air leak diagnostic questions
 

I am trying to track down an air leak in the fuel system of my 83 240d. The car has good compression and fires up readily. Idle is smooth, but has an intermittent miss. The miss seems to increase in frequency proportionate to the throttle up until about 2000rpm+-, then smooths out somewhat. There is white/gray smoke at idle and a lot of smoke when the engine is revved. I have set the timing by drip method and by an unapproved ip installation. The valve adjustment is done. The timing chain has been corrected by woodruff key, 4 degree elongation.
I got a new flexible line from the primer pump to the filter. Unfortunately. the line is semi opaque. I put a clear hose from the feed line to primary filter, no air. I installed a new bosch primer plunger and no change. I can see no fuel leaks. When I installed a clear hose in place of the cigar hose, I see some small bubbles coming through the line, but not many. If I pump the primer pump with the engine running, I see foamy bubbles in the line, more if I pump quickly. I also made flexible lines with saab fuel line to my banjo fittings. They seem good and secure, but no effect.
My question(s) are what procedure(s) are effective in tracing an air leak. Are there any shop tips and methods to help with this problem? Are certain fittings and areas more prone to leaks?
The car seems right to me under the miss and smoke issues.

skunk bump

Do you have the old style primer pump? the one with the white knob that has to be unscrewed. you say you see bubbles when pumping the primer.

replace it with the new bosch style black one, around $20.
then all you have to do is just pump, doesn`t have to be unscrewed.

Charlie

An excerpt from post #1:

Positive air pressure and a soapy water solution sprayed on connections usually works well.

Answer
 

* Inspect the fuel tank feed and return rubber hoses for age/cracking/road damage.
* Take a close look for corrosion/pin holes along the steel lines around the rubber mount clips, and the bends that pass over/around the rear sub frame.

.

"If I pump the primer pump with the engine running, I see foamy bubbles in the line, more if I pump quickly."

I guess when I read this, it sounded like possibly the primer pump letting air in.

Charlie

Yes, yes....
 

Very much agree with above. I will spare you the painful and costly details, but one time I had major headaches trying to figure out engine performance problems, only to find later that the rubber hose that connects the hard fuel line from the tank to the pre-filter needed to be replaced. There were cracks in the hose just under the band clamp...when I tightened the clamp, cracks would open and allow air in. A one-dollar piece of rubber fuel hose corrected the problem.

And yes....check hard lines under brackets....On my previous 300D, I needed to remove a few sections on these lines and replace with "bandaid" piece of rubber hose with band clamps. I used sufficient length of hose to allow two band clamps on each end to ensure no-fail.


Good luck,
Mark