350 MAG MPI temp/pressure sensor

Black_Diamond

I pulled my TMAP/PMAP sensor off my port engine to replace it since I was seeing RPM drops when throttling up compared to the starboard engine.  The one I pulled out was oddly covered in oil, not gas (no gas smell and it does not evaporate).   That cannot be good for it, especially the pressure sender side.  Anyone have ideas why this would be oil coated?  It is mounted in the intake manifold just behind the throttle body.

Wondering if I should replace the other one too, but they are pricy guys..2 boat units.

Thanks!

212rowboat

Didn't you just replace your pcv? Was there a reason for that? Same engine? Related? There is only a short list of ways oil can infiltrate the intake manifold, and the pcv is the biggest offender..

Black_Diamond

Just replaced both pcv's today. Pita to get at.

212rowboat

If your pcv hung you can pull a suprising amount of oil through and into the intake... Without addressing the cause of that or concerns surrounding it, let's hope that your pcv exchange addressed the product of the issue your map encountered.. it could truly be that simple..

If, after a few hours of operation, you pull the pcv hose (from either end) and there is enough oil to cause a single drip (not atomized) oil, it is time to figure out why there is excess positive pressure in your crankcase..

212rowboat

Also... Slap a vacuum gauge on that thing.. ain't no better way to determine what's happening inside it.. could be a bad valve guide, which is a lot less concerning $ wise as well as effort wise than bad rings... And, a lot more common on an engine I'd guess to be better cared for than most, as yours certainly are.

Black_Diamond

So a follow up to this: I changed out the sensor and the PCV on the port engine and finally got a change to run her today and worked like a champ!  No rpm drop at all. 

TikiHut2

Glad you found your gremlin BD. So, was it a stuck PCV that caused the TMAP sensor to foul? My PCV is 10y/o as far as I know. Is that something I should just check/replace as regular maintenance occasionally? Seems like I see a number of posts related to glitchy/neglected PCV valves creating complications.

212rowboat

if it rattles, Tiki, you're good..

the problem with PCV's, which I'm certain is indiscriminate to applications of engines, is that they are made by the cheapest bidder and there is a metric ton of crap in the market... this is one of those items you gotta purchase from the dealer, unfortunately..

fortunately, though, any GM dealership will work.. it's the crap at the box auto stores that will cause you grief..

there are a lot of parts I will use from those joints, but there is a host I won't.. any of the primary engine management sensors such as IAC, MAP/MAF, CPS, CKPS, o2 (where applicable), IAT, ect... those are going to be OEM replacements, even though they run likely twice the price of the aftermarket items.

TikiHut2

Thanks Drew I'll see if mine rattles. I assume it'll be easily found up on the manifold or right over a rubber  valve cover fitting/connector? If it doesn't I'll make sure to look for an OEM GM part or stick with Mercruiser.

212rowboat

yup.. extends through the valve cover.. the grommet hardens over time and makes it a PITA to get out sometimes, but that's what you'll have to do... you may want to pick up a grommet at the same time to replace the aging one... the softer more supple grommet is easy(r) to get into the valve covers, and doesn't grip the PCV until it starts to age.. a light coating of oil on the mating surfaces is a good idea..

there is a simple spring and ball valve in those things that gums up and causes them to stick.. at start-up, there will be some blow by on any engine.. that brief second before pressure equalizes can coat the ball and disallow it's seating over time.. which creates a situation where oil can be sucked right up into the induction process under high vacuum signal situations.. the Asian market make products that skimp on tolerances, which is pretty important at that junction... oil entering the induction can cause a lot of issues, and all because someone wanted to save $5 and a trip to the dealership, ya know?

TikiHut2

Occasionally guilty on that last point.

Ahh, the car/boat cross reference parts conundrum. It sounds like a pretty generic part so If I hit my local GM dealer (who is far closer than my Merc dealer) I'll ask for a GM PCV valve and grommet for an '04 350?  I can imagine the blank stare from the car parts kid who only knows parts based on auto model/year. Any idea of an auto application that might be close to set him on the right trail?

212rowboat

shouldn't be a problem... tell them it is a small block chevy MPI in a boat, but still a small block chevy MPI.. they ought not give you grief.. I don't even think the MPI makes a difference, but the heads, which will influence the valve covers design, may.. that is 'may', but I don't think that will either.

Black_Diamond

Tiki: when you change the PCV valve, the grommet has a lip to hold it in place, so it likely won't just pull out, use a thin flat screwdriver to pop it out. Also, the valve has a 90 deg angle, the plastic 90 deg piece may come off with the tube.

Wildboating

Can anyone tell me where on the engine the pcv valve and sensor is located?  Trying to determine what tools I need to take to boat too swap these on my motors.  Having a rpm issue and looking to eliminate or confirm this as a possible fault. 

Black_Diamond

The PCV valve is mounted on the starboard valve cover.

I'll be at the boat today and get a pic of the sensor location for you. 

Black_Diamond

This is the sensor so you know what it looks like:

http://www.ebay.com/itm/OEM-REPLACEMENT-Mercury-MAP-Temperature-Pressure-TMAP-Sensor-885165-mercruiser-/282068462856

For what is it worth, I bought the Mercury part, not a knock off.  Sells for near $200, but at least I know it is 'correct'.