[T3] On the subject of fuel senders and fuel gauge. Plus a fewother questions.

William Jahn willjahn975 at gmail.com
Sat Mar 30 18:13:01 PDT 2019


I tried plugging in the IAD sensor then unplugged the TPS . It’s difficult to describe the result. With the TPS unplugged it didn’t idle very well and I get the same miss with the IAD plugged in as before with the TPS connected or not, it’s just over all worse and more difficult to tell with the TPS unplugged. It just runs better with the IAD sensor unplugged . It just does run very good at all with the TPS unplugged / I just did this for idle . I think it needs the TPS park position to idle proper . If I tried to open the throttle TPS unplugged it just struggles then quits so I can’t tell if it has the unstable RPM as I do with the IAD sensor unplugged . The issue with mine happens when it’s warm to full temp , I can’t feel it driving under a load with the sensor plugged in yet with no  load the idle is not stable. Although with the IAD sensor plugged in and in drive the idle is not stable the engine RPM’s keep changing at every stop it’s different and I checked and the electric AAR is closed . It’s close to be called hunting just not as drastic. With everything plugged in the RPM drops 200 PRM  and if I raise it adjusting the IAD bypass then it becomes unstable and can idle @ 800 RPM to 1,200 RPM. It seems there is a vacuum leak somewhere like the extra % of fuel the unplugged IAD temp sensor compensates for. Even when it’s warmed up with that sensor plugged it I can feel and hear this miss at the tail pipe , it’s not a steady miss like one cylinder would be it’s random as in it will miss once then I hear 3 misses . Without  actually  hearing it it’s difficult to put in words. It does not seem to be lack of ignition spark and if it is it might be the pertronix  yet to me it is more like a lack of fuel . It’s a mystery why unplugging that sensor clears it all up in an instant. That sensors two wires do not have a short and the sensor reads what it should , it drops as it heats up and the readings are the same as they always were. Perhaps the sensor inside the IAD is covered in oil and is not getting the proper reading of the incoming air flow, all it needs is heat and it can get that just from the IAD’s temp , that’s just a guess. If I recall on older systems that sensor used oil temp , I thought I read that somewhere. 

William 

Sent from Mail for Windows 10

From: Jim Adney
Sent: Thursday, March 28, 2019 3:01 PM
To: type3 at vwtype3.org
Subject: Re: [T3] On the subject of fuel senders and fuel gauge. Plus a fewother questions.

On 28 Mar 2019 at 14:14, William Jahn wrote:

> Ever since then my gauge does not read consistent . If I make a turn it
> drops then comes back . I haven´t pulled the sender out yet since the
> sender has that cover isnTMt itTMs function to not allow fuel slosh to
> affect the float?

Yes, that's the function of the cover. Pull out your sender and check to make 
sure the cover is still attached.

>  I´m still trying to figure out why the engine when warm has that
> erratic miss and while giving it gas the RPM´s are not steady from
> 1,200 RPM to 2,100 RPM with the IAD temp sensor plugged in.

Please try the test of unplugging the TVS and see if that cures the 
staggering idle 

-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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