M103 fuel injector change
 

Happy thanksgiving all!

Being that the old workhorse has 212,000 miles under her belt:D and I'm pretty sure the injectors leak a little after shutoff, Im going to give it a new set. Looks pretty easy, just unscrew the fuel lines and the holders, pull em out and re-install with all new o-rings. Anything I should know before I proceed, or is this one of those jobs that looks way easier than it actually is? Any thoughts would be greatly appreciated!!

Thanks!

i did mine last summer and it was that easy!

Don't forget the white plastic seats as well as the 'O" rings.

In my country a set of injectors costs less than a proper Beru set of ignition leads.

It would be nice to take your injectors to a Bosch specialist to have them pressure tested. M103 injectors have been known to be faulty out of the box.

It is very possible to get a bad injector new in the box. I always pressure test new ones before I install them. In addition to bad injectors it's possible that new ones will be stuck closed with what ever they are assembled / tested with. I've seen new injectors where the initial crack pressure was over 100 psi. Typically once they crack open they clean out and work properly but every once in a while I will reject one.

A couple but not all of the fuel lines need to be removed or at least loosened at the fuel distributor to provide clearance. Be sure to have proper "line" wrench.

Why don't you test what you have before you buy new?

Remove the fuel distributor from the base with the injectors still connected but removed from the intake. Put a plastic bottle over each injector and you can then test static for drips, idle flow and anywhere between idle and WOT by pushing the plunger. You can check patterns then as well.

When done, weigh the bottles and see if you have matched flow.

EDIT:

I should note that mine has the same mileage as yours. I ordered four injectors from my vendor (only had four) after I checked mine and didn't like the difference in flow volume on my test stand. After I did the bottle flow test and adjusted the distributor a bit they all matched. Since the patterns were okay (same as a new one), I returned the four new injectors.

A few years ago I installed new injectors on another CIS car because I thought it made sense and it ran horribly. It sat until I learned enough about how to calibrate for the new / different flow rates.

If you pull the old ones at least number them for possible future use / reference.

How does this test whether the injector leaks or not when motor is off?

OK you've got my attention. I did a search and could find any answers to questions that came up after reading your reply.

Like mine, 150K+ on original injectors on my 1990 300E (my 1992 300E got new injectors with its new rebuilt head and head gasket). I'm thinking that since my son drives it, I should just go ahead and change the injectors with new ones to eliminate one more reason for Dad to get a call about a car broken down at the side of the road. I've also already gone ahead and replaced the EHA valve and O rings for that very reason. We also only use Chevron 91 in our cars.

1. How do you test new injectors?
2. Please give more detail on how this is done outside the car.
3. What do you mean by a "static" test?
4. Why continue to use injectors that are over 150K miles old?

thanks,

Al

Kent and Al,

Fuel pressure at the top port of the fuel distributor when the engine is turned off is just over 40 psi on my ’92 300E (CIS-E). It’s about 80 psi when running, so what I call a “static” test is an engine off, but fuel system still pressurized at “hold pressure.” (I’m sure it’s call something else, but “hold” comes to mind as I write.) When I did my flow testing/tuning I obviously cut power to the fuel pumps between runs . The injectors stopped flowing, I assume since 40 psi was below their threshold, and they did not leak…not even a drop.

I don’t know how much this means to any of you, but in the process of trying to get my car to run really well (idle has been really rich), I have noticed that fuel puddles at the bottom of the intake manifold, right under the butterfly. IF your injectors did leak, they would only leak until the pressure went to zero, which really is not much fuel. I know this because I have had to use my fuel pressure gauge to bleed the system down to 0 so many times. It’s about half an ounce each time.

1. How do you test new injectors?

I put them on my ASNU bench, cranked the pressure up until the injectors opened (noted that pressure) and then kept cranking the pressure up to watch the patterns. I then ran a flow test at 60 psi on all the injectors (I had no idea what the normal pressure was going to be, still had not installed the tank or new pumps) to see how they compared.

2. Please give more detail on how this is done outside the car.

After #1 above, I tested the entire system on the car. You could do it off the car but that seems harder to me.

3. What do you mean by a "static" test?

See above.

4. Why continue to use injectors that are over 150K miles old?

Because in my case they flowed in the same range as the new ones, both pattern and volume, and they did not leak at 40 psi. Off the top of my head they cracked open at about 50 psi.

I do a bunch of electronic injectors. They have tiny pintles that use their shape to generate a spray pattern. Those pintles wear out and those injectors will blow streams at some point. These injectors seem to have a plate that vibrates to cause the pattern. If they ever leak, my guess is that some good fuel additive/cleaner will bring them back to life since the screen should keep particles out.

Now if the injectors just don’t flow because they are clogged up that is a different story. Do the on car test and see.

Injector Testing
 

KJZ,

Thanks for the reply. I'm just a little foggy on the details you gave.

For the test while the existing injectors are still in place:

1. You first got a pressure reading from a port on the top of the fuel distributor while the engine was off- correct? Was this for each injector?

2. Then you got a pressure reading when the ingition was turned to power the fuel pump or while the engine was running? Again for each injector?

3. For those of us who don't have an ASNU (?) test bench, is there a way for the injectors to still be tested for volume flow?

A pic would be nice of your testing set up.

thanx,

Al