I suspect my IP is tired but to try to isolate it I put the feed and return lines into a glass jar filled with fuel. After starting it up and running it I immediately noticed that coming from the return line are tiny bubbles the size of what you'd see in a pint of beer. This is a bosch pump on a VW diesel and I tried that forum but no one seemed to know what would cause these tiny bubbles. It is a 1986 1.6 L turbo and it is making boost but there is very little throttle response between 1/4 and 5/8 throttle and sometimes it idles horrible. It only seems to respond when I floor it or darn near floor it and the injectors are brand new rebuilt ones from bosch. I know the guys here are smarter than the VW guys

 

air intrusion or air thats what would make the bubbles

 

new injectors have proper pop pressure again.this higher pressure (returned to normal) than the old ones with a tired ip will finally make the old worn out ip say uncle.

 

Sounds like air intrusion. I have a an 85 Jetta TD and I had to replace several clamps and hoses. Check for cracked fuel lines on the tank and at the filter, water separator (under pass rear) and IP; additionally, check to see if the water separator tank is leaking fuel, these typically crack and allow air in the system. There should be a "clear" supply line just before the IP to give you air indication. Additionally, if your air return lines off of the injectors are loose it will permit the system to leak and bleed down. I think the OEM had a clamp on each line; the VW dealer had the best replacement. Your fuel cut off solenoid acts as a check valve and if the return lines leak and the check has accumulated shmootz in it the system will siphon back to the tank. I also found my throttle-rod (uncertain of term) seal to be leaking as well. The IP seal rebuild kit, 2 years ago, was about $18 US and about $3 for the front seal. Feel free to PM me if you need additional help.

 

Hey now, be nice to the VW guys... Did you try vwdiesel.net? Some of the sharpest diesel guys in the world lurk there. As far as the bubbles are concerned, I can atleast tell you that all my vw diesels except my TDI have bubbles coming out of the return. Keep in mind that the return line is simply a hole in the top of the pump on the low pressure side. The lift pump inside the bosch rotary pump has only one job... to keep that pump full of fuel. It pulls in much more fuel than is needed so there will always be fuel coming from the return line. The only place you have to worry about air bubbles is the high pressure side... I guess you could call that the injector side... and you will know right away if there's air over there, it may not run at all. I've rebuilt these pumps from the ground up and I can say with a 95% certainty that these air bubbles mean nothing. If you know a bit about injection pump theory and bosch rotary construction it's clear this means nothing. Air just simply gets in, but it's nothing to worry about on the low pressure side.

With that said, it really does sound like you have a injection timing problem.... Like way retarded timing. Did you do the timing belt yourself? Or did you pay someone without the proper tools to do the job? Most mom and pop shops will time the engine by ear which never really works out unless it's too far advanced. Also, have you messed with the fuel screw or the star wheel? One easy thing you can check is to see if the boost enrichment diaphragm is stuck. Take the 4 screws off the top of that "UFO" looking thing... GENTLY! push the diapragm down to see if it's stuck. If it goes down, it's not stuck obviously.

 

Thanks for the insght here. I was on the vwdiesel forum and the consensus there was that the air bubbles are not normal. I will check the diaphram tonight. The timing belt was replaced by a german auto repair shop and as far as I know, the fuel screw has not been messed with. I have the adapter and metric dial indicator to check the timing so I will have to do that before deciding to get a rebuilt pump. The car is in great condition inside and out and I need it for commutting so I'd like to head off any potential problem here. The german auto place said that it needed new motor mounts but that is about it so I am wondering why they didn't say anything about the injection pump.

 

Sounds like you know what you are doing with the dial indicator. Check that... you can even advance it a few degrees for a bit more power and lower EGTs. Keep in mind that the 1.6TD at sea level does 68hp... Do you have experience with the car before it started acting up? Obviously then you would know what's normal and what's not. The 1.6D has a very even power band, but the 1.6TD has a crazy torque curve. It can REALLY feel like a dog until it hits boost. Who knows, it might not be boosting at all until it sees that 1/4-5/8 throttle. Check timing, make sure the pump is not 180 degrees out (it will still run that way). Advance the timing a few degrees. Connect a boost gauge and watch the boost pressure. You can also check the rearview mirror for volume and color of smoke. If there's no smoke at all, consider screwing the fuel screw clockwise 1/2 - 3/4 turn. As long as you haven't messed with the star wheel, don't... atleast until you know more about it. These pumps really are so very simple, there should be no need to replace it. For what it's worth, if you do have to replace it, I suggest finding a 1.6D (NA engine) in the junkyard and get the pump off that. You can dial in the fuel screw and get it pretty close to 60hp without messing up the idle too bad. They are plentiful and would work just fine for a daily driver... especially if you advance the timing, it would have more power than you would need really. Also, for the record, this engine will take 20-25psi stock and still stay reliable as long as the EGT and oil temp don't get too high. I ran a 1.6TD at 40psi, stock compression, stock head gasket, stocket head bolts. Only difference was I had a big front mount intercooler. Worked great until I blew up the turbo.

Good luck.