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Engine revs holding

Discussion in '308/328' started by Tonksy1, Dec 20, 2020.

  1. mike32

    mike32 F1 Rookie

    May 13, 2016
    3,200
    Uk
    A lot cleaner than my old mondial was, never had the engine out of mine in 20 years ownership
     
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  3. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Thanks for that.
    I'm not sure if the 308qv has a throttle position switch.
     
  4. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Hi Gordon, this engine hasn't been removed.
    I always wondered if all those washers was normal though.
    Cheers.
     
  5. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Hi Mike, yes it's now a very clean engine, I may have gotten a bit too excited tidying things up and now its hard to diagnose my problem as I've serviced/cleaned so many parts on it. Lesson learned...
     
  6. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Thanks Steve, I'll start up the car in the morning and I'll be able to answer your questions. Where do I find the O2 sensor?
    If its the exhaust, the car has an aftermarket exhaust with no O2 senser that I can tell. Im pretty sure all the US add ons have been disconnected, so I'm expecting the frequency valve will not be buzzing. I'll test the cold start injector is not squirting during warm idling.
    Can I test the injector by removing it from the plenum when warm with fuel line attached, and placing it in a clear container. Start engine and watch?
    Or does the electrical plug on the injector simply need to be disconnected..
    Thanks in advance.
    Dean
     
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  8. Imatk

    Imatk Karting

    May 6, 2007
    130
  9. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,942
    Texas
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    Not great, but:

    If the O2 sensor is unplugged/missing, the frequency valve would still be buzzing if the added injection ECU is still powered up, wired, and working. If the system is tweaked-up warm in this condition, it would still work OKish as a K-Jet without Lambda during both warm-running and cold-running (but should really have the VLV reinstated).

    If the O2 sensor is unplugged/missing and the injection ECU is disconnected, the frequency valve will not buzz (and just remain always closed). If the system is tweaked-up warm in this condition, it should run reasonably well when warm as a K-Jet without Lambda, but cold-running will be lean (and it should really have the VLV reinstated). For cold-running to work well, it would have to be tweaked-up "rich" -- might have been done intentionally for this reason (but, being K-Jet without Lambda, the WUR control pressure being wacko can also cause this).

    Physically removing the cold start injector (blocking the air hole in the plenum) and seeing what comes out the end (into a container) is best as this detects both mechanical and electrical problems with the cold start injector; whereas, unplugging the cold start injector only prevents electrical problems from wrongly causing it to squirt. It may still squirt a little at warm restart cranking, but should definitely be fully closed during warm idle.
     
  10. Brian Harper

    Brian Harper F1 Rookie
    Owner

    Feb 17, 2006
    3,827
    San Jose area
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    Brian Harper
    Could be. There's quite a bit of wiggle room in the motor mount holes. I think it's would be pretty easy to have the engine land 1/4" different when installed but that dog bone is a fixed length. And moving it wouldn't affect the throttle cable operation or position. Heck, it moves more than that under acceleration.
     
  11. Brian Harper

    Brian Harper F1 Rookie
    Owner

    Feb 17, 2006
    3,827
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    Brian Harper
    In the USA '83 QVs don't, '85s do, and I think '84s do. I think the switch shows up with lambda control.

    The car in question doesn't. If it should or not, I don't know. It's got a gray market mish-mash going on.
     
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  13. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Found some time to spend on the 308 today. I can confirm the cold start injector is not squirting when engine is warm.
    I couldn't hear the frequency valve buzzing, but to be honest, when the car is running, i couldn't hear anything...
    Can the frequency valve be tested without engine running?
    A couple things I noticed, cold start seems to be good and idols at 1200rpm which is the same as in the past, but once warmed up, idol gets up to 1500rpm.
    I will attach a link to the video of the car holding revs.



    Also what is the large bolt with Allen key head that is directly under the throttle body, pic attached. What does it adjust?
    I had it out for re zinc plating. Thought it went back in the same position, but maybe not.....



    Image Unavailable, Please Login
     
  14. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
    1,164
    California SF area
    Full Name:
    Paul
    It's the throttle bypass, it adjusts your idle speed. Wouldn't cause the issue you are having.
     
  15. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    10,530
    San Carlos, CA
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    Mitchell Le
    Earlier in the year I worked on a EU 308QV converted to US with this exact problem. Many things were inspected and tried, in the end adjusting the idle speed and mixture at the fuel distributor solved the problem.
     
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  16. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
    19,942
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    Just touch it while the engine is running -- you should feel it vibrating if it is working.

    To back up some -- was the engine running well before all this? Is the air bypass screw the only thing (affecting the airflow and mixture) that was messed with?
     
  17. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    10,530
    San Carlos, CA
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    The engine was running well before he decided to clean and rebuild every CIS components he could see.
     
  18. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Hi Steve, thanks for that, I'll check again today but I don't think I was feeling much vibration yesterday other than engine vibration.
    Yes the car has been running fine for years, so best I go back over what has been touched.
    Full set of cam gears and belts. (Still had original plastic cam gears on) and was due for cam belt change)
    Valve covers (to confirm all timing)
    New injectors and seals (Still had originals)
    New plastic fuel injection lines (verrel kit) and metal lines zinc plated when apart.
    Plenum came off to re paint.
    New gaskets under it.#oh just a thought, I remember discovering only 4 nuts were holding the plenum down much to my surprise, it now has all 8 nuts, (possibly air was getting in to the plenum before and not now?)
    Re plated the throttle linkage attached to the throttle body but didn't remove the gate inside it. (I can hear it snapping shut)
    Air bypass screw removed and re plated.
    Removed Air hoses going to plenum.
    Cold start injector was removed and pressure tested in shop.(worked fine)
    I did unplug the connection to the warm up regulator.(can I test the connection still has power to it?)
    2 x new distributor rotors.
    1 x new distributor carbon centre button. (End was chipped and jagged leaving a bad contacting mark on rotor)
    Other than that, everything else was cleaned in place.
    Really appreciate the feed back Steve.

    Dean NZ
     
  19. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Sure, the voltage between the two pins of the connector for the WUR should be +12V whenever the engine is running.
     
  20. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Thanks yelcab. Yes I'm hoping if it's not a simple mistake I've done, then let's hope adjusting will solve it.
    I'm just a little concerned that if there is a problem, I'll be adjusting things to compensate over it, (if that makes sense).
    Is it easy enough to try adjusting the mixing and if no luck just return it to it's original settings?
    Very interesting you have dealt with the same problem before.
    Had their been any similar work to what I've done to the engine before hand?
    Thanks.
    Dean
     
  21. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
    10,530
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    Before you cleaned everything including the injectors, your car was adjusted to deal with all the imperfection of the CIS system components. Now that you have cleaned everything, the combination of the setting is off and you have to re-adjust the idle speed, and the mixture to bring it back to optimal. On a US car with an O2 sensor, you can hook up a scope to the O2 sensor signal and adjust the mixture for 50% duty cycle. On a Euro car with no O2 sensor, you will have to wing it.

    On the car I worked on, some imperfect idle condition existed before I did a major service with all the timing belts, plugs, etc, and then I cleaned the throttle housing and a few other things. Since there was so much work done, I needed to reset the CIS pressure settings, the idle speed, and the mixture. The Euro car was more involved because there was no idle switch to tell the CPU ... "i'm at idle, or not"
     
  22. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,942
    Texas
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    Steve Magnusson
    This is why checking/verifying the cold and warm control pressures of the WUR is a must before tweaking the mixture screw (and airflow screws).
     
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  23. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Thanks for that yelcab, makes total sense.
     
  24. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    88
    New Zealand
    Thanks Steve, yes I will do this before any adjusting. This also gives me an excuse to buy a new tool and learn more about how things work. Summer holidays for me now so I'm off camping. Will update as soon as im back and do some testing.
    Cheers.
     
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  25. Jeka

    Jeka Formula 3
    Silver Subscribed

    Nov 20, 2010
    1,110
    Rotterdam
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    Johan
    One part worth checking is the bypass valve (81). If it leaks internally, it gives exactly the same symptoms. It is easy to check by clamping the hose(s) and see if the idle returns to normal. Image Unavailable, Please Login
     
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  26. Brian Harper

    Brian Harper F1 Rookie
    Owner

    Feb 17, 2006
    3,827
    San Jose area
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    I agree the vacuum limiting valve (VLV) would be a suspect for this symptom, I don't see that he has one. I certainly don't see one where it is on my USA '83 QV. I don't see any intake hoses that indicate it would be hidden away. But it could be somewhere not obvious in the engine photo.
     
  27. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    10,530
    San Carlos, CA
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    He does not have one. It would be to the right of the throttle housing but they removed it for the last years of the 308QV EU.
     
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  28. mexicruiser

    mexicruiser Karting
    Silver Subscribed

    Aug 28, 2012
    172
    Mexico
    Full Name:
    Jon Brinckmann
    Did the car ever have any backfires at some point? If so check the fuel dist sensor plate for flatness, mi 308 only idled at high rpm when warm and this was part of the problem.
     

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