Re: FI Gremlin

[stans4@ix.netcom.com]

On 01/08/97 23:37:31 you wrote:
>
>I spent much of my holiday visitation w/ my 69 squareback that I store in
>NC dealing w/ a vexing electric fuel pump problem.  I would start the car,
>no problems.  After a minute or so, the fuel pump relay would buzz, then
>click (removing power from the fuel pump) and the car would die.  After an
>hour or so, the relay would reset and the same thing would happen.  I
>replaced the relay ($7 what a bargain) but no improvement.  I replaced the
>main FI relay but no improvement.  Finally, I began running the fuel pump
>w/ the T1 connector in the engine compartment to see if it was
>overheating.  I had a devil of a time keeping it running by grounding the
>wire, I don't know why.  Anyway, after playing w/ this connection and
>confirming that the pump was not running hot, I taped up a few cracking
>wires in the FI harness on the engine, and lo and behold, problem solved.
>I have no idea why, however.  I'm assuming that the brain has the ability
>to turn off the pump when it senses shorts or other problems in the engine
>and that this is what was happening.  In any case, I'm a little concerned
>that the problem may return but on the highway this time.  Any suggestions
>or theories?  
>
>Rich
>69 Squareback
>71 Bus 
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For the real guts of how the D-Jetronic works, you can't go wrong with the Bosch manual, covers the basic principles as well as a lot of other systems.  It's only one chapter, you might be able to get it on inter-library loan if you don't want to buy it.  Don't have it handy for the exact title, check www.amazon.com for "Bosch" and "fuel injection".  Idiot's manual has a good section on debugging, you need to run the procedure for checking all the harness, I found a lot of stuff wrong on my basket-case '71 SB when I did that.  Of course you NEED the Bentley book on any of this, you're just wasting your time without it, because it has the exact harness diagram for your year, Idiot's just has a sort of middling generic diagram.

Enough on the documentation pushing, let's get down to some specifics.  In no particular order, here's some things which will cause your symtoms.  

You might have a set of trigger contacts(in the lower distributor) that are marginal, the control unit depends on those signals to not only tell it when to trigger the injectors, but to also tell it that the engine is turning over so it doesn't time out the fuel pump relay.  As you noticed, the pump buzzes for about two seconds when you turn on the key, then stops.  This is a safety feature to keep it from pumping gas into a wreck with the ignition still hot.  Lots of American cars with electric fuel pumps in the past didn't do that, a good feature.  Now if a wire to the contacts is broken or not making good contact(suspect the latter) the pump will run for that two seconds and quit. Since your engine runs with the relay grounded out, your relay and pump are good, although you might change out the fuel filter if you haven't already.  If the engine just stumbles along, check out both the contacts and the plug on the distributor going to the FI harness.  Clean the contacts, th!
 ere's two screw on the side, they just slide out.  Use an ohm-meter and check along every point where there's a rivit or solder joint from the center contact of the plug to each of the contact points and back to each outer contact.  I found a bad rivited joint that way on a set of trigger points.  Might make up when cold but open when hot, too. Put the contacts back in and turn the distributor while watching the ohm-meter on each contact(center to outside).  If one isn't consistantly opening and closing, you might need to bend the stationary contact a little so that it is completely open, the rubbing area may have worn.  I like to pull the distributor to do this sort of stuff, much easier doing it sitting down than bending over the hatch.

Another thing that will completely stop the engine is a bad joint to the head temperature sensor on the left head.  I didn't have this completely on the mating connector after putting the engine back in one time and it dropped off going down the road.  Was able to see right off that it wasn't connected, but a bad wire or connector joint could cause this problem.  A little corrosion or a loose connection could cause the thing to stop when it gets warmed up or vibrated.  This is why it's important to run the tests on the harness in the Idiot's manual if you haven't done it.

The control box should be the extremely last thing you should suspect, by all accounts these are bullet-proof.  The one problem I did read about was a car radio shop drilled through one mounting an antenna, that's about the only problem I've ever heard of.  That said, I still have a spare that I swap in occasionally, but it's never that.  I always have a connector or harness problem, have had to run a couple of wires to injectors because the ones in the harness broke somewhere in the jacketing.  It would be nice if someone had NOS harnesses, when I first got the thing, I went to the local VW place and the parts man had quite a giggle when I asked if they still had FI harnesses available.  Looks like homemade will have to be it, someday.

Hope all the above helps.