Low Boost Mode?

NemesisEJ22t · Post by **NemesisEJ22t** » Thu Feb 12, 2004 4:04 am

Hey, i searched for this and found nothing really relating to it. I have a MY 93 with a Saab intercooler and running at stock boost currently. Everything else is stock, no boost controller either. The problem i'm having is that sometimes the car will randomly go into some sort of low boost mode. The first time that it did this it was really warm out and i had 89 octane in it. This was last summer before i had the intercooler too (i know 89 is not good, i've learned from my past stupidity). The next time it happened was weird though. I had 93 octane and the intercooler on as well. It has done it about 15 times in between as well.

When this low boost mode kicks in, the gauge will not show more than 5 psi, and the turbo is more sluggish to get to 5psi than it is to 9 psi when its running normally. The way i usually fix this is to put it into 5th gear at around 2000 rpms and floor it, once i get to around 3000 the boost will usually go back up, but not always.

There are no check engine lights present, so i'm guessing that its not a major problem with a sensor, or its mechanical in nature. I'm leaning toward detonation, but i can't see how that would happen in the most recent occurance. It also seems weird that it would stick to 5 psi if it was mechanical. And it also spikes to maybe 5.5 or 6 before settling to 5, which in my mind rules out the wastegate spring controlling the boost only. Has anyone else experienced this? I would love to know whats going on here and if there's a problem so i can correct it as soon as possible.

Thanks

vrg3 · Post by **vrg3** » Thu Feb 12, 2004 7:27 am

The behavior you're seeing is precisely what happens if the wastegate control solenoid's not doing its job (yes, even that little occasional spiking).

I have seen on my car occasionally that if the ECU detects weirdness in the solenoid circuit or behavior or something it'll just stop using the solenoid but not throw a CEL. On my car, when that happens, if I put it in test mode (by connecting the green connectors), I get a fuel cut above about 50% throttle, but still no trouble code. I believe it's a bug in the ECU's code.

I suspect your problem would be solved with a new wastegate control solenoid, or maybe just a nice cleaning of your current one. I haven't tried cleaning mine yet, but my plan is to remove the hoses from it, leave it hooked up to the engine running with the revs held up around 1500 rpm (to make it cycle), and then spray some carb cleaner through it through each of the nipples while it cycles. After letting it dry out I expect it to work noticeably better.

Or you could just get a manual boost controller.

NemesisEJ22t · Post by **NemesisEJ22t** » Fri Feb 13, 2004 5:22 am

That sounds like a good plan, which one is the solenoid though? I think its the top most metal one with a vacuum hose nipple on both the top and bottom right? Of course it is, thats the only one that connects directly to the turbo and wastegate

. The only worry i'd have is messing up the solenoid with the spray, but it probably wouldn't be any worse than the oil/crap in there now.

vrg3 · Post by **vrg3** » Fri Feb 13, 2004 3:25 pm

NemesisEJ22t wrote:That sounds like a good plan, which one is the solenoid though?

http://www.graphics.cornell.edu/~v/pics ... eplace.jpg

(ignore the "pull off this hose" comment)

The only worry i'd have is messing up the solenoid with the spray, but it probably wouldn't be any worse than the oil/crap in there now.

I agree. Carb cleaner should liquefy most of the oil and it'll run out and the remaining cleaner should evaporate. So I guess what to do is be sure to rotate the solenoid to every angle while the cleaner is still liquid to make sure it runs out through the nipples, and then wait long enough for it to completely evaporate.

NemesisEJ22t · Post by **NemesisEJ22t** » Mon Feb 16, 2004 2:53 pm

True about the carb cleaner evaproating, but then you have the problem of all that grit possibly being placed on the moving surfaces of the solenoid. I'm thinking of just using compressed air now to see if that solves the problem. The solenoid isn't like a wastegate actuator right? It won't be damaged by high air pressures (60+ psi)?

vrg3 · Post by **vrg3** » Mon Feb 16, 2004 3:02 pm

Well, the idea is that you let the cleaner pour out the ports, carrying the grit with it. Then the small amount remaining inside needs to dry.

It's not especially sensitive, but I haven't seen its internals so I can't say for sure. Certainly it's meant to handle about 10psi on its two side ports, and to be able to bleed that pressure through the bottom port... I'd say about 20 psi would be safe but 60 it pretty high.

Dave G · Post by **Dave G** » Sun Apr 18, 2004 4:20 am

I just recognizd this familiar problem. Looks like I have been away for awhile, as I have been wondering about it for some time, and ypur post is old. All I can add is that my 94 is toally stock, with 125,000 miles, and I always run premium gas. My boost is limited intermitently to 5 psi, without regard to engine or ambient temp. I will be installing a boost control valve when I get around to it. Did you cure your problem?

NemesisEJ22t · Post by **NemesisEJ22t** » Tue Apr 20, 2004 1:48 pm

Yup, the MBC completely overrides the low boost problem, although i really want to find out if it was a mechanical problem or an ECU limp mode thing. If it was the ECU backing off the boost, there may be a problem with the engine that i want to address before i start turning up the boost.

vrg3 · Post by **vrg3** » Tue Apr 20, 2004 3:26 pm

Well, an easy way to check if the ECU is trying to use the solenoid or not is to listen for it clicking. If the car is parked with the engine running above 1000 rpm or so, the solenoid should be clicking (even if you have another boost controller installed). You may need a stethoscope to hear it though.

aspect · Post by **aspect** » Mon Apr 26, 2004 9:19 am

ok well, I was just going to make a post about this exact same problem. This has never happened to my car before, but since going from stock exhaust to 3" turboback with fancy downpipe (much much faster spool) my car behaves exactly as described above.

Just bombing around town I havn't run into it, but after pulling full boost on the highway and generally really pushing it, I'll suddenly get 6 psi which quickly drops to 5. Again, turbo is very slow to respond as well. This has now happened twice (two days ago and tonight) since I got the new exhaust.

The first time, I figured the ecu didnt like the change in the turbo spool, so after getting the car home I reset it, and everything was fine. Tonight, after pulling off the highway and stopping for coffee, boost was back up to 100% as soon as I hopped back in the car 10 minutes later.

Wtf is going on? I always run 94 octane and otherwise the car seems to be running great.

Should I buy a new knock sensor? Install a manual boost controller? Bash my ecu with a rock and buy a link plus?

Help!

Edit- Thought I should make this part clearer: Once the car gets into this mode, it stays that way. Every time you accellerate, you get the same crappy boost. It's really like the ecu is going into some sort of low boost safe mode. Like I said, after resetting it or even apparently just restarting the car, things go back to normal. This is why a malfunctioning soliniod doesn't really make sense to me.

vrg3 · Post by **vrg3** » Mon Apr 26, 2004 4:17 pm

I think you should try cleaning the solenoid out anyway. I understand how it doesn't sound right since resetting the ECU makes it go away, and I don't yet have a good explanation. I was getting the same problems, though, and they went away when I cleaned the solenoid.

Oh, try something else -- when you have this problem next time, pull over and connect the green test mode connectors under the dash. If your ECU is doing the same thing mine was, you'll start getting fuel cut preventing you from going on boost at all. All this without any trouble codes. I think there's some kind of glitch in the coding.

aspect · Post by **aspect** » Mon Apr 26, 2004 10:34 pm

Will do, I'll post up any results...

NemesisEJ22t · Post by **NemesisEJ22t** » Tue Apr 27, 2004 5:04 pm

When i had the problem, resetting the ECU didn't make the full boost come back. I left the battery terminal off overnight and it still didn't affect it.

vrg3 · Post by **vrg3** » Tue Apr 27, 2004 5:06 pm

Ben, did you ever try cleaning the solenoid?

NemesisEJ22t · Post by **NemesisEJ22t** » Wed Apr 28, 2004 2:10 am

Not yet, i haven't had the time recently with all the fun work that college is throwing at me right now, and with the MBC installed it hasn't been a problem. I will be removing the MBC for a while though to try to save the clutch which is getting progressively worse. I need to have the Legacy drivable until i can get my Celica back together sometime in May, then the Legacy goes in the garage for the summer while i get it completely road worhy again. If i start to have problems with the stock boost solenoid, i will attempt to clean it, but i want to blow it clean with compressed air after i'm finished to make sure all the crap doesn't get into the wastegate solenoid and cause problems there, but i don't have a compressor here at school.

aspect · Post by **aspect** » Sun May 09, 2004 8:04 am

So...hrm..

Problem got worse, and for the past week or so i've had 5-6psi solid, even after resetting ECU a couple times. Was driving home from work today, when I realized that if the wastegate control was stuck open, it would make sense that the turbo would only spool that high. There'd be a bit of lag as the pressure got from the turbo outlet through the manifold to the wastegate (spool to 6) but then it would hit the wastegate and keep it from spooling anymore (drop back to 5).

Anyways, about 8 seconds after I realized this, I gave it a bit of gas and suddenly had all my boost back again. Has been fine all night.

*shrug*

mikec · Post by **mikec** » Sun May 09, 2004 11:25 am

Dang... I was hoping there was something you had done to get the boost back. I've been stuck with 5-6 psi for the longest time, even after changing the stock controller.

Unfortunately, I've tried giving it gas a bunch of times...

aspect · Post by **aspect** » Mon May 10, 2004 6:10 pm

So I unhooked my diverter valve hose for some PSHHHH action the other night and it went back to 5psi an hour or so later.

I'm pretty sure its the controller, but if you've already changed it, perhaps you should check the actual wastegate? It's quite possible that it is simply stuck open. I'm sure mine is fine cos I just had a custom downpipe made up, and we blew some air into the wastegate control to check the clearance on the downpipe flange...

mikec · Post by **mikec** » Mon May 10, 2004 6:14 pm

It looked like it was sitting closed when I swapped my downpipe a couple of weekends ago. And I know when I hooked up my MBC I was able to get more than 6.

I'm going to try swapping ECU's with totech at some point, and see if that fixes it.

aspect · Post by **aspect** » Thu May 13, 2004 9:27 am

Ok, well, cleaned out the solinoid by spraying a lot of cleaner in there. No change at all, except I did suddenly get all my boost for about 20 seconds like 45 minutes later, which happened to be on my 3rd 0-100mph pull against a lightly modded WRX. Actually gave him a bit of a run for his money...

Drove home, and it was back to suck mode.

SOMEBODY FIGURE THIS OUT! MY CAR IS NO FUN ANYMORE!

Edit: I also just noticed you have a 3-in turboback. I do as well, and this started like right after I got it. hrmmm....

mikec · Post by **mikec** » Thu May 13, 2004 12:13 pm

I would like to blame the exhaust, but I had this problem before I got it installed. I should try cleaning my controller out.

totech · Post by **totech** » Thu May 13, 2004 5:09 pm

mikec wrote:I would like to blame the exhaust, but I had this problem before I got it installed. I should try cleaning my controller out.

I will re-swap back with you anytime....

aspect · Post by **aspect** » Thu May 13, 2004 9:20 pm

I just re-read this thread and now that I think about it, my cleaning method was kinda useless. I removed the whole unit from the car and cleaned it, which probably wouldn't really do much. I'll try it today with it connected to the car to get it to cycle a bit.

BAC5.2 · Post by **BAC5.2** » Fri May 14, 2004 8:14 am

I had this happen to me tonight. Very random too. Some times it would be regular boost, sometimes it would be 5psi.

I've got a VRG3-MBC here that'll go in this weekend along with my Saab cooler. That should solve all problems.

NICO · Post by **NICO** » Fri May 14, 2004 8:59 am

why is every one worryd about one psi and it going up or down thats its job, turbo up foot off gas turbo down, for me if it was, 22psi up bye one from 21psi i might blow up, but 5psi to 6psi i think its a gift.

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Low Boost Mode?

Low Boost Mode?