Rattlehead

Bought my friends rx8. Rotaries arent new to me, so i knew what i was getting into. Took it to a shop, used a mazda tester for compression and they had said that the compression is on the lower side but shop says its still decent, that i dont need to rebuild yet. It does have a hot start issue. Gotta wait about 20-30min.

"mods"
-Hks catback
-Aem intake
-Sohn omp adapter
-Ls coils
-*Used to have cobb but it broke*

Thats about it.
I bought the car with the intention of getting a new engine in it. But shop said it could go a bit longer even with lower compression numbers. They said oem coils could help. They didnt. I saw another thread with new engine still had to wait to restart but had way more done to it.
So if i replace the engine and still get the same issue then that means theres another problem.

Could it be the ecu? Any thoughts?

Loki

iTrader: (1)

What were the actual compression numbers? Their opinion is useless given the symptoms you're having.
It's not the ECU. I'm not sure why the shop would recommend stock coils, perhaps they're concerned about dwell time differences, but LS coils are a common reliability upgrade.

There aren't too many options for why you need to wait 20-30 minutes to restart it when warm: compression or fuel pump. Fuel pump would also manifest as the car dying on its own while driving, and having an easier time with a full tank than with an empty one. Compression, on the other hand, is very predictable. Having those numbers would help.

Rattlehead

Im gonna head to the shop thurs or fri get the numbers
from phone call i remember front 6.5< rear 7.0<
those are low but they said they seen lower. Ill also see if they did it cold or hot(i know, i shouldnt even have to)

The coils are new and the harnes is an old bhr harness. I was also skeptical of the oem coils, but wanted to see if it made a difference as i do think ls coils are better

Only reason i brought up the ecu is something went wrong with the flashing process due to the cobb getting broken

Thanks for some inital thoughts.
ill try and come back with numbers.

Loki

iTrader: (1)

Cool ok. 6.5 is not encouraging, depending on what rpm that's at, it's quite below the line. Make sure they give you the 3 numbers per rotor + rpm.
I think the ECU would either work or not, computers don't usually have a grey zone. How did the cobb get broken exactly? You don't need it for the car to run, you just can't change whatever flash is on there now. Do you know what was flashed on it? How is it broken exactly?

Rattlehead

Gotcha I'll see what they got.

As for the cobb. It just lights up and thats it. Doesnt do anything else
Whats flashed on there? Beats me. Im not too familiar yet
Intake and exhaust? Maybe injectors i think my friend replaced those.(I gotta question him too)

Im used to working with my FD's ecu which is not flashable
pre OBD II stuff.(miata, FC)


Oh right and probably shoulda lead with this he did his own rebuild, when i told him to replace engine. Why am i posting this even though i know? Well its due to what the shop said and the thread about issues even with new engine.
i was just gonna replace the engine from the start. False hope? Most likely

CaymanRotary

If you can get the numbers from them maybe. But sounds like probably low compression symptoms from a poor rebuild. It happens a lot.

Rattlehead

Yea most likely
just when i heard back from shop I was surprised and thought id explore this small possibility
classic "so youre saying theres a chance?"

MincVinyl

How many miles on this rebuild? It might be helpful to ask what components have what mileage, inside and outside the engine. Was this hotstart issue there from when the engine was first rebuilt?

Rattlehead

About 4k miles on "rebuild"
all seals new but reused irons/ internals and used housings which you arent supposed to do.(overall mileage idk)

you might say well theres your answer.

But i just wanted some thoughts based on what the shop told me so im not worried about new engine(I originally went to them to replace engine anyways as soon as i bought the car)

MincVinyl

Was it the mazda shop that did your compression test tell you the engine can go a bit longer? If it was.....then yeah maybe if it was a 100k mile engine with those compression numbers it could make it another 2k-5k miles if you baby the engine. Risking it dying at idle during a red light (and it will eventually) I drove an engine to the brink and let me tell you how anxiety ridden it is to have a car loose its power steering while at the same time have to deal with a 130k mile engine that dies if under 1500rpm. Every stoplight I would have to keep the revs up with the gas, downshift and then use the handbrake to stop the car. All while having blown coolant seals held together by stopleak using the heater pumped to max with the windows open to keep the engine cool.
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Considering this is a rebuild, it is likely that many components such as the irons/rotors/Eshaft and many of the "new" soft seals may be fine to reuse. What I'd be worried about is if something goes drastically wrong and you end scoring up all of these components because you tried to get 1k or 2k miles on an engine you know isn't right to begin with.

Housings could be reused potentially if they were 60k miles, with no scoring and even wear. Beyond that, yeah there should have been new housings. Its hard to **** up putting the apex seals in, but it is rather easy to mess up with side seals and drastically hurt compression numbers.

If it was the side seals being the issue, either they did the tolerances too tight or somehow did them too loose.

• Too tight should have been evident within the first 50 miles running the engine with hotstart issues, or the rotor managed to bind up a corner seal and adjacent side seals. (seeing the 6 individual compression numbers gives alot of insight into if this is happening, we should see 2 pulses on a rotor be less than the 3rd pulse)
• Too loose would mean they happened to cut the seals just right so that the engine ran fine and then wore ever so slightly enough to cause compression loss. (with the 6 pulses we should see an even low compression)

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OEM seals or aftermarket? People have had issues in the past with aftermarket solid corner seals.

Rattlehead

Minc- hahah I am already doing that stalled a few places. Im on edge and worry about getting stuck in a hill(due to clutch being unpredictable at times separate issue) but the car runs drives and idles like nothing is wrong passed smog easy
just that hot start

the shop mainly works on all mazdas but not a dealer and they used factory mazda tester

As for the engine it has, i wouldnt want to resue any of it really. i remember seeing spots of copper on the eshaft and also bearings. Maybe only irons would be good but still. Housings were second with some chrome already peeling and chatter marks.

I believe it was the atkins kit with everything in it

MincVinyl

Well I chased hot start issues before, and that was on a fresh rebuild using the atkins apex+ solid corners. I can't 100% say that the seals were the issue, but after doing another few rebuilds testing changing one component at a time I found that Mazda Oem had drastically better compression results. Like going from 60-70psi up to 110psi with 85psi being the hotstart issue area @250rpm.

Rattlehead

I just went back to look at it and I could sworn it was mazda oem stuff, maybe just oe spec. Well i have heard of things happening like that where the seals just happen to not work to unlucky people


I guess i need to go with a mazda reman which the shop can get and have the warranty or the IRP stage1 and do it myself(I have not been able to find a thread or or reviews on this)