1. Welcome to 4Runners.com!

    You are currently viewing as a guest! To get full-access, you need to register for a FREE account.

    As a registered member, you’ll be able to:
    • Participate in all 4Runner discussion topics
    • Transfer over your build thread from a different forum to this one
    • Communicate privately with other 4Runner owners from around the world
    • Post your own photos in our Members Gallery
    • Access all special features of the site

1990 3.0 Running Very Rich

Discussion in '2nd Gen 4Runners (1990-1995)' started by CM49, Sep 24, 2018.

  1. Sep 24, 2018 at 8:07 PM

    CM49 [OP] New Member

    Sep 24, 2018
    Hey all! I just purchased a 1990 4runner 3.0 for a pretty good price. The body is in great condition but the engine seems to be running verrrry rich.
    Upon accelerating *unless i very slowly ease into the accelerator* the car will stall for a second, shoot a small ploom of black smoke, then continue on its way. You can also smell the unburned fuel just having the car idle
    This has caused the car to stall out completely when trying to accelerate from a stop, especially going uphill.

    I had just changed the spark plugs today to no prevail, and the old ones were wet upon removal.. I also checked compression on each cylinder and compression is just fine.

    Any ideas on why the car would be running so rich?
  2. Oct 10, 2018 at 9:15 PM

    Dink New Member

    Aug 18, 2018
    First Name:
    1993 4Runner SR5
    Stock with roof rack
    Vacuum leak? Fuel pressure regulator?
  3. Jan 20, 2019 at 6:52 AM

    atgparker New Member

    Jun 20, 2018
    First Name:
    Mission Viejo, CA
    1991 White 4Runner 3.0 L
    Rebuilt Engine MLS and ARP on the heads, DT Header, 2-1/2" CARB compliant Flow-Master CAT with 2.0" Bosal CAT back Dayco 1-1/4" Spacers, SkyJacker M-Series Monotube Shocks, Ball Joint Spacers Next.
    Both my 3VZE equipped 4Runners are of this age and many of the vacuum lines at this later great date are beyond their useful service life if they are original. The pvc line vac booster and usually the lines that go to the PS pump are often no longer flexible. There is a real spiders web of hoses and vacuum switches for all of the OBD1 smog stuff to operate properly. So, diagnosis can be tricky! Assuming the hoses are not cracked or broken off on the plenum, then there are several things that the OBD1 engine control microprocessor (MP) uses to adjust the ignition and fuel injector timing. For the ignition side the distributor handles the spark distribution via the cap and rotor but it is also a crankshaft position sensor and that signal is sent to the MP for base timing adjustments which is why you have to place the jumper on the diagnostic connector when you set the ignition timing to 10° or the MP will alter things while you're twisting the distributor. Three things are on the fuel side to meet the engines demanded power when you step on the accelerator. The first is the throttle position sensor (TPS) that rotates on the same shaft as the throttle plate. This rotation of the throttle plate is going to tell the microprocessor how your asking the engine to respond to throttle changes. So the TPS is key for acceleration signaling to the MP. The second is the air flow meter (AFM) that is going to follow the TPS and open up more as you open up the throttle plate with your right foot when you accelerate. So if one or both of these i.e. the TPS or the AFM are failing to report correct information the fueling is going to be wrong and especially under acceleration the engine speed is changing so the system has to respond accurately which seems it is not doing. The third component would be the oxygen sensor which will be engaged once the operating temperature has been reached and the MP will then be running in a closed loop where the O2 sensor will give the MP feedback on rich/lean conditions. Then the MP's algorithm can adjust the injector timing to get the ratio corrected. Certainly with off-idle-stumble and black smoke it would seem that perhaps the ability to change in the engine speed is the problem. Also the fuel rail is a regulated pressure fed affair and that fuel pressure regulator is quite loud when it is working properly and if it is not then your injectors might be getting too much fuel pressure and are having trouble stopping the fuel flow i.e. black smoke!...

Products Discussed in

To Top