SR2 Revs low

[dax021]

Out of lurk mode for a while as I need some advice from you learned folks.  Firstly, thanks for a great forum, even tough I've hardly posted anything, I read the posts religiously most evenings.  I have picked up loads of theoretical knowledge, though sadly, pretty much no practical experience, mainly because my SR2 has been running faultlessly for 150 odd hours, and following the old saying that "if it aint broke, don't fix it"

About 2 weeks ago, I made the stupid mistake of starting up and forgetting to open the fuel valve.  She ran fine for about 1/2 hour then I noticed a rough sound and immediately realized my cock up.  The filter and feed line was devoid of fuel.  I shut down and bled the fuel right up to the banjo going into the block, but not further.  After startup she ran smoothly again, but it sounded like the revs were a bit on the low side.  I measured them at 1430 RPM, should be 1500 to suit my Hoffberg direct drive alternator.  After a while the revs seemed to have normalized and I thought all is well again.  Today I fired her up as I wanted to do some welding, but the inverter welder kept cutting out.  I checked the output and found it to be only 219VAC, should be 230 as far as I know.  Also the revs sound a bit slow again, which would explain the low voltage.  I haven't as yet checked the revs again, but will do in morning.

Any advice on what to do would be appreciated.  Like I said, I don't have much practical experience, so some step by step instructions will be great.  I would like to up the governor speed to 1500 RPM, but am not sure how much of a job this will be.

Thanks in advance.
Peter
 

[dieselgman]

You may still have some residual air within the fuel system... not all SR units had a self-purging capability. Since it is running, you should be able to open and close the fuel lines (one at a time) at the injector connections and the unit should stumble approximately the same on each cylinder and then return to speed as this is done.

Other possible issues could be: Sticky fuel pump rack - you can feel for smooth operation by hand on the rack pushing it forth and back through its full travel. Possibly dirt was drawn through the filter and partially clogged a pump or nozzle, injectors can be bench tested for pressure and spray pattern. You can also remove and install the injectors inverted outside of the engine and roll the engine over to visually see the spray patterns (after purging of air). Both nozzles should match one another and spray a very fine mist pattern with all equal lengths (for each orifice). Sometimes running a biodiesel (or similar) fuel system cleaner through can help.

dieselgman

[mike90045]

Beware the high pressure mist and leakage that can cut your skin

[dax021]

Thanks to you both.  What does it entail to purge the pump and injectors?  My manual does not explain things very well, i.e., in the manner in which, I as one who has never worked on a diesel before, feels comfortable to start stripping things.  Is it a matter of opening the cover and start pulling apart?  Can I take this chance?

[AdeV]

Thanks to you both.  What does it entail to purge the pump and injectors?  My manual does not explain things very well, i.e., in the manner in which, I as one who has never worked on a diesel before, feels comfortable to start stripping things.  Is it a matter of opening the cover and start pulling apart?  Can I take this chance?

Hope you don't mind, this reply was in the wrong place, so I moved it for you....

To answer the question, although I'm not familiar with the SR2, I can't believe it's much different to Lister's other engines... basically, pull the rocker cover off & you should see the top of the injector, with 2 pipes (ideally!) - a feed pipe, and a leak-off pipe. The latter returns to the fuel tank usually, and carries off any fuel that wasn't injected.

To bleed the system, simply loosen the nut holding the inlet pipe, and maybe back it off a few turns. Or if you're feeling brave (and don't mind getting your hands covered in diesel) you can pop the pipe all the way off. Now crank the engine over (or run it, if you don't mind making a mess). You should see a nice healthy spurt of diesel out of the pipe every time it injects. With the pipe just loosened, any air should seep out (often blowing bubbles), when it all goes quiet and liquidy, tighten the pipe back up. Repeat this process for the second cylinder.

That's the fuel system completely bled, so if that doesn't fix your issue, next stop is to pop the injectors out... This is also fairly simple, usually...

1) Undo the fuel lines to the injectors and move them out of the way.
2) Undo the bolts holding the first injector. See if it'll pull out.... if not...
  2a) Put the injector bolts back in, but leave about 1/16th" slack between bolt head and injector flange.
  2b) Spin the engine over until the compression pops the injector out. SEE WARNING BELOW
  2c) Remove bolts and injector (it should come out once unstuck from its seat).
3) Repeat for 2nd injector.
4) Now your injectors are out, turn them upside down and re-connect the inlet fuel line. Ignore the leak-off (this is going to make a mess anyway...)
5) Now turn the engine over by hand, or on the starter. Observe spray patterns from injectors. As per Mike's post... don't put anything (hand, eye, etc.) near the spray, it does have enough power to penetrate the skin!! And if you stick your eye over it, well, just don't do it, OK. Note that you need to turn the engine fast enough that the injctor gets a proper pulse of fuel; if you just roll it over the injection event, it'll just dribble. If that.

6) To re-assemble, just undo the fuel lines, carefully push the injectors back down their holes, bolt up nice and tight, re-connect fuel lines, job done.


WARNING! - Never EVER start (or even rapidly turn over) a diesel engine with the injector unbolted and the bolts removed! The compression can (and WILL) cause the injector to be fired out of the engine block, straight through you, clean across the yard, and it WILL kill or seriously injure the neighbours cat/child/wife (or all three) - so even if you survive, you'll be sued into oblivion by the trail of carnage left behind. YOU HAVE BEEN WARNED!

That said, sometimes, the only way to remove a stuck injector, is to run the engine hard with the injector fastinings loosened. And, sometimes, even that doesn't work... I went to replace the injectors on my old bus, of the 6 we got 5 done, the 6th will NOT move. Loosened the bolts, drove it 500 miles, and it STILL won't come out...

[dax021]

Thanks everybody for some good advice.  This definitely gave me the confidence to take the rocker cover off and see what's in there.  My usual mistake is to over complicate things, which gets me thinking "I'll never be able to do that".  So far, it turned out to be a very simple operation (don't laugh, I'm a novice).

Saw the injectors, pipes, in and out, and once again got cold feet.  Over thinking again, probably, but the manual states beware of leaking fuel into the crankcase, and it seemed impossible to bleed that line without doing precisely that.  While studying the manual, a bit more diligently this time, I saw a line about adjusting the speed by small amounts via a screw through the front cover.  I thought I'd try this first and if it didn't work, then pop the fuel lines.  Bearing in mind the engine is running smoothly, without missing, albeit a too low a RPM.  Put the rocker cover on, fired her up and played with this screw.  To my surprise and joy the revs started climbing.  Luckily I have a strobe light type tachometer, so turned until I got the desired 1500RPM.  I had to turn it more than the manual's stipulated 2 1/2% maximum (closer to 5%), but she still sounded good.  Checked the voltage and it's sitting nicely at 240.1VAC under no load.

I am going to run her like this for a while, change the fuel filter and see what happens.  I'm not much of a mechanic, but for some strange reason, I do have a good ear for mechanical noise, so if I hear any change of tones, or roughness, I'll then go further and flush and bleed the whole fuel system.

Thanks once again to all of you for the detailed and great advice.  You have surely given me confidence to put a bit more faith in myself and old Mr Lister.

If you don't hear from me soon, you'll know all is well, but know also that I'll still be lurking on the forum most nights, picking up useful bits of info all the time

Cheers,
Peter