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

William Jahn willjahn975 at gmail.com
Thu Mar 28 14:14:01 PDT 2019


 My fuel gauge works fine yet around 2012 when some red right runner caught my right front bumper guard which in turn through the bumper brackets moved the front over to the left about ½ “ . It was repaired . 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 isn’t it’s function to not allow fuel slosh to affect the float? I can’t imagine the float cover is off or I’d never have a steady reading since it only acts up when the tank is less than ½ full. 
   Before all of this the gauge would act up near the empty side , if I smacked the side of the dash near the gauge it would jump back up from being in the red then back to above the read . It’s always done this. Yet it used to read above the full mark when full now it reads a bit below it. 

 I was told to add a ground to the complete unit where the gauge is , on one of the two holding springs, yet on a 72 and 73 the black bakelite plug has it’s own ground which is an extra spade connector think it is 49A . Also last time I checked just from the sender lead unplugged to the unplugged backlite plug I read 44 ohms which might be one issue it always had. I do know the sender has a good ground to the tank and body. I had a spare black bakelite plug and used it because the rivet that secures the gauge brown wire ¼” male spade was loose , I thought for certain this was the issue I had since I got this car. Cleaning the sender connector and the one on the gauge did nothing and I doubt 44 ohms is normal for that brown wire , it’s not that long. When I got  this car I noticed the gauge acting odd and pulled the sender added a ground to it and with the cover off I moved the float slowly and the gauge responded well . 

 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. I’ve been told even a slight vacuum leak will alter the vacuum signature and in turn affect the MPS causing a lean condition and the unplugged temp sensor richens the baseline by 10% ..

 When I start the car it starts right up yet the idle is 950 then after a minute it’s 1300 ,put it in  drive it’s 1000 , drive a few blocks and see 850 then it seems to settle @ 950 . Today after a mile drive I got home and checked the electric AAR it was closed. I’m beginning to wonder if the AAR is stuck closed yet that does not explain the 1300 rpm unless it’s just part open then closes . Not long ago the idle was 1300 and held there for quite a while if I started the car and let it run while talking to someone then I’d hear it drop and I had the IAD sensor plugged in and I would hear the erratic miss. This is when I decided to see what might cause this and then found with no load I could not get a smooth transition between 1200 and 2100 RPM and found unplugging the IAD temp sensor fixed this. 

 I still have the oil soaked 4 runner boots and have not changed the vacuum line to the auto trans modulator or the two large hoses from the heads to the oil bath yet those two don’t seem to leak at least on the ends. The PCV seems to work . I’ve checked every single wire and terminal end and tightened all and repairs the grounds on the case center line . The head temp sensor and IAD sensor read what they say they should . I know the TPS is adjusted proper. 

 I know I’ve brought this up before and I do have the correct MPS and ECU . See if I ask on Samba I’ll get mainly no vacuum leaks allowed including crank case to pushrod tube seals . This is a 73 and having the PCV really only makes it a closed crankcase venting system before this there were no hoses to the valve covers and one breather cap , no PCV so 70-71? Which the crankcase in not closed doesn’t this sort of rule out running issues due to crankcase vacuum leaks or is it the difference in their ECU and MPS  and TPS that makes them act different? Plus even though there is a seal o the crank shaft it’s mainly there along with the oil slinger to keep oil from leaking out yet air still gets through , does that qualify as a vacuum leak?

 I don’t have anything other than a 72 and 73 system to compare with and the 72 was very much the same other than the EGR which I removed on mine ,it was just a pile of rust so I made a steel plate to block off the hole in the right heat exchanger where the EGR fitted and used the AID from the 72 so I did not have the extra pipe on top that was part of the EGR system other than that there is no difference between the two IAD’s both have the same boss the 72 had the extra vacuum port for the dual action vacuum can which I capped off. 

 I never kept notes so I don’t know how long this erratic /RPM unsteady crap began I just happened to notice it after 2009 when I changed fuel lines and plugs and checked for loose vacuum lines . I never felt it driving just in park no load idle when the engine was warm , even on longer drives when it’s hot it acts exactly the same way. I plug in that IAD sensor and the idle speed goes up and that issue arises , even if I back the idle down to 950 it still has the unsteady throttle response no load. It used to purr in park even on the original worn out engine. This  engine does not have more than 35k on it if that. 

Sent from Mail for Windows 10

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