Date:         Sun, 17 May 2020 11:12:39 -0700
Reply-To:     vw_van_fan_Mark <madvws@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         vw_van_fan_Mark <madvws@COX.NET>
Subject:      Re: Idle issues
In-Reply-To:  <F60CCB4D-F378-4831-BDF4-BDD07F79FA79@gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

The 88/89 Digifant injection harness uses the fuel pump relay to power
the ICU.
So the idle valve will only hum/buzz when the fuel pump is running.
This means it hums for just a second when the key is turned on, then not
unless the engine is turning.

In earlier AND later versions of the harness the ICU power comes from
the ECU relay so on those the idle valve hums whenever the key is on.

At this point any van could have had the injection harness replaced with
a different version and thus the expected behavior of the idle valve has
some uncertainty.

(note: the wiring diagrams have some errors in the fuel injection relay
wiring section for 88/89 and 90/91 diagrams, also the changes were not
at exact model year breaks)

Mark


Pat Spragge wrote:
> David,
>
> My understanding (while very basic) is that the ICU is powered through the relay that resides next to the fuel pump relay, but I am unsure what the sequence of events are that would trigger the relay to close and thus power the ICU. Does the initial, key on, pulse that triggers the fuel pump operation for a few seconds also closes the ICU relay which then operates the idle valve for a short burst and then once the engine starts and the fuel pump is operating continuously so does the ICU and idle valve? So if the ICU relay was not functioning, the idle valve could be good (confirmed via bench test) and the ICU could also be good, but the idle control “system” would not be working?
> I ask this because I seem to have an issue similar to Steven’s, difference being that I have no idling problems. I have an ‘89 Westy and haven’t been able to feel the idle valve vibrating. I put in a new ICU that Peter from VanCafe loaned me but that made no difference. I also had the valve “bench tested” and it functioned. I haven’t done a deep dive on this since my idle is rock solid, but suspect that everything is fine. I would, however, like to confirm that the idle system is working as intended.
> I get nervous about probing voltages around semiconductors (ICU) and the Bentley doesn’t seem to go into troubleshooting the ICU/RELAY/VALVE beyond the vibration test.
>
> Patrick
> 1989 Westfalia
>
>
>> On May 17, 2020, at 2:51 AM, David Beierl <dbeierl@gmail.com> wrote:
>>
>> On Sun, May 17, 2020 at 12:21 AM Steven Mills <lefthanddrive123@gmail.com>
>> wrote:
>>
>>> Idle control valve does not vibrate/hum but will open/close on bench test.
>>
>>
>> So -- valve is good but system is not operating.
>>
>>
>>> So, my question centers on whether or not the ECU can partially function
>>> but still be dysfunctional as to the idle. Any thoughts/ideas would be
>>> appreciated.
>>>
>>
>> The ECU does not control the operation of the ICU.  If the valve does not
>> hum at key-on (or when the fuel pump runs in late models) then either the
>> ICU or its wiring is bad (since the valve is known good).
>>
>> Yrs,
>> d
>>
>>>
>>> Sent from my iPad
>