Diagnose my S2 dyno
 

Stock 2010 series 2, new plugs and air filter. Original coils and leads at 24.5k.
It looks to me like I'm not making full power at the top end and I don't think I should have the 'w' shape. Is this a possible intake valve issue, ignition, or something else?

I tried searching for an hour or so on here and could not find a similar graph... but searching for 'dyno' is like searching for a particular piece of hay in a haystack.

Ignition issues seem to show up as erratic power (squiggly line) which I don't seem to have?

Thanks!

Ignition COULD be going out, just because the service manual says switch @30K doesn't mean they'll be 100% til then. Just my .02

Also, you need to spank it more. Seriously, I make more power on the drive cycle after a good spanking, clears all the carbon out.

The slight hiccup at 3,750 and 6,250 is normal, but I guess the top end squiggle could be attributed to my ignition theory.

Hope that helps.

P.S. Oil changes? Engine, tranny, diff...

^thanks

I did find this: https://www.rx8club.com/trouble-shoo...9/#post4302095

so I guess SSV or VIV is something to look at. AFR seems to drop at the same time, which could be another symptom, could be normal, or could be a sign of a different issue :confused:

And yes, I have just changed engine, tranny & diff oils.

I hear you on the spanking. I suspect this car has not had much of that before the start of my stewardship and I rarely rev it that much during my DD. The first run on the dyno was noticably lower in power than the following 3 and did eject a little bit of dark smoke. I am going to have it on track this weekend so that should clear it out, or kill it if my ignition fails :scared: That's what I'm trying to work out :-)

Awesome, mine sputters if I DON'T spank her ;) Lol, it won't die if your ignition fails, at least not this early in the game. (Could cause cat problems later in life.)

VIV could explain the power cap, but not the W-shape.

Let us know how it goes :)

P.S. I think the VIV would throw a CEL, not entirely sure though...

Hmm, I still have not worked out what or where the VIV is... I did go out and push open the VDI and SSV valves. Both seem to operate smoothly, although the VDI valve squeaks a bit over the first third of its movement. This is with a cold engine bay. Not sure if adding some heat will change anything. I also took a look at the MAF sensor and that looked very clean.

That VIV valve will get you every time - very few people know anything about it . :suspect:


Another possibility is that the VDI valve is oscillating somehow to cause the little known ' W effect' - this combined with an ignition tracking/coil issue is my best guess as to what is going on here .

"should" be nothing wrong with a low mileage 2010....

What does your Dyno but 'feel'???

Is there any hesitation @ 7600-7900??

You really are getting close to max power, as many have said before around the 8K mark you enter the black worm hole.

Next to no benefit going past that RPM line...in a stock set up.

Ok, I'll bite: wft is the VIV?

And yes, I searched. :angel:

New top secret Brettspeed product, I bet!

Yeah, it's getting really hard to distinguish the comedy from the serious statements in this thread...
[SERIOUS FACE ON]
I searched a whole bunch and as far as I can work out, VIV might stand for variable intake valve. The comment I linked above is the only place I have found refer to it in this way and I am now not sure that comment is completely technically correct. There seems to be some better info in this thread:
https://www.rx8club.com/rx-8-discuss...rts-rx8-15622/

and here: http://www.starmazda.com/competitors...isTutorial.pdf

So, the VDI valve opens at 7250 rpm and you can see an appropriate dip for that in my dyno plot. The question is, why does my power dip a 2nd time just after that?
[/SERIOUS FACE ON]

VDI is broken maybe

https://www.rx8club.com/do-yourself-...valves-174009/

Thanks for chiming in here Ash. I really appreciate you passing your eyes over this and the multitude of informative posts you have on this board...

I don't really have my "butt dyno" calibrated well enough yet to rely on it, but have not picked up on any glaring issues. I'm going to have to drive it more before I can answer your hesitation question with any certainty.

I agree, there "should" be nothing wrong, but that 3rd power dip at ~8000 rpm does not look completely normal to me. I was able to compare results with two other RX8s at the shop and neither of them had this. One made less power up top and apparently had some known issues. The other made more from 7k onwards with a plot that carried on up and to the right where mine levels off, but was running a 13:1 AFR so must have been tuned. Both had the 1st two dips, but not the 3rd.

As soon as you find out who Viv is you can ask her what her valve is doing .


Like I said the first time . Looks like the VDI is opening and closing on you .

And I do think you are losing power to another issue on top of that as well - ignition related .

Thanks Brettus. I'll check with Viv on Friday night ;-)

OK, I'll go spend more time trying to diagnose the VDI, and coils...

Check out Jon's excellent thread, and yes VDI..


How often do you 'exercise' higher RPM's 6900 +?

The Series 2 Inlet manifold is slightly different than his S1, (mainly different hang on parts) however the principal is of operation is identical.

I am very surprise such a low mileage S2 has this issue..you are going to have to investigate, you could have an issue with 12V Solenoid Valve which controls Vacuum to VDI Actuator, although intermittent problems usually don't exits, the 12V solenoid either works or it does not.
Or Actuator on VDI?...I don't think either of these.

IMO I believe you have some carbon build up which is causing a sticking motion of VDI, opening and then closing, it is working but not smoothly.

Have you or do you ever run pre-mix (in gas/fuel), currently also winter where you are, extra cold could be making it stick with carbon/soot build up....it needs some manual exercise, do you have a Mityvac to connect like in Jons Video?

Do a vacuum check on your VDI actuator to make sure it holds vacuum . When you see Viv you could do a similar check on her as well ....

snap!

disable the vdi and dyno again?
But actually I think something else is going on. !st place to look is coils and leads.
But- ---and this is a guess--injectors too?
I see the a/f's swinging back and forth during that dip?
I also wonder about compression---161 is low?
Hows the cat?
It could be a lot of things....

I am of no help....

OK, thanks, I do have a vacuum pump but it might have to wait until the weekend before I have time to hook it up to the car. I did try pushing the VDI valve open again by hand with a hot engine (carefully!) and the behavior is the same. Smooth operation with a slight squeak over the first 1/3 of movement.

So far it has not seen high rpms that often with me, but I have only had it a couple of months. I can't be sure how the previous owner treated it, but my impression was that it was not driven hard and also not driven very much or for any distance during the last few months of ownership.

I have not run any premix yet, and I doubt the previous owner did, but I will be using premix at the track this weekend... Perhaps that will be enough to clear it out :-)

dont run the cat on the track!

That chart looks about normal as far as my ass dyno is concerned. I don't really rev mine past 7k because it just makes more noise and power drops off like yours does. The myth that these cars pull hard to redline is about as accurate as the "vtec kicks in so hard" myth lol I guess it depends on the gear too because I know first is so short that you can't really tell as where 2nd and 3rd are more noticeable because there's more time spent in the rpm range. Idk though just my 2 cents but I honestly think you're chasing a non existent problem. On a side note that hp number makes me feel really sad :'-( lol

It's no myth - . Suggest you get yours checked as well .

compare the above dyno to this one .........

https://www.rx8club.com/tech-garage-...3/#post4408918

Yeah brettus your power also dropped off before 9k! Sometimes I think it's just me because sometimes the car feels different depending on wether i'm well rested or if i've been up for 24+ hrs working lmao Do you guys have some more graphs? Maybe an isuzu dyno sheet to compare with?

Yeah - I guess you are right - practically fell on its face :uhh: