I just replaced the injector nozzles on one of my '87 300SDL 's with new monarch nozzles. The engine now seems to be running hotter and a perceived slight loss in power. The engine does however run much more smoothly though. I rebuilt the injector halves to specification, pop tested and balanced them all to 2050 +/- psi.

My question is what would happen if I lowered the pop pressure closer to the lower tolerance of 1958 psi? (1958 - 2103 psi for new nozzles)

Does a higher pop pressure create a lean condition while a lower pop pressure creates a richer condition?

I'm thinking the engine is running too lean is why it's running hotter and seems to lack performance.


Note: *The old Bosh nozzles all varied between 1500 and 1800 psi.*

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1987 300SDL

A higher pressure will tend to retard the timing as the IP has to turn further to reach the higher pop pressure. How much, and whether this is enough to affect the engine running is up for discussion.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

All Diesels have more Air then is need compared to the Fuel so in that sense they are always lean.

As an example if your Engine had no Turbo Charger the amount of Air compressed in the Cylinders is always the same weather at Idle Fuel Amounts or Full Fuel amounts.

In the Turboed Engine once the Boost pressure goes up the ALDA allows more Fuel and that is OK because there is more Air.

However, in order for things to burn they need to be turned into a Vapor. Unlike Gasoline Diesel does not vaporize easily and takes more heat to do that and even the Heat is not enough.

So the Injector attempts to atomize the Fuel to make it easier to burn. But, even that does not allow all of the Fuel to burn.
(To see how the Fuel Burns internet search for Diesel Knock.)

The Fuel Injection Pump controls how much Fuel gets Injected as well as your Foot on the Pedal. However, if the Fuel is burning better now due to rebuilt nozzles you might need a little less pedal to stay at the same speed due to the better atomized Fuel Buring Better.

Fuel Burning better could result in higher heat. As long as your Engine Heat is within normal ranges I doubt if you have a problem.

Of course if your Timing is retarded/late that effects the Fuel Burning. Late Timing on a Gasoline Engine can cause abnormal heat but I am not so sure on Diesels it is the same. Diesel Engines and Trucks are ususally kept it a decent state of "Tune" and Drivers are quick too notice any loss of Power or increase in Fuel consumption. So I have never seen any results of late timming. And, I have never gotten the chance to be inside the Vehicle to see.

So, it is a good idea to get the Fuel Injection Pump re-timed.

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84 300D, 82 Volvo 244Gl Diesel

I agree with the last poster the timing should be checked. If it is good then the cooling system of the engine was good enough to function with the poor old injectors but perhaps inadequate with the normally flowing ones.

Do you notice a performance boost since installing them? This will generate more heat. As long as when sitting at idle the temperature remains as it always has been.

If this is not the same then pulling the injectors and double checking the pop or opening pressure might be a consideration.. They might have been set wrong because of equipment problems perhaps. Got to check the timing before anything though.

has anyone ever messed with pop pressures going to the lower side of spec or even slightly below like 1800 to try and gain power??

What exactly is "Nailing" and how does it happen? How do you stop it?

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI

My theory is your timing chain has worn and is retarding your IP timing a few degrees. The old injectors compensated for that by the reduced pop pressure. Now that you have new injectors and retarded timing, it exacerbates the problem. Check your timing.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

ok so my best bet would be to adjust them all up to the 1960-2000psi range and change my injection pump timing as needed? o and new nozzles while I have them out on the bench.

Right. Running a lower pop pressure is not the way to get the result of advancing your timing. Adjust the IP if you want to change the timing. Pop test your injectors first. If they pass the test, there is no good reason to disassemble them.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

mine are all low 1750 1800 1850 1900 and another 1850

I have read about #315 nozzles. They sound like what I need for my future plans,

is there another part number for them?

I cant find any place to get them...

How are the spray patterns? Do any of them leak?

I have only used Monark nozzles.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

patterns look good and no leaks I thought about just re-shimming them but there is 160K on them so I figure why not replace/upgrade them

were do you get the monarks?

Monark nozzles are made in Germany. I highly recommend them. Both of my vehicles and several members on this forum have rebuilt injectors from me using Monark nozzles. The "mercedes" "source" can't be linked to on this site but if you get what I am saying, you can google it. If you don't get it, I can PM you.

After 160K, it is not a bad idea to replace the nozzles in your injectors. Watch my video series and you should be able to rebuild a set of injectors like a pro. Keep in mind that shims may be needed. Don't get creative or jack around with these things; they are very precise and you will want to keep your warranty valid. Watch the videos in my sig and PM me with any questions. Do ONE injector and test it 3 times before you go on to the rest. You don't want to bork 5 injectors when you can get your bearings on one, first.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

thanks for the help I just ordered my monark nozzles and shims

Is that the "reason?"

Trustworthy or not, they seem to have the Monark market all to themselves.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.