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K-Jet diagnosis question - long post 200 1980

posted by  zrubin on  Sat Oct 16 11:13 CST 2004
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last visit: Thu Sep 20 15:45 CST 2012
[RELATED]

Car is a 1980 245DL B21F with 274k. Runs great when cold, runs well when warm but idle is inconsistent (sometimes smooth at 1100 RPM, somtimes lumpy at 950 RPM). Bad gas mileage (18 MPG, used to get 21 MPG for the same driving cycle). New O2 sensor, cap, rotor, plug wires. Checked and found the following:

O2 sensor reads 0.55 V when cold, 0.0 V when in closed loop (running lean).

Dwell is steady at 49 (a bit on the high side, checked with O2 sensor disconnected)

Frequency valve doesn't seem to be getting proper voltage (0.36 V) with the engine off/ignition on. Lambda relay is getting ~11 V but when I tried jumping the connector terminals with the relay out (engine off, ignition on per Haynes) the valve doesn't buzz. I'm pretty sure I heard the frequency valve buzzing when the engine was on.

I would've concluded it was a bad relay had the valve buzzed when I jumped the connector. I was told the "computer" "never" goes bad in K-Jet systems. I'm hoping it's not a wiring problem to the frequency valve (grounds seem tight/clean).

Any suggestions for what to check next or pointing out the obvious problem I'm missing? Thanks!

Zack
1980 245DL M46 274k
1988 745T+ M46 197k








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    K-Jet diagnosis question - long post 200 1980

    uid 18083's pic
    posted by  lucid on  Sun Oct 17 11:12 CST 2004
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    last visit: Fri Oct 24 12:31 CST 2014
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    IMO, it would be a mistake and mess with any fuel adjustments (O2 unplugged or otherwise) until you know the Control and System fuel pressures are correct.

    Unfortunately, the special pressure gauge set up costs somewhere between $75 and $100, unless you find a used one (maybe eBay?). It's essential if you expect to do much K-jet diagnosis (again, IMO).
    --
    Bruce Young
    '93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.








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    K-Jet diagnosis question - long post 200 1980

    posted by  81242DLB21FCA on  Sun Oct 17 00:47 CST 2004
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    last visit: Thu Oct 23 22:26 CST 2014
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    I would recommend disabling the Lambda and CIS systems. Then trouble shoot any idle speed or mixture/misfire problems. The Lambda should be disabled by disconnecting the O2 sensor. The CIS should be disabled by removing pin 12 at the control box, white/red wire in blue connector. I would recommend cutting and installing a fully insulated male and female spade connector in this wire for any future trouble shooting. The Lambda system should operate if 12 Volts is applied to pin 86 of the system relay (relay connected) or jumpering pin 30 to pins 87 and 87b in the socket (relay out). This info is from the 1981 Wiring and CIS green books.








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      K-Jet diagnosis question - long post 200 1980

      posted by  zrubin on  Sun Oct 17 05:14 CST 2004
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      last visit: Thu Sep 20 15:45 CST 2012
      [RELATED]

      Sounds like the "CIS" you're referring to is the Constant Idle Speed system, which my car does not have since it's a 1980.








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        K-Jet diagnosis question - long post 200 1980

        posted by  81242DLB21FCA on  Mon Oct 18 00:57 CST 2004
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        last visit: Thu Oct 23 22:26 CST 2014
        [RELATED]

        If your car has an auxiliary air valve, you could block the hose to prevent any chance of it not closing completely when the engine is warm. My suggestion is to disable as many variables as possible. Another thought is to check for vacuum leaks that may be masked by the fuel enrichment during warm up.








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    K-Jet diagnosis question - long post 200 1980

    posted by  someone claiming to be Ted on  Sat Oct 16 15:27 CST 2004 [RELATED]

    Test your Control pressure regulator. That what it sounds like to me.
    -Ted
    '74 144GL (K-Jet)
    '59 PV 445 (twin SUs)







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