aaz runing rought at ~2000 rpm

[vako]

hello, as you know i finished my rebuild 1 week ago there are used pistons + new rings and rebored block. i have also resealed the pump last winter, so now it is leak free.  engine has very good compression (when warm, it starts up without glowplugs with no problem). but the problem i had before is still there

car idles smooth, without misfiring or shaking . but when rev go up to maybe 1500 it starts to shake a bit (it has a slight misfire i think) and somewhere above 2000-2500 it revs smoothly again. i have noisy transmission and i hear intermittent whining noise... and also feel the car twitching. i happens every time i get in the problematic rev zone 

pump is timed to ~0.95mm, and fuel screw is set to the position where it does not smoke very much (only small puff of black smoke before the boost builds up). i have changed the filter jut before the rebuild, i thought it would solve the problem. i have slightly lighter flywheel and front pulley but  i remember exactly that i did not have that problem 1 or 2 years ago, so it must not be the cause.

i have not removed the injectors yet.

what could you advise me, what can be causing this strange behaviour of the engine ?  could it be the injectors? or i should be looking for the problem somewhere else.  the thing that misleads me is the fact that it idles well, and the problem starts only after revving it up a bit 



cheers , vako 

[vanbcguy]

Are all 4 securing bolts present on the pump, in particular the one under the pump head?

[vako]

Are all 4 securing bolts present on the pump, in particular the one under the pump head?

do you mean pump mounting bolts? they are all tightened well (i had that problem 3 years ago and after that i always dounble check mounting bolts

[Mark(The Miser)UK]

Try swapping the injectors around. Break the sequence,ie label 1 3 4 2   and swap a couple, ie 1 & 4, to give 4312. Check true difference by trying to insert into the sequence 134213421342.

No better? Check injectors operation:
 
Check leakoff flow rates by opening up all the barbs and plugging 'return' line to pump. Running temporary lines to a row of test-tubes is ideal, or I'd use 8 off, 5" stiff clear lines creating vertical manometers.

 Check spray and break pressures after an overnight rest; this I personally find, reveals faulty injectors at their worst. Look for variations;D

Nothing showing up? Insert your spare, preserved in aspic, set of injectors
No help? Slacken engine mount/s

[vako]

Try swapping the injectors around. Break the sequence,ie label 1 3 4 2   and swap a couple, ie 1 & 4, to give 4312. Check true difference by trying to insert into the sequence 134213421342.

No better? Check injectors operation:
 
Check leakoff flow rates by opening up all the barbs and plugging 'return' line to pump. Running temporary lines to a row of test-tubes is ideal, or I'd use 8 off, 5" stiff clear lines creating vertical manometers.

 Check spray and break pressures after an overnight rest; this I personally find, reveals faulty injectors at their worst. Look for variations;D

Nothing showing up? Insert your spare, preserved in aspic, set of injectors
No help? Slacken engine mount/s

what will i find out by swapping injectors?  compression is the same in all the cylinders. so there will not be "bad cylinder" there... :?

as for the return lines, do you mean to disconnect return lines from injectors and check how much fuel does each injector overflow?

can bad spray pattern on clogged injector be causing such uneven operation only in limited range of rpms? i know you have worked with plenty of vw diesels and did you have such case in your practice?

[vanbcguy]

Are all 4 securing bolts present on the pump, in particular the one under the pump head?

do you mean pump mounting bolts? they are all tightened well (i had that problem 3 years ago and after that i always dounble check mounting bolts

Yup, pump mounting bolts.    The 4th one at the high pressure end of the pump gets left out a lot and it causes the pump to oscillate in its mount at around the RPM range that you are having issues.  But it sounds like you have this covered.

[theman53]

I guess it is fuel related some how. Either you are not getting enough through the lines, filter, or something. If you look at where the gov. starts to cut fuel it is right around that 2000=2200 rpm range. so you have enough fuel before and after per RPM, the most fuel you will have per rpm is right in that range. Since it was with both engines it is probably in the fuel lines from the tank to the filter or pick up screen since you changed the filter. Like all of these diagnosis run it from a bottle into and out of the pump, if it takes care of it then you can start cleaning out lines/filter/etc. if it doesn't start looking at your pump.

[vako]

i forgot to mention, harder i push accelerator pedal less if feel the "rough running" period but still feel it a bit..). it is expressed the most when i barely touch the pedal and when i'm driving gently. also there are no bubbles in return line.
i ran it from bottle (i used atf to "clean" the fueling system) still it feels the same in problematic rpm-s.

pump rear bolt is tightened well i learned my lesson two years ago

i'm really confused now 

[Mark(The Miser)UK]

Checking leak off volumes, eliminates one that may be leaking more than others and so injecting a different quantity. Running the engine at idle and then at the offending rpm could show a dynamic injector issue. 

These engines have lots of harmonics, hence the ability to vibrate the ash tray or tool box in the back at different speeds.

[theman53]

I guess I assumed since it was bad enough to rebuild that it was misfiring badly in your first post...How bad is it? Is it a misfire or is it just vibration? When you lightened the flywheel and pulley were they neutrally balanced? If not that maybe your entire problem. For example my entire engine is balanced from pulley, crank sprocket all the way to the clutch, PP, and fly wheel to less than 1 gram. But it still has vibrations especially when cold and what you could perceive as a misfire if you didn't know because of all of the lightened stuff I have. Let us know more.

[vako]

Checking leak off volumes, eliminates one that may be leaking more than others and so injecting a different quantity. Running the engine at idle and then at the offending rpm could show a dynamic injector issue. 

These engines have lots of harmonics, hence the ability to vibrate the ash tray or tool box in the back at different speeds.

ok i will do the leakdown test as soon as i have time for that (i have to write an essay till tuesday, and then i will check the injectors) it can really give me some info about bad injector 

[vako]

I guess I assumed since it was bad enough to rebuild that it was misfiring badly in your first post...How bad is it? Is it a misfire or is it just vibration? When you lightened the flywheel and pulley were they neutrally balanced? If not that maybe your entire problem. For example my entire engine is balanced from pulley, crank sprocket all the way to the clutch, PP, and fly wheel to less than 1 gram. But it still has vibrations especially when cold and what you could perceive as a misfire if you didn't know because of all of the lightened stuff I have. Let us know more.

i forgot taht my "lightened" flywheel (that is just a flywheel from suzuki sidekick) was balanced after i did a rebore for fitting it on vw engine. it was balanced within 5 grams


i know how diesel misfire feels like (while the car is cold sometimes it missfires for 1 minute, if i did not have cold start lever out) on idle and cold missfire is felt very well, and in my case it is even feeld on drivers seat

    on problematic revs in my case the engine just starts to wobble a bit. if it is smooth through the rev range and on idle, it just starts to move from side to side a bit on that revs (but it is not felt at all inside the car, if teh car is not in gear and driving)... it seems that there is no enough power of combustion in one of the cylinders, but the combustion is still happening.


i think that at first i will have to check the injector overflow rate and after that at least take off the injectors and check for pop pressure and spray pattern.

[vako]

i will post a video as soon as i take the car out of teh garage

[745 turbogreasel]

Will it do it in neutral?

[vako]

yes it does it in neutral too. but in neutral you can only see the engine move from side to side a bit, it is not felt while sitting in the car