Date: Fri, 16 Oct 2015 17:04:18 -1000
Reply-To: "SDF ( aka ;jim lahey' - Scott )" <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "SDF ( aka ;jim lahey' - Scott )" <scottdaniel@TURBOVANS.COM>
Organization: Cosmic Reminders
Subject: Re: Hesitation while driving (manual)
In-Reply-To: <CAFdLW6kRVjqYGfG9wDL_gdQwky2RH+CZfKndeavVKix-BkvrcA@mail.gmail.com>
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the way Digifant EFI works ...
basicallly the ECU 'reads' the air the engine gulps..
measures 'how much' via the AFM.
Senses air intake temperature,
( and coolant temp )
there can't be ANY air leaks anywhere..downstream of the throttle and
between throttle plate and AFM.
it also reads the air situation via throttle switches that show idle and
WOT.
it also operates the Air Idle Valve , based on rpm.
The ecu also reads engine rpm via the ignition system ...
after it sees all that, AFM info, air and coolant temps, some throttle
position info, rpm ..
( plus NO air leaks anywhere important )
it holds the injectors ( as one big 4 part injector btw ) open so many
milliseconds.
there is some fine tuning of mixture via 02 sensor part of the time.
some quick tricks to try ....run it with 02 disconnected ..
and/or Air Idle Valve .
Re 'ignition' ..
mostly the plugs, wires, cap and rotor are long liffed and well made, if
you get good parts, like Bosch.
'usually' I don't see issues in those parts..
although ...'spark plug wires' ...can be nebulous....intermittantly not
doing a good job , etc.
Watch them with engine running in total darkness. Little sparks are leaks.
spray a fine mist of water on them, see if engine stumbles.
AFM ...can be a weak area for sure ..that sweeper track thing.
Virtually all EFI systems more evolved than Bosch Digifant use an Air
Mass Meter with no moving parts..
no physcial electrical contacts on anything that moves ...very nice,
and generally superior.
I have seen lots of AFM's get 'uneven' ....
I've seen 'em with a dead spot on the sweeper ..not uncommon actually.
it's nice to have another one to try.
also , grounds and connections ..
I find lots of those that are wonky or weak.
if you havn't done so already ..start inspecting 'everything' ..and
there are many tests to do in the Bently.
Fuel pressure should be considered ..
I just leave a fuel pressure gauge on the thing until I've sorted
whatever it is out.
Coil..
do the tests. I only rarely replace a coil. Nice to have another one
to try.
here is one of my Diagnostic Rules...
applies to many things ..
wherever electricity and somehing that moves interfact ...that's a weak
spot.
Examples are switches, ignition points, phongraph needles, and AFM wiper
tracks.
doubt your exhaust system could be a factor ..but consider that too.
In the old says people would say about hesitation ..
'feels like fuel ' ( did you check the fuel filter btw ..and fuel
pressure ..and the vac line to the FP regulator ? )
but you can't really say that in Electronic Fuel Injection .
you might check the spray pattern on your injectors.
oh ..I've seen this ...
I found 5 things that could cause it ...and each one needed to be
cleaned, fixed, replaced etc..
and each one was not 'it'.
It does sound like if opening the throttle does not produce more 'go' ...
I saw this on a waterboxer once..
open throttle and it tried to rev out ...could hear it sucking air in ,
like a moan, but obviously fuell wasn't being added to go with that air.
On that one I found about 8 tiny air intake leaks on the plenun and runners.
A listening tube works great for that.
let us know what you find !
scott
On 10/16/2015 4:29 PM, Dan N wrote:
> spark, fuel and air
>
> when the engine is idling, you already have spark
>
> when you press on the accelerator, fuel and air will going in, the amount
> of each was regulated to make your engine runs good...
>
> so.... what should you look at? fuel delivery and/or air intake?
>
> :-)
>
