Topic: inconsistent boost levels and 4500rpm rev-limit? Any advice?

[Way_Gone]

Hello guys and gals...

So this is an issue that has just come up tonight... When driving today I noticed that my boost levels seemed strangely inconsistent in that if I hit 3/4 to full throttle, boost would build as normal, then rapidly spike to about 8 or 9, then build again, then spike again to about 13, then fall on a resting 10-11psi... Which is what it is normally maxed at... The motor seemed to be running fine, everything was smooth, no strange noises... Just seemed to be spiking for some reason... Then, mystery number two appeared..

After a short while, my engine light came on and I noticed I know can't rev any higher than 4500, right on the money. It is acting like it is being limited though, not like it's being held back mechanically, but like it's being limited by the ECM... Now, I have a theory for this but really don't know how accurate it is...

Here's my train of thought, but I am very new to the EJ20:
Last night I had my dash apart as I was doing some work and as I realized this morning, I must have mucked up reconnecting everything behind the dash because my speedo wasn't working this morning... Big deal, I can go a couple days without a speedo, I know the car well enough to know how fast I'm going... but then I starting thinking, I know a lot of cars come built with an idling rev-limiter... So that when you're not in motion, you can't rev out your motor, usually limiting them to around 3000-4000 or so... So if the car doesn't think I'm moving, it might being trying to limit the motor rpm?... Make sense? But I've never seen one in a car this old before, does anyone know if they came equipped with such a thing? Because if that's the case, then hook the speedo back up properly and voila, problem solved... I just didn't think it would have had this in 1993..

But I can't really think of how that solves the boost spiking issues... If anyone has any advice, I would greatly appreciate it... I've only had the car a short while and of course the first place my mind goes is that something is terribly wrong...

I some details about the car would be good: it's a 1993 GF8 EJ20... APEX'i intake, 3" turbo-back, HKS BOV, stock tune... Up until today was running like a dream.

Unfortunately, I don't have the ability to try and hook the speedo back up tonight, will likely have to wait until tomorrow or Thursday so I'll see if that takes care of any issues then... But otherwise, I'll take any bright ideas

Thanks in advance,

Corey

[Way_Gone]

Also, forgot to mention... coil packs were done very recently.. I know those early ej20 coils can cause a lot of issues but they should be good... they aren't converted to late ej30 coils but are new ones from subaru...

[VanCharvel]

It sounds more like ECU Limp Mode to me. I believe it's caused by a faulty speed sensor or something similar... Hang on, there's a thread here somewhere about it...

EDIT: Here's one. http://www.westernsubaruclub.com/smf/index.php?topic=14354.0

Looks like your best bet is to pull the codes and see what's up.

[blessthekellen]

was also going to say limp mode. typically reduces boost & gives you a terrible rev limit.

[Way_Gone]

Thanks a bunch guys, I am thinking it's definitely limp from what I'm reading... I'll see if I can figure out what codes it's throwing and go from there...

Any more advice will be happily taken until then

[SLO GTR]

Hook the speedometer back up and your issues will go away

[KLZCYA]

I had my speedo disconnected for a bit and it didn't put me into limp mode =/

Pretty sure if you reset the ECU the limp mode will go away, temporarily anyways.

[Way_Gone]

Cool, well hopefully I'll get it taken care of in time for Wings night tomorrow... I'll get the speedo hooked up properly and run the codes anyway, just to be safe

[Jarrod]

Haha it is definitely because of the speedo cable not being plugged in.  All you have to do is get on your back under the dash and reach up and shove it in.  Might have to twist the cable a little as it's a square.
I believe as soon as you have that in and your speedo works, your limp mode is gone, but do a reset just for funzies.

Oh and your car will behave fine without the speedo until you hit that 4500 rpm mark.  Then it's effed.

[KLZCYA]

Just an fyi on the speedo cable; you wont be able to connect it into the back of the cluster without releasing the quick release on the tranny (right by the tranny fill spout), as its too short. So, pull the cluster, undo the quick connect - plug it back into cluster and then back into the tranny

[Jarrod]

I've never had to do that myself heh.  I always put the cable into the transmission first.  You do need to get all the slack out of the line though so just shove it through the firewall as much as you can.

[KLZCYA]

Mine was definitely not long enough to do that

[Way_Gone]

Thanks for the heads up guys, at least I now have some idea of what to do, should speed up the process

[cmyles]

It might not be a stock tune if its doing that.
Also, you can pull the code if you havent by doing this:

http://www.perth-wrx.com/vb/stock-ecu-discussion/30024-how-read-subaru-cel-gc8-stock-engine-control-unit-only.html

And the boosting issue, if it has nothing to do with the issues your having with limp mode may be your wastegate, or your factory boost control solenod going.
Its bound to happen sooner or later, get yourself a manual boost controller, or electronic if you wanna spend a bit more.
You can get them for cheap and i've seen them fix, as most people have, tones of problems with the GC8.

[Way_Gone]

Thanks again for the advice from everyone... Reset the ECU and while that was happening, hooked the speedo back up properly... Was a pain the butt to get attached again but all things considered, not a big deal at all.

CEL was gone when I fired it up, no more limp mode and boosting full and strong again! Phew!