Injectors: Replace Nozzels or The Whole Thing?
 

I have a 1991 350 SDL (original owner) with 148K miles. It's been a wonderful car.

Have a rough idle issue now. One shop wants to start with new calibrated injectors another wants to replace the nozzels and recalibrate the original injectors. The shop that wants to replace the nozzels says the new injectors are assembled in Mexico and are not very good.

I could use some input on what others have experienced with this issue.

Thank you.

Unless you have complete faith in either of the shops, try replacing the delivery valve seals and see if that does it.

Sixto
91 300SE
87 300SDL
83 300SD

sixto,

Would you replace both the copper an O ring seals? While in there and would it be a good idea to replace the pressure valves as it runs really rough when starting fresh each morning, maybe nothing to lose?

Thank you

Also, one of the shops told me the nozzels wear out by 90K miles?

" Do the nozzels wear out in 90k miles?"
 

The above refers to the general thought that injectors should be checked about every 100k miles.This is true for commercial trucks, also. The injectors need to be "pop" tested and the spray pattern observed. This is a very simple and fast procedure, but you need the specialized equipment. Thus, I would pull the injectors and take them to any "fuel injection pump shop" (or "fuel injection service") that you can find in the phone book.Try not to take them to a car or truck dealer because they will be more expensive. A small fuel injection pump shop should be a lot cheaper: maybe $10 per injector to check. They can also try to clean any slightly clogged injectors. If you need parts, go for the whole injector because the nozzel only isn't that much cheaper. This web site has great prices on injectors - in the low $40's I believe. Good luck. :)

ALSO -
 

If you do take out the injectors, do not let the nozzels touch anything. It is easy to damage the nozzels. I wrap each injector in thin foam to protect the nozzels, put them in a box, and take them to the shop.

I am with Paul on this.. I would find a good injector shop that does just injectors , pumps and Turbos.. Talk to them and get a date and time.. Pull the injectors.. They can test them on the bench.. Tell you if there is a problem with any of them.. What pressure they open.. If the spray is right or just a dripple.. and if they leak... and run Cleaner thru them.. If needed they can rebuild one or two to open at the same pressures as the others... If most are bad.. Let them rebuild them.. or sell you rebuilt ones that all open at the same pressures... Taking it to a shop and letting them change them just in case one may be bad is a waste of money.. Unless you just have money to spend.. And if one of the ones they put in is not right you will still have the miss and look at spending more money perhaps for nothing..

Ken

ezrider,

I don't think bad delivery valves will act one way when cold and another way when hot.

I replaced the o-rings and copper rings. Made a big difference in smoothness and got rid of intermittent nailing before I replaced the head.

Note the way the delivery valve carrier is installed. I think the picture in the manual has the groove down. When I got my car, some carriers had the groove up.

What I did was torque to 30Nm, torque to 30Nm again, torque to 35Nm, torque to 35Nm again. I rechecked when I had the intake manifold off and they didn't budge when the torque wrench clicked at 35Nm... with the retainers off, of course.

Sixto
91 300SE
87 300SDL
83 300SD

Ken is right on with the details. And, if the shop doesn't have the info about what pressure the injectors should "pop" (open), you may have to call MB to get this info for them. They would need this info if they are to rebuild any of them. :)

First,

150k, while not bad... does not kill injectors alone. Fuel quality and regular filtler changes help!!

Have you tried a double dose of pure "diesel purge" yet? It might be the place to start.

I *thought* bosch/mb replacement were all rebuilds, and hence it really doesn't matter where it's assembled. Quality control matters. There are many aftermarket injector manufactures and rebuilders.

I agree a competent rebuilder is better than someone that suggests replacing parts. OM60X engines do sometimes need valveseals.

Rough idle can be overtightened injector lines. Make sure you do the MB crazy proceedure=)

Michael

It's almost always bad fuel quality and especially the presence of water that "kills" injectors. Water actually screws up the spray pattern by wearing the metal in the nozzel openings. That's why the "100,000 mile fuel injector check" is only estimate of when to pull the injectors. Many truck fleets just do this at about 100,000 miles as regular maintenance, while other truck owners wait till they start to see more smoke than usual. The test is so simple, there's no reason not to get it done. It's cheap insurance. :)

Michael,

Please explain overtightened injector lines and where can I find the procedure? I do have the W126 maintenance CD but didn't see the injector line tightening procedure.

Thank you.

I do not have the proceedure handy..

You torque them 3 times with new sealing washers. The latter model pumps will warp if you over tighten them. Not like a OM617- all the OM60X engines should be the same. I think it's 20NM with waiting ?? 15+ minutes between torquing.


Michael

Are we talking about overtightened injector lines or overtightened delivery valve covers? The delivery valve covers have a splined lock. You'd really have to bear on the injection lines to get the delivery valve covers to move against the splined locks.

Sixto
91 300SE
87 300SDL
83 300SD

Can someone here post the correct torque, retourque procedure and torque value for the pressure valve seals? My W126 CD says simply to torque at 35Nm.

sixto, did you find your above torque procedure in a manual, what you describe makes sense.

Thank you.