'85 300TD dying out - Page 3 - PeachParts Mercedes-Benz Forum

Stono-see-um · #31 05-30-2012, 01:03 PM

Quote:

Originally Posted by Graplr

Have you checked for air bubbles in the return line yet? I suggested in an earlier post to put clear (opaque) fuel line to check for air bubbles. Just get some 5/16" poly line from just about any parts store, Wal-Mart, Farm Supply, etc. It is often blue or pink and you can easily see fuel passing through with a flashlight. Rev the engine with the linkages and check to see if you have air.

I have not tried that! I will pick some up today and give it a shot.
Thanks Graplr

Stono-see-um · #32 06-01-2012, 05:09 PM

Quote:

Originally Posted by Graplr

Have you checked for air bubbles in the return line yet? I suggested in an earlier post to put clear (opaque) fuel line to check for air bubbles. Just get some 5/16" poly line from just about any parts store, Wal-Mart, Farm Supply, etc. It is often blue or pink and you can easily see fuel passing through with a flashlight. Rev the engine with the linkages and check to see if you have air.

Yep, yep, yep! Replaced the "cigar" return line with a clear line. Pushing manual prime pump, I get at least a thousand little bubbles pumping through every time I press the prime. Now, the bubbles seemed to stop flowing through while running the engine. But I still had air in the line from all of the bubbles from before. I could never clear them all out.

I know someone mentioned possibly replacing the crush washer on the prime pump. The pump is a "black Bosch" pump. I removed it when I rebuilt the Lift Pump and it looked practially brand new. Not gunked up like everything else in the engine compartment. I have seen a copper crush washer set at Harbor Freight, but I believe the sizes are standard, not metric. Is it possible to use a standard size or am I going to be way off and not get a good seal.

I am guessing this is my next step, unless someone tells me I am going to need to replace the whole push prime assembly. While I have a chance to mess with it today, I am going to try barry123400's method to close off the return line from the Injection Pump.

Thanks everyone for sticking with me through my troubled times! I will report back with any updates I can.
Cheers!

Graplr · #33 06-02-2012, 11:15 AM

Quote:

Originally Posted by Stono-see-um

Yep, yep, yep! Replaced the "cigar" return line with a clear line. Pushing manual prime pump, I get at least a thousand little bubbles pumping through every time I press the prime. Now, the bubbles seemed to stop flowing through while running the engine. But I still had air in the line from all of the bubbles from before. I could never clear them all out.

I know someone mentioned possibly replacing the crush washer on the prime pump. The pump is a "black Bosch" pump. I removed it when I rebuilt the Lift Pump and it looked practially brand new. Not gunked up like everything else in the engine compartment. I have seen a copper crush washer set at Harbor Freight, but I believe the sizes are standard, not metric. Is it possible to use a standard size or am I going to be way off and not get a good seal.

I am guessing this is my next step, unless someone tells me I am going to need to replace the whole push prime assembly. While I have a chance to mess with it today, I am going to try barry123400's method to close off the return line from the Injection Pump.

Thanks everyone for sticking with me through my troubled times! I will report back with any updates I can.
Cheers!

It seems you have found your issue.

Yes, I would replace the whole primer pump. I haven't heard of many black primer pumps leaking, just the older white ones. I would double, triple check the large fuel filter fittings as well, especially the banjo bolt.

Stono-see-um · #34 06-11-2012, 11:44 AM

Still...getting...bubbles.. Tried to just replace the crush washer first, under the primer. Still had bubbles, so I ordered and replaced the primer pump. Still getting bubbles now. Replace all hose clamps, made sure all lines and fittings/bolts were tight, still getting bubbles. Tried pressuring system from before primary filter with compressed air, couldn't find a leak.

Next step is I am going to replace the rubber line from the tank to the metal fuel line.

This is my last hope before I give up and take it to a shop. Man I hate to say that. Leaves a bad taste in my mouth.

On a side note, while pressurizing with air, I noticed the fuel tank was building pressure. Can anyone tell me where the fuel tank vent location is??

kerry · #35 06-11-2012, 12:17 PM

Try running it from a soda bottle filled with diesel in the engine compartment with feed and return lines running into the soda bottle. If it's bubble free, leak is upstream on the fuel lines. If you still have bubbles, problem is downstream.

Stono-see-um · #36 06-14-2012, 09:11 AM

I will give that a shot. I haven't done that since before I replaced most of these parts. And even then, I think I only had the supply running into the bottle. Thanks Kerry. Always good to double check things!
May be a few days before I get to it. Have some things to replace on my truck (with multiple out of state trips in the next 2 weeks) and brakes on sister's car today...

funola · #37 06-14-2012, 11:06 AM

Check the metal fuel lines under the car (especially under the clamps) for corrosion. A small pinhole leak there could cause the problem you are having. It would idle due to small fuel demand and suck a little bit of air but still idle. At high throttle with much more fuel demand thus higher vacuum in the line, a lot more air can be sucked in, enough to cause it to stall.

Easiest way to test the metal fuel line is disconnect the rubber hoses from it, plug one end and test it with a Mityvac from the other end. It should hold vacuum. If not, there is a hole.