So I just bought an 04 rx8 auto. Last week I noticed it crawls slowly from 0 to 30km/ hr, smoothly at 2-3krpm, then the rpms rocket through to 7k and it accelerates like a bat out of hell. I replaced plugs and wires, noticed a small change but the dealership checked it out, said the cat and intake were fine, fuel pump fine, injectors fine, sensors fine. The only thing they could find wrong was excessive carbon buildup on the old plugs. Compression for first cylinder was mid 6's, rear was mid 7's. Is there anything I should check before I put 3g's into a new motor? It only has 80000 kilometres

 

If your motor failed a compression test, then it's been confirmed as failing. "mid 6s" is failing, assuming that it was normalized to 250rpm and altitude correctly.

 

While I don't think this is the issue, your list doesn't mention checking/replacing the ignition coils. You want those to be fresh ( < 30,000mi). And you probably don't want to get them from a dealer, that's expensive.

But, that aside, these cars do not have a lot of torque down low, so what you're describing isn't necessarily abnormal as a first impression. Especially the 4-port automatics. I think a video would help us understand what's happening though.

 

It sounds like it stumbles a bit, then runs great. Right?

Does it start well? ++ on the coils. I would do a set of autozone or some other place basic ones. Then do the clean up stuff in the $100 thread below (MAF, ESS, Grounds) and see what happens. You might be surprised. You may still have low compression (need to see the sheet from the test and know the compression and altitude) but it may take care of the problem. And, if it starts and runs, enjoy it.

 

 

The compression test results were as follows

Front Rotor: 7.5/ 7.3/7.4 @236RPM

Rear Rotor: 6.7/6.7/6.8 @238RPM

fuel pressure test- 56PSI

Going to buy new coils today and clean the sensors, fingers crossed.

 

Done, or near done no matter which way you slice it.

 

I found my compression test from when i bought the car, July 28.


Test was as follows


front 7.6/7.7/7.5 at 226rpm


rear, 7.1/7.3/7.2 at 226rpm.


how did the compression drop from 7.1/7.3/7.2 to 6.7/6.7/6.8 in ONE MONTH?

 

Describe your driving habits?

 

Its an automatic. I drive it to work on an 80km/hr rd, and on days off take it for drives on the highway driving between 110-130km/h. fast starts from red lights and on highway on ramps will get the rpms to 7500rpm and occasional red line beep. I dont race/stunt or do anything stupid. I'm old and boring. Checked the oil every 2nd gas fill and top it up with regular oil when needed. Had the oil changed when I had the first compression test done in July. other than that i dont know what to tell you.


Could it be a carbon buildup issue? Perhaps the seals are sticking? I've been looking at seafoam products, I bought a couple cans of the fuel additive and the combustion chamber cleaner. I was going to seafoam the engine through the plug holes, and add a can to the fuel mix. It says you can add it directly to the oil to clean carbon/help restore compression. Has anyone tried adding this product to their oil and driven with it? any potential problems with this? I'm at the point of trying anything now, since its been labelled as toast i cant really screw it up anymore i guess.

 

Oil habits, good or bad, will never cause or help a compression problem. The first sign that oil habits are giving the engine a problem is the oil light coming on. The second sign will be the engine knocking itself to pieces as the e-shaft bearings fail.


Automatic... yeah, that could be part of the problem. They have such a significantly harder time staying carbon free than the manuals, since the ECU shifting choices keep the RPMs much lower on average. It may be worth trying to decarb this engine first, to see if this is just carbon buildup, which can indeed get that bad that fast.

 

could it be possible the dealer overfilled my car with oil and f#$%ed it? It worked fine for about a week after i had the oil changed/compression test then it went downhill from there.

I took off the mazdaspeed cold air intake and noticed the filter is dirty/oily and theres a small amound of oil residue throughout the length of the intake tube.

 

No, that wouldn't affect your compression scores.

 

ok so check this out. I replaced the ignition coils and BAM! no more sluggish low speeds. works better than ever. Now, for the compression. is it possible because of the poor ignition coil it lead to excessive carbon buildup causing the lower compression scores?

 

Yup. Misfires cause fuel wash, reducing oil film increasing wear, at the same time as it increases carbon buildup. Either pay a dealer for a decarb, or do a steam clean, and then give it a few weeks to see if the numbers improve.

 

Could be a combination of things but the damage might already be done, the ignition coil problem will have no effect on compression numbers. I would check you cat converter as well. It may improve a bit after a decarb but that engine will likely need replacing soon enough. Your compression number from your first test were also at a low 226 cranking RPM so comparing is useless for the most part.

 

Oh and those numbers on the rear from the first test would be marginal at best even at 250RPM.

 

I don't trust my dealer. The service manager is a lying #$%^. I'll try to decarb it following info i find on this board!!

 

If that method is to suck in seafoam and then let the engine sit, that doesn't do anything, and I proved it. If you found the steam clean option, then go with that

 

Time to accept it and start thinking logically as to what your next steps should be.

 

If you pre mix a ton of oil, you may get better compression readings. Also, the temperature of the engine affects the results, (I.e hot engine w/ bad seals will test lower compared to same engine that's cooled off)