LSJ M62 Low Boost ~3.5psi max

[baustin]

I need a little help troubleshooting my low boost issue. I've been running my Goblin since early 2020 and only ran into a low boost situation once, either replacing or fiddling with the boost bypass valve fixed the problem at that point. Let me know if you see where my understanding is wrong but I'll describe how I found this system works so far.

One morning I had normal throttle/boost response and then the next drive I don't get anything above ~3.5psi at any throttle position in any gear. I've done a few steps of troubleshooting but so far things haven't been fixed though I know there is a workaround, I'm trying to not leave my setup with the workaround yet.

It's a fairly simply system, here's the diagram for when the boost control solenoid (item 3) is open and the bypass valve (technically the bypass valve actuator, item 1) is open:

Here's the diagram for when the boost control solenoid is closed and the bypass valve is closed:

The boost control solenoid receives voltage from the PCM with the 1st wire and the 2nd wire to the solenoid is the ground wire. 0V signal causes the solenoid to stay open, high voltage signal closes the solenoid fully. I'm not sure what triggers the partial % between 0 and 100, if it's just a decreased voltage or if it's pulsing.
As long as the solenoid is closed, the bypass valve stays closed and the butterfly valve inside the supercharger stays closed. When the you are building boost and the solenoid opens, the bypass valve opens and turns the internal butterfly valve.

Places that can fail or cause problems: PCM configuration, wire from the PCM to the solenoid, ground wire to the solenoid, boost control solenoid internally fails to respond to voltage, hose leakage at any of the 3 hoses (items 2 / 4 / 11 in the diagrams), bypass valve actuator stoppage, bypass valve actuator leakage, bypass valve stuck.


All 3 hoses appear in good condition, no cracking. 1 or both of the top side hoses were replaced 3 years ago from hoses that were cracking significantly. I'm not 100% sure the hard to see hose (item 4) going to the intake manifold is perfect but I don't expect this could even be the issue based on other details.

To test the bypass valve (item 7): Disconnect the bypass valve actuator and check if the linkage spins freely.
-This worked normally for mine, no difficulty moving.

To test the bypass valve actuator (item 1): Disconnect the attached hoses and remove from the supercharger, depress plunger, place finger over 1 port at a time, release plunger, the plunger should not return to normal until you release your finger. You should not be able to blow air into 1 port and it come out the 2nd port.
-The plunger moved freely and did not return to normal while a finger was plugging each port, this should mean the internal diaphragm around the spring is still air tight. I don't have a number on how strong this spring should be, it feels like it did 3 years ago when I fiddled with it.

To test the boost control solenoid: You should be able to blow air through from the silver port or from the plastic port when no voltage is applied. The internal solenoid can be tested with a 9V battery and some alligator clips. When 9V is applied, you should hear a click noise from the solenoid and should no longer be able to blow air through the silver port. When 9V is applied, you should still be able to blow through the plastic port but the air will come out the foam covered port only and no air from the silver port
-My boost control solenoid tested open for the air but failed to actuate or change with a 9V. I ordered a new one and it did actuate properly with 9V and all these test steps

My tune call for 100% boost control solenoid (BCS) once the engine is turned on, expect for when in first gear. First gear is limited to 85% per the typical Cobalt tune and in the Goblin I'm not sure I could make use of those few extra psi in 1st gear.

To test the wiring and verify the tune is trying to control the boost control solenoid as expected: Disconnect the wire plug for the boost control solenoid, turn the key to 'run' without starting the engine, use a multimeter for the voltage on the 2 wires.
-My voltage is a constant 10.59V sitting during idle, I'm not sure if 10.59 is a problem but since a 9V battery actuates the solenoid I expect this is within the normal operating range

Nothing has changed with my tune for a long time, it's set to limit to 85% boost in first gear and then 100% boost allowed in all other situations:

When I data logged what was happening when I started troubleshooting this was the result. 2nd set of graphs, bright green line is the boost value. BCS is graphed in the top data set and is correctly indicating it's calling for 85% during first gear though the flat line of boost shows that 85% and 100% has no impact currently. My stock boost gauge is showing exactly the same pressures that HPTuners is graphing.

What's next?

• I installed my replacement boost control solenoid that passed the bench test and went for a drive. Exactly 0 difference, the boost was still limited to ~3.5-3.7psi.
• I then tried the manual override setup of disconnecting the hose from the boost control solenoid to the bypass valve actuator, keeping it attached to the boost control solenoid and plugging the empty end with a bolt (and I added some tape around the bolt to ensure it was pressure tight). This effectively removes the electronic control of the boost level. The next data log is the result, boost was fully back in action. Keep in mind I have 2.9" pulley, not the stock size.

• ZZP offers replacement bypass valves (~$130 before tax currently), it could be that the bypass valve I have passes my simple bench test but should be replaced.
• Given that I'm getting a constant 10.59V on multimeter, I don't think I have a PCM / wire / ground issue.
• The original boost control solenoid does fail my bench test and the new solenoid passes the bench test but the boost pressure behavior is identical.
• I can leave the hose plugged to defeat the entire boost control solenoid but this isn't my first preference but it would be better than not having any useful boost pressure.

Any suggestions or anyone have other troubleshooting steps to use?

 

[Gtstorey]

I’m pretty sure that is the longest single post on the entire forum.
Without trying to scroll through that on my phone, are you just trying to explain the stock system or is your modified. The piecemeal reading that I did just sounded like the stock setup.

 

[Ross]

... I'm not sure what triggers the partial % between 0 and 100, if it's just a decreased voltage or if it's pulsing. ...

I read it is PWM (pulse width modulation) controlled.

• I then tried the manual override setup of disconnecting the hose from the boost control solenoid to the bypass valve actuator, keeping it attached to the boost control solenoid and plugging the empty end with a bolt (and I added some tape around the bolt to ensure it was pressure tight). This effectively removes the electronic control of the boost level. The next data log is the result, boost was fully back in action. Keep in mind I have 2.9" pulley, not the stock size.

So this test bypasses the boost control solenoid, and proves that the bypass valve, and its bellows are working. The supercharger is working too. Right?

Given that I'm getting a constant 10.59V on multimeter, I don't think I have a PCM / wire / ground issue.

I worry about this low voltage. Seems too low even at idle. Trade the battery out, and see if the issue persists. Or does the electrical system have an erroneous high amperage draw?

 

[baustin]

I’m pretty sure that is the longest single post on the entire forum.
Without trying to scroll through that on my phone, are you just trying to explain the stock system or is your modified. The piecemeal reading that I did just sounded like the stock setup.

My boost bypass setup is stock, but not working right suddenly. I haven't found the issue yet and in order to troubleshoot it, I need to make sure I'm understanding it fully.

 

[baustin]

So this test bypasses the boost control solenoid, and proves that the bypass valve, and its bellows are working. The supercharger is working too. Right?

Yes, I think it proves the bypass valve is working. It definitely shows the supercharger is working.

 

[baustin]

I worry about this low voltage. Seems too low even at idle. Trade the battery out, and see if the issue persists. Or does the electrical system have an erroneous high amperage draw?

Keep in mind this if voltage on the connector to the solenoid when it's not plugged into the solenoid, not measured at the battery or fuse box post. I should probably compare the voltage with one lead direct to chassis ground to see if my ground wire on that circuit is failing and becoming too much resistance (and just measure that directly).

I don't have any other batteries to try and this is an AGM type from last year.

 

[Gtstorey]

Have you checked for trouble codes?

and on some of these, codes that are turned off in the tune are still ran, put the car into reduced power, don’t register, but will self clear when the car is shut off, so make sure there aren’t any boost or throttle codes turned off.

 

[baustin]

Have you checked for trouble codes?

Yes, there are none current, none pending, none in history.

 

[Robinjo]

Yes, I think it proves the bypass valve is working. It definitely shows the supercharger is working.

Did you do the test to both the upper and lower ports? I watched a video where a guy said that most only check the upper port but that both passing the suction test are important.

 

[Ross]

I was guessing that the PCM isn't requesting full power, and is in some kind of limp mode. Usually that would throw an OBDii code... If it was my car, I would hook my oscilliscope up to the boost solenoid and see if it is getting a proper PWM signal. Maybe check a wiring diagram, and test the leads going to the solenoid for resistance? Should be almost 0 resistance, but since you are getting low voltage, maybe they are bad.
The Pink wire goes to the fuse block C1, E6. (Should be 12V, maybe check it at the ECM Fuse)
The Gray wire goes to the PCM C2 29.

 

[baustin]

Did you do the test to both the upper and lower ports? I watched a video where a guy said that most only check the upper port but that both passing the suction test are important.

Yes, both ports. I had the valve on my workbench and checked both. I also used my air compressor to put positive pressure on the lower port and the valve moved like expected and didn't leak as far as I could tell.

 

[baustin]

I was guessing that the PCM isn't requesting full power, and is in some kind of limp mode. Usually that would throw an OBDii code... If it was my car, I would hook my oscilliscope up to the boost solenoid and see if it is getting a proper PWM signal. Maybe check a wiring diagram, and test the leads going to the solenoid for resistance? Should be almost 0 resistance, but since you are getting low voltage, maybe they are bad.
The Pink wire goes to the fuse block C1, E6. (Should be 12V, maybe check it at the ECM Fuse)
The Gray wire goes to the PCM C2 29.
View attachment 43098

I'll try to check this next chance I have. Thanks for the pin info. I hadn't pulled that specific diagram up yet but the system diagrams I copied initially came from your login...

 

[baustin]

I checked resistance between the fuse block (touching top of ECM/trans fuse, either side) and the boost control solenoid pink wire: 0.2 ohms (this also confirms the connector under the fuse box is still fully mated). I checked resistance between the boost control solenoid gray wire and the PCM C2:29: 0.6 ohms. The C2:29 pin has no discoloration, in fact all the pins are nice and bright/clean.
-I think this confirms the wires are not the issue

The ECM/trans fuse has identical voltage to chassis ground as the fuse block stud coming from the battery. My battery voltage this evening is 12.47V, car entirely off. I double checked my 9V battery and it's at 9.22V, so I would expect anything 9.22V or higher from the 12V system would actuate the solenoid.

I turned the key to 'run' and set HPTuners VCM Scanner to turn on the boost control, but I'm not sure I'll notice this working without going for a drive to build boost. To manually test the solenoid while it's plugged into the circuit, I have a short hose connected to the silver port on the solenoid. Regardless of whether the HPTuners option is set to off or on and any value 0 to 100, I can still blow air through and I don't hear the solenoid click. This is with a solenoid I can touch a 9V battery to and hear it click closed. I didn't write down the voltage I was seeing on that circuit but I did see the voltage increase as I adjusted from 0 to 100. I'm assuming the PWM aspect is why I'm not seeing full battery voltage reading.

Next up:

• Go for a drive with HPTuners running to control the off/on of the solenoid. I think if this fails then it suggests my PCM has failed on that internal grounding switch. I'm not sure what the future step would be if HPTuners does manage to make the boost control solenoid close correctly while in manual control, possibly my PCM just needs the tune loaded to it again but this doesn't seem likely since the BCS circuit charted earlier is exactly as I expected from my tune, and I haven't touched the tune in the last year.

 

[devianteng]

Nothing to contribute, but following along. I’ve dealt with the same with my donor and my Goblin, and have it bypassed and gave up on it. New solenoid, checked my wiring, checked the valve itself…I’ve had no luck. Seems a lot of people report this problem on the LSJ but I’ve never really seen any resolution. Maybe you’ll get it figured out!

 

[baustin]

Seems a lot of people report this problem on the LSJ but I’ve never really seen any resolution. Maybe you’ll get it figured out!

Yeah, that's what I was finding as well.

 

[baustin]

Good news and bad news after my last test drive. I did try a rewrite of my tune onto the Goblin and then did a 2nd test drive, same results from both.

Good news:
HPTuners boost control option does directly impact the BCS percent commanded according to the scanning.

Bad news (at least it's what I expected):
No change at all in the boost behavior.

Current solution:
Just loop the hose that originally goes from the boost control solenoid to the boost bypass valve and just have both ends on the boost control solenoid to defeat the electrical control of the boot level and prevent the possibility of a vacuum leak. Unless I look into getting/trying a replacement PCM, I'll be running 100% boost in all situations instead of 85% in first gear.