Engine revs holding | FerrariChat

Engine revs holding

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

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  1. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Hello ferrari chatters.
    I have just finnished a job on my 308 qv.
    Problem I have is that when I rev the engine, it holds its revs for a moment before slowly dropping.
    Car ran fine before I did work on it.
    I've done a cam belt change and also re done my fuel injection lines, new set of injectors and had the plenum off.
    Accelerator cable is fine, and I can't find any obvious air leak.
    Am I missing something?
    Any tips would be much appreciated.
    Thanks
    Dean
     
  2. theunissenguido

    theunissenguido Formula 3
    Owner Silver Subscribed

    Jan 21, 2004
    2,371
    Argent/Brasil
    Full Name:
    Guido
    Check fuel pressure. Check operation electrical fuel pump, cold controle pressure, warm control pressure...
     
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  3. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,829
    Isle of man- uk
    The cable under the carpet is one and the quadrant where the cable connects at the engine might need a bit wd40, thats on the mondial so assume it similar. Enough slack in cable ?
     
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  4. Iain

    Iain F1 Rookie

    Jan 21, 2005
    3,257
    UK
    Check the mechanism at the side of the throttle body. There is a sort of roller bearing there & they get stuck. I had one that wore a flat on one side. Doesn't help when that happens.

    General advice to all: the part is very hard to come by, keep them well greased!

    Also, check the inside of the TB where the butterfly seats to make sure there is no build up of crap there that is stopping it from closing properly.
     
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  5. pshoejberg

    pshoejberg Formula 3
    Silver Subscribed

    Dec 22, 2007
    1,694
    Denmark
    Full Name:
    Peter H
    Re-done fuel injection lines? Does that include plating work on the steel lines? If, then check if they are partly blocked. I would also check again for vacuum line leaks or misplacing.

    Best, Peter
     
  6. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Thanks Peter.
    Yes I checked them before installing.
    I'll re check my vacume lines again tonight.
     
  7. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Thanks for that.
    What kind of test would I be doing to check correct pressure?
    If the engine is running lean, could I simply check the colour of the spark plug tips? White tips = not enough fuel?
    Cheers.
     
  8. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Thanks lain.
    I've checked them and all is good.
     
  9. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,829
    Isle of man- uk
    Running lean is not going to make it keep a higher idle, then drop. Wondering if you have got dirt in an injector when fitting the pipes, doesn't take much. After that might be worth fitting repair kit to fuel distributor if it has no history of being done. About £50 on e bay- id tag on side of distributor head to ensure right kit.
    i think best to be sure it is returning to the stop when no accelerator, turn it against the spring and let it go, you should hear it snap shut.
     
  10. 4right

    4right F1 Rookie
    Rossa Subscribed

    Sounds like a distributor advance curve issue potentially. I had a similar issue where the rpms would hold between shifts.

    Has the distributor ever been rebuilt?
     
    waymar likes this.
  11. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,685
    Full Name:
    Mike 996
    Some years ago I spent 4 hours troubleshooting a Turbo Porsche 911 with similar symptoms to discover it was the floor mat causing the problem... ;)
     
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  12. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Thanks mike.
    Yes spring is definitely snapping it shut.
    Could possibly be a dirty "new" injector.
    Cheers
     
  13. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Ok
    So I got home tonight and had a look at the 308 I can confirm that the throttle body is closing and the carpet is not interfering with the accelerator I still find no obvious vacuum leak.is there a test I can do for a leak?
    Can someone please educate me on how dirty/blocked injectors or distributor can possibly give the result of holding revs and slowly returning to idle. I would like to get my line of thinking right. The engine is running fine when idling and revving.
    It does however have a slightly faster idol than previously.

    Thanks in advance.
    Dean NZ
     
  14. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,829
    Isle of man- uk
    Only reason i mention the fuel distributor is that a lot of them have the original internals , diaphagm etc. this controls the balanced volume of fuel to each injector. A friend of mine had severe problems with backfiring/ missing and fuel passing the pistons into the sump- diluted the oil and sump rising- thats the extreme end. The internals of the distributor were shot. For £50 it is worth doing sometime.. if one or more cylinders are getting more fuel and you let off the gas, it might just be burning off the excess in some cylinders.
    The accelerator cables have been known to stick .
     
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  15. waymar

    waymar Formula 3

    Sep 2, 2008
    1,321
    Northeast, PA - USA
    Full Name:
    Wayne Martin
    Is it possible to take a short video clip showing 2 or 3 times ? Might help in diagnosing......
     
  16. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #16 Steve Magnusson, Dec 21, 2020
    Last edited: Dec 21, 2020
    No ;)

    Can you post a picture of the engine bay, or give the engine family number shown on top of cylinder #1 of the engine block (F...something)? I'd be more suspicious of devices that can allow extra air into the engine (and I would rule those in, or out, initially, by just manually "pinching" or blocking those air hoses), or maybe one of the Digiplex ignition ECU getting stuck at large advance. Not a good sign that you report that the idle speed changed unexpectedly...
     
  17. Brian Harper

    Brian Harper F1 Rookie
    Owner Silver Subscribed

    Feb 17, 2006
    4,078
    San Jose area
    Full Name:
    Brian Harper
    On the QV the advance isn't controlled by the distributor, it's done by the electronics. No spinning weights and springs on the QV.
     
  18. theunissenguido

    theunissenguido Formula 3
    Owner Silver Subscribed

    Jan 21, 2004
    2,371
    Argent/Brasil
    Full Name:
    Guido
    Can you remove the air intake duct and push air flow sensor plate completely down when engine is running.Do this several times and see if plate is returning to initial position without hasitation. Its posible your idle is to high and it gets normal with hasitation. So fuel plunger can be stuck at some point.
     
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  19. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Will see what I can do waymar, I have a good video of it.
     
  20. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
    1,109
    Mansfield, TX
    Full Name:
    Ron
    Check the brake booster check valve as see if its stuck open. It is connected directly to the plenum.
     
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  21. Tonksy1

    Tonksy1 Karting

    Jun 21, 2016
    91
    New Zealand
    Hi Steve, my engine is F105A
    It was a grey market car in the USA.
    I just looked at a spark plug and it's very black at the tip.
    One thing I noticed when starting it this morning, was that it started and reved fine when cold. I turned it off and started it 10mins later,engine was warm and it was holding revs again. Cold start was idling at 1200rpm and when I did a warm start it was idling around 1500rpm.
    Could this be a cold start injector issue? Not shutting off? Just a thought. I did get the injector cleaned and tested during the project.
    Here are a couple of pics.
    Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
     
  22. Imatk

    Imatk Formula Junior

    May 6, 2007
    290
    Sounds like a similar problem I just had but not with my Ferrari. Check the throttle position switch. Might have gone bad. I had the same thing hanging between shifts, and then high idle.
     
  23. EP328

    EP328 Formula Junior
    Silver Subscribed

    Sep 3, 2008
    616
    Northern California
    Full Name:
    Ed
    I was chasing an intermittent high idle. Turned out to be crack in one of the cloth covered air lines under the auxiliary air valve. Really tough to see because of the cloth covered lines. As engine moved, the vac leak would get larger or go away.
     
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  24. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Not any more ;) (excellent photo BTW). Being imported to the US, it's had quite a few modifications -- VLV removed, frequency valve added, injection ECU added, and I'm guessing the added clump by the coolant expansion tank might be some sort of coolant temperature thermoswitch. That spark plug shows a definite over-richness problem (but that still wouldn't explain the RPM holding high IMO) -- so you probably are faced with confirming the cold and warm control pressures are reasonable and then tweaking the A/F mixture (assuming you've confirmed the cold start injector is not leaking/squirting when warm). Couple basic questions:

    1. Is your added frequency valve (the thing with the yellow plastic near the oil filler cap) "buzzing"/vibrating during warm idle? (it should)

    2. If you unplug the added O2 sensor during warm idle, does the idle RPM/behavior change significantly? (it shouldn't)
     
  25. GordonC

    GordonC F1 Rookie
    Owner Rossa Subscribed

    Aug 28, 2005
    4,119
    Calgary, AB, Canada
    Full Name:
    Gordon
    Did you remove the engine for the work that was done? The reason I ask is...

    :eek: That's a LOT of washers spacing forward the rear bulkhead mount on the engine stabilizer bar from the rear cam cover. (5 washers on each side?) My 84 Euro QV (un-modified for grey market compliance) has one washer on each side, that's more than 1/4" difference in the cam cover position between our cars (relative to the rear bulkhead).

    If you had the engine out, were there 5 washers per side on that engine stabilizer mount? If not, it might be that there's a spacer or two on the engine mounts that weren't re-installed the same way they were when the engine came out? What I'm wondering is if the engine isn't in exactly the same position it was in before the work, then perhaps the throttle cable length needs adjustment to compensate for the shifted position.

    If you didn't have the engine out, and the stabilizer bar mount always had 5 spacers per side - then never mind! ;)

    Cheers,
    Gordon
     

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