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  1. #1
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    Hesitation again...

    Any thoughts on the following would be appreciated:

    M5 sometimes runs great and at other times hesitates around 3500 rpm. Replaced: in tank pump, fuel/air filter, wires, plugs, adjusted valves, 02, and fiddled with the AFM by moving the pointer "down" the shaft slightly.

    Symptoms occur when at speed (60+) when near full throttle is applied. It will either accelerate great and through the range, or hesitate and throw a puff of unburned gas out the tail pipe (I can see this in the rear view mirror under the right light conditions).
    It might be pinging, but I am not 100% sure.

    Without any research, I am thinking that perhaps the AFM is still not sending a clear signal and drops out causing the computer to cycle? Any thoughts... This is my daily driver and it is painful to baby it...
    thanks again,
    Dean M5 '88 ///M5
    '95 RRC
    '60 Healey BN7
    '72 Kabota :)

  2. #2
    Dean M5
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    Re: Hesitation again... Could it be fixed?

    Well... I guess you can say I am slow to catch on and fix a problem. The slight hesitation that I had would come and go and at times was so slight I would forget about it.

    It happened more on hot days and less on cold. It wouldn't happen when the car was warming up, but only at full temperature. It seemed worse is I left the car outside on warm days and not as bad if the car was inside. Over the past two years I replaced everything that could possibly contribute - sometimes twice. AFM, wires, in tank pumps, O2s sensors you name it.

    I hate to post this, but I think I found the problem. It is the purge valve. For the past two weeks I have been driving with the vac line disconnected and plugged. It runs great. I guess I am no longer getting that slight vac leak that I felt. It makes some sense if you look objectively at the symptoms. Warmer temps the gas would expand and need to be expelled. I am guessing the purge valve operates based on DME values from a table that uses temperature and RPM to determine how long the valve stay open.

    I have no intention of reconnecting the line. I suspect that it is operating at intended by the factory. So, should I vent the canister to the ground after the purge valve, and let the valve continue to open and close without the vac assist or is there another work around.

    Dean

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    Member No: 35097 bbojangles is an unknown quantity at this point bbojangles's Avatar
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    my car has everything hooked up and there is no

    hesitation. I dont think that this is the root cause..

  4. #4
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    You are probably right... and now

    I have something to trace to find the true root cause.

    On the top of the purge valve the flared metal tube (where the intake hose is attached) is loose. It swivels around in the housing. I wonder if I was getting unmetered air in addition to purge gases?

    I would think if the charcoal canister is plugged there would be little or no venting.

    Any thoughts?

    Dean '88 ///M5
    '95 RRC
    '60 Healey BN7
    '71 Lotus S2
    '72 Kabota :)

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    Re: You are probably right... and now

    My car is away for the winter. in a barn 45 mins away from here. I cant look and see.

    I dont think that a cannister can get plugged, there is really no source of dirt to get inside and it would take a whole lot of dirt to plug it.

    I think you could simply try blowing into the hose and you would see if there are leaks or restrictions in the system. maybe you can find the other end of the hose in the trunk and pinch it with visegrips and then blow from under the hood. the system should be airtight.

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