JDM

Hey all, I just got back from classes today (automotive student at SIU) and I am doing a presentation on the 13B-MSP. As part of that, I was collecting engine compression graphs on the Picoscope.

My compression was 86 PSI on all rotor faces, in both housings, and this alarmed me as low. (compared to the spec of 120psi, with the minimum being 98.6psi)

I also hooked up a vacuum gauge to the spot that the service manual suggests (between purge solenoid valve and intake manifold (short U shaped hose on top of the upper plastic intake). the gauge read 14.5 ~15 "Hg, which was low compared to the spec of 16.x-19.8 "Hg.

on top of this i have been getting worse then usual MPG, at 16-18mpg.

The car has always idled rough since i bought it.

So, does this mean I am ready for a new engine? this one only has 48,000 miles on it. It starts fine every day and it drives fine every day, just a shaky idle here and there, but never stalls. the only modification I have done to the car is a K & N short ram intake, obviously not the cause of the low compression, as its always acted the same before and after the intake was on there... but my issue is will the dealership dismiss a warranty claim because of a simple modification such as that. ( I have the stock air box, but it is in chicago, some 400 miles away currently).

Also, a side note, my spark plugs had hard light brown deposits on them, that i cleaned off with a wire brush before re installing them. My teacher recognized them as probably being deposits from the "additives and other crap" that gets added to alot of the fuel down here.

Brettus

iTrader: (2)

sea foam , then put in some new plugs and retest a few weeks later .

You didn't say at what RPM you got those compression readings ?

JDM

Thanks for the replies!

I am not sure as to the RPM's because I disconnected the eccentric shaft position sensor while doing the compressions test ( to disable spark and fuel).

but I would imagine they were in the 200-400 range, and looking on the chart, the compression was much too low even after correcting it. I have the upgraded starter and my battery is fully charged. The poor idle I am attributing to the low idle vacuum (14.5"hg).

I used a wire brush only around the edges and away from the electrode as not to damage it, and I was careful about it, it was all that was on hand at the time.

Mine is an 04, and we have the 100,000 mile warranty on the engine, so I will drive it until it gets worse.

My question is, when they replace an 04-05 engine under warranty, do we get the 06+ updated one?

JDM

Thanks, makes me kinda wish I would have looked for an 06+ in the first place, but hindsight is 20/20.

Thanks for the help so far! I just wish i knew what my engine was like with full compression, its still pretty lively with it hurt the way it is! (although it is def. slower than an s2000 currently, which is what I traded in for this upgrade)

JDM

I have been reading about that, and I did get that PCM flash about a year ago, (I have only had the car for a year and a half, almost 2 years) so it was probably running around most it's life with the out of date flash.

I am pretty excited to see what a fresh reman would feel like, as this is the only rx8 i have ever been in, so I have never had anything to compare too.

heyarnold69

iTrader: (1)

a toothbrush and some brake cleaner is my preferred spark plug cleaning method .. the powered ones make it easy

the cobb has made my 04 much better....

TheWulf

iTrader: (4)

As you should... wouldn't want to ignite fuel with that sensor in there.

However if you did the test with a rotary compression tool you should still be able to pickup the RPM, which is pretty crucial in determining compression as the spec readings are for 250rpm and you need to readjust them. from 200 to 250 is nearly* 25% difference in compression, which is huge, and would mean you would pass.


* I say nearly because the relation is not linear but almost
** 400 is very high... highest I've personally seen is about 290.

JDM

I was actually thinking about getting the BHR ls2 ignition upgrade in due time, I have been eyeing that for some time now. Cobb AP would be sweet too, I am graduating in a few weeks (from college) so hopefully I will find a job that can pay for all this!

I wish I had access to the special rotary compression tool, because that would give me a definitive answer on my compression, but 85 psi still seems pretty low to me.

Burton

Quick sideline question...
I have on 04' Rx-8 and I am a college student at app state in NC. My 8 is out of the range of Mazdas extended warranty and I am having some serious problems with Warm Starts... I understand the possible implications of this and it really is likely I will be looking at needing a new engine. I will have a compression test done soon as I can get her to a dealer. I am currently having the plugs, coils and wire replaced out of unsubstianted hope and a little bit of dread and will get some seafoam in there ASAP. My question is (and I have searched, found anywhere between 2200 and 7000) what is a reasonable price to expect to have my engine remanned if/when it comes to it? And any other advice the more eperienced members might have to help me try to make it by with the car in the meantime.

JDM

extended warranty for engines is 100,000 miles or 8 years i believe

TheWulf

iTrader: (4)

Source: https://www.rx8club.com/showpost.php...87&postcount=4

85 psi @ 200 RPM = 101.63 @ 250 RPM = Barely Pass
85 psi @ 175 RPM = 111.60 @ 250 RPM = Good Pass

As you can see it does make a big difference. If you are showing RPMs this low, you might have a bad starter. And it does happen. A friend of mine had his RPM in the 170s just last year and he replaced his starter. I'm actually going to retest his compression tonight so I can keep you posted..

Burton

Im aware, Im 130000+ at this point, no coverage

BigTurbo74

Price or an overhaul varies like you said earlier. The important thing to gauge value is to figure out what parts are being replaced. For instance, I believe rotary resurrection is a popular choice because Kevin will replace what's needed to get you back on the road and do it at a low price. On the other hand I think a shop like turblown.net uses new rotor housings in all of their builds to ensure long service life. New housings will definitely bump the price up but in many people's eyes it's worth it. Just call around for details.

In the meantime, keeping your current engine going... Go the normal checking of plugs, wires, coils route. Have you had the updated starter installed? When you go to get your compression checked ask the service advisor about any available tsb's or warranty work.

JDM

This makes me think, I should leave the eccentric shaft position sensor in and just pull the fuse for the fuel pump, this way I can still read RPM's with the Ford WDS.

I don't know the RPM's at all so that was just a guess. and obviously it can mean the difference in condemning a good engine bad, etc.

the worst part about it though, is the low idle vacuum, the engine is rough at idle and idle only, and I cannot find a vacuum leak anywhere. ( i know this can be engine mounts, but i have new ones, and i have all the up to date flashes for my PCM)

all are used

iTrader: (1)

I apologize for hijacking with a noob question, but is this only for original owners and those with extended warranties? I've only had my car less than 2 weeks and I'm trying to learn as much as I can.

yiksing

I believe US owners get the extended warranty as long as the first engine is showing bad compression before 100k mileage.

enamel

HI guys,

i also want to add to this discussion.

My compression test results are the following:


1)6.8 6.7 6.7
2)7.1 7.1 6.9

BTW, I have a 2006 RX8, with 20,600 miles driven.

How bad is this? Is this bad enough that warranty might try to fix it in the future?

How much decrease in power would be expected to experience with these current numbers?

Also, if I were to rebuild this, how much would it cost me?

Thanks a lot!

Jon316G

iTrader: (1)

Standard- 8.5
Minimum- 6.9

Since it is under the minimum tolerance, they should cover it.
You'll likely not notice a performance difference at this point.

enamel

Hey guys,

How would I go about trying to get this engine replaced, or rebuilt by Mazda? Since one of the rotors is technically OK, but the other is not OK.

I imagine that they would not try to fix this, as they already mentioned that the compression test was OK.

Furthemore, I was told that my warranty will expire soon (2006, with 20,600 miles driven).

Thanks -appreciate any comments.

Jon316G

iTrader: (1)

Mazda will cover the engine core 8yr 100k miles.
You'll need to show proof of proper maintenance.
Long as you can do that it shouldn't be a problem.

enamel

Thanks buddy.

Final piece of advice:
Do you think I should try to get them to fix/replace/rebuild the engine now, or wait a couple years when the compression is even lower?

Thanks

Jon316G

iTrader: (1)

They'll just replace the motor instead of rebuilding it.
If you can get it replaced now, I would just do it.

Jon316G

iTrader: (1)

My fault... you're right Charles (as always)
I'll try to be more careful with my wording.

epikeddie

Well....

I might be joining this group very shortly. Car has been developing a shaky idle even with brand new plugs, brand new BHR plug wires (thanks CRH), and a brand new cat.

Taking it by a buddy's place to go do a compression test. I'll let you guys know the results.

JDM

SO i found out the 86 psi is at 204 RPM