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Discussion Starter · #1 ·
Crossposted from sky forum because I know this one is a bit more active


Guys, I'm having an intermittent low power mode without any CEL aka limp mode lite.
'08 Redline Automatic. All stock internals with RPM Tune done about 2 years ago.

Here's what happens most days:
Starts up, sometimes it will run ok during full key cycle.
Most times though it will start up in limp mode lite, boost maxing at 2-4psi, throttle limited to 45%.
Sometimes it eventually 'wakes up' mid- drive and then I have full boost and power until key cycle again.
I have not yet experienced it reverting to limp mode lite during that key cycle, even with extended (30+ min) on time.
Sometimes happens 2-3 min in, sometimes 20 mins in.

Research online has pointed to several potential causes: wiring, air leak, solenoids, wastegate, MAF
I've seen a lot of threads where the car will start fine then go in/out of limp, but not where it behaves as mine where it wakes up then is good for the rest of the drive.

I've checked all my intake and IC hoses and tightened them all up. Intercooler looks intact from visual inspection (no ballooning).
I bought a VCX Nano (Chinese Tech2) to see if I can pull a code from that but I am still not seeing anything.
Not sure if I'm just not looking in the right place though as I'm still learning it, and I don't know what baseline should be on some of the readings either to know if they're out of spec.

I've got some time today to do some troubleshooting so any suggestions are welcome.
 

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I just got a VCX Nano myself the other day. If you are willing to do a phone conversation I can connect it to my car and we can go over what you are seeing. I don't have an Automatic transmission but we can go over all of the other systems to see what is gong on.

My vehicle is tuned as well and I have upgraded the turbo but we should still be able to get an idea as to what is going on.
 

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also let me look at the shop manual and see what I can dig up. I need to now what the error is you are seeing on the DIC, verbatim.
 

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I just read the posts in the sky forum. I do not think your issue would be the wastegate actuator. You stated the error comes up as soon as you start the car. the actuator would not be in use when you initially start the car. if the actuator wasn't moving enough then you would also have an overboost DTC that gets set along with the vehicle going into limp mode.

Now the solenoid that the wastegate connects to on compressor housing of the turbo could be having an issue...

When the system going into limp mode you said there is a high idle event taking place at the same time. Does the high idle also exist when the system does not go into limp mode.

If you let the car sit at high idle for 5 minutes does the idle drop back down within that time?
What are the RPM's when the car is idling high?

I am asking these things because there is a cold start mode on our cars. This cold start mode kicks up the idle and because of the higher idle the turbo will start to develop boost. The boost should not go over 1PSI. The system may be seeing a high boost pressure in this cold start mode and the only way for the ECM to handle it is to go into "limp" mode. All limp mode does is it opens the wastegate to 100% not allowing the turbo to spool up unless the engine is under full load and higher RPM. at most you would get 2-3 PSI or so. That happens because the wategate is not physically large enough to allow all of the exhaust gases to escape without spinning the turbo..

Technically speaking there is no problem, the ECM just doesn't like how high the boost pressure is during cold start. If you let the vehicle idle at the high RPM's until it drops on it's own then shut the car off and restart it if the car is no longer in limp mode then this could be what the issue is.

IDK what has changed when my tune was done by my car no longer goes into cold start at all and is a bit of a pain to get started when it's -20°F
 

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Discussion Starter · #5 ·
also let me look at the shop manual and see what I can dig up. I need to now what the error is you are seeing on the DIC, verbatim.
There is no error on the DIC, that's my main trouble finding out what's wrong.

I just read the posts in the sky forum. I do not think your issue would be the wastegate actuator. You stated the error comes up as soon as you start the car. the actuator would not be in use when you initially start the car. if the actuator wasn't moving enough then you would also have an overboost DTC that gets set along with the vehicle going into limp mode.

Now the solenoid that the wastegate connects to on compressor housing of the turbo could be having an issue...

When the system going into limp mode you said there is a high idle event taking place at the same time. Does the high idle also exist when the system does not go into limp mode.

If you let the car sit at high idle for 5 minutes does the idle drop back down within that time?
What are the RPM's when the car is idling high?

I am asking these things because there is a cold start mode on our cars. This cold start mode kicks up the idle and because of the higher idle the turbo will start to develop boost. The boost should not go over 1PSI. The system may be seeing a high boost pressure in this cold start mode and the only way for the ECM to handle it is to go into "limp" mode. All limp mode does is it opens the wastegate to 100% not allowing the turbo to spool up unless the engine is under full load and higher RPM. at most you would get 2-3 PSI or so. That happens because the wategate is not physically large enough to allow all of the exhaust gases to escape without spinning the turbo..

Technically speaking there is no problem, the ECM just doesn't like how high the boost pressure is during cold start. If you let the vehicle idle at the high RPM's until it drops on it's own then shut the car off and restart it if the car is no longer in limp mode then this could be what the issue is.

IDK what has changed when my tune was done by my car no longer goes into cold start at all and is a bit of a pain to get started when it's -20°F
This sounds somewhat likely, and fits mostly with the behavior I'm seeing.
However, it does come back upon a warm restart. I can literally turn it off while it's operating normally and turn it back on within seconds and it'll start the behavior all over again.
Cold start, rpms are at almost 2k for about 10-20s, then drop to 1k and tend to stay there. Not sure about after 5 min but I think so.
Maybe you're onto something about the solenoid

I can send you a PM with my number if you'd like to get on the phone I'd appreciate it.
 

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I am wondering if it is your ECT sensor. it may be reading incorrectly.

The 2K RPM hold for a few seconds then the drop to 1000 - 1200 RPM is the engine going into cold start mode.

Try this..When the RPM's are high like that tap the accelerator a couple of times. This will bump it out of cold start mode and the RPM's will drop. I want to verify that it is indeed in cold start mode.

This is not going to solve the issue with the reduced power but it gives us something to work off of.

Also when the RPM's are high let the car idle for the full 5 minutes,. The RPM's should drop all on their own within that time, if they don't then we know something is up.

I also need to know if the times that the power reduction does not occur did the car enter cold start (high RPM). If it didn't that will also confirm that it has something to do with the cold start on the vehicle.

It could be that you are getting a hung boost control solenoid or possibly a stuck recirc valve that is causing the issue. and it is getting hung up when the engine is started cold. It may release it's self it may not once the engine warms up.
 

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Using Tech2Win we can check what the duty cycle is on the turbo bypass solenoid. This solenoid controls the bypass valve located on the front of the turbo compressor housing. I think that either your bypass valve is getting stuck, not sealing properly or the bypass solenoid is getting stuck. The bypass solenoid is only monitored for the PWM signal wire being shorted to ground, shorted to hot or an open circuit. It does not know if the PWM signal is moving it properly.

The bypass valve is a diaphram and a spring that gets actuated from vacuum that is supplied to it by the solenoid. The ECM has a set of parameters that are stored in it. So it knows that at 1000 RPMs with the wastegate fully closed the air pressure reading from the sensor located on the intake pipe right before the throttle body should be reading x amount. if it is not then there is a leak somewhere. Because the ECM is not seeing a rich condition and it is not seeing a failure in the boost control solenoid there is no DTC to be set. So the ECM simply limits the boost pressure so no damage can be caused.
 

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The facebook group is private. I did apply don't know how long it will be before I get accepted.
 

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If you take the bypass valve off the front of the turbo you can inspect it.It is 3 Allen screws and a vacuum hose. It consists of a plastic cover, a spring and a diaphragm. Before you remove it mark the turbo and the plastic cover so you can put it back on the same exact way.

Make sure there are no holes in the diaphragm and that there is no oil residu on it or anythign that can cause it to get hung up.

You will laugh when you see how cheezy the bypass valve is made and you might consider changing it to a turbosmart compact shorty. This would require a reprogram of your ECM if you get the dual port version of the valve. I am not sure if the ECM would need anything done to it is using the single port version.
 

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Discussion Starter · #11 · (Edited)
Using Tech2Win we can check what the duty cycle is on the turbo bypass solenoid. This solenoid controls the bypass valve located on the front of the turbo compressor housing. I think that either your bypass valve is getting stuck, not sealing properly or the bypass solenoid is getting stuck. The bypass solenoid is only monitored for the PWM signal wire being shorted to ground, shorted to hot or an open circuit. It does not know if the PWM signal is moving it properly.

The bypass valve is a diaphram and a spring that gets actuated from vacuum that is supplied to it by the solenoid. The ECM has a set of parameters that are stored in it. So it knows that at 1000 RPMs with the wastegate fully closed the air pressure reading from the sensor located on the intake pipe right before the throttle body should be reading x amount. if it is not then there is a leak somewhere. Because the ECM is not seeing a rich condition and it is not seeing a failure in the boost control solenoid there is no DTC to be set. So the ECM simply limits the boost pressure so no damage can be caused.
I did look at the bypass solenoid in the Tech2 this morning. It reported working properly. I think I heard it clicking too when manually activating it via the tech2 also. I'll take it apart probably later this week and see if the diaphragm is sticking. I know I saw something to this effect happen to someone I think in a cobalt forum.
 

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Chances are you have a "pending" code. Did you do a scan for codes? Pending codes will limit your boost, but not set a CEL. There are only a handful of codes that can "pend". So do a scan for CELs and see if you have a pending code.
 

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Discussion Starter · #13 ·
Chances are you have a "pending" code. Did you do a scan for codes? Pending codes will limit your boost, but not set a CEL. There are only a handful of codes that can "pend". So do a scan for CELs and see if you have a pending code.
Neither the Torque app nor the Tech2 show any pending codes.
I did multiple scans for DTC's in the Tech2, both while driving and idle. When I unplugged my MAF it did pop some codes without the CEL, but those then cleared when I plugged that back in.
 

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Also keep a log of each time you start the car. I know it is going to be a pain in the a$$ to remember to do it but it is important. We need know if there is a pattern to when the reduced power occurs.

In the log write down how long it has been since you last ran the car, if the high idle occurred and if the power was reduced. Lets see if we can reveal when it is actually happening and take the "intermittent" out of the equation.

I hate calling a problem with a car "intermittent". All that is really saying is "I don't know what the cause is."
 

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Did you by chance check the DTC's for the EBCM, BCM and TCM??
 

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Neither the Torque app nor the Tech2 show any pending codes.
I did multiple scans for DTC's in the Tech2, both while driving and idle. When I unplugged my MAF it did pop some codes without the CEL, but those then cleared when I plugged that back in.
Pending codes only last:
  • certain number of key cycles
  • length of run time without the issue detected (IMSMC it's 5-10 minutes)

I used to pend my p2178 (or p2188, can't remember) coming home from work in a certain area because of all of the traffic lights. That's why I chased my hpfp issue for so long (over a year). By the time I would get home and check it, there was no pending code any longer as the system will clear the pending code. So if you can, run with the OBDII reader plugged in, and when you notice the lack of boost, run the diag for codes and pending codes. If you've done that and no code, then I have nothing else to contribute.
 

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I know what I suggest will be met with "here we go again" by some, but here goes anyway. Your problem (at least in part) may be the O-ring seals on the MAP sensors and the EVAP solenoid. If they are leaking by they will be the source of some of your intermittent 'limp mode' problem if they have never been replaced or greased. Usually no codes are thrown or you may get a P0106. I had some of the problems you are experiencing and the very simple fix was to be sure of the sealing of the MAPs and EVAP solenoid. No cost, just some labor. Takes about 10-15 minutes or less once you know what to do. Silicone grease on the O-rings will usually give you a short term "fix". I finally came up with a more or less permanent fix by installing flat gaskets under the units and my car has never run better. Do you have the Bosch MAPs? They have only 1 bolt hold-downs. If the Bosch then you will need to make a couple of brackets to hold down the non-bolt side. Confused? Let me know and I will give you more explicit information.
grandpop07
 

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Discussion Starter · #18 · (Edited)
Pending codes only last:
  • certain number of key cycles
  • length of run time without the issue detected (IMSMC it's 5-10 minutes)
I used to pend my p2178 (or p2188, can't remember) coming home from work in a certain area because of all of the traffic lights. That's why I chased my hpfp issue for so long (over a year). By the time I would get home and check it, there was no pending code any longer as the system will clear the pending code. So if you can, run with the OBDII reader plugged in, and when you notice the lack of boost, run the diag for codes and pending codes. If you've done that and no code, then I have nothing else to contribute.
Did you by chance check the DTC's for the EBCM, BCM and TCM??
Yes and yes. Checked codes while driving while the behavior is occurring, both with OBD reader+torque and looking with the Tech2win for DTCs, on all systems. Did checks multiple times while driving as well on both systems. I thought for a second maybe it could be a TCM issue but I'm really leaning on it being related to the turbo system. This is the most frustrating thing about this problem is not finding any codes to help troubleshoot.

Also keep a log of each time you start the car. I know it is going to be a pain in the a$$ to remember to do it but it is important. We need know if there is a pattern to when the reduced power occurs.

In the log write down how long it has been since you last ran the car, if the high idle occurred and if the power was reduced. Lets see if we can reveal when it is actually happening and take the "intermittent" out of the equation.

I hate calling a problem with a car "intermittent". All that is really saying is "I don't know what the cause is."
Agreed. At this point it's behavior is consistent - low power at startup, occasionally waking up to full power mid-drive, persisting until key cycle. I'd say it's been a while (10-20+ key cycles) since I've had full power from startup.

Question on tech2win: I know I can set logging triggers (start logging when parameter reaches defined value), but does it log any time before the trigger? I'll have to test this. I can easily determine when the vehicle comes out of limp mode by defining boost or throttle values outside of limp mode.
 

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Again, check the O-ring seals as I said in my previous post. Until you ascertain they are good you are wasting your time with further checking for codes, etc.. This is very easy to do and may save you a lot of wasted time with all the other things that have been suggested. Once you have made sure those seals are good you will have a good basis for proceeding with the other things that have been suggested. What I don't understand is the apparent hesitancy to do what I've suggested. This will take about 5-10 minutes of your time and may entirely solve your problem, believe it or not.
Good luck.
grandpop07
 

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Discussion Starter · #20 ·
Again, check the O-ring seals as I said in my previous post. Until you ascertain they are good you are wasting your time with further checking for codes, etc.. This is very easy to do and may save you a lot of wasted time with all the other things that have been suggested. Once you have made sure those seals are good you will have a good basis for proceeding with the other things that have been suggested. What I don't understand is the apparent hesitancy to do what I've suggested. This will take about 5-10 minutes of your time and may entirely solve your problem, believe it or not.
Good luck.
grandpop07
I did check the seals earlier this week. Haven't had time to return to report, and was hoping to get a chance to drive the car a little more too.
I put a little silicon grease on all of them, the EVAP in particular looked very dry - almost had a white powder look to it.
I also checked the bypass diaphragm and it looked fine. The service manual says to remove the intake hose which I did but as I was reinstalling it...snap went the little coupler that sticks out of it. So I had to spend some time fixing that too.

Once everything was back together and good I finally got a drive in. On cold startup, I didn't experience the pronounced gurgling pressure when going from open to closed loop that is evident in the video. It didn't, however, clear up the limp mode lite. I only ran 3 key cycles, but for the first it remained in limp mode. the second it woke up shortly after starting - car had cooled over a few hours but wasn't entirely cold. During that drive, while I was at a light I key cycled the car and back in limp mode light it was for about 4 blocks until I got home. Haven't had
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