94 RS TT cutting out randomly

[dimin]

Having a problem with my BD5 TT Legacy cutting out at random. It appears to be losing power to the ecu for a a few seconds, drop it to 3rd to pass for example and itll get through VOD, then just as it reaches fully secondary boost it cuts out violently, the tacho drops to 0, and when it kicks back in you can here what im sure is the main relay click back in. Coincidently it seems to happen at higher boost not sure if its got anything to do with the problem. Have replaced main relay and no luck. Almost seems like its happening right where the boost cut should come in, and seems worse when the air temp is cooler. Anyone else had issues like this on a legacy BG/BD ? Thinking possibly AFM but thought it would simply throw a CEL not completely kill power to the ECU?

[Guest boostcut]

check spark plugs, i think its sounds like its blowing the spark out and momentarily shutting the engine down.

[dimin]

Pretty sure not the plugs. When the engine "cuts out" it stays out until the revs drop back down - up to 10 secs at times. I find pushing the clutch in lets it fire back up into idle. Pretty sure whatever is happening the ECU is losing power completely, but only the ECU, which is what made me think main relay. Replaced it however and no luck.

[Guest the_return_of_the_jedi]

twin turbo...

what more can i say

[pl0x]

 dimin said:

Pretty sure not the plugs. When the engine "cuts out" it stays out until the revs drop back down - up to 10 secs at times. I find pushing the clutch in lets it fire back up into idle. Pretty sure whatever is happening the ECU is losing power completely, but only the ECU, which is what made me think main relay. Replaced it however and no luck.

If your not going to take advise you get from people why bother asking? :

[Drunkenmonkey]

wire in a Volt meter to the ecu see if it is losing power...

[rexxxy]

hmmmmmm...... hmmmmmm.....hmmmmmm not a clue.... never heard of that one before, only in 3rd and worse in the cooler weather... both my turbos leak like a siv and it goes into limp mode when im holding 4th down, or third on a hill, quick flick of the ignition and im back in business, and thats worse in the hot weather.. so im thinking if it temp related its not electrical.. dunno im a just a builder!!

[dimin]

 pl0x']

[quote name='dimin said:

Pretty sure not the plugs. When the engine "cuts out" it stays out until the revs drop back down - up to 10 secs at times. I find pushing the clutch in lets it fire back up into idle. Pretty sure whatever is happening the ECU is losing power completely, but only the ECU, which is what made me think main relay. Replaced it however and no luck.

/quote]

If your not going to take advise you get from people why bother asking? :

Sorry mate, just that I can already ascertain its not plugs. Should be asking has anyone had this issue before and how did you sort it ??

Will check the ecu power with my meter tomorow to confirm it looses power.

Also forgot to mention that it happens in 4th and 5th as well as third, at full boost usually too so wondering if its some form of boost cut. Other wise the car runs mint.

[Guest boostcut]

what are the factors that lead you to believe its not plugs? have you even looked at them? also, just looking at the plug doesnt always mean its fine. it sounds to me very much like an ignition problem, as a high gear and high boost means load on the ignition system. maybe you could spend 5 minutes checking things and save some money? but what do i know.... i didnt do 6 years of study to be an ATech mechanic for nothing

[Guest the_return_of_the_jedi]

 boostcut said:

what are the factors that lead you to believe its not plugs? have you even looked at them? also, just looking at the plug doesnt always mean its fine. it sounds to me very much like an ignition problem, as a high gear and high boost means load on the ignition system. maybe you could spend 5 minutes checking things and save some money? but what do i know.... i didnt do 6 years of study to be an ATech mechanic for nothing

yeah im pickin check the spark plugs. maybe one of them is broken..

failing that maybe a coil?

oh and no one has asked about any upgrades or "backyard mods"

so its not throwin cels?

[dimin]

 boostcut said:

what are the factors that lead you to believe its not plugs? have you even looked at them? also, just looking at the plug doesnt always mean its fine. it sounds to me very much like an ignition problem, as a high gear and high boost means load on the ignition system. maybe you could spend 5 minutes checking things and save some money? but what do i know.... i didnt do 6 years of study to be an ATech mechanic for nothing

One big factor is the plugs are near new, regapped to 0.6mm to stop blowing out of spark. Im no mechanic, but in my experience I havent had spark plug issues cause the car to completely cut out(as in no spark, rev gauge stops dead, all the twin turbo system solenoids drop out, pretty much as if the key is turned off yet lights/acc etc stil going fine) for up to 10 secs at a a time, misfires yes, but this is definately not a misfire. Even a coil dying I dont see causing the issues im having.

Appreciate your help though, the point of the post was hopefully someone may have had the same problem before and could let me know how they went about repairing it. My parents had a 94 RS TT back in the day and it had an almost identical issue to this, however they never got round to fixing it as they traded it in, so thought maybe it may be common-ish problem with this gen legacy.

Also no CEL, and no backyard mods. Have cleaned and resoldered MAF, checked plugs, wired in new relay in place of main relay, will do some more investigating tomorow.

[rexxxy]

id just drop it off at subaru, get them to diagnose it for ya, may cost ya a hundy, then take it away and fix yourself..

[rexxxy]

whats it boosting at on secondary?

[kamineko]

i'd be checking the cam/crank sensors. usually when they're naffed the car just won't start but our old BG would do some weird mid-driving cut out as well

see if you can borrow a pair to try, they are easy to swap but fairly expensive to replace

however you would normally expect a cel code with erroneous cam/crank signals so maybe its a make/break electrical problem when the engine twists on its mounts during high load

[Durty-Sanchez]

 boostcut said:

what are the factors that lead you to believe its not plugs? have you even looked at them? also, just looking at the plug doesnt always mean its fine. it sounds to me very much like an ignition problem, as a high gear and high boost means load on the ignition system. maybe you could spend 5 minutes checking things and save some money? but what do i know.... i didnt do 6 years of study to be an ATech mechanic for nothing

If spark plugs blow out/fuel pump dies/AFM dies I can still see what RPM my engine is doing... how else can I coast down a hill and still see the tacho working?? I didn't spend 10 seconds working that one for nothing Tacho dying at the same time suggests that it's cam/crank angle sensor, ECU, or dud connection somewhere. Cam/crank sensor signal is piped through the ECU, which then outputs the tacho display signal.

There's an outside chance that *something* is shorting out the ECU - possibly in the solenoid box or on the ECU itself. Check for ECU power at all of its power sources. One good way might be to plug in the diagnostic connectors and go for a drive. If the problem is repeatable (and you have no error codes) then it will flash a steady pulse at you. If you lose that pulse for the duration of your power loss then you know the ECU has ceased executing its firmware.

I believe the ECU requires both cam and crank signals to work in order to synch them on startup. After that it only cares about one of them, but there's still a chance that one or both of them doesn't like heavy acceleration so dies. Same goes for a bunch of other connections, but it's just a matter of ruling all the causes out one by one until you've got it. You're on the right track it seems so keep poking around, you'll find it eventually! Do you have a spare ECU you can test? If not PM me and I can send you a spare one to try out.

[dimin]

 Durty-Sanchez']

[quote name='boostcut said:

what are the factors that lead you to believe its not plugs? have you even looked at them? also, just looking at the plug doesnt always mean its fine. it sounds to me very much like an ignition problem, as a high gear and high boost means load on the ignition system. maybe you could spend 5 minutes checking things and save some money? but what do i know.... i didnt do 6 years of study to be an ATech mechanic for nothing

/quote]

If spark plugs blow out/fuel pump dies/AFM dies I can still see what RPM my engine is doing... how else can I coast down a hill and still see the tacho working?? I didn't spend 10 seconds working that one for nothing Tacho dying at the same time suggests that it's cam/crank angle sensor, ECU, or dud connection somewhere. Cam/crank sensor signal is piped through the ECU, which then outputs the tacho display signal.

There's an outside chance that *something* is shorting out the ECU - possibly in the solenoid box or on the ECU itself. Check for ECU power at all of its power sources. One good way might be to plug in the diagnostic connectors and go for a drive. If the problem is repeatable (and you have no error codes) then it will flash a steady pulse at you. If you lose that pulse for the duration of your power loss then you know the ECU has ceased executing its firmware.

I believe the ECU requires both cam and crank signals to work in order to synch them on startup. After that it only cares about one of them, but there's still a chance that one or both of them doesn't like heavy acceleration so dies. Same goes for a bunch of other connections, but it's just a matter of ruling all the causes out one by one until you've got it. You're on the right track it seems so keep poking around, you'll find it eventually! Do you have a spare ECU you can test? If not PM me and I can send you a spare one to try out.

Cheers for that advice mate, exaclty what I was after. Mentioning cam/crank angle sensor makes sense, especially as the tacho feed drops out too(which ECU obviously gets from either of those sensors' signals)! Went out yesterday with multimeter but typical, damn thing ran perfect, gave it a good hard drive for over half an hour and not a hiccup. Anyway once the problem repeats itself I can see whether its the main ECU power dropping out and go from there. Will update if I get any progress ! cheers

[Guest boostcut]

i bet this problem lasts forever. : the owner doesnt want to/ cant even be bothered to check the simplest of things first

[nickmcgill]

This sounds kinda stupid compared to what has been said so far, But try checking / cleaning your battery terminals.

Mine had done it a couple of times in last few days with the taco and speedo both dropping off dash fading and flashing and the car shaking violently as it missed.

Cleaned the terminals and tightened them. Been fine since.

[Guest the_return_of_the_jedi]

it could be anything really... a loose wire, bad earth, trolls ;D or any of the above things..

diagnostic for sure in this case

[dimin]

Update....managed to make it play up again, ECU is not losing power. Still the rev counter dropping to zero, and wont restart until the revs drop back below 3k rpm. Plugs are fine, battery terminals tight, no CEL codes, also can get it to do it at less than full boost so not boost cut. Cam/crank sensor possibly ? seeing as it loses tacho signal, and also theres a click from under the dash when it fires back to life which im thinking is the fuel pump relay, IIRC ECU only activates fuel pump when theres an rpm signal(cam/crank sensors). Might have to try borrow a couple of those sensors and give it a go at some stage.

[Guest]

hey just wondering if this issue was ever resolved because I have the exact same issue with my bd5 rs, thanks