1990 A2 non-turbo idle & running issues after fuel filte

[VR6-Guy]

Hi all, I was doing some simple maintenace on the nighhboors 1990 - 1992 A2 Jetta with the non-turbo diesel motor and now the car has issues. I basically pulled the old filter out and put a new one in without filling it and then started the motor up. It came to life quickly and would idle but it wouldn't rev so I shut it off and searched the site and read that it should be filled with fuel first then started. I grabbed my mighty-vac and sucked some from the feed hose on the fuel system and then filled the filter and started it again and once again it would run. It would idle and rev a bit but it wasn't running properly and the feed & return hoses had a lot of air in them, the return is like foam at times. The motor would stall out and run roughly then idle fine and crap out when revved. I had the same issue with a TDI when I had to pull the motor and on this car I just loosened the #3 injector fuel line which is at the highest point of the fuel system and this allowed all the air to bleed out and the car ran fine after this. I tried the same on the A2 and it didn't make any difference although I only loosened the #3 injector feed line.

It sounds like there is air in the system as this is all I really did to cause the motor to run strangely but how do I bleed the system on this motor? I have a mighty-vac hand operated bleeder so should I just try pulling fuel through the pump and seeing if this gets rid of the air? I tried doing this from the return line to the fuel filter from the injection pump with the mighty-vac and it did run a bit better but it still stalls out and runs rough.

Where should I go from here? I work on a lot of VW's but not many diesels so I am not sure of a lot of the 'small important facts' you learn over the years with this motor.

Thanks for any input.

[bert]

Mate,make shure the filter pipes are tight,start it up and just leave it tick over for 5 mins,it will bleed itself,it will take time,i never fill the filter when i change them,
Bert

[Op-Ivy]

Yeap. Make sure lines are tight and then just let it run for a bit. Prefilling your filter with automatic transmission fluid is a good thing to do while you are there to lube up your pump a bit. (helps as well if you dont have any diesel around)

-Matt

[jtanguay]

hmmm i would definitely recommend 'priming' the fuel filter first... the pump will be sucking air.. which is not good.  your pump won't die from it, but it could potentially cause problems since the fuel actually lubricates the pump... (air is a really really really weak lubricator...  :lol: )

all you need is a brake bleeder pump to do it... pull a vacuum on the return line and there you go!  or buy a cheapie solid state pump to make it that much easier.

[VR6-Guy]

Thanks for the tips gents, I will give that a try and see how it goes. The fuel filter currently has ring-gear hose clamps and these have dug into the fuel lines so I will replace these with fuel-injection type hoses clamps first. It does seem to be sucking a fair bit of air in the system so a loose fuel hose makes a lot of sense.

Thanks again, Dennis

[VR6-Guy]

Still a no go on this car. I started it up to let it idle for 5 or so minutes to bleed the system and still it runs really rough and will barely rev at times and not at others. I pulled the feed line from the fuel filter and used my hand pump to pull some fuel through it then I pulled one of the return lines from the injectors and did the same thing and started it to the same effect. When the car was first started it was using the choke which I turned off after a few attempts of letting it run. It will idle then get really rough then smooth out and get rough again and then stall out. It will semi-rev which usually causes the motor to crap out. I guess it could be a bad fuel filter but it is an OE Bosch one so it doesn't seem likely. When I worked at VW I did not see one of these come back on warranty so I think it is somthing I am doing.

I cut the ends of the main feed & return lines from the fuel filter as they were really damaged from the old fuel lines and put fuel injection clamps on. The fuel filter is one of the heated filters which comes with a new seal so the lines all seem to be good although the crimp clamps on the return lines may not be tight enough but they don't spin.

What am I missing with this diesel powered nightmare? The fuel line coming from the tank is going into the spiggot that has an arrow pointing to the filter and the one going to the injection pump is coming from the spiggot that is pointing away from the fuel filter. Very confusing, I can't see any other damage on the fuel lines that would allow it to suck air into the system. The main feed line going to the pump has more air than fuel and the return line from the injection pump is full of foam.

Cheers, Dennis

[VR6-Guy]

Thanks for all of the input, I finally had some extra time to invest into this motor to figure it out. To make it short it was a defective fuel filter. My parts guy hadn't had many warranty returns on the fuel fuel filter but I guess there is a first for everything. I replaced the pre-heater valve because it was making some noise but this didn't correct the problem so I put the old fuel filter in and the car started to run properly and bleed all of the air out of the system. I had grabbed a second fuel filter when I went back for the pre-heater valve so I took the old filter back out and put the 2nd new one in dry and within a minute the motor was running perfectly with no air in the system.

I compared the three filters and the old one and the 2nd new one looked the same but the first new one was a little different. The old one wasn't a Bosch filter but the two new ones were and they both had the same part number but the drain on the bottom was different and the shape was a little off. Either way, the car is now up and running and seems to be fine.

On a side note when I put the old filter back in I did not pre-fill it with fuel nor did I pre-fill the 2nd new filter and both of these bled the air out in less than a minute. Although it is a good idea to pre-fill the filters it is not needed if you do not want to do this.

Thanks again for all of the help, Dennis

[935racer]

I definitely recommend filling the fuel filters with atf or diesel, especially if you aren't using a lift pump, if you are than its not as big of a deal. But you really don;t want to be pumping any air through the pump and injectors than absolutely necessary.