Saturn Sky Forum banner

HELP Send the Boost Doctor

5K views 26 replies 7 participants last post by  Nova-Exarch 
#1 ·
Had the Redline at the track this weekend. I'll keep this short. I just installed a new intercooler but Idon't think that has anything to do with my problem. I could only get about 17lbs of boost in the tuned mode. Was 22lbs right after intercooler instal. So I thought I have a leak which I could not find. I think what is key to this problem is it only shows 8lbs in the stock tune. Before always around 14 lbs.

Is there only one sensor for the boost pressure ??? Car ran great and I'm not sure I could tell the difference between 17 lbs and 22 lbs.So maybe I had full boost but it was under reported.

The Super Sky had no problems passing a few C6 corvettes, a few Porsches, throw in a couple of BMWs for good measure. A friend of mine was there in another Redline. He is waiting on his tune and then the dog fight begins.

Larry
 
#3 ·
I think he said the DDM Street, but had some problems with it. would not align, had to cut charge tubes. We never had a single problem with mine. Went right in, bolted up perfectly. Should have ordered the aftermarket couplers, but got the DDM ones to work. The new intercooler inlets are the same size as the DDM charge tubes.

The intercooler does not have a seal ring on them, so cutting the charge tube shorter should not be any problem for boost loss, or at least more so than the intercooler side.

I have driven mine quite a bit, but have not check the boost since installation. Runs fine though.
 
#4 ·
Skersfan, check your boost pressures and see if they are lower than before. A lot goes into what determines boost pressure (temperature, humidity, tune, flow) so I just want to get an idea of what has been changed and what is on the car. Trying to think what could cause such a dramatic drop in pressure. I mean, 6 psi is a big drop.
 
#6 ·
Keep in mind you had 14 psi in the stock tune and up to 22 psi in the Trifecta tune before you had issues. Now you say you have 8 with the stock and 17 with the Trifecta. Thus you've lost about 5-6psi in both tunes. Since the loss is about the same either way, then it is something else (most likely) that is causing the loss in pressure.

Larry, here is what I know about the LNF system. I don't have an LNF, I have a boosted LE5 and so I encourage anyone to correct any mistakes I have in my explanation that know the system better than I do.

The LNF's system uses a combination of Manifold Air Pressure (MAP) reading and manipulation of a Wastegate Control Actuator Solenoid to control boost output.

With a turbo setup like mine, you have the turbo's compressor housing (where boost is generated) connected to a wastegate actuator. Inside this actuator is a spring keeping the wastegate valve shut on the turbine side (exhaust) of the turbo. As boost builds, it starts to press against this spring. Once boost pressure is greater than the force of the spring holding the wastegate shut, the wastegate begins to open allowing excess boost to bleed out into the exhaust. This is what sets how much boost is produced by the turbo. The factory spring in the K04 turbo on your car is rated to about 6-7 psi on the LNF (about 4-5 psi on the larger 2.4 LE5). This is why when you go into limp mode, you only see about 6-7 psi of pressure.

As you have seen though, your car has been able to produce a LOT more than 7 psi of boost. This is where your ECM, MAP and Wastegate Actuator Control Solenoid come into play. The solenoid goes between the turbo's compressor and the wastegate actuator. It also has a reference line to the turbo intake as well that will always read a vacuum. See the attached diagram of this layout.



This solenoid can open and close to allow some or all the boost pressure from reaching the wastegate actuator. What happens here is your ECM is reading the boost level the MAP is sensing and comparing that to an entry in it's programming that basically says how much boost you want to run. When your MAP reports this boost level to the ECM, the ECM commands the solenoid to open and allow some boost pressure to go to the wastegate actuator and allow it to start opening in order to maintain the boost pressure the ECM is trying to maintain. If you have ever dealt with an electronic boost controller in another vehicle, that is what you are essentially dealing with here.

Now with the factory tune and it's "learn down" feature, the ECM is programmed to expect a certain torque output under varying conditions. When the calculated actual torque measurement for a particular condition exceeds the expected torque output stored in the computer, the computer will try to reduce power output so that actual calculated torque matches what is programmed into the ECM for expected torque output.

What this means is if, for whatever reason, the DDM intercooler allowed you to produce more power (due to better cooling of the air charge, better flow to allow more air to get sucked in to the engine with each stroke, magic pixie dust...whatever is allowing the car to make more power) the stock tune would reduce boost levels to bring calculated actual torque back where it thinks it should be.

On the other hand, the Trifecta tune is supposed to do away with the learn down feature and thus the ECM shouldn't be trying to reduce power output. Now I don't know if Trifecta kills the learn down feature in BOTH tunes...stock and their tune...or just in their tune but considering you're seeing the drop in both tunes I would suspect it is something else.

Hotter air temperatures can also cause lower boost readings. Hotter air = thinner air = less boost. 6 psi though would be a huge swing...like say going from 50 degrees to 110 degrees in temp. Better flow through the intercooler could also cause a reduction in boost. More restrictions mean higher boost levels and lower restrictions lower boost levels but since your MAPs are AFTER the intercooler, I'm not sure how this would affect readings. That is a question for someone who knows more than I. I'm still learning some of this turbo stuff too.

So when you're comparing boost readings, you have to compare them based off the same tune. If you try to compare base tune boost readings to Trifecta tune boost readings, you're always going to be off.
 

Attachments

#9 ·
I could be wrong, but it seems to me that there is a second manifold pressure (temperature) sensor mounted directly on the intake manifold, but I don't remember how it functions differently from the one on the cold pipe. Seems like it only measures one parameter: temperature OR pressure, but NOT both. Seems like it looks identical to the one on the cold pipe.

Yogi
 
#10 ·
Yogi, that is a MAP also and currently there is some debate over which one actually is the "MAP" reading in the ECM. My argument is that this sensor mounted in the manifold past the throttle body is the MAP sensor we think about when we discuss manifold air pressure.

The second MAP is located in the cold pipe. It is believed that this sensor reads pressure and temperature.

It is reasoned that these sensors work as such:

Air enters the intake at the air filter and passes over the Mass Air Flow Sensor (MAF). This sensor reads how much air is entering the system and the ECM uses this value as part of fueling calculations. This sensor also reads the temperature of the incoming air and calls this Intake Air Temperature 1 (IAT1). This is also used for fueling as well as other checks.

From here the air enters the turbo, is compressed and heated, then sent through the intercooler to be cooled off. After leaving the intercooler it passes through the cold side charge pipe and the Manifold Air Pressure sensor located there. This sensor reads the pressure of the air before the throttle body. It also reads the air charge's temperature and this is seen as Intake Air Temperature 2 (IAT2). It is believed that the IAT2 reading is compared against the IAT1 reading to determine whether or not the intercooler is working as it should. Not really sure here what happens if it is not. It is also believed that the IAT2 reading is the primary air temperature reading used by the ECM for timing and fueling calculations since this is the last air temp reading taken before the air charge enters the engine and thus the most accurate temperature reading for these kinds of calculations.

This is a picture of the cold pipe MAP (often referred to as an air temperature sensor. GM part number 12592017):


From here the air enters the throttle body and it's flow is regulated by the butterfly valve in the throttle body. After the throttle body the air charge enters the intake manifold, then the heads and then the combustion chambers. In the manifold is the second Manifold Air Pressure sensor. The reading from this sensor, I believe, is compared to the reading in the cold side charge pipe's MAP sensor reading to determine if there are any problems between these two readings. I believe it is this second sensor that is the main MAP reading value due to the fact that it is after the throttle body and the last pressure sensor before the air charge enters the engine thus it is the most accurate pressure reading in relation to what pressure the air is entering the engine. This second MAP sensor only reads pressure and is not a dual role sensor like the one in the cold pipe.

Here is a picture of the Manifold's MAP sensor (GM part number 12592016):


As you can see, they are very different looking sensors right down the part of the sensor that comes in contact with the air it is measuring. I also want to say the 12592016 sensor is a 2 wire sensor while the 12592017 is a 3 or 5 wire sensor (can't remember exactly...hell, may even be a 4...just remember it being more than 2). We know that the GMPP Stage 1 upgrade replaces BOTH MAP sensors with three bar sensors so it is logical to conclude that both sensors and their readings are used by the ECM.
 
#11 · (Edited)
Well, skersfan has the same intercooler and he's seeing 18 psi on the stock tune and 25.8 on the Trifecta....so the intercooler isn't affecting it at all. These are the same numbers he saw before the installation of the IC.

This means something is up with your car and I bet it has to do with the installation. After all, you said it looked good when you first put it on. Wonder if all your clamps on the plumbing are good and tight. Are you running t-clamp fittings or the stock worm clamps?
 
#12 ·
Your explanation sounds correct, Robo. Thanks for the clarification!

Yogi
 
#13 ·
SUPER SKY IS BACK !!!!!! :smile::smile::smile:

I forgot the 1st rule in trouble shooting.

Rule #1 Disconnect the battery for 1 hour and reconnect.

Like Donald Trump said "What do you have to lose"

All is well now. Boost is back to the levels before the intercooler instal.

I did not mention that between the instal of the intercooler and checking the levels at the track I did have a roll bar support welded in. They unhooked the battery during the welding.

Who knows !!!!

Skersfan's numbers seem to be high. I thought the PCM limited the stock boost to 14PSI ??? As he is reading 25.8 I guess it is not on the DIC ??
 
#15 ·
Glad to hear that got it resolved. Yea, always best to rest fuel trims when making mods. LOL No, the PCM doesn't limit boost to 14 psi. I believe some have seen as high as 20 psi on the stock tune. It all depends on what torque output the ECM is expecting depending on the current conditions.

Stock tune was 17, 3rd gear WOT, Trifecta adjusted by Dave at DDM, 23 on the DIC. Thru the Aero gauges, 18.3 I think it was and 25.8 with the Trifecta on.

I do not have the higher end sensors, will talk with Dave about it tomorrow.
Yea, the reading from the Aero gauge of 25.8 PSI is concerning since this would be at the end of the stock 2.75 bar MAP sensors range (though technically it should run out at 25.3 psi). While it may be accurate, with those kind of readings I would want 3 bar MAPs in there to make sure the reading is accurate and that your boost level isn't higher than you think it is.
 
#18 · (Edited)
Robo, are you saying with 2 cars on stock tune and say mine limits the boost to 13lbs and a 2nd car needs 17lbs of boost to make the same power????

I will be the first to admit I don't understand this whole thing.

Thank you, Larry
Correct. Say you are at sea level at 60 degrees. The air pressure at that level is going to be at or above 14.7 psi. Also the air will be very dense. Now put your car in Denver Colorado at 110 degrees. The air pressure there will be below 12.0 psi and the density will be much lower. That means a car in Denver will show a higher boost level because it needs to overcome the thinner density air.

Remember boost is a relative number. 1 psi of boost equals a total of 15.7 psi at sea level but up at Denver you may have to run 3.7 psi of booat to equal a total of 15.7 psi even though your boost level is greater.

Here is a neat resource to see what altitude does to the base air pressure you start with.

http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

This is how I understand it.
 
#21 ·
OK Robo back to work !!!!!

I drove it 30 miles after the battery reset. On the way home tonight I'm back to the 8lb and 17lbs of boost.

Got home, unhooked battery for 30 seconds and took her out and back to 14lbs and 22lbs.

NO check engine light set.

Only thing I can think of it must be flowing more air and running lean. With the factory intercooler it's AFR at full throtle in tuned mode was a very fat low elevens.

A while back, before the new intercooler, I did get a check engine, something like too lean at idle. I think I'm fine at full throtle but maybe the idle condition is causing the issue.

Will probably have to call Dave @ DDM.

Larry
 
#23 ·
Lol I didn't even see skersfan had done that! Lol

As for the problem, because you can reset the ECM and temporarily fix the issue this tells us the ECM is what is pulling boost. It is putting you into limp mode...but usually you get a check engine light with that. You could have a pending code too. Do you have a way to scan it and pull codes?
 
#25 ·
I did not realize I was dealing with counter intelligence CIA proof readers. I need to be more careful.

Any way the wraps are off. The trip to Gunnison made it a daily driver so to speak. I have the Mallett to keep stock!!!, and the damned green one has become the garage princess.
 
#26 ·
Well good. Was a shame to see you deprive yourself of so many opportunities for face-bending fun when you have NO intention of selling it anyway. DRIVE IT! They didn't make the thing for it to sit there looking pretty. Okay, JUST to sit there looking pretty. It looks pretty damn sweet in motion too.
 
Top