Ive had a hot starting issue with my FD for over a year,,, starts perfect cold,,but hot just cranks and doesnt seem to catch even though there is an odd pop, like its trying..
First thing to check compression. ive performed this test now twice once 3 months ago and again recently.. here are results

Front rotor cold 92 103 99 / front rotor hot 80 87 83
rear rotor cold 103 105 98 / rear rotor hot 94 95 90

and todays results
Front rotor cold 95 103 99 / front rotor hot 82 89 84
Rear rotor cold 99 103 95 / rear rotor hot 91 94 89

im lead to beleive that these results are fine?? is that true
compression results are calculated to 250rpm although actual engine crank speed is 225 rpm.


where am i trying to find a problem ,,, faulty coil when hot (trailing coil or both)
leaky injector??
possibly bad fuel??
faulty spark plugs??

plugs were new 1 year ago but car has only done 300km
i have hks twin power i unplugged it,, made no difference still wouldnt start hot..

my next step was to replace all coils and have injectors cleaned??

let me know what you think.

 

Those hot compression results aren't great, but they are not poor enough to prevent the car from starting hot, so I would suspect a fuel or ignition issue. After trying to start hot, if you remove the plugs are they wet with fuel? Do they look like they are carbon fouled? If you see either of these, it's probably flooding which can foul new plugs in short order. Next time it happens, do the de-flooding procedure and try starting it with fresh plugs.

Your cranking speed is a bit on the low side and isn't helping the situation - is the battery relocated? What about the condition of all the battery/starter/alternator power & ground electrical connections?

 

Hi pete i was told the compression numbers are ok,,, somwhere in the middle (i was told low 70s would be low). The battery is getting a bit old but if charged it will crank at 250rpm (starter is an upgraded rx8 apparently) alternator is brand new..Do you know what cranking speed i should be seeing?
Battery relocated to storage bins.

 

225rpm is a bit low, but pretty average. since the spec is at 250rpm, that is probably what one should expect. the FSM mentions the minimum starter rpm (3000), but we don't know the gearing, so its a bit silly
compression is low as well, the spec in the FSM is the minimum, 7kg/100psi.

if you're testing stuff though, you might check the fuel pump, and its also possible that the fuel temp sensor isn't working like it should be

 

Numbers aren’t great and low 80s will cause some starting issues if crank speed is low which you’re is. I’d verify your starter is actually upgraded. I did the upgrade myself swapping the rx8 starter intervals and I also run a $750 lithium ion battery that has 1000 CCAs. My starter will crank around 330-350rpms if I remember correctly. It’s not a permanent fix for you but it will but you time. Switching the starter and battery is a 1 hour job vs. 40 plus hours for engine removal, tear down, rebuild and reinstall.

 

How did you ground the battery on your relocation mod? Poor battery grounds with the relocation mod is a common problem. Cranking speed for the OEM FD starter should be somewhere in the ballpark of 250~300RPMs IIRC.

 

As said here, wiring could be an issue - low voltage to the ignition coils, etc., will make starting more difficult even if the cranking speed is OK.

 

I have 1 large wire ground at the battery to the chassis, do I need more? I'm thinking at moment to get a larger battery. Put more grounds in car replace the trailing coil with a brand new one

 

Has the fuel filter been serviced?

The entire (G) section of the FSM would be good to check out:
-Coil inspection
-Ignitor inspection
-Spark plugs

My relocated battery in the bins had a ground just to an exposed stud near there. This worked but in an effort to avoid any future issues with the AEM smartcoils (which are more sensitive to grounding issues), I ran a ground from the battery to the block to maintain a star grounding pattern.

Far as compression numbers are concerned, I personally didn't suffer from any hot start issues with worse numbers to yours. I do have a XSPower AGM and my crank speeds are significantly higher though, around 290 RPM.

Taken hot with throttle fully open after Thunderhill HPDE:
Rear Lowest reading of 3: 76 78 73
Front Lowest reading of 3: 79 77 68

That being said, I don't know how much I can trust my tester since after another Buttonwillow HPDE I got the following using the same procedure:

Rear Lowest of 3: 94 91 89
Front Lowest of 3: 77 79 74

The same tester on a S2 RX8 was reading in the mid 60s for both rotors but that car also started up cold and hot fine...
It read in the mid 40s for a S1 RX8 my friend was considering buying and that car also started up cold and hot fine...

At this rate, after another couple HPDEs I should have a motor with near perfect compression

I would say that the tester is inaccurate but it gives relatively consistent results for each car. If anything, it has just made me question how reliable compression numbers are for determining the health of an engine considering that idle vacuum is great on my FD and the tuner said it was making very healthy amounts of boost.

 

Yeah your compression is mid-range or a bit higher. Lots of people would LOVE to have those numbers.

I'd look into various hot start issues. And as stated relocated batteries can give fits to cranking speed. If the ground is poor enough I could see the ECU not getting good voltage to do its thing while cranking.

Dale

 

Interesting. I'm gonna fit new battery run more grounds and maybe replace coils plugs and leads

 

My FD started in the 60's, but had to floor the pedal when starting. You may want to try that. Compression probably isn't your problem (you may have injector issues). Check if you have gas on the plugs. Only real way to test is to pull them but if you do that, you may as well get them cleaned.

And it doesn't hurt to have more grounds and a beefy positive conductor from the battery to the fuse block

 

right i neeed help still,,, compression test good,, old coil tested good,, but replaced with new leading coil, new plugs and a new battery 700CCA. ran a bunch of new grounds cleaned up all old ones,
car still struggles to start hot (the only thing left to do is have inectors cleaned?? possibly)

one thing ive noticed and this is where i need some input,, when cranking hot the car will only start 10% of the time anything over 80degree water temprature.. but i read another hot start post here while searching where a guy said pumping fuel pedal worked for him.
So i tried it,, Works!!,, if i crank hot and pump the fuel peddal up and down fast it starts right up,,,, what does this mean??

 

I'd love better pics of exactly where engine block grounds A and B are.

 

subbing

 

I’m assuming it’s the pinion gear rpm, which seems to work


[engine cranking rpm] x [# of flywheel teeth] / [# of starter teeth] = starter rpm


or any combination thereof depending on which variable is unknown.

FD3 manual flywheel teeth = 125

FD3 manual starter teeth = 12(?)

RX8 S1 2004 - 2008 manual starter teeth = 13 (2005 MY+, early 2004 is 11)

RX8 S2 2009 - 2011 manual starter teeth = 14

11T @ 3000 rpm = 264 engine rpm

12T @ 3000 rpm = 288 engine rpm

13T @ 3000 rpm = 312 engine rpm

14T @ 3000 rpm = 336 engine rpm

hth
.

 

One is the top of a rotor housing, where the solenoid/coil rack is attached. The other is top of the front iron where the hook for lifting the engine attaches.

Jack