So you think your an expert? Boost control issues

[Radial GT1]

My can under load (uphill pulls). Just driving it normal, doing my best to get good gas mileage you know. When I am in boost the boost will move around all by its self. IE; when I am going up long hills with my foot at the same position the whole way, the boost will move from 8psi to 5psi. Also when it is doing this it feels like it changes the timing around because it looses I would say 40% of its power. And then the power will come back on and the boost stays low at 5psi, and than it jumps up to 8 psi for a second and back down again. It is a viscious cycle. Everyday I have to drive 3 miles up hill after work on the freeway it is driving me crazy.

It seems to get less noticable at about 3700 RPM, the boost still moves but the power doesn't flow around.

What I have and have tried to replace thus far:

It is a 93 SS 4Eat, all stock, with exception of boost gauge
New parts: Knock sensor, Water temp sensor, TPS, MAP sensor, Plugs, Wires, Fuel filter, vacume lines.

Would the O2 sensor have control over the wastegast actuator? What other sensors has this much control over the engine? I wish this thing had ODB II.

Thanks for helping.

[smh0101]

Could it just be the wastegate?

Do you have an MBC? If so could it be bad?

I am in noooo way an expert just throwin out thoughts...

[Dynamic Entry]

+1 for checking the wastegate

http://www.bbs.legacycentral.org/viewtopic.php?t=33341

I have not actaully gotten around to troubleshooting it but I have similar symptoms to what you describe. I think about checking/replacing all those sensors but then I hear from guys like you that say it didn't help. So I really want to check out my BPV and wastegate.

Unfortunately that will mean subscription of help. That means you Mike if you are lurking

[dscoobydoo]

How many miles on the car?
Ever replaced the BCS hoses? ( the boost solenoid hoses)

Maybe your solenoid has gone bad?

Try putting in a Manual boost controller and see.

[Radial GT1]

+1 for checking the wastegate

http://www.bbs.legacycentral.org/viewtopic.php?t=33341

I have not actaully gotten around to troubleshooting it but I have similar symptoms to what you describe. I think about checking/replacing all those sensors but then I hear from guys like you that say it didn't help. So I really want to check out my BPV and wastegate.

Unfortunately that will mean subscription of help. That means you Mike if you are lurking

My car does make a wierd noise like the one described here. I will do some farting around with this and see if it helps.

Why does Subaru run the wastegate off a electrical solenoid like that? Most other cars I have owned that are turbo run the wastegate right off the manifold.

[Radial GT1]

How many miles on the car?
Ever replaced the BCS hoses? ( the boost solenoid hoses)

Maybe your solenoid has gone bad?

Try putting in a Manual boost controller and see.

The car has 99930 miles on it. Never replaced those hoses that go down to the turbo. I will run to home depot and get some pieces to rig together a MBC and see if it helps at all. Thanks!

[Legacy777]

Why does Subaru run the wastegate off a electrical solenoid like that? Most other cars I have owned that are turbo run the wastegate right off the manifold.

Because it allows for finer boost control.

[Radial GT1]

Well, update.

I just bought a MBC off ebay, and got it working good and dialed in. Stock boost now holds steady. Still has the same problem with lacking power. It does seem more defined now however. The transition to power from under powered happens when the car is traveling with the RPMs at about 3200 RPM. Anything under that and the power comes and goes. Feels good from a couple senconds (3 Seconds), and than back to driving like a geo metro (5-8 seconds). I know it is going to be something just silly, but I just need to be pointed in the right direction.

Thanks!!

[555BCTurbo]

Sounds like you could have a knock sensor problem...

Any CELs?

[asc_up]

Sounds like you could have a knock sensor problem...

Any CELs?

+1

[Radial GT1]

no CELs

I have hooked up the diagnostic connections to see if there are any stored and also nothing. The knock sensor is brand new from subaru. Perhaps wiring for that sensor is bad. When I bought the car that sensor was bad and some dumbass tried grounding the wiring under the dash that goes to the cpu for the knock sensor (which fried the computer that I had to replace when I bought it). I will have to double check the repair job I did.

[BXSS]

That does sound like a knock sensor issue, but If you changed the KS already it should be resolved.
+1 on making sure the KS wiring is OK.

Could it really be getting some knock?

[ciper]

Can you take out a spark plug or two and take a picture?

[Radial GT1]

I sure can. I took them all out a little while back to see if I was loading up. It is not, they are a nice light brown color. So from what I can tell it is not a fuel delivery problem but a spark issue.

It seems like something is retarding the timing. I have tuned many stand alone computers on RX7's and when you retard the timing too far it feels just like my car feels like it is doing.

It does not make any knocking sounds at all. I have owned it over a year with it doing this and never hear a knock. I never drove it with the bad KS, I changed it right away after purchase.

Thanks for the continuing help guys!

[ciper]

Strange... usually spark issues get worse with higher rpm on a turbo. Do you have an old set of plug wires you can try?

[All_talk]

I sure can. I took them all out a little while back to see if I was loading up. It is not, they are a nice light brown color. So from what I can tell it is not a fuel delivery problem but a spark issue.

It seems like something is retarding the timing. I have tuned many stand alone computers on RX7's and when you retard the timing too far it feels just like my car feels like it is doing.

It does not make any knocking sounds at all. I have owned it over a year with it doing this and never hear a knock. I never drove it with the bad KS, I changed it right away after purchase.

Thanks for the continuing help guys!

This may be a silly question but... What grade fuel are you running?

With both my old RX and my Legacy SS I noted a similar issue when running low octane fuel. I would punch it, it would start to pull then kinda fall on its face. Then one summer day with thw windows down I noticed just a slight bit of knock preceding the power loss. I switched to high octane and the problem went away. Seems the stock system was doing exactly what is was intended to... sensing knock and retarding the timing.

Note: once I tracked the mileage with low and high octane fuel and noted that the increased MPG with the high octane more that payed for the difference in price I've never looked back.

Gary

[vrg3]

It really really sounds to me like your ECU is detecting knock. Excessive knock makes it cut down to wastegate boost and retard timing. Then, after a while, it tries pushing it back up. If it detects detonation again, it'll back everything down again.

From what I've been told, our engines can knock significantly without it being audible without instruments.

Can you run my scan tool and see what the knock correction is?

[Radial GT1]

Thanks for everyone taking a look and offering suggestions!!

I run premium grade fuel all the time (91 oct.). That is the highest we have in these parts so that shouldn't be an issue.

The plugs in it right now are Premium Iridium plugs. And the wires are also brand new. I replaced them when I first got the car running because I thought that they might have been my problem. Sadly it was not the problem, it did not effect the power loss at all.

I am wondering about my ECU detecting knock. What would lead to engine knock other than low grade fuel?

I would love to hook up an engine diagnostic tool to tell me the problem! Where do I get this scan tool? And how exacly would I hook it up? My friend has a $3000 snap on scan tool that we have hooked up and it tells us everything is fine (damn ODB1). Is there something special that I need?

Thanks!

[Radial GT1]

OOop Your scan tool is a sticky. Wow, just a little slow. I will have to get building on this thing! Good stuff.

I have a laptop that is running XP. Is this too new to use your software? I see you mention very very low amounts of memory required, and am just wondering if my computer is too new.

[All_talk]

...I am wondering about my ECU detecting knock. What would lead to engine knock other than low grade fuel?...

Just another thought, how’s your oil consumption? Oil vapor in the burn acts like an octane reducer. Excessive blow by, bad turbo seals and issues with the PCV system are all common causes.

BTW, 91 octane is that best I have here as well and runs fine in my car, so you’re right that shouldn’t be the issue.

Gary

[vrg3]

If you can boot it off a CD, that should work.

Your car shouldn't knock on 91 octane but that doesn't mean it isn't knocking.

Knock can be caused by using the wrong plugs -- are you sure the spark plugs you put in are intended for this engine?

Cooling system problems can also cause knock. Have you gone over the cooling system recently?

Carbon buildup in the heads can do it too; a Seafoam treatment might help with that.

It's even possible for an incorrectly installed timing belt to cause knock. A bad MAF sensor or injector could do it, but that seems unlikely if the engine runs okay otherwise without any oxygen sensor trouble codes.

[Radial GT1]

I never have to add oil. However, on one note with that. When you check the oil when it is cold, it reads like a quart over. When you check the engine after it has been running for a while and let it sit for a minute it reads right on the full line.

Could I be putting too much oil in the thing causing issues? When I have removed the catch tank between the compressor inlet and the MAF there is a quite a bit of oil in there. Not just a residue, but actual little pools of oil. But the engine never smokes, not even when at redline.

I pulled the engine a while back to fix a oil leak off the back of the engine. And changed the timing belt at the same time. Now the problem existed before I pulled the engine, so the timing is not the issue. I set the timing 100% correct. Also the coolant was completely changed at that time too. Also on another note I did change out the coolant temp sensor (ecu sensor) with a new one from subaru as well.

I will try the seafoam treatment, I have been thinking about doing that as well. It worked well in the old snow blower, perhaps it will work magic on my car too.

Is it possible that a bad MAF, or O2 sensor would be sending the wrong information to the ECU but not tripping the Engine light?

[vrg3]

Little pools of oil in the intake tract are common.

Burning oil can cause knock on boost, though, because oil lowers the effective octane of the fuel.

It is possible in principle that a bad MAF and oxygen sensor could cause the problem, yeah... You can eliminate the oyxgen sensor from the equation by just unplugging it; the car will run happily without it aside from a CEL when cruising on the freeway.

Any chance you can borrow a MAF to swap in temporarily?

[ciper]

"Premium Iridium plugs"
Could be your problem. NGK V-Power BKR6E-11 are OEM parts and should cost you about 6$ at the local parts place. There is a thread all about "high end" plugs causing the car to run badly.

[Radial GT1]

Thanks for the info on the correct plugs, I will be replacing those this week. It would be silly if it was just having the incorrect plugs that would cause this. But it would rock if it solved the problem!

I do not know of anyone in town that would have a MAF to use. I may just have to buy an extra just to see if it works.

Thank you guys!