[T3] gas mileage, voltage, etc.

[Daniel Nohejl]

Okay, so I went back out to the car and gave another look and would you believe that the MPS hose WAS actually disconnected from the plenum? When I looked at it yesterday, it was after the first really loud pop out the exhaust and I’d only driven a few hundred yards. I guess by the time I got back to my house it had vibrated further away b/c it’s pretty obvious in this pic:

https://www.thesamba.com/vw/forum/album_page.php?pic_id=1659004

Oops. 

Well, I also checked the #3 spark plug and while it was pretty black, there was a fair amount of almost chocolate brown on the electrode area too. I wasn’t too worried so I put it back and didn’t check the others b/c after realizing the MPS hose had come off I figured I’d found the answer to all my problems. 

The car started up right away and it idled normally: the exhaust note was right and it was appropriately lumpy for a cold start. Then, instead of the idle climbing, it got lumpier and lumpier and slower and slower until it just stalled. Then it’d start but stall right away. Then it wouldn’t start. Now, it’s at a point where it’ll only stay idling if I keep my foot on the pedal. I didn’t have time to take it on a test drive to see if it’d idle better when warmer. This one of the things that was wrong with the car when we first got it in June of 2012 so maybe it’s just throwing a 5 year anniversary present at us. But still…..I have to rethink what we looked at back then in diagnosing the issue. 

It could be that when I drove with the MPS hose off, the other plugs got carboned up from running so rich. Wouldn’t it run rich with the hose off? Maybe the #3 one looks best b/c I unplugged the injector. Should I look at the others? I adjusted the idle speed a bit last weekend. Perhaps the MPS hose was loose and leaky and I adjusted the idle based on wrong MPS conditions and now it’s set too low? I’ll think through what the next best move is, but if anyone has an idea of where to start, I’m all ears. 

I’m guessing that I didn’t damage the MPS or put any undue strain on another part in my 5 minute 3/4 mile drive at under 30mph from where I did my work back to my house yesterday. 


> On Jun 23, 2017, at 2:06 PM, Jim Adney <jadney at vwtype3.org> wrote:
> 
> On 23 Jun 2017 at 13:41, Daniel Nohejl wrote:
> 
>>> Okay, that's a good thing to find. Do you need another SP connector?
>> 
>> No, I replaced the whole wire. A wire with as much resistance as mine
>> wouldn´t fire the plug all that well at all, would it? In other words,
>> was the likely cause of my miss or not? 
> 
> All the resistance is in the connector at the SP end. Our wires should be 
> metal core and only need to be replaced if they get hard and the insulation 
> cracks.
> 
> There's a wire-wound resistor molded into the brown SP connectors. These 
> tend to fail at some point, leaving a gap that the spark must jump across. 
> The gap in tiny at first, so the spark jumps that gap easily, but the gap grows 
> as the spark erodes it away. Eventually it gets so large that the spark can't 
> always jump across. The time between the first tiny gap and the appearance 
> of running symptoms could be months, even on a daily driver.
> 
> I check each wire for ~1000 Ohms resistance every time I do a tuneup. This 
> lets me catch failed resistors while the gap is still tiny and before there are 
> any symptoms. Each of us should do the same, as it's easy to do while 
> you're already in there and it saves a lot of grief.
> 
> Take a look at your plugs and see what they look like. If just #3 is black, try 
> swapping it with #2 (because that's easy to get to.) It may clean up. If not, 
> put in a fresh one. If they are all black, we need to look elsewhere for the 
> cause.
> 
> Your distributor should be fine.
> 
> Try a different brain if things are still bad. Even the A would be better than a 
> bad B.
> 
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> 
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