davesan1

iTrader: (4)

I'm chasing the cause of an overboost + boost creep problem. I've read the threads and everything checks out so far - wastegate solenoid, actuator, etc etc all seem OK. Specically, I have gone as far as using a simulated boost of 8 PSI , (from my compressor), applied to the wastegate actuator instead of the boost supply port on the primary turbo. I also rigged up the wastegate relay so that I can actuate it at will via the battery. All works as it should EXCEPT that I notice it takes a longer time than I would expect to open the wastegate. For the first 2 to 3 seconds the actuator rod doesn't move and then it starts to move slowly and reaches full open after approx another 4 seconds. During this time the solenoid is definitely "off," and no pressure "leak-through" can be heard, (like what you can hear when the solenoid is acivated). I also checked with my Miti Vac that there are no pressure leaks with the solenoid "off."

I realize that during this actuation period the pressure has to meter through the pill, (which I checked is there and not blocked), but it still seems to take a long time. It seems to me that this slow actuation situation could cause overboost at the 4500 RPM secondary cut-in time if the turbo actuator valve is significantly open by the time the wastegate opens enough to control magnitude of the added boost. Anyone any idea on how fast the wastegate acuator usually reacts?

If this is not the problem I am almost reigned to the fact that my mods are the culprit because they may prevent the stock wastegate coping with the increased boost. Still, the mods are fairly modest, (downpipe + Apex N1 duals), and I find it difficult to believe that just these mods could make the stock wastegate capability inadequate to control the boost. Worst case I may have to invest in a new, non-stock computer, but first, any comments from the experts out there? Would you expect just these 2 mods to cause a wastegate problem?

Thanks

Dave

BobfisH

check the actuator rod isnt rusted or anything and that it operates freely...it shouldnt take that long.

DaleClark

iTrader: (55)

When I had the stock ECU, cat-back, and downpipe, I had boost spiking going to the second turbo. Not much, but enough to be concerned with.

Make sure the pill in the line is in there properly - if it's turned a bit and not straight, it can block the airflow a bit.

I would also check that the wastegate diaphragm isn't torn or leaking. If you get it to move with air pressure, pinch the hose shut, then release the air pressure, the wastegate should stay open. If it closes up, there might be a leak somewhere. Not common, though - the wastegate diaphragms are fortunately quite hardy.

Also, what is your boost pattern? Do you have a *good* boost gauge with a reading you can trust?

Dale

DaveW

No.

I have the mods in my signature, and no boost creep or spike. I am running dual boost controllers as noted.

DaleClark

iTrader: (55)

With a boost controller and those mods, spike/creep would totally be controlled. With just the ECU's stock control of boost, you can have a spike at transition - I did.

Dale

DaveW

No argument, Dale - that's why I mentioned my boost controllers. He asked if it would cause a wastegate problem. It's not a WG problem, it's a control problem, as you alluded to.

davesan1

iTrader: (4)

Thanks guys.

BobfisH- Actuator looks OK and seems loose enough

Dale-Checked the pill this AM. It is a little bit in the curve of the pipe so I will try to move it to a straighter part. Also checked the size of the pill, (still in the pipe). Looks like "a bit bigger" than 0.05, (near as I can get with an existing drill as a measure), so it probably is stock 0.052."
Already checked for leaks doing the test you describe and there is no leak - the actuator holds its pressure.
Boost on standard check is 10-8-10, then creeps fairly quickly up to 13+ and then drops back to about 11+. The interesting thing is that when I got the car a few months ago it was a perfect 10-8-10. Since then I fixed a couple of boost leaks and now I have the overboosting. I've triple checked everthing I touched during the boost fixes and all is OK, so I concluded that the boost leaks were hiding the overboost problem before I fixed them. Boost gauge is 60mm Greddy
Also, I gave you both some incorrect information. The test I originally described was done by applying the air while the solenoid is closed. I realized that this is not real life, so this AM I applied the air with the solenoid open, (wastegate closed), and then applied power to the solenoid to open it and actuate the wastegate. This time it took 2 or 3 seconds total to actuate, which sounds better, but may be still slow? (not sure?). Also, to be honest, I have some doubts as to the accuracy of the air pressure I am applying as I'm using a 100+ max PSI gauge to measure it, and I'm probably erring on the low pressure side for fear of damaging the actuator. Still 2 or 3 seconds is somehow longer than I expected.

Also, while I was at it, I checked the turbo precontrol (spool-up) actuator in the same way. This is definitely slower than the wastegate, using the (new) test above it is takes around 4 or 5 seconds to fully actuate. If this also seems too long, maybe my pressure is low for both tests. I'll look into a more accurate gauge.
In the meanwhile, what do you think about the new figure of 2 to 3 seconds fior the wastegate - as expected or still slow?

Thanks

Dave

davesan1

iTrader: (4)

Last email was written before the additional response(s) from DaveW and Dale. So are you saying that, without a boost controller you would not be surprised at the overboost situation with the current mods? If so what is the best/easiest solution - boost controller or something else?

Thanks

Dave

DaveW

No, I am not surprised that you have overboost with the stock system.

The stock "boost control" balances two orifices for the PC and for the WG - the pill vs. the duty-controlled solenoids. This is OK if there are no intake or exhaust mods. However, this is not very good (even with a change in the pill size) in compensating for modifications, since the stock ECU uses a pre-programmed map, and does not rely on actual boost values to control boost.

The ball/spring or electronic controllers control boost directly, and as long as the WG is big enough, can precisely control boost.

There have been many posts on MBC's (manual boost controllers). The ball/spring types do the best job. Needle valve types are just adjustable pills, and as such still rely on the duty-controlled solenoids, and don't control as well. Electronic controllers do well, but are more expensive and complex. However, the electronic ones are more easily adjustable - you don't have to turn screws in the engine compartment, you can just dial in what you want..

pincusa

iTrader: (1)

Interesting as I seem to be having the same problems now that the weather is turning cold in NY and the car is making more power in the cold air.
I started to think that I would need to port my wastegate, but with only exhaust changes to the car, I couldn't believe that I was out flowing the stock wastegate. So I also have started to track the problem down to the actuator. I am currently thinking that the actuator has become stiff from the constant heat cycling and either isn't moving its full travel or needs more pressure to move - both resulting in overboost and creep.
Has anyone replaced the actuators? Are they just a simple spring loaded diaphragm?

dgeesaman

iTrader: (7)

Hook the Mityvac up to the wastegate actuator. If the rod moves as you add pressure, it's probably good.

Unless you have a huge pressure chamber loaded on the wastegate solenoid, it should vent almost instantly.
Try hooking up the hoses and plug to the wastegate on the precontrol solenoid and try the test again. I'll bet that solves it.

DAve

DaveW

If you have a straight through exhaust, even w/o intake mods, you may be having boost creep (WG not flowing enuf).

What are your mods?

dgeesaman

iTrader: (7)

Believe it. A full exhaust will usually choke the vent flow out the wastegate. Wastegate porting is in order. Space in the stock turbo manifold is at a premium - Mazda did not make that door much larger than necessary to save weight/space/efficiency.

If you've got a full exhaust, I'm betting on creep due to an overwhelmed wastegate. However, a slow solenoid could do it too. If you suspect the solenoid, switch both the hoses and electrical connectors on the wg and pc solenoid and see if you observe a difference - usually one fails before the other and if they are working the boost pattern will not change.

Yep, you can just unbolt them and replace them, but be sure the arms are the right length (as in, there should be about 1/16th of an inch (half a pin width) of stretch required to get the arm to hook on the door pin). They are spring loaded diaphragm, and I don't think the springs jam or stiffen very often - usually the diaphragm leaks.