New Injectors | Trouble Starting at Altitude | Related? - PeachParts Mercedes-Benz Forum

Nestor · #1 12-25-2018, 11:30 PM

Hello: I have a 78 300D to which I just dropped new Monark injectors a couple months back. Huge gain in performance and about 4 more mpg with these things. Very impressive.

But I'm having a couple issues:

+ RUMBLING: The car went from rumbling a little to A LOT at idle. When its moving, it's very smooth...but idling is a shaky business. I increased the throttle/choke a bit and that helped but now my rpms at idle are pretty heavy. Flustered, I took it to my mechanic and he told me there's nothing wrong..the car is just old and the rumble is a natural result of the wider spray from the new injectors.

Question: Would dropping in new motor mounts help with the rumble or should I try some other adjustments to the injectors? I've adjusted the valves but maybe I need to do it again? I've done a big Diesel Purge and changed all filters as well.

I'm NOT very mechanically inclined, but I do what I can with this car within my limited range.

+ STARTING AT ALTITUDE: I've got a cabin at about 2,200 ft. Whenever I'm up there and try to start the car in the morning it takes about three attempts before it "catches" and holds, then takes a long while to warm up. I have none of these issues at sea level (in SF, where I live) -- it starts right up every time. All glow plugs etc are working fine. My previous injectors (very old Bosch's) started up instantly at elevation. No probs at all.

So, wondering if there is some compression issue that's been exacerbated by these new Monark injectors, or if the car is just old and this is just part of life now. It's not the end of the world, but don't want to put more wear on this engine than needed.

Wondering if anyone has any ideas on how to fix these problems, or if they are even fixable. I've had this car for a decade and won't be giving up on it, would just like to find a way to keeping it rolling...

Thank you.

Stretch · #2 12-26-2018, 04:42 AM

If the injectors have not been balanced as a set then you could get an uneven idle.

The heat shields should have been replaced with the injectors - they are a fit only once item.

New engine mounts might help as might the engine shock absorbers

Starting at altitude problem:- Is it cold up there?

cleeves · #3 01-05-2019, 05:59 PM

I also replaced my nozzles ('76 300D) with Monarks and balanced them with the pop test kit from Kent Bergsma. I achieved similar performance gains. It was a substantial difference.

How many miles have you driven it since you replaced the nozzles? My engine sounded like a rock crusher for the first 500 miles. It was so loud I thought it was going to blow up. But then it went away. I believe these nozzles need some time to break in.

If you have already gone 500 miles and still have problems, here is my second thought: How sure are you that they are properly balanced? I believe altitude has a clear impact on the fuel injection system, otherwise the car would not have that knob you use to adjust the pump at different elevations. If they aren't quite balanced, I suspect the altitude perhaps worsens the effect.

My pop test kit came with extra washer shims to adjust the pressure. Some of my injectors required a re-balance, which in my case involved adding shims as the springs had slightly collapsed over time/use. I had them all within +/- 50 psi when I put them back in the car. It seems logical that the engine would idle poorly with imbalanced injectors, because they release the fuel at a time offset based on the pop pressure difference.

Warmth,

-Henry C.

maclaveau · #4 01-12-2019, 07:14 AM

I know on my76 300D there is an knob on top of the IP to adjust for when you are at different altitudes. Yours my have one?

Diseasel300 · #5 01-12-2019, 10:47 AM

Quote:

Originally Posted by Nestor

Hello: I have a 78 300D to which I just dropped new Monark injectors a couple months back. Huge gain in performance and about 4 more mpg with these things. Very impressive.

But I'm having a couple issues:

+ RUMBLING: The car went from rumbling a little to A LOT at idle. When its moving, it's very smooth...but idling is a shaky business. I increased the throttle/choke a bit and that helped but now my rpms at idle are pretty heavy. Flustered, I took it to my mechanic and he told me there's nothing wrong..the car is just old and the rumble is a natural result of the wider spray from the new injectors.

Question: Would dropping in new motor mounts help with the rumble or should I try some other adjustments to the injectors? I've adjusted the valves but maybe I need to do it again? I've done a big Diesel Purge and changed all filters as well.

I'm NOT very mechanically inclined, but I do what I can with this car within my limited range.

+ STARTING AT ALTITUDE: I've got a cabin at about 2,200 ft. Whenever I'm up there and try to start the car in the morning it takes about three attempts before it "catches" and holds, then takes a long while to warm up. I have none of these issues at sea level (in SF, where I live) -- it starts right up every time. All glow plugs etc are working fine. My previous injectors (very old Bosch's) started up instantly at elevation. No probs at all.

So, wondering if there is some compression issue that's been exacerbated by these new Monark injectors, or if the car is just old and this is just part of life now. It's not the end of the world, but don't want to put more wear on this engine than needed.

Wondering if anyone has any ideas on how to fix these problems, or if they are even fixable. I've had this car for a decade and won't be giving up on it, would just like to find a way to keeping it rolling...

Thank you.

How were the nozzles changed? Did you do it, or did you have someone else do it? Were the injector halves lapped and the finished injector assembly pop tested or shimmed? If not, you may have a poor spray pattern or internal leakdown. Both of which can cause excessive noise and hard starting. Be aware that the Monark nozzles have a sharper "knock" than the Bosch nozzles and can lead to more "chatter" at idle which is normal.

I live at an altitude of 2000ft. As far as the car is concerned, that's not much more than sea level. Typically altitude is not considered "high" until you're above 5000 ft.

Growling and noise in the cabin is usually a result of resonance, sympathetic, or synchronous vibrations. If the motor mounts are old, replacing them can definitely help isolate the engine from the rest of the car.