion Starter · #8 ·
I reset the ecm and put the tune on fresh again before my trip. The car showed 27.5 mpg while cruising for 80 miles at 70mph and only dropped to 25.0 overall once I did the last 10-15 miles stop and go. So, I guess she's at least running well as far as fuel is concerned. I know it's a small sample, but it was good to see fwiw.

I should be able to get some logging done later today. Would it be worth checking the plug gaps just in case?
 

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Flash it back to 100% stock, drive around like that for a week and then put your tune back on and see if you feel a difference. I'd be more willing to guess you're just getting so used to the power level and you're feeling bored with it.
 

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^^ he could be right. I don't think you would have a plug gap issue. My car feels slow to me many days now too. I guess I've gotten used to it.
 

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Were are you at? The weather was cold and then went up 20* in like a week here in the south. Makes the cars feel like turds for sure.
 

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Were are you at? The weather was cold and then went up 20* in like a week here in the south. Makes the cars feel like turds for sure.
Truth. +1750' DA today......very noticeable difference in power versus a cooler negative DA day.
 

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Discussion Starter · #13 ·
Were are you at? The weather was cold and then went up 20* in like a week here in the south. Makes the cars feel like turds for sure.
I'm sure it's not a weather issue as it's been going on for more than just a day or two...but fwiw I'm in the DC area mostly. I would say it's been consistently underperforming for at least a month, if not two.

I ran the 87 tune all winter, and have been running the 93 tune ever since. The timing of changing the cortex tune doesn't seem to line up with when I felt things dropping off. I'm going to put the tune back to stock and see if anything is noticeable, and try to establish a baseline and do the logging.

As to the "getting used to it factor"...just as recently as a few months ago, I would romp around and be giggling like a girl while running errands etc. I would drive past my house and double back just for 5 extra minutes in the car - and that was after 3 and a half years of ownership. Anytime I hit the gas pretty hard, I could break the tires loose in 1st or chirp em hard in 2nd and would crack a huuuge smile. Now, it's just not there...it's like I'm trying to convince myself it's a quick car, whereas before it would be surprising me how fast it was. Maybe that makes sense...probably not:dunno:


Thanks again for the input guys, appreciated
 

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Did you start noticing the problem before or after cleaning the MAF?
 

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Discussion Starter · #15 ·
Did you start noticing the problem before or after cleaning the MAF?
Noticed it well before...the rotofab, maf and tb cleaning were all done last week as trouble shooting measures.
 

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Discussion Starter · #16 ·
Things keep getting interesting...threw the A/C belt this week, but that's nothing new around here.

Ran the stock tune and it definitely felt better than the 93, but not "normal." I ran the 91 tune and that seemed about the same as well, but my mileage dropped considerably compared to the 93 (down 3 mpg over the exact same route).

I let someone else drive the car spiritedly without saying anything beforehand, and without prompting he asked if something was up. When I rev in neutral, the car sounds a little "cammy" now. It also seems slow to build revs when I am WOT, even high in the rpm range.

When I looked at instantaneous timing advance, it was around 30 cruising off-throttle, then dropped to 10 when wot starting at around 50mph. AFAIK kr can't be directly measured with our cortex, right? 10 seems low, my understanding was that 20-25 would be about right for the 93 tune.

Sorry to keep beating this to death, but I know something is wrong and it's killing me because I love this car as you all love yours, and hate that I can't figure it out.
 

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It could be a cat problem. Mine was being all screwy because of a bad cat (so the dealer thinks) they are under warranty. Mine eventually caused teh car to backfire into the intake and misfire, run lean and rich.
 
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It also seems slow to build revs when I am WOT, even high in the rpm range.
Ya, sounds like restricted exhaust or KR problem. Can you safely remove the front O2 sensors & run it without to see if your power comes back. That or I think their might be a tool to measure exhaust restriction. Makes sense that the power is more responsive with the lesser tune. the lesser tune is creating less back pressure through the exhaust.

I had a similar problem with my GP GTP after I put a smaller pulley on the SC. only at top end WOT though. If I backed off the throttle a bit then it would keep pulling. No one, including PFYC whop I purchased the pulley from, knew what was causing it. Then a couple years later I heard about the U-bend removal mod to free up some horses, did it & found that it cured my top end WOT problems. (sorry for the long story...)
 

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10 is low. You definitely are seeing some major knock retard I would imagine.
 

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Discussion Starter · #20 ·
In case anyone was following this thread, I thought I would update.

I ran a bottle of Techron through three or so weeks ago (some like it, some find it to be snake oil...not worth debating here). I also cleared the tune out again, reset the ecm, uploaded the 93 and logged the timing. It is now around 23 when giving it the spurs as opposed to 10. So, I'm trying to figure out what the hell was causing the KR and why it's mostly gone.

About the time that I fixed the AC belt, the car started to wake up again. I would say it's probably back to "normal," if not still a little soft. It'll chirp into 3rd again, which it certainly was not doing when it was running so crappy. Mileage is good, engine sounds okay (considering the racket that's considered normal for the top end) and the exhaust smells normal.

At this point, I need to get it on a dyno or to the track to quantify any other problems I guess. I'm just happy things are getting better. Thanks to those who chimed in with insight
 
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