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Map Sensor

pitterpat

By pitterpat
in Ask A GM Technician

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pitterpat Enthusiast

pitterpat

Posted
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98 GMC Sierra, 2wd 5.7

 

Did intake manifold gasket replacement. Had multiple misfires 4 & 8cyl. Took plenum off removed spider, removed each injector individually cleaned & put back in same spot. Put spider /injectors back in. More problems, rough idle, acceleration hesitation at start up from light, had to throw into Park @ light to keep from dying; threw MAF sensor code from scan @ Advance Auto . Cleaned MAF with MAF cleaner, still threw code. Replaced MAF (NAPA) , took to Auto Zone for scan showed MAF or Map sensor.
Yesterday tested volts to Map sensor 4.72 volts, not 5 but close.
Now I need to decide if it is the MAP sensor or not. Could it be anything else. My budget is TIGHT I don't want to throw in another part and that be the problem.
Any help is appreciated.

Carder09 Senior Enthusiast

Carder09

Posted
Posted

Maybe you didn't correctly align the gasket up. Doesn't take much for it to NOT line up and cause a serious leak. I would take everything back off, make sure gasket is sitting properly then very carefully re-install the manifold and check to see if there is any small off-set gap anywhere before you start tightening things back down. Good luck!

pitterpat Enthusiast

pitterpat

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Maybe you didn't correctly align the gasket up. Doesn't take much for it to NOT line up and cause a serious leak. I would take everything back off, make sure gasket is sitting properly then very carefully re-install the manifold and check to see if there is any small off-set gap anywhere before you start tightening things back down. Good luck!

I didn't put this in the 1st post but I didn't get the MAF/MAP sensor code until after I took the plenum off the 2nd time. When I originally did the intake manifold gaskets (2 wks ago) I got the Multiple misfires on cyl 4 & 8. When I took the plenum off after this to check the spider I found out I had put the 4 injector in the #2 hole. That's why when I removed the injectors from the spider I did them one by one, I took each out one at a time and put it back in before the spider body before doing the next one. This was so that if I had an injector that wasn't working properly I could make sure it was the same one that misfired before cleaning them.

 

Also, it is pretty difficult to get the gasket shifted because of the nubs on the gasket that go on the engine block. I also took some other precautions when I installed

  1. Put a dab of RTV (black) on the four corners where the bottom tab of the gaskets sit before putting the gasket's on the engine block.
  2. I was sitting/kneeling in the engine compartment over the engine block when I put only the lower (not black plenum attached) on the engine block. I set it right down where it was supposed to go, no sliding the lower intake in.

I would have had the MAF / MAP sensor code originally if this had happened. Thanks.

pitterpat Enthusiast

pitterpat

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I think I have it figured out. I think it is the gasket that goes around the fuel injector body. The first one stretched out like crazy and when I took the plenum off the 2nd time I remember that gasket just being really limp and barely being on. Problem is I think I have to buy the entire plenum gasket set to get the one gasket.

pitterpat Enthusiast

pitterpat

Posted
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Here's what the fuel body gasket looked like when I raised up the plenum. 77cf210b67038e6322b9fc9b3f0144e0.jpg2f0c794707e18c605b65b2f16f529d8f.jpg

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