My 4AGE, coughs, backfires, splutters and then stalls at 4000RPM, but only once warm?

[phrostbyte]

Hey once again peeps.... Yet another day in my life of post-conversion 4AG problems...

Ok, was cruising over to a friends house yesterday after fixing my starting problem and feeling all safe and secure with my 4AGE. Halfway there (just after it finished its warm-up cycle and dropped down to the set idle RPM), all of a sudden it went "COUGH BACKFIRE SPLUTTER COUGH STALL". I pulled over, started it again and it started perfect. Another 50M up the road and I'm on the side of the road again going "OMGWTFBBQ?!" . Three or four more stops on the side of the road and my passenger turns to me and says "Dude it's only happening after you go over 4000RPM." So I then drove the whole way to my friends house and back home at a mind-set 3500RPM redline, no problems, no visits to the side of the road.

This morning I fiddled with some wires, tried the check engine light (which doesnt work for some strange reason, the ECU just doesn't want to ground it at all, diagnostics mode or not..). Went for another drive and went "OMG it works again!". For the 2 minutes or so while it warmed up I was so happy with my re-aquired 7800RPM redline. Then, after it had warmed up, disaster struck and the second i hit 4000RPM on a take off and it went "COUGH BACKFIRE SPLUTTER COUGH STALL". I pulled over, started it again and very angrily drove it back home with another mind-set 3500RPM redline...

What in the hell could cause this?!

Cheers,
Kev.

[45aken]

maybe MAP or AFM? there the usual problems in my subaru.

[phrostbyte]

Hmm I'm pretty sure the MAP sensor is fine, the engine itself was working perfectly in my last KE70, so I'm pretty sure its a wiring problem somewhere rather than mechanical.. Just wondering if anyone knows where the problem could be, not in the mood to rip my entire loom apart to find one wire buried in it somewhere disconnected...

I just can't understand why the problem doesn't appear until after it's warmed up?!

Kev.

[4agte]

ISCV? (character limit)

[wiso]

a 4age doesn't have an ISCV, they have an auxilary air valve, that shouldn't affect it once its warm though,

hmmm did you wire the car yourself? could be the ecu not getting proper signal down the t-vis vsv perhaps, something to look at cause thats when the t-vis about kicks in

[JustCallMeOrlando]

Although on a 1G this happens at 2000rpm, it sounds very similar to what mine does when the knock sensors are loose.

That is about when the TVIS kicks in, but it shouldn't be able to cause the car to stall, whether it's open all the time, or locked shut like mine.

[wiso]

the knock sensor won't cause this, when i converted my 4age to a ze usignt he gze ecu i didn't have a knock sensor and it still reved all the way out, plus a 4age doesn't have a knock sensor.

i know the t-vis wouldn't cause this, but i was thinking the ecu might not be getting the signal causing it to go wtf? i know its a long shot, if i can think of something better i would

[phrostbyte]

Nup checked the TVIS, unplugged it, replugged it, removed its power, no luck. Lol that was my first guess too..

Kev.

[devolutio]

It seems you are having a lot of intermittend problems with this engine, Can I recommend taking the loom off (now you know where everything goes and that it all works) and re-wiring it? check every wire from the ecu especially any dodgy looking connections (what was that about wires twisted together?). While you're at it get hold of another ecu and do some testing.

possibly the vibrations at 4000rpm are messing with something not connected well (injector wiring?).

[DigitalPho3nix]

You redline a cold engine? You do know there is next to no oil flow when cold?

Harmonic Vibrations at 4000rpm in engine mounts or something similar causing a wire to rattle off its connection? Bad solder joint somewhere?

[phrostbyte]

I really REALLY doubt that this problem would be in any way related to a loose wire.. It's too specific for that kind of problem...

Anyway, after delving into it a bit further today with a friend (Thanks James), we managed to figure out that it is infact going into limp home mode (diagnostics mode), not just completely dying, (If you do hold the throttle down, it backfires like hell and just all over wants to die, but will get you that few streets back home).

Obviously the ECU is detecting a problem after 4000RPM and enabling diagnostics mode. If only my check engine light worked...

Will be delving even further into the shit tomorrow, but if anyone else has any ideas, please do post them up...

Edit: I use 10W/40 (Semi-synthetic) oil which is thin even when cold, and even so I usually wait until atleast the oil has warmed up a bit before redlining the thing.

Cheers,
Kev.

[takai]

Money here is on the warm idle up valve underneath the throttle body. My guess is that when the car warms up the idle valve opens completely so at high RPM you end up leaning out the engine, hence the spluttering and stalling.

[devolutio]

what is this 'limp home mode' you speak of? The TPS fell off my throttle body the other day, so I just unplugged it... i imagine this would set off any limping modes... but my engine is making (butt dyno) just as much power, just a bit laggy on throttle response and has the same 7,800rpm rev limit as always (yeah yeah i will fix it, but I have another car now and not much spare time).

are you running the coolant lines to the throttle body?

I agree with takai, have a look around the throttle body area.

oh and wire up your ecu properly to get a engine light.

[takai]

Im 99% sure that 4AGs dont have a limp mode. The TPS doesnt do anything except for accel/decel enrichment, and also closed/open loop when at WOT. Everything else is handled by the MAP sensor.

[phrostbyte]

Yeah 4AG's do have a limp mode, can either be triggered by a sensor giving a really bad signal or you can trigger it manually by grounding the T connector on the ECU or diagnostics connector if you have one, to set timing.

TPS is not a sensor that is required for the engine to run right, hence if it comes unplugged, the ECU won't care. As you said it will give you a bad throttle response because there is no idle switch, but the actual throttle position, the ECU will replace with readings from the MAP sensor.

But if you are right and there is no limp mode, then it could well be a sensor completely carking it somewhere. I just can't understand that once it goes into this "limp mode", I can either drive around with it like that, backfiring and wanting to die all over, or stop for a second, restart the car straight away, and drive up to 3990RPM no problems... Doesn't make sense??

Edit: For another example, it went into limp mode on one of the many many test drives yesterday, I clutched in, let it stall, turned ignition off then back on, put it in second, dumped the clutch and drove home again?!

Edit no.2:

oh and wire up your ecu properly to get a engine light.

Just found out I was using the wrong pin in the ECU as the engine light ground, I'll try it again in about half an hour with the RIGHT pin hahaha. I was using EGW instead of W.


Kev.