Engine & Gearbox Mistery to be solved - Vaccum Solenoid Valve - Turbo actuator

Discussion in 'Honda N-Series' started by Joao Vieira, Tuesday 16th Aug, 2016.

  1. Joao Vieira Junior Member ☆ ☆ ☆ ☆ ☆

    Portugal João Leiria
    Hi all,

    Does any one knows exactly how the Vacuum Solenoid Valve works in the turbodiesel models? In this specific case I'm referring to the one that connect directly to the turbo actuator. The valve contains 2 connections, one to turbo and other one to Vacuum Solenoid Valve located in the front of the engine, plus one connection that have small air filter, why this connection with air filter is necessary?

    I'm going to explain the background behind this question and what is the mystery to be solved.

    Around 320Ks Km I begin to feel a lack of power between 2.000 and 2.500 RPM, but it only in recoverings after a slowdown, per example, I was riding at 3.000rpm, if I took the foot from throttle till it reach down 2.000 RPM, when I press it again there was no response from turbo, or at least a very faint one. This symptom only happen in this situation, didn't happen with straight acceleration from idle RPM. When happen, the way to recover power was pushing clutch without taking foot from throttle making the RPM go high and take the foot again from clutch or tapping several times with the foot in the throttle, first technique always work, second some times not.

    I ignored this symptom for some time, at 370ks Km, the turbo failed, I thought that probably the described symptom was related to an already starting to fail turbo, I exchange turbo and to my surprise, the symptom was still there with exactly the same behaviour.

    I decided to try to make something about it, and after some threads analysed in several forums, I decide to have a go in cleaning and eventually replacing the EGR valve, I've done both things and no result, the behaviour was the same.

    At 390Ks km, I had an gas smell inside the car, it was the exhaust manifold that had a crack, it was repaired and for my surprise... the lack of power symptom disappeared....

    Happily I drove the car for more 10 - 15ks km and for my dismay, the problem returned...

    Ok, this can't be turbo, can't be EGR, well, I decide to ignore it again and I drove the car without giving it a though till recently reached 500Ks km, to be honest I was waiting to have a very expensive failure in the car sooner or later so I was already thinking what car I was buying next, but since the car reached this nice Kms qty, I decide to have again a serious look at this problem.

    If turbo and EGR was ok, maybe was something about the mechanism that control turbo actuator, like vacuum lines or Solenoid itself, so I began taking it out and then I notice the the little air filter that the solenoid should have was not there, in attach you can find two pictures taken from internet, with and without the filter exactly like mine was.

    Well, I began to think that maybe some dirt had enter the solenoid or vacuum lines and was creating a bad behaviour somewhere creating the described symptom. I cleaned all lines, the solenoid and put it together again in the car, looking at the solenoid, I decided to put a screw in the open hole of the solenoid, the one lacking the filter (don't ask me why), I tested the car and... no lack of power symptom, well, I decided to take out the screw and the symptom returned back, I put the screw again and the symptom disappear again!!!!

    Well, to be honest, I have to test the car in a more intensive environment, only next week I will drive the car for some hundred miles wit a lot of de-aceleration and acceleration, that will be the real test to check if the symptom completely disappear with the screw put on.

    I've try to find on the net an explanation how the vacuum control acts on the turbo actuator and why is necessary this air input in the solenoid valve and now I return to the question in the beginning of this post, how this system works?

    Have in mind that all the explained din't create any ECU error.

    Best regards, With filter. Without Filter.JPG
  2. Zebster Guest

    The air filter is on the air admittance path to the electro-vacuum regulator (EVR)/solenoid actuator. Without an air admittance path, the turbo VNT boost mechanism would be operated by the application of vacuum, but then be unable return back to the default position when required... Air must be admitted to relieve the 'trapped' vacuum, and so this ability is a complementary function of the EVR.

    The IMRC (and the EGR valve on 2006+ models) function in a similar way. I believe that (some of) these EVRs are interchangeable on the later models?

    My IMRC actuator is currently playing up, so I have disabled it by removing the electrical connector..
    Last edited by a moderator: Tuesday 16th Aug, 2016
  3. Joao Vieira Junior Member ☆ ☆ ☆ ☆ ☆

    Portugal João Leiria
    Hi Zebster,

    Are you saying that disconnecting the plug like you have done and closing the air input is similar?

    Whal wil be consequece of having always vacuum on the turbo actuator?
  4. Zebster Guest

    Yes. Your turbo is now running with the VNT boost mechanism in a fixed position (like my IMRC). This issue is a little more significant in relation to the turbo, as the demands for boost vary greatly depending upon running conditions. At certain times your available boost will now be incorrect for the demanded/expected figure and cause fueling problems, this may be seen as excess smoke and/or poor economy/performance. Additionally I'd expect you to also get an engine warning light for excessive boost ( I think it's that way round with vacuum permanently applied, but I could be wrong and you'll get a warning for low boost). The stored error codes P1236 and P1237 are the relevant DTCs to look for using an OBD2 scanner, even if the warning light hadn't yet come on they may be registered as 'pending'?
    Last edited by a moderator: Thursday 18th Aug, 2016
  5. Joao Vieira Junior Member ☆ ☆ ☆ ☆ ☆

    Portugal João Leiria
    Hi Zebster, thanks for your explanation.

    I found this page Understanding Solenoids - MiniMopar Resources where the Vacuum Solenoid is clearly explained, the clear consequence of having the air input closed will be that turbo actuator will always have full vacuum applied, this will cause the vans to be always open making the turbo work as an old turbo. This is not happening because the consequence will be low power on low RPM and a sudden kick as the turbo lag threshold is passed, isn't it right?

    About errors, well, indeed there are errors, but apparently not related with the subject is discussion, I get errors: P1065, P0088, usually associated with OEM fuel filter per example and this is not new for me, I had this codes with limp mode about 200ks km ago and it disappeared when I changed the fuel filter.

    I will perform more tests during driving next week to make sure what is the behaviour of the car.
  6. Zebster Guest

    P1065 and P0087 are the usual (low fuel pressure) codes that indicate a possible fuel filter issue. P0088 is excess fuel rail pressure, but isn't unusual.
  7. Joao Vieira Junior Member ☆ ☆ ☆ ☆ ☆

    Portugal João Leiria
    Hi, an update.

    I've already performed 600kms on intense driving conditions and without any doubt that with the solenoid air input closed the lack of power in speed recovering almost disappear completely, I say almost because in about 50 situations were the symptom appear 45 times, now it happened no more than 1 or 2 times.

    I understand what would be the consequences of blocking this air input but I'm not noticing any off them, there are no errors (I cleared previous mentioned errors and they din't appear again), no obvious difference in fuel economy, no turbo lag.

    The only explanation that I find for this behaviour is that the original problem is located somewhere else and closing the air input hide the problem, for me at this time I see two options:

    - Vacuum leak - I doubt because I've already checked all connections and if exist would influence the turbo actuator in all conditions, in this case the symptom only appear after throttle depress and press again
    - Problems in Vacuum pump - Since a long time ago, that in certain situations, like when driving in high revs in highway and sudden slowing to exit highway, that the clutch pedal turn very hard. this can point for an vacuum pump problem.

    I will perform more tests and see if I can get a vacuum test on the car.

    Best Regards,
  8. Zebster Guest

    I don't understand how the vacuum pump (or any of the vacuum system) could affect the clutch?
  9. Joao Vieira Junior Member ☆ ☆ ☆ ☆ ☆

    Portugal João Leiria
    HUM, I was mixing brake system with clutch, yes, there is no vacuum relation with clutch.

    This bring me another question, why big changes in speed/RPM change the clucth pedal stifeness.
  10. Zebster Guest

    That doesn't happen on my diesel Honda. I can only think that the clutch mechanism is faulty?
    Nighthawk likes this.
  11. Joao Vieira Junior Member ☆ ☆ ☆ ☆ ☆

    Portugal João Leiria
    Is not something that happen all the time, I would say that don't happen more than 10 times a year, but have in mind that in a year I drive 50-60Ks KM so is not with such a big frequency. After some internet search I think that is related with heat, since it happens in high speeds/RPM I think that I can point that happen when car is hotter. For sure is not a failing component because I drove it more than 200ks KM since I felt this for the first time, by now for sure that the clutch would already stop working.