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lb/min values from MAF?

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  • lb/min values from MAF?

    Didn't see anything in a search so I thought I'd ask here. My '97 zetec died leaving the driveway and threw a P1121. I have voltage 5V to TPS and scan gage says idle throttle percentage is about 18% which seems consistent with search results. I did clean the MAF with electronic cleaner a few months ago and again last night plus checked all wiring. Car wouldn't start or wouldn't idle for long when it does so I suspected IAC. Went ahead and banged a symphony out on the IAC and car started back up and idled smoothly. I cleared the CEL with scan gage and watched datalogger for a few minutes.

    Question is about MAP and MAF expected values - does anybody have rough numbers?
    MAP shows 30 to 40 g/s above 2000rpm
    MAF shows .22 lb/min at idle and jumps to 1.0 lb/min at 2000rpm and then tapers back to .7 or .8 lb/min. This looks suspect especially compared to all my other cars but this is my only 4 cylinder car and the only one not supercharged and tuned for 101. The other cars I have run 3 or 4 lb/min MAF values at idle and teens and twenties on throttle up but they're all FI'd.

    I'm thinking the MAF caused the P1121 and it's failing(?) MAF values should increase and hold fairly constant at throttle up and should be at least be somewhere close to 10lb/min or higher??

  • #2
    that's what my zetec shows from the MAF at idle and revved up. mine is a 98 with vct but i don't think that's gonna affect anything.
    98.5 t-red Zetec mtx
    207,000 and counting
    i love bring my car into class, it give a new "special circumstance" every day.


    • #3
      Went out after dinner thinking I was actually going to get to drive the car but it started stalling again .
      It's acting like bad gas because I can rev up to 3K and it stalls from that rpm intermittently too. We just put a full tank of gas the night before problem started. No way to know if it's fuel pressure return regulator or pump going out w/out schrader gage but I got good solid priming sound and flow out schrader valve. I can hear all injectors ticking away happily though.

      Back to the original thought - I did notice that my MAF was now reading 3.x to 5.x lb/mn at idle now before it stalled. I'll gut the top end tomorrow and actually pull the IAC for the hell of it. Fuel rail and EGR all need to be moved. May be ultimately heading to the shop though...


      • #4
        Recording this for future searchers - hope this helps.

        The suspicious values on the MAF was key. Coworker (ex Ford mechanic of 12yrs) told me to tap on the MAF or put strain on wires to MAF, if it was bad it will surge the engine. Sure enough, tapping on housing of MAF made car rev up and down. $89 later and car is as good as new. Shop wanted $90 just to diagnose and then $91/hr labor plus parts. Mama is taking me out for steak tonight with the $$$ I just saved.