Low boost problems

pnwjk · **Joined:** Tue May 21, 2019 7:12 pm **Posts:** 11

Hi All!
I recently bought an 06 crd with 168,000 miles.

I’m having trouble with low boost. On full throttle runs, it will boost to 22 lbs, but after around maybe 10-15 sec and 60 mph the boost drops to 2 lbs and the car stops accelerating. If I stop and shut the engine off and turn it right back on it boosts like normal again. It also intermittently throws a low boost code.

So far I’ve checked all the hoses, cleaned the MAP sensor, disconnected the MAF sensor, and tried an Italian tune-up in case the vanes on the turbo are stuck. I tried pulling the vacuum line on the turbo while at idle and watched the rod on the actuator under the turbo drop close to ½ in and then go back up when I reconnected it.

Any ideas? Thanks!

GordnadoCRD · **Posted:** Wed May 22, 2019 5:13 am

Have you disconnected the turbo inlet hose, and checked for bearing wear?
edit - Also how and where are you checking the boost value?

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

This sounds very similar to an issue I had about three months ago - you'd get one good boost after starting up, then no more turbo until the next startup. Codes P0299 and P1252 were thrown when this happened. The cause was a faulty turbo vacuum modulator; it's not uncommon on these vehicles.

There is a workaround (and this will also help to determine if this is in fact the problem): bypassing the vacuum solenoid that feeds the turbo modulator. See this post for info on how to do that.

Once bypassed, if this fixes the issue, order parts and replace; it's OK to drive like this until parts arrive. I'd recommend doing the solenoid, modulator, and air filter to the vacuum modulator at the same time since they're probably all factory-original, but it's your call on that one.

WWDiesel · **Posted:** Wed May 22, 2019 10:18 am

pnwjk wrote:

Hi All!
I recently bought an 06 crd with 168,000 miles.
I’m having trouble with low boost. On full throttle runs, it will boost to 22 lbs, but after around maybe 10-15 sec and 60 mph the boost drops to 2 lbs and the car stops accelerating. If I stop and shut the engine off and turn it right back on it boosts like normal again. It also intermittently throws a low boost code.
So far I’ve checked all the hoses, cleaned the MAP sensor, disconnected the MAF sensor, and tried an Italian tune-up in case the vanes on the turbo are stuck. I tried pulling the vacuum line on the turbo while at idle and watched the rod on the actuator under the turbo drop close to ½ in and then go back up when I reconnected it.
Any ideas? Thanks!

May be a vacuum leak or vacuum problem with the turbo vane controller or the small vacuum reservoir or the vacuum solenoid not opening all the way or one of the hoses leaking.
Hooking up a small vacuum gauge using a small "tee" in the vacuum hose going to the turbo vanes and using a long hose on the gauge that will allow you view the gauge while driving down the road would allow easy diagnostics of what the controller is telling the turbo to do boost wise.
:idea:

pnwjk · **Joined:** Tue May 21, 2019 7:12 pm **Posts:** 11

casm wrote:

This sounds very similar to an issue I had about three months ago - you'd get one good boost after starting up, then no more turbo until the next startup. Codes P0299 and P1252 were thrown when this happened. The cause was a faulty turbo vacuum modulator; it's not uncommon on these vehicles.

There is a workaround (and this will also help to determine if this is in fact the problem): bypassing the vacuum solenoid that feeds the turbo modulator. See this post for info on how to do that.

Once bypassed, if this fixes the issue, order parts and replace; it's OK to drive like this until parts arrive. I'd recommend doing the solenoid, modulator, and air filter to the vacuum modulator at the same time since they're probably all factory-original, but it's your call on that one.

I tried bypassing the vacuum solenoid. It still loses boost as before, but now, instead of dropping down to 2 lbs, it will still boost to 15-16 lbs. I can tell it has a bit more power, but still not much.

Also as before, restarting it restores full boost.

pnwjk · **Joined:** Tue May 21, 2019 7:12 pm **Posts:** 11

GordnadoCRD wrote:

Have you disconnected the turbo inlet hose, and checked for bearing wear?
edit - Also how and where are you checking the boost value?

No I haven't checked for bearing wear yet.
I'm checking boost values via OBD2

WWDiesel · **Posted:** Wed May 22, 2019 10:25 pm

pnwjk wrote:

I tried bypassing the vacuum solenoid. It still loses boost as before, but now, instead of dropping down to 2 lbs, it will still boost to 15-16 lbs. I can tell it has a bit more power, but still not much. Also as before, restarting it restores full boost.

It definitely sounds like you have a boost control issue going on.
Since restarting it resets it, I would replace the vacuum modulator.
You already know you can bypass the vacuum solenoid for testing purposes.

pnwjk · **Joined:** Tue May 21, 2019 7:12 pm **Posts:** 11

WWDiesel wrote:

pnwjk wrote:

I tried bypassing the vacuum solenoid. It still loses boost as before, but now, instead of dropping down to 2 lbs, it will still boost to 15-16 lbs. I can tell it has a bit more power, but still not much. Also as before, restarting it restores full boost.

It definitely sounds like you have a boost control issue going on.
Since restarting it resets it, I would replace the vacuum modulator.
You already know you can bypass the vacuum solenoid for testing purposes.

Thanks for the help! Is there any way to test the vacuum modulator before replacing it?

I might be really far off with this one, but, since the cruise control relies on a vacuum, wouldn't the cruise stop working if the vacuum modular isn't providing enough vacuum?

flash7210 · **Posted:** Fri May 24, 2019 12:05 pm

No, your cruise control does not rely on vacuum. Its 100% electronic.

Things that rely on vacuum are:
power brake booster
VNT turbo modulation
cabin vent controls

The vacuum reservoir, small vacuum solenoid, and large vacuum modulator solenoid are all specifically for the turbo.
And they are all located directly behind the air filter box.

I know of no specific test for the vacuum modulator solenoid, but when mine went bad it was making a loud buzzing noise that could be heard with the engine running.
If in doubt, just replace the solenoid(s).

WWDiesel · **Posted:** Fri May 24, 2019 1:25 pm

pnwjk wrote:

Thanks for the help! Is there any way to test the vacuum modulator before replacing it?
I might be really far off with this one, but, since the cruise control relies on a vacuum, wouldn't the cruise stop working if the vacuum modular isn't providing enough vacuum?

flash7210 wrote:

I know of no specific test for the vacuum modulator solenoid, but when mine went bad it was making a loud buzzing noise that could be heard with the engine running.
If in doubt, just replace the solenoid(s).
X2

Replacing the turbo vacuum modulator is the only way I know of to rule it out as a problem.
IDParts sale them along with many online retailers. :google:

https://www.idparts.com/turbocharger-va ... -3210.html

Low boost problems

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