Underboost issue

[jpulll]

Hi guys,

Ive been trying to do my homework and figure out my problem but I've been having troubles. I have a motoza 1+ tune, which I've had for a while now and have only gotten one revision. When I got the tune I had a bunch of problems. Misfires and underboost codes. Well I managed to fix the misfires (injector harnesses) but I am still experiencing the underboost codes.

When I got the tune, I could only see 15 psi. I had a couple of boost leaks, that i fixed. After all said was done, I saw 18psi being the peak boost. Dave replied after checking out my logs that i should be seeing more, I should be around 20-21psi. He said everything looks good, fuel trims are spot on, N75 duty cycle looks good, MAP looks good, but he said the actual vs requested boost are just not meeting. After I told him everything that I've done to try and diagnose this boost leak and fix it, he responded with the wastage being the possible issue.

So i followed Fletcher's post in some other thread to clamp down the boost inlet line on the N75 (the hose that connects to the compressor housing). What I found was that I could not boost over 18psi. After a couple more pulls to confirm, the car went into limp mode, followed with an overboost code, which i could clear. One of the questions I have is, what does that mean?

And that's where Im at now. I let Dave know about my little wastegate test, I sent him an email last Thursday.

Mods will be in sig. TIA

[old guy]

If you are absolutely sure you don't have any boost leaks I would suspect you may have a wastegate problem. Once you clamp off the boost signal line to the wastegate you are essentially running unregulated boost.

One more thing to check. When you perform a boost pressure test from the TIP opening you are pressurizing the DV from both sides so you really can't tell if it is holding properly. You can test the vacuum/boost signal line to the DV for an external leak but you can't check the DV for an internal leak.

There are two additional tests you can perform to check the DV for an internal leak. Do the easy one first. Use an air nozzle and pressurize the hose that connects the DV to the intake manifold. You should not be able to blow any air through that line.

The other test is a bit of a pain. Disconnect the DV from the TIP and plug the TIP port. Then do a standard boost pressure test from the TIP. The DV should be able to hold the pressure. If it blows off any pressure at all through the open DV discharge port you have a problem with the DV (Worn out piston, broken spring etc)

Good luck!

[jpulll]

Good luck!

Thanks fletcher! I'll report back sometime in the afternoon tomorrow after work.

[jpulll]

The other test is a bit of a pain. Disconnect the DV from the TIP and plug the TIP port. Then do a standard boost pressure test from the TIP. The DV should be able to hold the pressure. If it blows off any pressure at all through the open DV discharge port you have a problem with the DV (Worn out piston, broken spring etc)

Good luck!

Is this with the diverter in standard location where the discharge is the side of the valve?

[Detroiter]

I am having very similar issues with my tune from Motoza. I simply cannot boost over 18psi. I have done several boost leak tests and have replaced the diverter valve with no luck in solving the problem. The only other thing I can think of is the wastegate not working properly. I am interested to see if you find the source of yours as I am almost out of ideas.

[old guy]

Is this with the diverter in standard location where the discharge is the side of the valve?

Orientation doesn't matter. It should still hold pressure.

[jpulll]

I am having very similar issues with my tune from Motoza. I simply cannot boost over 18psi. I have done several boost leak tests and have replaced the diverter valve with no luck in solving the problem. The only other thing I can think of is the wastegate not working properly. I am interested to see if you find the source of yours as I am almost out of ideas.

I'll let you know later in the day about those tests old guy mentioned. I doubt that's what it is as I have a 007 and those are known to be reliable so I have my doubts but still nonetheless, always nice to cross something off the possible causes list.

[jpulll]

After my tests i found the diverter valve is functioning as it should. I did however find a small leak on one of the intercooler hoses; now tight.

Although the car feels more peppy after tightening the clamp a little more, the gauge still reads 16-18psi; I'm still not seeing full boost. Any other ideas?

[B6A4Dave]

After my tests i found the diverter valve is functioning as it should. I did however find a small leak on one of the intercooler hoses; now tight.

Although the car feels more peppy after tightening the clamp a little more, the gauge still reads 16-18psi; I'm still not seeing full boost. Any other ideas?

Check the Throttle body size IC pipe... My frame rail, the pinch weld ended up essentially sawing through my IC pipe lol..

[jpulll]

could a check valve(s) be my issue? I have yet to replace those. none are busted open but could they be internally leaking?

[old guy]

could a check valve(s) be my issue? I have yet to replace those. none are busted open but could they be internally leaking?

Test the check valves for internal leaks the same way you tested the DV. Pull the hoses from the intake manifold one at a time and use an air nozzle to pressurize the hose. No air should go through the hose at all. If air does go through you have a problem that needs to be corrected.

[WB650]

I would just replace the valves if they have never been done.

[jpulll]

I would just replace the valves if they have never been done.

Exactly what I plan on doing. Along with those n75 hoses. Probably be a week-week/half before i report back.

[jpulll]

okay to use 4mm hose for n75? I noticed the nozzle on turbo and wastegate will accept the 4mm but the nipples on the n75 are like 1/4". this alright?

[jpulll]

I'm thinkin just lube it up with oil and slide her on there. any objections to 4mm size?

[old guy]

Another possibility is a loose wastegate actuator. Video and symptoms from this thread: Clicky click®

[jpulll]

okay, so unhooking the wastegate actuator hose runs unmetered boost meaning you can over boost very quickly and unhooking the n75 connector harness runs what the wastegate spring is set at? so these are the two tests I should try if the check valves don't fix my problem?

[old guy]

Correct.

Edit: I should add that all you really need to do is clamp the actuator hose. You can unhook it if you find that easier to do but then you will have to plug the hose so you don't create a boost leak.

[jpulll]

okay thanks oG. check valves will probably be at my house when I get home from this exam. after I install those and drive around and still have troubles- I'll unplug n75 harness to test the spring pressure. if it's set to 4-6psi am I good? no adjustment needed?

and then I'll proceed with clamping the actuator hose and checking that. if I don't boost over 18psi, what does that point to? bad n75/turbo...something else?

[KHARDa4]

okay, so unhooking the wastegate actuator hose runs unmetered boost meaning you can over boost very quickly and unhooking the n75 connector harness runs what the wastegate spring is set at? so these are the two tests I should try if the check valves don't fix my problem?

Actually disconnecting the harness connector from the n75 creates an open ciruit. The ecm see the boost regulation fault stored and will not allow the car to make boost at all, it does this by keeping the throttle plate closed not allowing charged air pressure to enter the intake manifold. So disconnecting the n75 connector will not help an underboost condition.

[old guy]

If you disconnect your N75 electrically your engine will start and run normally with the exception of the boost being controlled by the wastegate spring. For example, when I unplug my N75 I can only hit around 3→5 psi in the lower gears. If I go WOT at 3,000 rpm in 5th gear my boost will max out at 8 psi which is the wastegate setting for my F21L. A K03 will max out around 5→6 psi.

If you come up significantly lower and you are absolutely sure that you have eliminated all boost pressure leaks then I would suspect you have a mechanical problem with your turbo.

[KHARDa4]

If you disconnect your N75 electrically your engine will start and run normally with the exception of the boost being controlled by the wastegate spring. For example, when I unplug my N75 I can only hit around 3→5 psi in the lower gears. If I go WOT at 3,000 rpm in 5th gear my boost will max out at 8 psi which is the wastegate setting for my F21L. A K03 will max out around 5→6 psi.

If you come up significantly lower and you are absolutely sure that you have eliminated all boost pressure leaks then I would suspect you have a mechanical problem with your turbo.

Interesting, I iust installed my 3076 and set spring tension to .8 bar (12 psi). My boost regulation was completely mechanical at this point (no n75). It had a hard fault for n75 boost regulation open circuit. The car would not boost at all and would fall on its face at the time it should be boosting. I did some research and found that the ecm closes the throttle plate to prevent boost. Where my boost gauge is plummed to is a mani source. If I could test pre throttle plate im sure I would of seen boost but since it wasnt passing into the mani it showed none on my gauge. I plugged my n75 back in to the connector and laid it in the engine bay cleared the fault and the car boosted as it should.

[old guy]

Interesting indeed. When I read your post it inspired me at lunch time to double check my wastegate pressure to see if anything had changed. Heading out I unplugged the N75 and boosted from 5→8 psi depending upon how much load I could apply. Picked up my lunch and plugged it back in. Boost returned to normal. I have done the same thing in the past with my K03 with the same results. Maximum load on a K03 typically will generate around 5→6 psi.

Whenever I do it I get a pending fault for a P0243 –Powertrain Turbocharger Wastegate Solenoid “A”. Maybe if I did it several times in a row the fault will go from pending to a hard code and cause the throttle cut that you experienced. I may try that later this week just for the hell of it and see if I can provoke a throttle cut.

[jpulll]

alright well a couple check valves were indeed bad. I could blow a slight amount of air through them. and that was with my mouth so I can imagine 18psi of pressure. but... still only seeing 18psi. although I haven't figured out the underboost issue, my car is much more responsive now. I'll do some wastegate tests probably tomorrow.

[KHARDa4]

Interesting indeed. When I read your post it inspired me at lunch time to double check my wastegate pressure to see if anything had changed. Heading out I unplugged the N75 and boosted from 5→8 psi depending upon how much load I could apply. Picked up my lunch and plugged it back in. Boost returned to normal. I have done the same thing in the past with my K03 with the same results. Maximum load on a K03 typically will generate around 5→6 psi.

Whenever I do it I get a pending fault for a P0243 –Powertrain Turbocharger Wastegate Solenoid “A”. Maybe if I did it several times in a row the fault will go from pending to a hard code and cause the throttle cut that you experienced. I may try that later this week just for the hell of it and see if I can provoke a throttle cut.

Yeah even though the n75 is disconnected in your car it still bleeds boost pressure to the wastegate. Mine being completely removed may be picked up by the MAP sensor along with the hard n75 boost regulation open circuit code causes the closing of the throttle plate. Whatever it may be there are other saftey precautions programed into our ecm's. Geez these things are damn smart.

[AutoMax]

I had an issue not meeting requested boost, after boost leak tests, and making sure the n75 was working properly i bit the bullet and adjusted the wastegate rod.

Problem solved.

Sent from my SM-N910T using Tapatalk

[old guy]

Yeah even though the n75 is disconnected in your car it still bleeds boost pressure to the wastegate. Mine being completely removed may be picked up by the MAP sensor along with the hard n75 boost regulation open circuit code causes the closing of the throttle plate. Whatever it may be there are other saftey precautions programed into our ecm's. Geez these things are damn smart.

When the N75 is unplugged it passes the full boost signal to the wastegate. Once the boost signal exceeds the wastegate actuator spring setting the wastegate opens.

[KHARDa4]

When the N75 is unplugged it passes the full boost signal to the wastegate. Once the boost signal exceeds the wastegate actuator spring setting the wastegate opens.

In my case I had a full boost signal being passed through my MBC to my wastegate but it did not overcome my spring tesnsion. I was still was getting absolutely no boost at all.

EDIT: Let me rephrase. My boost signal probably would have overcome spring tension had the turbo had time to spool and make boost. With the throttle plate closed or slightly closed it wasnt allowing the charged air pressure through the motor to spin the turbine wheel, so my problem wasn't wastegate related.

[jpulll]

Got 2 logs out to Dave at Motoza. One before and one after I disconnected the n75 connector. Max boost was 4psi, dependent upon load. Saw more 2-3psi than I did 4psi.

[old guy]

Got 2 logs out to Dave at Motoza. One before and one after I disconnected the n75 connector. Max boost was 4psi, dependent upon load. Saw more 2-3psi than I did 4psi.

That sounds a tad low for a K03 under full load. Let's see what Dave has to say.

Did you try clamping off the boost signal line to the wastegate to see if the turbo can go past 20 psi?

[jpulll]

Did you try clamping off the boost signal line to the wastegate to see if the turbo can go past 20 psi?

I did not, buddy came over to get his brakes done. Probably do that sometime tomorrow.

[old guy]

I did not, buddy came over to get his brakes done. Probably do that sometime tomorrow.

It's worth doing. It will tell you if your turbo is capable of more boost than you are currently getting.

[jpulll]

It's worth doing. It will tell you if your turbo is capable of more boost than you are currently getting.

just got another log out to Dave with the actuator line plugged. my gauge read 18psi still.

[old guy]

just got another log out to Dave with the actuator line plugged. my gauge read 18psi still.

With the wastegate actuator disconnected the N75 no longer has any control over the boost level. A healthy K03 is capable of running well over 20 psi. I recall a few years back when Mike2ptZero was running 26 psi with a custom GIAC "hammer" file before he went bonkers with a BAT set-up. I routinely ran 22 psi with my GIAC big injector file.

I can only think of four things that would prevent you from running over 18 psi with no boost regulation.

Boost leak: I believe you have checked and rechecked for potential boost leaks.

Intake restriction: Clogged air filter. Collapsed TIP. Restriction in the intake snorkle.

Exhaust restriction: Clogged cat, clogged mufflers. Collapsed exhaust line.

Turbo itself: Wastegate set too loose. Damaged turbines. I don't think you have turbine damage since you don't report any turbo noise issues.

It will be interesting to see what Dave has to say about your recent log.

[jpulll]

It will be interesting to see what Dave has to say about your recent log.

I am set on Dave's schedule for Monday.

[Detroiter]

Also interested in what Dave has to say about it as he has been working with me on figuring out my boost issues for a while now. I think I'm going to drop the cat sometime this next week and attempt to adjust the waste gate. I'll report back with what happens. It is very interesting that we both are having the same 18psi max boost.

Does your turbo seem to spool up slower than what it should also? Mine seems to take until 3k rpms to get above 10 psi of boost unless I am in 5th gear.

[old guy]

Also interested in what Dave has to say about it as he has been working with me on figuring out my boost issues for a while now. I think I'm going to drop the cat sometime this next week and attempt to adjust the waste gate. I'll report back with what happens. It is very interesting that we both are having the same 18psi max boost.

Does your turbo seem to spool up slower than what it should also? Mine seems to take until 3k rpms to get above 10 psi of boost unless I am in 5th gear.

That is definitely an issue. A k03 should be able to easily hit full boost by 3k rpm. Wastegate and exhaust restrictions are certainly worth checking.

[jpulll]

Detroiter- With all of the check valves changed, leaks tightened and the n75 hoses replaced, I've gotten much better throttle response. just not hitting requested boost.

[jpulll]

Got a response to the logs from Dave. He said it's either the diverter valve or the wastegate. He said "The MAF readings look correct for the boost level and the fuel trim is tight so there's no indication of it being a boost leak." He continued saying, the diverter valve itself cannot give indication of a leak during the test.

I believe the diverter valve is ruled out with the test I performed by plugging the diverter port on the TIP and letting the DV breath to the atmosphere. correct?

lastly, he said "the other option is that the WG is soft enough that with no additional pressure at the WG actuator, it is opening up once you get decent pressure in the turbine housing."

[old guy]

That is correct. You ruled out the DV by testing it to atmosphere. If it held in that configuration you know that it is working to hold boost properly. It's sounding more and more like a soft wastegate adjustment.