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'04 GT down on power

Old 07-26-2015, 12:12 AM
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'04 GT down on power

I picked my 8 up almost 6 months ago and I have loved it ever since I've bought it. I changed the plugs and wires back in March but I couldn't get to the coils. I didn't think to have a compression test done on it when I bought it... after all, it was VERY spur of the moment that I purchased the car. Recently, however, I have noticed that she seems to be a little down on power. I have been running 89 octane all summer and I lost some performance. I filled up on 91 a few days ago and have noticed two things: a significant drop in mpg and it seems to not be a quick as she was before the summer. I'm thinking the coils may have gone bad since they go bad with the engine heat anyway not to mention that it has been over 90 degrees for the past month everyday. Do you guys think it could be the coils? Any and all advice is appreciated guys!
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Old 07-26-2015, 12:30 AM
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Do not run 89, thats your first mistake. 91 or higher is needed. Coils, Plugs, and wires are a pretty common maintenance item that should be replaced every 30K miles or so. I would have the engines compression checked, thats the only way to know for sure. Are you having any hot start issues? Thats a good sign of low compression.

Also, have you checked your cat? the stock cats can clog and cause all sorts of issues, including power loss.
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Old 07-26-2015, 01:03 AM
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Originally Posted by Chrishoky View Post
Do not run 89, thats your first mistake. 91 or higher is needed. Coils, Plugs, and wires are a pretty common maintenance item that should be replaced every 30K miles or so. I would have the engines compression checked, thats the only way to know for sure. Are you having any hot start issues? Thats a good sign of low compression.

Also, have you checked your cat? the stock cats can clog and cause all sorts of issues, including power loss.

All of the above + IAT, MAF, SSV and ESS. All easily doable.
v
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Old 07-26-2015, 07:41 AM
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Originally Posted by Colon Terminus View Post
All of the above + "Clean" IAT, MAF, and ESS. All easily doable.
And if you like to work on cars and have the tools and space clean the SSV
fixed
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Old 07-26-2015, 12:54 PM
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Alright, I'll be sure to check all of those sensors. I'm probably gonna get new coils soon anyway just because I think they do need to be replaced because I don't know when they last were replaced. As far as fuel goes, premium is only "Recommended." The owner's manual reads that "Your Mazda will perform best on 91 or above" and that "You may use a regular unleaded fuel with an Octane Rating from 87 to 90 but this will slightly reduce performance." I have ran it on 87, 89, 91, and 93 and have found no noticeable differences mpg wise but there is a significant drop in performance from 87 to 89 but less so from 89 to 91/93. So, as far as I have read, there would be no problem running on 87 Octane not that I plan to do it. I have only done it twice in 6 months and I was in a very tight pinch at the time. Sorry if that sounded rude.
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Old 07-26-2015, 10:00 PM
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Just run 91 or above. Its "recommended" for a reason. The manual states 87 or 89 can be used in emergency situations, but high temps can cause engine damage. Doesnt sound worth it to me for another $2.00 at the pump.
Attached Thumbnails '04 GT down on power-169099d1299264713-what-lowest-octane-rx8-can-safely-use-fuel.jpg  

Last edited by Chrishoky; 07-26-2015 at 10:05 PM.
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Old 07-27-2015, 06:27 AM
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Runs better on lower octane? Down on power? Maybe time for a comp test to see what you are working with. Also check the cat.
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Old 07-27-2015, 12:06 PM
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One thought. Take care of the things in the Congrats Thread below. Some have been mentioned. Good DIYs for getting started. Then, yeah, Coils. Disconnect the battery for awhile as well to reset stuff. Car could easily learned how to run on the 89. Likely pulled out timing. 91 has less overall energy, but will allow more timing to make up for it and then some. You could be at worst of all worlds.

again, welcome.
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Old 07-28-2015, 02:53 AM
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Well, you know the old saying "Curiosity killed the cat?" Yeah, I just experienced that. I was putting my manual back in the glovebox and started looking over the documents I got when I took my car in for the airbag recall. The Mazda dealership was nice enough to print off the history of the car for me [history meaning documents from previous work at other Mazda dealers] As it turns out, the original engine number was one of the documents listed. Well, curiosity got the better of me so I decided to make sure what engine this was because "there was no way a rotary has 116,000 miles on it." I popped the hood, checked the number, and my heart dropped. I'm running an '04 with 116,000 miles on the original engine. I'm just gonna guess that it has probably started to lose compression but I am going out on a limb I'm definitely replacing coils, keeping the thing on 91 Octane, and going easy on it until my broke college butt can afford a new engine... or at least the parts to rebuild it...
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Old 07-28-2015, 08:56 AM
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Don't just ASSUME it's compression. It's much cheaper to have a compression check instead of buying a new engine.
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Old 07-28-2015, 10:36 AM
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Well, if the engine goes bad at this point it's more than likely compression, right? I'd definitely get a compression check before I bought a new engine or did a rebuild anyway. Also, which would be better? Getting a new engine or just rebuilding the one I already have?
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Old 07-28-2015, 10:41 AM
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A remanufactured engine is the way to go. Unless you have the tools, knowledge and time to rebuild it correctly.
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Old 07-28-2015, 05:39 PM
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I would have to disagree with the above. I would only go with a remanufactured engine if I was still under Mazda warranty. I would have it rebuilt by a reputable builder, say pettit or rotary resurrection or pineapple racing. The cost will be similar but at least you will know what you are getting with a reputable builder. The Mazda remans are a total crap shoot.
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Old 07-28-2015, 06:22 PM
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Alright, do you know how much it would be to have the engine rebuilt? I know it sort of depends on a variety of things but just a rough estimate would be nice. I know a guy that has been working on cars since the 80's and he specializes in imports so I'll give him a call and see what he says.
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Old 07-29-2015, 12:22 AM
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Need a specialty shop for rotary not a piston engine guy, no matter how good he is.

Stop talking new engine until you get a compression check.
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Old 07-29-2015, 02:07 PM
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Agree with Razz1. Get the compression checked and then come back and post the results here. Once we know how the engine is doing we can suggest next steps. A proper rebuild can cost anywhere from $3K+ depending of the condition of the current parts they can reuse, etc.

I would not allow a mechanic that didn't do exclusive work with rotary engines touch the motor. Even some of the RX7 guys don't totally understand the renesis.
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