Edmunds Answers



  • tony78 12/02/08 6:05 pm PST

    Dear charlie, i am not an expert on your vehicles fuel system, but in reading directly out of the book and already knowing how the cmfi unit is constructed and with an understanding of how all the components operate, this is what it says in the chilton book # 8141 for chevy S-10 and blazers.

    The same basic engine is used in your astro.

    As verbatim " The non-repairable CMFI assembly or injection unit consists of a fuel meter body, gasket seal,fuel pressure regulator, fuel injector and six poppet nozzels with fuel tubes. Should a failure occur in the CMFI assembly the entire component must be replaced as an assembly.

    Apparently what is happening is that one of these non replaceable parts contained in the lower part of the CMFI assembly is leaking fuel.

    The upper part of the CMFI is called the plenum assembly.

    That fuel in turn is being drawn into the the intake manifold by vacuum during engine operation and is thus creating the overly rich exhaust mixture,

    Then when the engine is shut off,,the now pressurized fuel system is relievng itself and liquid fuel is bypassing gaskets and is draining down into the galley between the cylinder banks and into the oil pan via the oil drain ports adjacent to the hydraulic lifters

  • macinlover 02/10/09 1:45 am PST

    You probably have a leaking fuel pressure regulator (FPR), which is part of the CMFI assembly.  You can buy just the pressure regulator on eBay for on the order of $30.  To test to see if you have a leaking CMFI assembly, attach your fuel pressure gage, then turn on the key to energize the fuel pump, which will run for about two seconds, if the van is not started.  Now turn off the key, and see if the pressure holds for a minute.  After one minute the pressure should be at least 45 PSI, if not, you have a leak.

    The fuel pressure regulator is located on the passenger side of the CMFI assembly.  You can remove the idle air control valve located on the top of the manifold to have a way of peeking inside the manifold, with the aid of a small mirror and light, without having to first remove the upper manifold.

    I had a similar problem to the one you described, except in my case the leak was so bad that the three cylinders on the passenger side of the vehicle were not firing, because the mixture was so rich.  And because the leak was so large, gasoline was being forced around the rings into the oil, which resulted in the low oil pressure reading that you mentioned.

    There much more info at the web site I've included at link to, and also picture of my leaking FPR there.

    Source: http://www.BlazerForum.com/m_96735/tm.h

  • mrcbrwn 05/03/09 7:51 am PST

    The answer to this particular vehicle would be failed fuel injector system. Located inside the plenum, or upper intake manifold. The fuel pressure regulator may fail causing raw fuel to run down into the valley and eventually into the crankcase. The fix is usually to replace the entire injector system.

  • stoner4204ever 11/05/11 4:56 pm PST

    CMFI is one injector that has 6 poppet lines coming off of it and has regulator built in. you cannot replace just the regulator on cmfi. CSFI is a spider assembly with 6 individual injectors. and a replacable regulator.


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