[T3] Bad day at the (FI) office

Daniel Nohejl d.nohejl at gmail.com
Sun Apr 10 17:58:33 PDT 2016


Well, we had a breakthrough or two this week. The first was in reference to the MPS. Early in the week, I thought I’d gather up all my spares and see how well they held vacuum using the unscientific suck test. It turned out that the ones with epoxy were much “tighter” than my spare without epoxy. However, the one without epoxy was comparable to the ones with epoxy as long as I held my finger over the adjusting screw end. I tested out the one in the car (also without epoxy) and it, too, was loose unless I held my finger over the screw. 

I thought this was interesting because when I was having trouble with the engine cutting out and stranding us on the highway last summer, I decided to do the suck test on the MPS on the side of the road. I recall reporting either on this forum or The Samba that I felt the adjusting screw move in and out. Really, I was just feeling suction while air was leaking around the adjusting screw. This is also noticeable in the car with the engine running. If I put my finger near the screw, I could feel suction. When I put my finger over the screw, the dreaded AFR gauge showed slightly leaner. I took all of this as proof that the screw end needs to be covered once the epoxy is gone because the MPS sucks air otherwise!

For the short term, I have a piece of high temp tape over the screw and readings held very steadily and rationally over a 200 mile trip of mostly highway driving at 70+ mph this weekend. We only got around 24 mpg, but I’m not complaining yet. Perhaps it’s that dreaded winter gas? I’m not sure when it gets replaced with summer gas.

I replaced the CHTS but it had no effect on drivability or AFR readings at all while driving. 

It turns out that we have a German muffler….Leistritz no less so can’t we trust the internals of it? I suspect yes.

Also, I re-caibrated the 02 sensor on the AFR gauge…..I realized that the last time I did so, the sensor was plugged into the tailpipe but it’s supposed to be calibrated in open air. Big goof there. After the re-calibration, the numbers were more or less fine. So In the end, after some good driving experience and AFR data, I decided to unplug the gauge which I’m so, so, so, so, so, so sick of looking at. I read around online about the sensor I’m using and no one really has any accuracy issues with it so I guess that my calibration error is/was to blame? People use this gauge with carbs, FI, catalytic converters, EGR’s, etc. and no one has really complained about inaccurate readings. 

Anyway, fingers are tightly crossed!!!



> On Apr 10, 2016, at 5:28 PM, Jim Adney <jadney at VWType3.org> wrote:
> 
> On 9 Apr 2016 at 19:31, Keith Park wrote:
> 
>> Having a fuel pump switch does add a way to deal with certain situations
>> like this.
> 
> Yes, adding the switch made it POSSIBLE to drive the car again. 
> Unfortunately that 3-position special function switch was expensive 
> and hard to find. The good news is that it's a nice heavy duty toggle 
> switch.  
> 
>> Jim, you left us in suspense,
>> what WAS causing your 2 cylinders to flood?
> 
> The short answer is, "I don't know."
> 
> The longer answer is that I suspected there was a problem with 1 or 2 
> injectors, which were sticking open at first and letting too much 
> fuel in. I also had a couple times when the engine was hydrolocked on 
> startup, making me think that a leaky injector had filled a cylinder 
> after shutdown. Now I'm beginning to wonder if my CHTS resistance has 
> gone to infinity when cold. That car sits most of the time in the 
> winter, so the gas mileage is always awful then, but I've had a few 
> medium sized trips with it this spring and the mileage was still down 
> to 15 mi/gal. That's what made me think this resembled Daniel and 
> Jessica's troubles.
> 
> We've had minimal good weather here so far, so I've been unable to do 
> any real troubleshooting, so far.
> 
> On a cheerier note, I just picked up a new (to me) Bosch D-jet 
> tester. This is the latest, GOOD Bosch tester, with the snap action 
> switches. I haven't had a chance to try it yet, but I think it'll be 
> in good shape once I get it cleaned up. This is one I used years ago 
> and it worked well then. If all goes well, this means that I should 
> be able to rent out my other one to anyone willing to put down a 
> significant security deposit.  
> 
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> 
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