96 Passat GLS. Starter cranks but engine won't start

Just a followup to my note. I did some homework that I should have done before this posting by checking online parts catalogs and Bentley. Please don't curse me for not doing that before writing. Anyway, if I understood correctly, this car has a single Fuel Pump located in the trunk accessible through the luggage compartment. I also pulled out the FP relay and fuse and tested them. They are both fine.

Now, the Bentley says that I have to "connect a remote control VAG

Thanks to all who will respond!

Andrew

I'm not 100% positive but on many cars the fuel pump will run for a few seconds while you have the key in the ON position. If you do not hear yours come on and the fuse and the f.p.relay are fine you are probably looking at a burned up pump.

Just an update on the situation. Today the weather was nice and dry and the car started at once. I figured I still have to try diagnosing the problem and since the fuel pump was the main suspect, I got to it through the luggage compartment. The top of the pump assembly has a for pin connector on top (two conductors to power up the pump and the other two for the gauge). The + conductor of the pump (a thick red wire) had a visible damage near the connector. The insulation was worn out and about 0.5 cm of the wire was exposed. Also, the wire was corroded with about 3-4 of about 7 strands visibly broken.

I will fix it with a butt connector but it was getting late and dark, so I just put some electrical tape on the damaged wire. It seems to me that this may explain the symptoms. In high humidity the pump was getting to low voltage because of the leak from the exposed wire. Hence the symptoms.

I also found out that the spark-plug wire boot was cracked. I was able to see the spark in the dark. So, I am looking at replacing an ignition wire set or at least one damaged wire.

Thanks for the suggesting to check for the buzz, when ignition is on. The pump is indeed supposed to turn on briefly to pressurize the injection system and I could not hear the buzz. However, I can hear the pump when the engine is running. I find this strange and would appreciate any advise as well as any comments on this repair.

Thanks again! Andrew

I would look for a different explanation for this part of your problems. Humidity shorting the wires should not have much effect at low voltage.

Tom, thanks for your reply. I agree with you low voltage cables are less prone to humidity effects. However, let's remember that this wire goes simply along the car body and about 0.5 cm of its length was exposed due to damaged insulation. Of course paint provides some insulation from the car metal but on the wet day there may well be moisture in that area, so I would assume it could drain down the voltage that the pump actually gets to the value not sufficient for the pump to operate. Is this an unlikely scenario?

Also, the wire in the vicinity of the damaged spot is corroded. This looks like a 7 stranded wire and some strands are broken. So, this may result in heat losses (the pump may well draw several amps I think) and again the voltage drop. I plan to cut off the damaged part, install a butt connector and seal it with shrink tubing.

Right now the engine starts OK. I still don't understand why I can't hear the pump turning on briefly when I turn on the ignition. I can hear the pump buzzing when the engine is running when I get close to the pump.

Thanks again! Andrew

Yes, unlikely to impossible.

The reason is that even salty water is not going to short out enough current to keep the wiring from supplying enough current. The resistance of a short due to moisture is unlikely to be under 100 ohms. If there were a conductive-enough short, I would expect the fuse supplying the pump to blow rather than having the pump be starved for voltage.

Now if you have moisture what I would not be surprised to find with it would be a corroded connector. That would be the opposite of a short: an open. An open can be intermittent and might start working again after some vibration. I guess it is possible that the air humidity to affect when the open circuit keeps current from flowing. It is hard to see how that would occur at just those times, but I could see that.

So the action item in addition to adding tape to prevent a real short would be to clean any contacts. I don't know if there are any connectors there. If there were, I would clean them up. I would apply deoxit or other contact cleaner. I am not saying there is a connector. I am saying that if it is, that I would clean it. I am not at all experienced with dealing with the rear fuel pump, and I am glad it has not come up for me.

Now for trouble shooting, here is what I would do from your case. I would get a multimeter and set it to the 15 volt or next higher range. When turn on the ignition. When the pump does not start, I would go back to those wires and probe to see if there is voltage. If you do have an intermittent open, what may well happen is the pump starts up as you are wiggling the wires. That is a legitimate troubleshooting indication. But if you can see voltage to the pump and the pump is not running, expect the pump is the problem. If you cannot see voltage, then you cannot be expecting the pump to run. Somebody may be able to tell us how long that voltage should be there with the ignition switch on and the engine uncranked.

I have gotten way past what I know (a moist/wet pair of wires will not short enough current to keep the pump from running.) A problem like yours is interesting. When you do find what it is, please let us know.

Tom, thanks again.

Yes, there is a connector on top of the fuel pump assembly. It is a four point connector (2 wires for a pump and 2 for a fuel gauge). The wire bundle ends with a mating connector that plugs into the connector on the assembly. The damaged wire is in the bundle and the location of an insulation wear is about an inch from the connector. I looked at the connector yesterday and it looked OK.I sprayed the contact points with a contact cleaner from the can (don't remember the name) that the local parts store sells.

There is a little chance for the hypothetical open at the connector area to be closed by vibration. The car didn't start in the rain and on the sunny day it just started. It was sitting motionless. Well, of course opening and shutting the door may be enough vibration too, so it is not impossible but unlikely. Your point that the fuse didn't blow is a good one. Too much current due to the current leak should have blown a fuse. As for your question for how long the voltage should be at the pump with the ignition switch on and the engine uncranked, Bentley only says "briefly". In my Golf I estimate It to be about a second.

I will tell what I find out and I would appreciate more opinions. Andrew

I could see two ways for that voltage to be there briefly. One would be that it is timed. The other is that a controller would shut down the power once sufficient pressure is a achieved. I don't know which way it is done.

Don't know. My Golf's Bentley, which is written in by far more plain language than Passat Bentley, says that the pump turns on briefly to pressurize the system. I thought maybe Passat, being ten years younger, simply holds pressure better than the Golf, and, that's why I could not hear it. To check I pulled out the fuel pump fuse with the engine running, so that it would stall by itself after a some seconds. Still didn't hear this pressurizing buzz after that when turning on the ignition. The engine started instantly though, as if it was pressurized. Maybe it pressurizes in no time and I cannot hear it.

To see the voltage appearing at the connector when turning on the ignition would be a good check. Will try it when I get to continue with the car.

Thanks!

Did you do a wet test of the spark plug wires and ign coil (AKA ign. transformer) to see if that is your problem now that the engine is running? Take a spray water bottle and start misting your spark plugs, then wires to the distributor working your water to the ign. coil. I would say that your ign. coil is the problem. Engine will probably die when the coil gets misted. You can either replace the coil (BUY ONE FROM THE DEALER ONLY) or take it off, clean it well and coat it with a thick application of epoxy. I have done this to some ign. coils and coil packs with success. Some coil packs go for over $400. yuck! If the coil is bad you may want to change plugs, cap, rotor and wires too. ;-)