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Slow down cyl 7-12 light + air pump not disengaging

Discussion in 'Boxers/TR/M' started by Elberoth, Jun 18, 2024.

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  1. Elberoth

    Elberoth Karting

    Feb 12, 2022
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    Adam
    #1 Elberoth, Jun 18, 2024
    Last edited: Jun 18, 2024
    My 1991 TR US spec has developed two problems today:

    1. Some fan is constantly running on the left side of the engine and it is NOT the coolant fan (I can hear those kicking in). It does not switch off, not even after 20min drive. It only switches off after I switch the engine off (ignition can stay ON).

    Are there any other fans other than secondary air injection pump? I have never heard this sound before, but my car is stored in a garage at room temp, so maybe secondary air injection pump never had a reason to kick in on startup (not cold enough).

    2. Slow down cyl 7-12 light came on.

    I'm not sure if both problems are interconnected. They both have shown up today.

    I have restarted the engine after 3h, so it was still a bit warm but definately not hot and the Slow down cyl 7-12 light imediately came on and stayed on irrespective of RPM. My understanding is that It is not possible to overheat the sensor on a barely warm engine, from the get go, right? You would need 20-40s or even a few minutes.

    At one point I have accelerated heavily and it went off, but then came back 15s later or so. The Slow down cyl 7-12 light stays on even at idle.

    Is it possible that the Secondary Air injection is messing with o2 sensors readings?

    Is there a relay/fuse on the car to easily disconnect the air pump?
     
  2. lagunacc

    lagunacc F1 Rookie
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    #2 lagunacc, Jun 18, 2024
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  3. Elberoth

    Elberoth Karting

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    #3 Elberoth, Jun 18, 2024
    Thanks. I did wash the car today - which may explain the reason for o2 sensor going crazy (water in the connectors).
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Jun 18, 2024
    Last edited: Jun 18, 2024
    Yes, the thermal inertia of heating up the thermocouple would never allow the slow-down light to come "on" immediately after 3h. Seems more like the 7-12 warning light ECU is bad -- you can always just swap the two warning light ECUs and see if the fault moves to the 1-6 light or not.

    AFAIK (or maybe I need to start saying "As far as I remember" ;)), the air pump is the only other electrically-actuated rotary device on the front LH side of the TR engine. If something is (wrongly) causing the air pump clutch to stay "on" during warm running, the behavior you describe is normal as the +12V power to run the air pump system is only present when the engine is running or the starter motor is cranking (not when just the key is "on" and the engine is not running nor cranking).

    Probably not if something electrical is causing the air pump to wrongly run -- as the same signal that causes the air pump to run also "tells" the injection ECUs to ignore the O2 sensor outputs (and just run open-loop). If something more bizarre is causing the air pump to wrongly run (and the injection ECUs are trying to run closed-loop) = that would really mess things up, but it would affect both banks.

    There's no separate fuse for the air pump EM clutch, and the relay that controls it is in the black triangular box on top of the RR wheel well -- and I wouldn't call getting into that easy (but you may wind up needing to do that). You can unplug the air pump EM clutch, but that requires getting under the car -- so also not easy. My suggestion for a first diagnostic step would be to unplug one of the wires from the water thermoswitch on the LH side of the water Y-pipe during warm idle (simulating a properly open warm water thermoswitch) and see if that turns the air pump "off". If it does = strong sign that your water thermoswitch has failed in a closed cold state. As the picture below describes, the two terminals of the water thermoswtich should be closed (connected) together when cold, and open (not connected) when warm:

    Image Unavailable, Please Login

    If it doesn't (and your air pump is wrongly operating during what should be the warm running mode) = you probably will need to get to that relay (with a "K" printed on it) in the black triangular box and make some measurements there.
     
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  5. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #5 Rifledriver, Jun 20, 2024
    Steve, the airpump remaining on when not running isn't something to hear. Its not running, just an energized clutch. Could he be hearing a fuel pump.?
    I had one here recently with some creative wiring that had the fuel pumps running full time with the key in ign position.
     
  6. Elberoth

    Elberoth Karting

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    #6 Elberoth, Jun 20, 2024
    I just had both fuel pumps replaced (I got the car back from a major service - we have replaced fuel pumps, fuel filters, fuel acumulators, fuel pressure regulators and injectors; both K-Jet distributors also were fully rebuilt).

    However, what is interesting - I can hear more of that noise from inside the cabin, than staring at the engine with the hood open.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #7 Steve Magnusson, Jun 20, 2024
    The rotating vanes of the air pump (when the clutch is energized) make a sort of "whirring" motor sound (and the OP indicated that the noise only occurs when the engine is running), but...

    ...that seems very possible based on his latest post. And "new" doesn't necessarily mean "good" ;).

    I'd suggest that (with key "off") you remove each fuel pump relay and place a jumper wire from the female metal 30 terminal in the relay socket to the female metal 87 terminal in the relay socket like this:

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    The corresponding fuel pump should run (even with the key off) so you can see if one fuel pump is abnormally noisier than the other.
     
  8. Elberoth

    Elberoth Karting

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    #8 Elberoth, Jun 21, 2024
    Guys, you are the best!

    I have made a jumper @Steve Magnusson suggested and indeed - one of the fuel pumps is making funny noises!

    How it is possible a brand new Bosch fuel pump failed within 50km or so is beyound me, but fail it did.
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #9 Steve Magnusson, Jun 21, 2024
    One other possibility is that is isn't quite mounted correctly, and is touching something that it shouldn't be touching (like the cap nut on the check valve wrongly touching the fuel tank). The two pumps are mounted on a separate plate that is suspended on rubber vibration isolation mounts, but it is a very "tight" area:

    Image Unavailable, Please Login

    May still just be a defective pump, but you'll need to get into the area to replace it anyway so that will give you a chance to see if things are mounted correctly, or not, and to retest audibly with the jumper when you know that things are OK mounting-wise.
     
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  10. Elberoth

    Elberoth Karting

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    #10 Elberoth, Jun 21, 2024
    Thanks. I just bought a new pump anyway (it is like $80 from Bosch) and will pay a visit to my tech later this week. Worst case scenario, I will have a spare. But I have a feeling this is the pump.
     
  11. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #11 Rifledriver, Jun 21, 2024
    If as Steve suggests one is touching a hard part of the car it can make a lot of noise.
     
  12. Elberoth

    Elberoth Karting

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    #12 Elberoth, Jun 21, 2024
    I get this, but this is a very different kind of noise. It is more like grinding with some up/down modulation. I can see the lights dimming when it does this, indicating much greater current draw from the pump. Healthy fuel pump touching the car chassis would rather just pass the even (or constant if you will) resonace, only making it louder. Plus, the lights woudn't get dimmer in sync.
     
  13. Elberoth

    Elberoth Karting

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    #13 Elberoth, Jul 12, 2024
    Fuel pump replaced and everything is back to normal. Even the 7-12 cyl light is gone.

    Why two brand new Bosch fuel pumps have failed within 50km is a mistery.

    Thanks again for your invaluable feedback. The collective knowledge of FChat community is nothing short of incredible!
     
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  14. turbo-joe

    turbo-joe F1 Veteran

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    #14 turbo-joe, Jul 12, 2024
    too long stored in a wrong place
     
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