On my 4th MAP sensor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jokershockey29 · 02-16-2010, 03:36 PM

the MAP sensor in my 87 Chevy 350 TBI keeps going bad. I have checked for vacuum leaks and everything is fine. Checked the voltage at the sensor and with just the key on it reads about 4.69. Using a vacuum gage the voltage drops about 1 volt for every 5 psi. I installed a clear hose from the TBI to the MAP sensor and I have noticed fuel in the line. Not vapors but actual fuel that is sloshing around. I'm thinking that is not normal and could be causing my sensor to keep going bad. Anyone have any thoughts on this? Thanks.

cableguy0 · 02-16-2010, 09:22 PM

You likely found your problem. there should be no fuel in the vacuum lines period. Im sure the fuel is killing the map sensors. Its not designed to handle the fuel. I would suspect the throttle body is leaking fuel internally allowing it to get into the vacuum circuit.

STOCKISH · 02-16-2010, 09:44 PM

You just hit the nail right on the head. Time to rebuild that throttle body.

jokershockey29 · 02-17-2010, 12:36 AM

Thanks, thats kind of what i was thinking. But I've already rebuilt it once. I was going to do it again anyway so i was hoping that might fix the problem.

02-16-2010, 03:36 PM	#1
jokershockey29 Registered User Join Date: Jan 2009 Location: Pittsburgh PA Posts: 16	On my 4th MAP sensor the MAP sensor in my 87 Chevy 350 TBI keeps going bad. I have checked for vacuum leaks and everything is fine. Checked the voltage at the sensor and with just the key on it reads about 4.69. Using a vacuum gage the voltage drops about 1 volt for every 5 psi. I installed a clear hose from the TBI to the MAP sensor and I have noticed fuel in the line. Not vapors but actual fuel that is sloshing around. I'm thinking that is not normal and could be causing my sensor to keep going bad. Anyone have any thoughts on this? Thanks.

02-16-2010, 09:22 PM	#2
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	Re: On my 4th MAP sensor You likely found your problem. there should be no fuel in the vacuum lines period. Im sure the fuel is killing the map sensors. Its not designed to handle the fuel. I would suspect the throttle body is leaking fuel internally allowing it to get into the vacuum circuit. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

02-16-2010, 09:44 PM	#3
STOCKISH Formerly- 1972SuperCheyenne Join Date: Oct 2008 Location: Wake Forest NC Posts: 5,782	Re: On my 4th MAP sensor You just hit the nail right on the head. Time to rebuild that throttle body. __________________ --Josh My Build Thread:http://67-72chevytrucks.com/vboard/s...d.php?t=799218 A good crossthread is better than Loctite any day. Life is not about what you have, but who you have to share it with.

02-17-2010, 12:36 AM	#4
jokershockey29 Registered User Join Date: Jan 2009 Location: Pittsburgh PA Posts: 16	Re: On my 4th MAP sensor Thanks, thats kind of what i was thinking. But I've already rebuilt it once. I was going to do it again anyway so i was hoping that might fix the problem.



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