stumped!

[Ltsmash]

Hey guys, new to this forum although ive searched through millions of times and it has been very helpful.  However i cannot find a problem/solution to a problem that has still evaded me  :x

So ill start off, i have a 91 jetta 1.6TD (MF) 360,000km 5 speed tranny etc. what im having a problem with lately is damned air in the fuel lines.  Now i have read on the forums all the posts i can seem to find about this problem, and none have helped.

I have checked my fuel lines from the sending unit, to the IP, back to the sending unit and found out that at all the factory crimp fittings that the rubber hose was brittle and cracked, so i replaced all the lines with 5/16" fuel spec hose, low pressure stuff for carburetors, im guessing that stuff is suitable, and proper fuel injection clamps...bypassed my water seperator in the back there, redid all rubber portions of lines, now the thing is i still get air in the fuel lines...

fuel filter has been replaced within the last 10,000km and was primed full, water seperator on the bottom is tight, i actually replaced the fuel filter with one from an 85 diesel to get rid of the pre-heater valve.  just replaced my one-way check valve as well.  

Now the symptoms, on initial start-up she bucks like mad and huge pockets of air run through the clear feed line to the IP, so much that im surprised it runs...return line gets full of tiny little air bubbles, exactly what i would expect, however no air-lock in the injectors.  It does this for only a few seconds on start-up then smooths out and runs beautiful, but i feel a shudder under load.  Then when i shut it off, air pockets feed backwards in the feed line towards the filter...one every 8 seconds...just like clock work.

If anyone has any ideas that would be great!

Lieutenant Lt Smash haha

[Patrick]

I had a similar problem last summer, wound up putting a new seal in the driven end of the injection pump. Every time I shut it off, fuel was dripping out of the pump and letting air back in. Pull the timing cover off and look for wet at the end of the pump.

A new seal cost me about 20 bucks, put a new timing belt on while I was a it, there was deisel on the belt.

[Quantum TD]

I had a similar problem last summer, wound up putting a new seal in the driven end of the injection pump. Every time I shut it off, fuel was dripping out of the pump and letting air back in. Pull the timing cover off and look for wet at the end of the pump.

A new seal cost me about 20 bucks, put a new timing belt on while I was a it, there was deisel on the belt.

X2

That sounds like a classic symptom of sucking air in through the input shaft seal. You might consider a complete reseal.

[dieselweasel]

That's what I was going to suggest as well:  check for any leaks at the inj pump that could be allowing air entry.  Also did you have a really good look at the sending unit...the steel lines could be rusted and porous.

[Ltsmash]

Oh wow, ya ok that makes perfect sense, i had thought it may have been leaking at the pump...guess i was just in denial  

Ill definitely take a closer look at that input shaft seal see if i see any moisture around there...i have now come to think of it noticed a slight diesel smell under the hood from time to time...

I took a pretty close look at the sending unit, it didnt look too bad, the rubber lines and check valve there looked good...although i think this car may have fallen off a jack/hoist at one point in its life, kinked the spare tire well, it juts up about 3 inches from the floor of the trunk right by the sending unit, but the tank/unit look unscathed  :?

I was considering doing the reseal as well, some diesel shops around here can do it for $200...tight budget and dont really have the cash to do it, dont trust myself with these pumps  :lol:

thanks for the quick responses too guys!

[fatmobile]

You didn't mention cleaning the screen on the pickup.
 Air in the line is almost always a fuel line restriction.
 I had to remove 2 check valves last year because they stopped flowing.
 With a working check valve a leaky shaft seal probably won't cause air to leak back into the fuel system because the check valve will keep it from syphening back to the tank.
 Without the check valve; leaks around the small lines can even let air be pulled into the pump as fuel trys to drain back to the tank.
 I think the check valve is there so the fuel doesn't syphen back when you drain the water seperator.... the Rabbits didn't have one.
 I heard the A3s didn't have a water seperator either,... but I don't know if they came with a check valve.

[Ltsmash]

ya, I have just replaced my check valve, tested my old one it was working ok though...havent popped the sending unit out of the tank yet to take a better look at it...and i havent gotten a chance to take a look at the shaft seal yet either...

Whats a good cleaner for the screen if it turns out to be dirty? I have some pretty heavy solvent (gunk hydroseal), but I was worried about it damaging the screen, the last thing i want is to have to replace the whole sending unit...

I dont know what everyones opinions are on the matter, had some old diesel tractor guy tell me to put a one way check valve in the feed line from the filter to the IP so that the air couldnt siphon back...in my opinion this is doing 2 things, only band-aiding a potentially worse problem or restricting flow to the IP..

also out of curiosity, could bum injector return lines also cause this problem?  and if the return lines were damaged/leaking, would you not also see air bubbles feeding towards the tank in the IP return line? or do i have my direction of flow misconstrued?  

thanks for the help along the way too guys!

[Ltsmash]

So i had some time to take a better look at my car, and this is what i've found...there is only a slight amount of moisture at the input shaft seal, not excessive, and no large drops of diesel fuel.  

However, i took a look around my IP, and there is a large amount of moisture/diesel smell between the IP and the block...so much that the side of the block from #1-#2 cylinder is damp...looks like perhaps a seal in the backside of the pump is shot there...havent a clue which one as moisture is everywhere...im going to clean it up and see where the leak could be starting from...

The sending unit itself doesnt look to bad...the screen is pretty dirty, but im not sure of a good cleaner to clean it with, so im going to leave it for now...

[Quantum TD]

Cold start lever is leaking. You can change just that seal, but trust me: the rest will start leaking soon enough. Just take it off and have the whole thing resealed. Plus, there is really no way to replace the rear seal without pulling the pump. So, if you have it off anyway, might as well do it right.

[Zulfiqar]

sorry for threadjack

but where is the checkvalve in the fuel line? - I have the pump drain issue sometimes too.

[Quantum TD]

AFIK the check valve only applies to MK2 and up cars. To find it, remove the inspection cover for the fuel tank sending unit. You'll see the check valve in line for the OUT line leading to the pump. It's pretty small, and usually gray or white. I don't think that they fail very often. Most times loss of prime is due to a leaking IP.

[madmedix]

There's another just downstream of the water seperator underneath the passenger rear floorpan. Really fragile. It'll pull apart before the fuel line releases its death grip on it. The stealership charges a small fortune for these puppies too.    I deleted my water seperator because the Jetta spends all of her time on the highway. The road debris was slowly blasting it apart.

[Ltsmash]

There's another just downstream of the water seperator underneath the passenger rear floorpan.

Yep, mine has one of the return line, thats right before the sending unit. The other one is just slightly down line of the sending unit above the water serperator.  You have much more room to work if you take the water seperator out.

I deleted my water seperator because the Jetta spends all of her time on the highway. The road debris was slowly blasting it apart.

I as well just eliminated my water seperator out of the equation...they can leak at the drain valve, real irritating.

[Ltsmash]

Well guys, it's been a few months and still having this same problem.  i thought it was bad before but now its getting much worse.  My car will stall out on me multiple times in the mornings unless i'm sitting with my foot on the throttle, even then it will still stall, not as often.  I'm actually surprised its still running! its at 375,000km now haha. hopefully make it to 400!  :lol:

I need some professional opinions, from anyone on this forum.  Do I have the pump pulled at $70/hour labour, approx 3-4 hours for re and re on the pump, $200 for the reseal.  I would do it myself, but chances are i'll end up screwing things up even more, and i don't have any of the timing equipment.  so there that is about $450 said and done.  My car also has a pretty decent exhaust leak off the manifold on the #4 cylinder..which is even more $$ to fix.  After 375,000km all the suspension is shot, i can't actually carry more than 2 people in my car without it scraping in the back over slight bumps in the road.  As well as some pretty decent dents here and there which were there when i got the car.  And the huge screwed up dent in the spare tire well, which still eludes me on how the heck that one happened. Not to mention a crack in the windshield thats almost from side to side $200 for a new one and a tranny who's syncros are shot and grinds into second.  

Now...do i even bother with the pump reseal? or see how far the thing will go until it just won't run and sell it for scrap?