MitchAu

I'll lay out the symptoms and diagnostic measures i have undertaken so far, any help would be greatly appreciated.

I have a 2008 series 2 rx8, and only recently whilst at full throttle i am experiencing stumbling power changes above 6500-7000RPM with my foot to the floor. Additionally to this there are no check engine lights or codes stored in the ecu. At first i thought maybe it was the CAT, so i took it all the way off and replaced it with a catless mid pipe. This didn't fix the issue, after i figured my ignition may be on it's way out so as preventative i replaced plugs, coils and wires. The issue still pertained. Comp tested, and came out as 110/110/105PSI normalised @ 250RPM rotor 1 and 110/110/110PSI normalised @ 250 RPM rotor 2. At this point i am scratching my head, i'm thinking maybe it's the fuel pump or something related but would like some input before i purchase a new fuel pump.

To add if it helps, about 4 months ago the car started to experience harder cold and hot starting (About 1-2 seconds of cranking to get it started either hot or cold).

Thanks so much for your help, sorry if this has been posted before i couldn't find anything.

CaymanRotary

First thing you need to do is make sure you know it's a series 2. Those didnt come out until 2009 model year. Both cars are different so just want to make sure it's a series 2 before continuing.

MitchAu

I'm 99.9% sure it's a series 2, GT trim (R3 alternate name). Registration documents also have it down as a Series 2.

CaymanRotary

Could be a fuel issue, could also be a vacuum leak. Surprising you get no engine codes if it pegs at 7000 rpm. The good news is you can test for fuel by looking at fuel trim data and by actually testing fuel pressure. Vacuum lines can be tested with smoke (cheap cigar works perfect). If those check out, I wouldn’t really know for sure without an engine code. There has to be some kind of clue.

Loki

iTrader: (1)

6800-7000rpm is when the VDI opens. If you have a vacuum leak on the vac line to it, it maybe sluggish to open. It could be carboned up, or somewhat less likely without codes, the solenoid may be dying.

MitchAu

Alrighty, to help narrow it down i took her out for a drive testing lots and lots of different things. A bit of pre information that i forgot is the car is on 155,000kms second engine only used 98 since i've had it.

Before driving, i checked coolant and it hasn't gone down at all. Checked spark plugs and they look almost new, all wires are on properly. I got it warmed up and started revving it out. I've found that with light application to the throttle, the car will freely and happily rev up to 8500rpm in 1st and 2nd gear. As soon as you depress it further than halfway, it starts to stumble and have the power issues described. Additionally, i plugged my obd scanner in and got it to read some fuel stats, i'll upload a part of the graph when i'm under full throttle from what i can see it jumps like there is a fueling issue. To add to the physical symptoms, with my foot flat in higher gears like 3rd after the stumbling it just hits a wall and slowly revs higher with no more power. Also, 1st gear seems to be the least affected.

Thanks again for your help keep the ideas coming please because past the fuel pump i'm lost.

sinkas

ld say ssv stuck or sticking

Loki

iTrader: (1)

That's not a fueling issue. You need commanded AFR, actual AFR, rpm and calculated load on the graph. Maybe MAF g/sec for good measure.

Fuel injection volume is a function of what the computer commands, not actual flow measurement. So the graph is showing you that for whatever reason the car needed a variable amount of fuel. This might be normal in that part of the rev range.

Keep in mind, there is a switch from secondaries to primaries + secondary injectors somewhere in that rev range too.

MitchAu

Thanks for the suggestion, i'm hesitant to say it's this due to the 5000-6500rpm range having no issues at all. Will definitely be looking at this though thanks for the suggestion!


Sadly like an idiot, i didn't get the obd reader to record all data it can, i only got it do specific types. I'll just set it up to record all data next time. Does the graphs i posted help at all? Also i got a check engine but it's for the decat as expected. Do you still suspect a VDI issue or could it be something else? Cleaning out the throttle body will post back if any improvements come from it.

On a side note if it helps, owner before me had the car religiously serviced by Mazda, what is the chance they overfilled the oil when changing it and oil was sucked into the intake and overtime this has gummed something up down in the lower intake manifold. Thanks for your help and patience.

CaymanRotary

The chance is always there. Could also clean your MAF while you're there. Also for fun, try to manually move your VDI and SSV actuators and ensure they move freely.

Loki

iTrader: (1)

Still suspect the VDI, the graph doesn't really add any new information.
When you get the AFR, load and airflow data we might know more. Like I said somewhere in that range, depending on load, is when the primary-2 injectors kick in (not secondaries as originally state.. there are 3 injector stages). Could be that, you'll see AFR dip momentarily during the transition if that's the case. But I would be surprised.

jcbrx8

Concur w/ the "possibilities" which h/b mentioned...

These symptoms c/b
- fuel system related: e.g. pump, pressure, injectors.
- LIM valve related...namely SSV which opens at ~6000 rpm, but slowly. As h/b said manually actuate it to "feel" if there's any gummy resistance. The SSV runs thru a test cycle, open & close, on engine cut. So, have someone else turn off your engine while you visually confirm that the SSV actuates properly.
- Ignition related: You said you replaced the plugs as part of t-shooting. Did you install OEM plugs...or go with something else?

Having addressed the cat...your symptoms sound like a stuck closed SSV or ignition related IMO, but I'd expect misfire CELs. ??? Feeling as though it's "hit a wall" after the stumbling c/b the ECU richening afrs as a precaution.

Of course, you'll need to systematically walk thru t-shooting each "system" to confirm or eliminate each as a cause.

CaymanRotary

Agreed on the VDI. That opens up right around 7200 RPM so it's likely there is some kind of issue there. My only thought is why wouldn't it throw a code or anything if there was something wrong with it? I've gotten codes both times I had VDI issues.

jcbrx8

I certainly c/b wrong...that's why t-shooting is req'd.

But MitchAu, you said in your first post that your issues begin ~ 6500-7000, ...particularly under WOT; which is the range when the SSV s/b "opening", and if not, would begin to starve the engine. The VDI doesn't open until IIRC ~ 7200RPM, and is therefore beyond the rpm range of "the onset" of when you're experiencing issues. In addition, it's suspicious b/c the VDI just doesn't do that much. Heck, we disable it on FI applications.

Additionally, you said that you were experiencing hard starts, hot & cold a while back, w/ solid comp #s... which IMO casts suspicion on the ignition system. Do you KNOW that your ignition system is good? Have you tested each coil, lead, and plug series w/ a HEI ignition tester?

I would avoid just ripping it apart and reinstalling... b/c it c/b a component issue..., and w/ everything you touch you risk doing unintended harm. You could get lucky...or chase your tail. Trust me..., been there. Better to methodically walk thru and test each "system" good or bad.

sinkas

my 2010 did the same sort o f thing , it was stuck shut ssv,