MAP Sensor for a "94
Thread Starter
Racer
Joined: Oct 2003
Posts: 475
Likes: 21
From: CLAREMONT Ca
MAP Sensor for a "94
Hi guys,
I need to check the voltage reading on the MAP Sensor (got a 34 reading) and wanted to know the best way to do it. The manual states to test terminals A & B with the ignition on then apply vacuum but do I do this by removing it off the engine while plugged in and sticking the volt meter probes into the terminals?
I need to check the voltage reading on the MAP Sensor (got a 34 reading) and wanted to know the best way to do it. The manual states to test terminals A & B with the ignition on then apply vacuum but do I do this by removing it off the engine while plugged in and sticking the volt meter probes into the terminals?
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
If you have a scanner, you can read MAP voltage with the scanner with the car idling. You can watch it's v output thru open loop into closed loop.
If you don't have or can't borrow a scanner then you will have to back probe the MAP's wires with the KOEO while applying a vacuum using a mity-vac hand pump. I think most of the vette sites like MAD & Camerica sell made up harness that plug in and have tails for the VOM meter's probes to make it easy. With out those harness it is tough to back probe the weather tight connectors. I use straight pins and go in thru the connector that way and then i have some place to touch the VOM meter's probes to. It's a test of my patience, that's why I bought a used scanner off flea bay.
If you don't have or can't borrow a scanner then you will have to back probe the MAP's wires with the KOEO while applying a vacuum using a mity-vac hand pump. I think most of the vette sites like MAD & Camerica sell made up harness that plug in and have tails for the VOM meter's probes to make it easy. With out those harness it is tough to back probe the weather tight connectors. I use straight pins and go in thru the connector that way and then i have some place to touch the VOM meter's probes to. It's a test of my patience, that's why I bought a used scanner off flea bay.
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
Are you getting a DTC for the MAP? You know if they get oil in the hose that supplies the vacuum to the sensor it will create a situation that the MAP will not "see" the correct vacuum and thus not send the correct v signal back to the ECM.
Also, pardon this one...but a MAP on an L98, LT1 motor???? I thought MAP sensors were only used on speed density systems, and I was under the idea that the only speed density system in C4's was on the LT5....you a BOB????
Thread Starter
Racer
Joined: Oct 2003
Posts: 475
Likes: 21
From: CLAREMONT Ca
Are you getting a DTC for the MAP? You know if they get oil in the hose that supplies the vacuum to the sensor it will create a situation that the MAP will not "see" the correct vacuum and thus not send the correct v signal back to the ECM.
Also, pardon this one...but a MAP on an L98, LT1 motor???? I thought MAP sensors were only used on speed density systems, and I was under the idea that the only speed density system in C4's was on the LT5....you a BOB????
Yes, this has a MAP sensor placed directly on the manifold. From what I've read, GM began using MAP sensors on the late '94 models since they soon had to switch to OBDII the following year.
What's a BOB??
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
I just learned something...
....about MAP sensors, thanks I didn't know the fact that you just related to me.
DTC, Diagnostic Trouble Code
BOB, Brother of the Beast, is what us ZR-1 owners refer to ourselves as, unless we use "GM's red headed step children"
MAP directly on the Intake manifold? You are sure you are not looking at the EGR valve? The carbon comment has me wondering, that's all. No, or there should not be any carbon on the vac line that feeds a MAP sensor. I'm not trying to be a smart a$$, just lend a hand.
Tom
DTC, Diagnostic Trouble Code
BOB, Brother of the Beast, is what us ZR-1 owners refer to ourselves as, unless we use "GM's red headed step children"
MAP directly on the Intake manifold? You are sure you are not looking at the EGR valve? The carbon comment has me wondering, that's all. No, or there should not be any carbon on the vac line that feeds a MAP sensor. I'm not trying to be a smart a$$, just lend a hand.
Tom
Thread Starter
Racer
Joined: Oct 2003
Posts: 475
Likes: 21
From: CLAREMONT Ca
Yes, I got a CODE 34 (MAP sensor) and yes, according to the manual which shows a picture of it, it is the MAP sensor. I've even looked the part up online and the pictures match.
I found a testing procedure on you tube and learned how to test it. Sticking a probe into the "B" wire and touching it with a volt meter and of course grounding the other wire thus allowing me to get a reading. I'm hoping I get no reading which would indicate a faulty sensor so all I'll have to do it buy a new one for $34.00 as opposed to finding out it's my CPU which I highly doubt.
I found a testing procedure on you tube and learned how to test it. Sticking a probe into the "B" wire and touching it with a volt meter and of course grounding the other wire thus allowing me to get a reading. I'm hoping I get no reading which would indicate a faulty sensor so all I'll have to do it buy a new one for $34.00 as opposed to finding out it's my CPU which I highly doubt.
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
Okay, you are on the way. Leave it connected, the MAP sensor. Prepare the back probe. Start the car and let it idle up thru open loop into closed loop (normal coolant temp is gained, about 150* or greater) and then have the Volt meter connected so you can watch the v readings. The bad part is that unless you know what the mv reading is supposed to be @ idle in closed loop, you really need to see a 0 v reading. Ofcourse, the vacuum side of the MAP could be bad and for that you have to use a mity-vac hand pump to diagnoise, it either holds the vacuum you apply to the MAP port or it don't.
If you have a FSM, in the Emissions and Driveability section, usually section 6E in the Helm manual, there is a page that is a data snap shot of a healthy motor @ idle in closed loop. If I had a 94 FSM I'd give you the mv reading, but I have a 90 FSM. I looked up the L98 stats and the range for the MAP is 1.02 v thru 1.50 v.
If you have a FSM, in the Emissions and Driveability section, usually section 6E in the Helm manual, there is a page that is a data snap shot of a healthy motor @ idle in closed loop. If I had a 94 FSM I'd give you the mv reading, but I have a 90 FSM. I looked up the L98 stats and the range for the MAP is 1.02 v thru 1.50 v.
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