05TouringRX8

Of course, I know about the rotary's potential issues when shutting it off cold and trying to restart it. Have lived through it a few times since getting it a couple of years ago. But, have started noticing a scenario that we haven't really noticed being a pattern until recently. Mainly because it's less frequent for us. My daughter recently complained that, right after filling it up with gas, it doesn't seem like it wants to start back up. It doesn't get flooded but it is harder to get started. Today, she drove home from school, decent day out temperature wise, and the distance was more than enough to fully warm the motor. I asked her to go back out and move it and it did the same thing it does when she stops for gas. So, now we are thinking it may be related to warm restarting, something we don't do very often. Typically, we start the car, drive to a destination, it sits long enough to cool off, then we start it back up and go the other way and do the same thing.

Car has a new battery, new plugs, new coils. Any ideas what might contribute to this issue that I could check/fix?

1.3_LittersOfFurry

iTrader: (4)

I would check the cat first and see if it's somehow related, next would be to Mazda for a compression test.

RX8Soldier

iTrader: (24)

how many miles on your engine?
When were the plugs/ coils changed?

Not to jump the gun just yet, but you may have low compression, which would lead to you needing a new engine

edit: how are the cold starts?

alnielsen

iTrader: (4)

Yes, check the cat, ignition components, clean out the carbon (https://www.rx8club.com/series-i-do-yourself-forum-73/diy-mazda-zoom-power-engine-cleaner-engine-cleaning-seaform-142852/) and then the compression test. Is the car under 100,000 miles? If it fails the compression test, you could get a engine replacement under warranty.

05TouringRX8

Will they do a compression test for free? How involved is that?

Car has 50k or so on it and it wasn't long ago at all that the cat was checked and okayed, plugs, coils, and wires were changed, and a new battery installed.

expo1

Compression test will not be free, but is needed if they are going to give you a new engine. I just had one done today myself it was $100. Takes less than an hour and all they do it replace a spark plug with a sensor and crank the engine over. They do this for each rotor. For each rotor you will get 3 readings and the cranking RPM. Mine didn't come out well, under 6 kgf/cm2 for all 6 rotor faces, sucks to be me.

05TouringRX8

Some asked how the cold starts are and I forgot to answer. First start of the day or starting after the car has completely cooled off seem to be normal. Car seems to drive and run as usual as far as power, acceleration, etc.

Are there any other signs of compression loss other than difficulty starting?

jasonrxeight

loss of power if you want to dyno it.

05TouringRX8

I haven't driven the car in a while. I'm going to take it for a test spin and maybe a redline or two. I'll let it warm up, stop for a couple minutes, and then try to start it again. Will see what happens.

If the engine were going south with a compression loss issue, wouldn't it be even harder to start cold than a warm restart?

lta_ds_fs7

iTrader: (2)

Actually, there's an easy trick to gettting a free compression test...I called 3 dealerships to have one done...The first was going to charge me $338...So naturally, I said f*** that, and called other surrounding dealerships...The 2nd dealership was going to charge me $130 (much better deal), but since I found such a huge jump in price, I decided to test my luck even more...Then I called the 3rd dealership, and the conversation went something like this...

Dealership: "Thank you for calling Mazda service, what can we do for you today?"

Me: "I'm calling to see how much you charge for an engine compression test."

D: "What kind of car do you drive?"

Me: "An RX8"

D: "Well are you having problems starting your engine?"

Me: "No, I just want to have it checked...I recently bought the car, so I thought I should see what condition the engine is in while it's still under warranty."

D: "So you're having problems starting your engine?"

Me: "No, I just wanted to...."

D: cuts in - "Sooo what you're telling me is......you're having problems starting your engine..."

Me: "Oh, yeah"

D: "That's the trick by the way...You have to say your engine is having problems starting..."


Lol...and there you go!...A free compression test...Hopefully it works for some of you!

applepwnz

That sounds like a good plan, I may just have to try that (I've been having some warm start issues as well)

lta_ds_fs7

iTrader: (2)

Don't give too many details...Just say your engine is having issues and won't start 30%, 40%, 50% of the time...Choose your own number...lol...Luckily I was speaking to somebody who was nice and extremely honest...He said if you are having engine problems, the warranty has to cover the compression test.

05TouringRX8

Based on the symptoms, I technically wouldn't be lying. We are having problems - just not bad ones, yet.

But I still haven't seen an answer to my question - if it's a compression issue, why wouldn't it pop up at any given time and not just when the engine is warm and has been shut off for only a few minutes?

jasonrxeight

I think it has something to do with air mixture when the engine is cold and warmed up. when cold its more rich which means its easier to start.

RX8Soldier

iTrader: (24)

heat expands the housings, thus increasing the sealing distance.

lepichichi

iTrader: (10)

I was gonna say battery but you said it's brand new right?? i think it could be something electrical, i had the same issue when my battery was going bad

The Reverend

iTrader: (1)

+1.

Mazurfer

Does she putz around town in a high gear at low RPM's most of the time?
Sounds like mucho carbon build up to me..............check that CAT and then get a compression check.

lta_ds_fs7

iTrader: (2)

If it is a carbon build up issue, you may want to try using seafoam and see if that helps at all...However, this is a very common problem that can be caused by a variety of things...Your best bet is to start with the seafoam and a compression test...My engine has a great start in the cold, and a weaker start when it's warm outside...But only twice has it ever not started for me when warm...After that, I made it a point to rev the engine harder when I drive to help with cleaning it out...I have a new CAT, good engine, good coils, new plugs, and just used seafoam myself...It still has a weaker start in warm weather, but it always starts...Anywho, like I was saying, seafoam it, and have a compression test done.

05TouringRX8

CAT was checked just a few months ago related to another issue and was okayed. This is an AT and she does putz around in the car for the most part. I try to jump in it every now and then and go redline it but I've been out of town a lot and haven't done that lately. Maybe that will help and I'll try some sea foam as well.

RotaryResurrection

iTrader: (3)

(Bunch of semi-mis-information in this thread so far...)

Because rotary engines make more compression when cold than when hot. You lose a few psi of cranking compression when hot. I've done back to back tests to prove it to myself, when I first found this out I found it hard to believe but sure enough it is true in my observation.

When new the engine may be sealing perfectly and making 120psi compression hot. The cranking fuel injection maps are set up with this in mind. Remember that compression means moving air, and even during cranking there is an air/fuel ratio guideline that the PCM follows (based on perfect compression).

As the engine wears, compression drops.

After a time, you may have 100psi cold. And it starts fine.

When hot, you lose about 5psi. This puts you just across a threshold (around 90-95psi for most of the rx8s according to my observations) at which you have too much fuel injected at startup for the (now lower) cranking compression actually being generated. And under this circumstance, the engine has difficulty starting, because it is on the verge of flooding.

IF you let it cool off, compression creeps up a few psi, just enough to put you on the good side of the cranking compression threshold and it responds better.

If you continue to run it the problem will advance...because the wear in the engine is increasing slowly and so the compression will continue to drop slowly. The more it drops the more difficult hot starts will be.

Everybody here loves to yell "carbon buildup" and "decarb" for the automatic models. While they do carbon up a bit more than most manual models that see higher rpm, they still turn 3-4 thousand rpm driving normally and that's enough to keep severe carbon buildup from occurring unless you use some sort of high ash content oil that leaves deposits behind. If anything, carbon can sometimes actually increase dynamic compression because it reduces overall chamber volume slightly. The reason we worry about carbon buildup with a rotary is that it tends to make the seals stick in place rather than move freely and do their jobs well (sealing). This is not as big of a problem as everyone lets on or has been lead to believe.

What I feel is the major problem is lack of sufficient lubrication for the rotor seals due to the OMP (oil injection) system. As mazda turns down the oil injection rate to try and meet emissions and also reduce oil burning, they run the seals dry of lubrication which wears them out. Imagine a piston engine where the piston rings did not see natural lubrication in the cylinder bores. They'd wear out! Same thing here. We're running seals dry in some areas and they are wearing unevenly, producing gaps in sealing and blowby, compression loss, and then you have hot restart, idle, and low rpm power/torque/pullout deficiencies. By the time these issues show up, the wear has occurred and it's too late to do anything to help other than a rebuild or replacement.

In my opinion, if you bought one of these things new and were able to give it better/more lubrication from day one, the thing could probably go 200k or more (speaking of the engine itself, not the other suspect parts like the coils/cat/trans/etc.). This would be a combination of more OMP injection, different oils than mazda recommends/people blindly follow, and generous application of 2 cycle oil in the fuel supply.

Yanzer Rx

Hi everyone,
I have the same problem here. Can't start after engine is hot.

Now its worse. Engine dies when switching from Neutral to Drive ( in a hot engine, while geting stuck in traffic )

My mechanic confirms its Engine Low Compression Issue.
My question is, what can i do to fix it?
My car is a second hand and has no warranties anymore
Changing engine is not an option as its very expensive here in Malaysia.

Pls help.

RotaryResurrection

iTrader: (3)

YOu don't have a choice. You either rebuild the engine you have, or you find another used one in better condition and use it, or you buy a new/rebuilt engine from mazda or another rebuilder, or you continue attempting to drive the car as-is knowing that the problems will grow worse, or you stop driving the car. There is no "band aid" that will magically make it all better again without doing anything to fix the engine.

Yanzer Rx

Hi 05TouringRX8,

how is your car now? had the warm restart issue fixed? I still have the issue, and i confirm its not my Engine Low Compression problem, because my engine is overhauled and the Engine Compression is very healthy ( about 9 to 12 bars )

05TouringRX8

I haven't had a compression test done and this doesn't seem to be a consistent issue for us. My daughter is the primary driver of the 8 and she doesn't do a lot of running around and stopping and starting. She typically gets in the car and goes from point A to B and then the car sits for a while before being restarted and going back from B to A. The normal exception to this is stopping between A and B or B and A when the car needs more gas. It does happen often, though. After filling up with gas, we turn the key and it's as if the engine is going to start so we let off the key and it doesn't start after all. Immediately repeat and it starts right up.