Boost Pressure Sensor

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

greiswig wrote:

Ranger1 wrote:

Exactly what was soot covered on yours - just the sensor, or the housing as well? Was the sensor blocked by soot from direct air flow?

From your pix, it appeared that the cage surrounding the sensors was actually packed with soot, or at least had a blanket of it that pretty much shrouded the thermistor. On mine, all four of the windows in that cage were open...but there was a thin (maybe .5mm) film of soot on all exposed surfaces.

HTH,

Packed from the sensor solid out through the cage and formed a solid layer over the cage. And this was with many long distance, highway trips, probably 90% Interstate driving. I'm wondering if the diesel in Oregon was lower sulfer content prior to national ULSD becoming available this past September. If yours never had an egr failure, or excessive oil blow into the intake, that might explain some of the difference in soot levels.

greiswig · **Posted:** Thu Jan 04, 2007 5:58 pm

Ranger1 wrote:

greiswig wrote:

Ranger1 wrote:

Exactly what was soot covered on yours - just the sensor, or the housing as well? Was the sensor blocked by soot from direct air flow?

From your pix, it appeared that the cage surrounding the sensors was actually packed with soot, or at least had a blanket of it that pretty much shrouded the thermistor. On mine, all four of the windows in that cage were open...but there was a thin (maybe .5mm) film of soot on all exposed surfaces.

HTH,

Packed from the sensor solid out through the cage and formed a solid layer over the cage. And this was with many long distance, highway trips, probably 90% Interstate driving. I'm wondering if the diesel in Oregon was lower sulfer content prior to national ULSD becoming available this past September. If yours never had an egr failure, or excessive oil blow into the intake, that might explain some of the difference in soot levels.

I know for a fact that my fuel has lower sulpher content, higher cetane number, better lubricity, and lower particulate emissions (all emissions other than NOX, for that matter) than pump diesel. I monitor its quality very closely. My driving is a fair amount of city driving, but with 20 miles or so of highway per day thrown in...although there is often traffic.

As far as the soot clogging the intake valves, keep in mind that the velocity of airflow is going to affect how soot gets deposited, along with the temps of the components. I'd expect less deposit near the valves than what I see on that sensor because of those factors. Still, as you imply, any deposit will change the airflow parameters and may cause performance degradation. You could always just block off the EGR pipe and put up with the constant P0104 code. :wink:

Not that I'd recommend that...

MACKJ · **Posted:** Thu Jan 04, 2007 9:36 pm

greiswig wrote:

Ranger1 wrote:

According to the FSM, its a dual pressure/intake air temperature sensor. It's difficult to see in web page resolution, but on the other side of the yellow sensor, the bottom has an almost translucent half moon coating on the bottom. Just guessing, I'd say the yellow probe is the temperature probe and the other is the pressure sensor. Or the yellow sensor could be both...

Aha! Yes, that would explain it. I bet the yellow thing IS a thermistor, so it's the temperature sensor. That would be affected by deposits, especially a lot of insulating carbon. Still, I'd expect a pressure transducer to withstand a fair amount of soot or soot/oil before it wasn't working properly.

Guys,
Now I start this by saying that I’m no expert but from experience and applying engineering logic these MAP sensors (or boost sensor as DC calls it) work by differential pressure measurement. Therefore there must be a hole in this sensor to measure the differential pressure. If you look at the sensor upside down, that is past the cage that holds the temp probe, you will see a tiny hole. I was very careful when I cleaned my unit as I wanted to ensure this was not blocked.
I am pretty sure the boost or relative pressure sensor part is in the main body of the switch and is a piezo resistive type unit. That is, it has a little silicon wafer (which has replaced the old style diaphragm in earlier MAP sensors) that moves with changes in manifold pressure.
This movement of the wafer causes a change in resistance and a corresponding electric signal that is sent to the ECU.
Suffice to say that this poor little bugger is in a pretty crappy environment and probably at some stage down the track that little hole will become blocked and the sensor will require replacement.
By the way I would guess the MAF (mass air flow sensor) is a Karman vortex type unit that counts the number of vortices (air disturbances) passing over the sensor. The number or frequency of the vortices is proportional to air flow. The measurement is accomplished using a metal foil mirror together with a light or photo transistor.
The measurement would be surely inaccurate if this foil or sensor is dirty.
There endith the lecture… :wink:

TDI4BY · **Joined:** Sun Apr 02, 2006 11:56 pm **Posts:** 644

I had a check engine light because of K&N oil on the MAF sensor. A little bit of cleaner and a day later and the light has been out ever since.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

Whatever its architecture, I doubt its designers intended it to operate in a soot and oil rich environment.

MACKJ · **Posted:** Fri Jan 05, 2007 8:26 am

Ranger1 wrote:

Whatever its architecture, I doubt its designers intended it to operate in a soot and oil rich environment.

Exactly Ranger1.
Er sorry...just re-read my previous post. I didn't mean to sound a little condescending or patronizing...just trying to add to the general knowledge base.
The point I was trying to make, whilst getting lost in the technicalities, was that when I found this problem originally I was really p#ssed that senior technical people in Jeep Australia had for so long dismissed my logic. Logic that asked how can such a complex little beast be expected to work at optimum efficiency in such a crap environment that mixes oil and carbon together in an intake manifold. An environment caused by poor design and/or cost cutting and without a recognised maintenance regime to keep it in good working order. Surprise, surprise the customer has to pick up the can again!!

onthehunt · **Posted:** Fri Jan 05, 2007 9:22 pm

Quote:

Surprise, surprise the customer has to pick up the can again!!

Join the crowd!! Anyone that buys a diesel in the next 10 years should just consider themselves a beta tester for all purposes until they finally outlaw diesel power in passenger vehicles.

europachris · **Posted:** Sun Jan 07, 2007 11:16 am

Here is our sensor, '05 model with about 34,000 miles.

Totally clogged solid with soot of the dry crumbly variety.

Haven't driven it yet, but we'll see how it improves!

Great forum here!

Chris

retmil46 · **Posted:** Sun Jan 07, 2007 12:24 pm

Did mine yesterday with 18,000 miles on it. Same story as everyone else, totally clogged to where it looked like a lump of coal. Soot was of the dry crumbly kind, chunks dropping off on the manifold as I pulled it out. Hole in the manifold actually looked rather clean considering.

Sensor cleaned right up with a spray can of brake cleaner, no scrubbing required.

Took it on a 20 mile run to Home Depot in Huntersville last night. To me, it again performed as it did when it first rolled off the lot, a noticeable before/after difference.

Another theory on why it becomes so clogged - this sensor could literally be a soot "magnet". An exposed sensor with an electrical charge/potential across it, there could be an electrostatic attraction that is causing even dry soot to accumulate and clump on the sensor. Akin to the way a Xerox printer makes use of toner.

DnA Diesel · **Posted:** Sun Jan 07, 2007 12:53 pm

Mitchell, I think any such effect would be minimal compared to the aerodynamic forces due to the flow in the manifold. I think it gets most of this junk because it pokes directly down into the airflow within the manifold and the particulate matter really doesn't like moving out of the way of an object, thus it impacts the sensor housing and builds up.

Cheers,
Duey

kb61751 · **Posted:** Sun Jan 07, 2007 1:47 pm

I just looked at mine, only slightly clogged, carb cleaner worked great, looks like new. I have 12000 miles on it.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

I just spent 30 minutes looking through the FSM maintenance schedule for an 05 CRD. Not a single word on inspection, cleaning or replacement of boost (MAP) sensor in it. They never expected this behavior.

alvanko · **Posted:** Sun Jan 07, 2007 6:57 pm

I pulled and cleaned mine last Sunday. 18,000 miles. Clogged. Filled up after 300 miles normal driving to work. Mileage is the same. No difference. No performance change. :cry:

CATCRD · **Posted:** Sun Jan 07, 2007 7:40 pm

Mine was packed slap full of carbon at under 17000 miles. It was just a black lump. I cleaned it out with some solvent and I'll post if I notice any difference. I'm hoping it'll cure this surging/hesitation I've been having at very light throttle application when the engine is cold.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

alvanko wrote:

I pulled and cleaned mine last Sunday. 18,000 miles. Clogged. Filled up after 300 miles normal driving to work. Mileage is the same. No difference. No performance change. :cry:

iirc, the poster from australia had to disconnect his battery for 15 or 20 minutes after cleaning to get his power back. I think it had something to do with the PCM adapting to incorrect sensor readings and needing to relearn once it was cleaned. Another area might be to check to see that the yellow sensor is clear of soot - if it has a mm or two of soot on it, that might be enough to insulate it.

RFCRD · **Posted:** Sun Jan 07, 2007 9:33 pm

For those with the question: To clean, or not to clean?

CRD tech at the dealer told me yesterday to do exactly as posted here, clean them and reinstall. Said to just make sure you get all the carbon out of the base of the protective cage. Recommended carefully using shop air with a blow-tip.

MACKJ · **Posted:** Sun Jan 07, 2007 10:09 pm

Ranger1 wrote:

alvanko wrote:

I pulled and cleaned mine last Sunday. 18,000 miles. Clogged. Filled up after 300 miles normal driving to work. Mileage is the same. No difference. No performance change. :cry:

iirc, the poster from australia had to disconnect his battery for 15 or 20 minutes after cleaning to get his power back. I think it had something to do with the PCM adapting to incorrect sensor readings and needing to relearn once it was cleaned. Another area might be to check to see that the yellow sensor is clear of soot - if it has a mm or two of soot on it, that might be enough to insulate it.

Ranger1, any luck on a price for a new sensor?. They are about A$100 here direct from Bosch. Jeep's price is A$165.
BTW the info I found out from Bosch states..."thanks to a special coating, both the pressure sensor and temperature sensor are insensitive to the gases and liquids which are present in the intake manifold..." therefore we can assume cleaning with a good carby cleaner or similar is not going to cause any harm. Maybe we don't need a spare if we can clean it so easily.

MACKJ · **Posted:** Sun Jan 07, 2007 10:17 pm

Ranger1 wrote:

I just spent 30 minutes looking through the FSM maintenance schedule for an 05 CRD. Not a single word on inspection, cleaning or replacement of boost (MAP) sensor in it. They never expected this behavior.

Maybe they prefer the "head in the sand" approach or "does it really, well I never" or "performing to manufacturer's specification" !

DZL_LOU · **Posted:** Sun Jan 07, 2007 10:41 pm

All this discussion about boost sensors, boosted my energy to pull the lil bugger and take a look at how bad it was.
Well at 35K miles on an 05 CRD it had the whole cage caked up with a fine packed soot.
Here's a peek

I also called the dealership and the boost sensor is $42.00 US Dollars but needs to be shipped from a warehouse in Chicago. I'm going to keep a spare, just in case. I cleaned the bugger'd up one, and noticed no change in engine operation.

kb61751 · **Posted:** Sun Jan 07, 2007 10:44 pm

Here it is... Under electrical

AIR INTAKE TEMP SENSOR, Liberty, 2.8L 05-06 List $48.50 Cost $38.80

http://www.mopar-parts-dealer.com/

Boost Pressure Sensor

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