Many of you may already know this, if so, it'll be here for those that have not encountered this before. I have been working on my Excursion trying to solve an issue where the EBP and MAP sensor readings were different by about 1.4 to 1.8 psi at KOEO. I live at about 4300' ASL so the proper reading for both should be approximately 12.6 psi plus or minus a tenth. The EBP sensor was reading correctly when adjusted for altitude however the MAP sensor was reading lower than expected. I saw this with FORScan before I purchased it and assumed that the MAP sensor was tweeked due to the 160/0's creating an overboost situation. I also saw that there was an professional looking homemade OCR with a manual adjustment valve installed which caused me to question whether the OCR had been installed after damage to the MAP sensor had occurred. The PO stated that the OCR had been on the truck since he first tuned it in '03....hmmm!

So, I drove the truck home thinking that this would be an easy fix and it eventually was. The first thing that I did was install a spare MAP sensor. I thought that it was fixed until I drove it. Post test drive, it had the same low reading. Crap! I then went to the e99 and removed another known good MAP sensor to test on the Ex. Same exact initial reading and then low again post test drive. So, I then decided to remove the OCR to see if anything changed and to check for "actual" max boost readings on a test run. The truck produces 30 psi easily with the stock turbo, new Riffraff boots, and 4" exhaust.

Upon removing the tube between the MAP sensor and the spider about an ounce of oil poured out of the tube. I then noticed that the tube was about six to eight inches too long and dipped down into the valley which created a reservoir for the oil in the tube due to the MAP sensor being a dead end for the oil. I then trimmed the extra length off of the tube and reinstalled it on the MAP sensor. The MAP sensor was then reading within .1-.2 psi of the EBP sensor pre and post drive. Problem solved! Each time I placed a different MAP sensor in the equation it equalized the pressure when the seal was broken at the sensor.

Installation tip: make sure that the tube from the MAP sensor to the spider is almost a straight down hill run. If someone doesn't, oil from the CCV will collect in the hose and create a suction that the MAP sensor sees at KOEO in the absence of positive boost while the engine is running. I am not certain how much this affects the boost numbers at KOER but it seemed a tiny bit low when compared to EBP prior to the fix. I deleted all of my logs from the last time that I had 160/0's so I have nothing to compare to at this point. Now the numbers are a bit closer together.

 

What an odd thing to happen. I can see how fluid in the tube can create a slight vacuum, lowering the MAP reading. Great find! I guess the best way to troubleshoot the MAP sensor is disconnect the tube and see what it reads.

 

I learn something new every day. When I installed my OCR I made sure the line had little slack in it but never cosidered the consequences of leaving extra in case I had to cut the end.

Thanks for sharing!

 

Amazing that that much oil ended up in the hose. I wonder how many quarts are in the intercooler?

 

A few drops in a tiny stretch of skinny hose is not at the same scale as a few drops in an intercooler. This is what it looks like inside an intercooler after over 13 years:

 

I know that's not the worst design in the world but I don't understand what the engineers were thinking other than cost savings/simplicity. There's no way this has any positive effect on heat transfer.

 

 

The water in there tells me it's doing just fine, that is condensation being pulled out of the air from the heat transfer. I live in the desert, so this is no minor feat.

Yeah... I too have lost a MAP sensor. It's rare, but it happens.