Map Sensor or not? TIGHT budget

[pitterpat]

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.

 

[someotherguy]

I'm gonna go out on a limb here and say you either have an intake leak from improper gasket installation, or maybe one slipped a little while you were dropping on the lower manifold. You can check by removing the PCV, breather tube, and oil fill cap - plug those valve cover holes up tightly with something that won't get sucked in under vacuum, like rubber plugs, corks, whatever you can find. Start the engine and pull the dipstick, check the dipstick tube, there should be NO vacuum present. If there is any, intake gaskets still leaking.

MAP sensors don't often go bad.

Richard

 

[pitterpat]

I'm gonna go out on a limb here and say you either have an intake leak from improper gasket installation, or maybe one slipped a little while you were dropping on the lower manifold. You can check by removing the PCV, breather tube, and oil fill cap - plug those valve cover holes up tightly with something that won't get sucked in under vacuum, like rubber plugs, corks, whatever you can find. Start the engine and pull the dipstick, check the dipstick tube, there should be NO vacuum present. If there is any, intake gaskets still leaking.

MAP sensors don't often go bad.

Richard

Stupid question here but how can I tell if there is no vacuum present?

Not to question your knowledge, I have a couple of other questions:

1. Also, if this is the case wouldn't I still have antifreeze leaking?
2. This code only came up after I took the plenum off the 2nd time; I didn't take the lower off then.
3. After I finished the gasket install I took the truck to my regular shop and had them set the distributor. The mechanic (which I trust) ran the codes and MAF / MAP code was not one of them.

Can you shed some light?

 

[pitterpat]

I'm gonna go out on a limb here and say you either have an intake leak from improper gasket installation, or maybe one slipped a little while you were dropping on the lower manifold. You can check by removing the PCV, breather tube, and oil fill cap - plug those valve cover holes up tightly with something that won't get sucked in under vacuum, like rubber plugs, corks, whatever you can find. Start the engine and pull the dipstick, check the dipstick tube, there should be NO vacuum present. If there is any, intake gaskets still leaking.<br />
<br />
MAP sensors don't often go bad.<br />
<br />
Richard<br/>

Did that, NO vacuum. But seems to be running better. Funny thing, I noticed that my fuel gauge needle was really shakey/fluttering quite a bit. I have never seen it do that.
So MAP bad? Will take battery cable off to reset codes.

 

[pitterpat]

I think I have it figured out....it is not the intake gaskets, I think it is the gasket around the spider. I remember the 3rd time I took the plenum off it was really loose. Going to get a new gasket for it now.

 

[pitterpat]

This is what it looked like when I took the plenum off again. That regard gasket around the fuel body had broke and was letting in a lot of air. Replaced last night, drove today and it was fine.

You must be registered for see images

You must be registered for see images

You must be registered for see images