Surging during light throttle

[zen]

SD33 now turbo,was n/a..has always "surged" on light loads ie keeping to 30mph hardly any throttle,can drive out of it by giving some gas, or releasing throtle..

Now have done search on this very recently discovered kool forum and it seems possible cause is dodgy diaphragm on pump..ie gone hard??don't think its holed as can get really good fuel figures if i wish..ie 27 MPG..any thoughts?? oh otherwise engine is sweet..

[philip]

sd33 now turbo,was n/a..has always "surged" on light loads ie keeping to 30mph hardly any throttle, can drive out of it by giving some gas, or releasing throtle.

From a governor perspective, surging is most often the result of the fuel rack being modulated back and forth instead of being held steady. For instance, when a small hole develops in the pneumatic governor, the size (and therefor the leak) may vary with the diaphragm's deflection. Also, when there is resistance to movement (tar, goo) on the rack linkage betwen the pneumatic and mechanical governor, the rack's movement may become notchy. Pneumatic Governor

From a fuel delivery perspective, a series of air bubbles arriving at the injection pump can bring about surging. Purging Air

Now have done search on this very recently discovered kool forum and it seems possible cause is dodgy diaphram on pump..ie gone hard??

Glad you found nissandiesel / SD22 forum. Al and I hope to maintain a reference site of reliable information. The Pub is across the street.

Dont think its holed as can get really good fuel figures if i wish..ie 27mpg..any thoughts?? oh otherwise engine is sweet..

"Holed" is a matter of degree. When a hole becomes a tear, then you will have unmistakable driveability and fuel consumption complaints.

[zen]

thanks..will be checking (well replacing) the diaphragm..(if i can find one here)

there is no smoke when surging..(its not bad, just annoying..now that i have replaced the transfer box, props etc. (was bad with shagged transmission))

and checking for air in line..(you never know)

oh. wot to coat new diaphragm with...not cod liver oil that is for sure!! silicon oil??

[philip]

thanks..will be checking(well replacing) the diaphram..(if i can find one here) _SNIP_

oh. what to coat new diaphram with...not cod liver oil that is for sure!!silicon oil??

Jury is still out. Obviously the leather "preservative" needs to resist polymerization under operating conditions (temperatures possibly reaching 200 degrees F).

[asavage]

Don't we have an ongoing thread about the diaphragm lubricant?

[philip]

Don't we have an ongoing thread about the diaphragm lubricant?

HERE. but some people just don't want to meddle with stuff when "it don't need fixin'". Now you or I would without trepidation whip those screws out, pull the cover off, and take stock of our experiment.

[zen]

finally got around to sorting this surging out...

twas the inlet/exhaust gasket leaking a wee bit...replaced and all sorted now..

[philip]

finally got around to sorting this surging out...

twas the inlet/exhaust gasket leaking a wee bit...replaced and all sorted now..

Does your SD33 have an operational EGR system?

[zen]

no Philip..

It didn't come with one..infact i have never seen one on the SDs over here at all...( i envy just about everything in cali (compared to england) except your emission laws and the amount of guns! )

[the-486]

what does Surging sound like?

[zen]

it was the engine hunting..abit like a learner kangerooing but nowhere as bad..caused this time by air leak on inlet manifold gasket upseting the ip.