How could i test a Map sensor?

**Thom** · 14th January 2012, 14:47

As many of you are aware im having issues with my car and have done ever since cleaning the entire inlet manifold but never before this. I thought i had an air leak as i has stripped the thread on the swirl valve piece however since replacing this i still get the problem (although not as badly).

Ive done all the usual air leaks tests and checks including replacing various hoses.

I've decided to go back to the start and think about what i touched when sorting the cars inlet, i had the boost sensor off, as well as the vacuum things around the inlet area.

My problem is the car goes into limp mode when under heavy load, particularly in 3rd gear around 60mph and 5th gear when trying to accelerate from about 60mph under load, on the flat the cars fine.

For this reason im blaming the map sensor as i know theyre delicate - how could i test its function without buying a new one?

Also, what are the correct names for the vacuum thingies that sit on the side of the inlet manifold for the switl bar and the one that sits at the front of the engine bay.

Car is a 2.0 dti 2003

**Rapala** · 14th January 2012, 15:05

QUOTE: Also, what are the correct names for the vacuum thingies that sit on the side of the inlet manifold for the switl bar and the one that sits at the front of the engine bay.
The name you are looking for is vacuum solenoids.
Have you checked all of the small vacuum pipes and the rubber connectors at each end of the said pipes for splitting or any other sort of damage. The slightest leak in any of these pipes can cause the symptoms that you have.

**Thom** · 14th January 2012, 15:16

Thanks mate, and yeah i have ive replaced them with 2mm id silicone hose to ensure there was no fault. I've just been out there now checking everything moves freely under a vacuum too.

The only things i can think of that could be to blame is:
1) A stripped engine cover bolt/thread allowing air to escape this way instead of into the vacuum pump (long shot - i know)
2) Boost sensor fault (although opcom says nothing about it i do have P0234) I have cleaned this since having my limp mode problems and it improved slightly but not completely.
3) Vacuum solenoid - perhaps some dirt got into one as ive had hoses on and off - or perhaps i've damaged the swirl flap vacuum solenoid when ive been cleaning the inlet.

If i did infact cause this fault rather than it being a coincidence i can't see any other explanation, i used new gaskets all round when refitting and everything is torqued correctly too so it cant be a manifold air leak.

**gtr1000** · 14th January 2012, 15:57

How I tested the MAP sensor on my V6 CDTi http://vectra-c.com/forum/showpost.p...0&postcount=32.

You don't need a vacuum pump, just suck on a length of hose attached to the MAP. As you suck, the voltage should change.

HTH

.

EDIT - is the boost sensor not the same as the MAP sensor? That's the conclusion us V6 guys came to.

**Thom** · 14th January 2012, 23:58

Yes Map sensor is simply the "proper" term for the sensor that dictates boost pressure as far as i gathered!

I'll try that once i get a voltmetre!

**Ste** · 15th January 2012, 01:01

Manifold Absolute Pressure...... it's a pressure sensor that measures inlet manifold pressure, either boost or depression on non boosted engines.

**Thom** · 15th January 2012, 01:14

Right - A long night of google searching has revealed three potential enemies - if you wish!
Going by the fact i seem to have created this problem through cleaning my inlet manifold (and subsequent components) i am thinking logically for a change as to what i may have touched as the car was fine prior. Most common problems, even though the fault code is still P0234 without any additional codes are:

The MAP sensor needs testing as this can be to blame so a multimeter shall be purchased shortly. Why wouldnt a fault with this show on op-com?

The Boost control solenoid (Part number 09128022) may be at fault, i don't know what can go wrong with this or how to test it.

Finally, the third most common problem is that the turbo vanes may be sticking - i don't know how i could have affected this unless ive dislodged engine gunk that has clogged it when cleaning my inlet however if both of the above are fine then this is next on my list for checking.

Some users online have suggested lengthening the turbo actuator rod is an option which will reduce the amount of boost the turbo creates however this appears to be a bodge rather than a fix.

**Ste** · 15th January 2012, 01:36

If the boost control is controlled by vacuum (i'm not sure on your engine) then disconnect the pipe from the other end and fit it to a syringe. Moving the plunger may move the actuator arm and hence show the controller is functional. This is the waste-gate actuator.

P0234 Engine Overboost Condition.

Do you have a vacuum guage? If so connect to the actuator pipe and rev the engine a little. It should change as wastegate control opens it.

I would check again for vacuum leaks and also the vacuum control solenoids for the pipe to the actuator.

(assumptions, DTi is fixed geometry turbo, actuator is vacuum and not boost pressure controlled, swirl valves on DTi?, wastegate normally closed and vac opens it, )

Some engines have a normally open wastegate and vacuum closes it. This is safer as any vacuum failure will open the wastegate and boost pressure is limited.

**Thom** · 15th January 2012, 19:26

I'm going to buy a multimetre and test the vacuum pressure when i get home too, cheers ste!

**Thom** · 20th January 2012, 13:26

Is it suggested that i attache a piece of hose to the actual sensor piece of the MAP?

I couldnt figure out how to do it but i was getting about 5v with just the ignition and no pressure.