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D24t rough idle

500dollar744ti

still rides with MrDoug
300+ Club
Joined
Feb 2, 2007
Location
Falls Church, VA
I got a 1984 760 turbodiesel with a rough idle. I resealed the injection pump a few weeks ago and timed it with the proper tools. The engine was running absolutely smooth and perfect.

Just a couple days ago the engine started running rough at idle, above 1000rpm everything is normal and power delivery is good.

I just need a starting point with this. I'm used to pulling spark plug wires to check for cylinders not firing, what do I do to find out if there's a bad injector or something else that could be causing it?

Thanks.
 
Having no experience with the VW motor in question, but some time around diesels, check for easy things first;
Loose fuel hoses and fittings
2. Injector lines weeping
3. Fuel filter leaking air or clogged (unlikely in this case)

Sometimes you can hold on to an injector line and feel the fuel pulse go through. Try several different lines and see if you can tell a difference between them.
 
Does it smoke? Does it start easy? What did you time it to? .95mm has worked best for me. What is your idle speed?

D24t.com
 
On the TDI I had some luck finding leaks by putting a Mityvac on the pump return line (with the brake bleeder bottle attached, to catch any fuel). Obviously if it doesn't hold the vacuum pretty solid, you have a leak someplace, and you can trace forward from the pump to each injector.

Did you use Viton seals? The newer ultra-low-sulfur diesel will ruin the older style seals in a very short while.
 
Does it smoke? Does it start easy? What did you time it to? .95mm has worked best for me. What is your idle speed?

D24t.com

Timed at .93mm, starts real easy, no smoke, not sure of idle speed, a little below what it should be but not struggling to idle.

Bringing the engine speed up slightly eliminates the shake, there's no missing or hesitation under load.
 
I might be getting somewhere because spraying parts cleaner around the #6 injector causes the idle speed to smooth out and noticeably increase.

What could this indicate?
 
What could this indicate?
Not sure what it could indicate. Where exactly "spraying parts cleaner around the #6 injector" does that mean. Top of injector, seam where the two injector halves screw together, injector hole boss on the head, sprayed where? Those injectors pop at over 2000 PSI, never see vacuum, how would parts cleaner sprayed on them manage to raise idle like with a carburetor vacuum leak?

Maybe a better test would be to loosen each injection-line-to-injector one by one and see which one has little effect on idle? Try to avoid getting fuel on the coolant hoses below.

If you think it's an injector problem, get a set of new heat shields and move the injectors around, see if the problem follows a specific injector.
 
I'm going to pull the injector out and investigate, how spraying aerosol cleaner causes the idle to clean up is interesting but I have a feeling that's going to lead me to the cause.
 
^I'd believe that. Those things are just miserable in this regard. Never finish on time, stink of diesel after working on one, easily warp side-side miserable, cracking, counterflow things. 1/8" (.125"!!!) cracks between the valve seats allowed in the green book. What a miserable design POS.

On the bright side, if the head isn't warped, a metal HG and studs will probably shut it up with a tropical fan clutch and perfect cooling system with an EGT gauge.

A diesel engine with a timing belt, short lived water pump, that you can't really run at full load without problems :roll: Hitler's revenge...Volkswagen :roll:
 
I'm about to do a compression test and see what I find.

We'll stand by. I wasn't a fan of the longevity of the 4 cylinder version in the Rabbit, and I'm not much of a fan of this version either, from what I've read. Stick a little Toyota:omg: or Isuzu:omg: diesel in there and only go about another 200,000 miles almost trouble free. I know, sacrilege..:oops:;-) Just my opinion, of course.
 
Check the valve clearances.

Blown HG will pressurize the cooling system 99 times out of 100 -- bubble test is your friend there, much easier and more conclusive than compression test.

Faulty injector spray can happen but usually not sudden unless the system ingested some crud.

Any air in the translucent line from the fuel filter head to the IP inlet?
 
I'm used to pulling spark plug wires to check for cylinders not firing, what do I do to find out if there's a bad injector or something else that could be causing it?

Isolating the miss works the same way as a gasser, hold a steady fast idle and crack open fuel line unions one by one, see which one causes largest RPM change. Works even better if it's an automatic and you can do it in gear with someone's foot on the brake. Spraying around injector bodies cannot really provide any information here -- not really possible to cause any change to the way the engine operates since there is no suction anywhere for the stuff to get pulled into, unless it's got a wacky injector with a needle that's hanging up in the nozzle, and the evaporating carb cleaner cools the injector enough to make it happier.

Do you notice the issue hot, cold, or both?
 
The issue is pretty much constant.

Fortunately it's not an engine mechanical fault, not the HG either. Compression checks out okay, as follows..

1- 410 psi
2- 460
3- 440
4- 450
5- 460
6- 450
 
In my experience with these diesel, the injectors get neglected no one replaces the nozzles or checks the spray patterns. The valve clearance need to be check every 10k miles
 
How can I service the injectors without any special tools? I don't suppose there's a way to check spray pattern without a bench type injector tester?
 
How can I service the injectors without any special tools? I don't suppose there's a way to check spray pattern without a bench type injector tester?

Diconnect the injectors Pull it out have friend start it sqirt into a mason jar and look....

I was gonna say maybe the nozzle is worn

Nkws the time for monarch injector nozzles.
 
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