A little fuel injector advice please?

[Blu 420Sel]

Had a wonderful weekend tuning (idler arm kit, voltage reg, assorted filters, etc) and getting ready to plan next weekend's fun. Fuel injectors.....

'Big Blu' is a 1988 420sel with 167k pampered miles. The car runs idles so perfectly you have to focus to tell its running but sometimes it takes several seconds to roar to life. Lately I've also noticed a little whiff of gas occassionally on start up. The weather has just started getting nice so I'm not sure if its been there a long time and I just idn't notice because I had the windows rolled up or if it's a new thing.

So this weekend I started poking around. I checked the infamous EHA and it looks fine but I noticed a bit of moisture (gas) around one of the fuel injector seats. Then I thought that might also explain my slightly slow start if it was sucking a little air in there too. Either way, it deserves quick attention so I don't risk a fire under the hood.

Anyway, I'm too much of a cheapskate to replace them :p and it doesn't seem neccesary since my performance is otherwise fine. Obviously, I do plan to clean them since I'll be in there to reseal and remount them.

I haven't pulled one off a MB before, and I would love any advice folks have to offer. Is it too dangerous to drive it in this condition? Are there any tricky problems to avoid? Special tools? What cleaners would folks recommend? and is there anything else I should do/check while I'm there?

Thanks!

[mhingram]

blu,
This is a very easy and satisfying job. Takes about 1.5 hrs. Plan on replacing the rubber breathers to the injectors I would also replace the main breathers that feed them too. The rubber at your cars age will be brittle. I would also recommend having something to blow out the area, compressed air works very well. Also buy the plastic injector holders they come with green seals. I would also buy new injector seals too, with out the injectors probably about $4 an injector for both parts. I also replaced my injectors but need to as two where questionable.
Have fun!
m
p.s. No special tools although using a pipe wrench makes it easier than standard wrenches.

[Blu 420Sel]

M,

thanks for the post, that's exactly what I was hoping to hear. Makes sense to do the breathers too, I'm going to place an order for everything tomorrow. I love cheap repairs with noticable results!

BTW: any tips on cleaning the injectors themselves? is there anyway to test/inspect them when removed?

thanks again!

Tim

[ctaylor738]

You can use spray carb cleaner with one of those plastic tubes to force cleaner through the injector and/or soak them in it.

You can have the spray pattern tested. I was quoted $75 for a set of eight. With 167K on the clock, and since you have them out, you might consider replacing them since it will have to be done eventually.

[Blu 420Sel]

I have considered replacing them. The thing is I inherited the car and although I don't have much in the way of records I do know it had an upper engine rebuild within the last two years or so. I think they should've been replaced at that time. It seems like the silky smooth idle also supports this but I just don't know for sure.

So I suspect that my leaky injector is the result of a bad/incorrectly installed o-ring and not really age related. I'm curious to see the condition of the plastic/rubber pieces because I think it might give me some hints about their overall age. Actually, I just took a peek at the breathers and all the topside rubber looks virtually new (some pieces still have tags).

If they are only two years old it should be pretty obvious just by looking right?

[mhingram]

No tips on cleaning them, some bosch shops will test them for you but, if you have a smooth idle I would not mess with getting them tested. If the rubber is pliable I would not replace it.

m

[Blu 420Sel]

Martin,

That makes sense, I think I'll stick with the simplest plan for now. I doesn't seem like it'll be tough to get back in there if its necessary. Thanks for the advice!

Tim

[emmydotnet]

does anyone have a picture of the fuel injectors, holders, breathers on a 91 560 SEL to show where they are all located at?

thx

[Blu 420Sel]

They are pretty clearly illustrated in the maintainence CD's, which are a must have if you don't already. Baring that, I could probably take a few shots when I do the job. It should be this weekend weather permitting. Basically take off your air filter housing and you can't miss them.

[mbtjc]

Chuck, where did you get a quote of $75 for 8? Everywhere I have looked has them for around $30 each. That is the only reason I have not replaced mine....cost. Close to $300 with everything. Also, didn't they use steel injectors certain years? Isn't another reason to replace them is to change to brass?

From researching posts...it looks like before changing injectors it would be wise to get all the crap out of the fuel system that is making them dirty in the first place. I've read about rusty fuel lines. Would it be smart to have the gas tank flushed (I'm sure there's lots of crap in there) and replace the fuel lines before changing injectors?

Also, would it be possible to install a small inline fuel filter closer to the engine to prevent crap that the main filter missed (or it originated after the filter like the rusty fuel lines) from getting in your system?

[Blu 420Sel]

MBTJC,

I think $75 was for testing only but maybe I misunderstood, either way Fastlane has them for $25 each. Its interesting that you mention the brass/steel swap. I noticed that mine were brass while I was poking around which would imply they've been changed.

I am curious to hear responses about the in-line filter. I had planned to replace the main filter this weekend as part of the job. I considered doing an in-line filter as well but decided not to for fear of messing with the fuel pressure/flow.

[maheath]

Remove the air cleaner and they'll all be exposed. Four injectors, holders and seals per side. Each side will also have a straight black rubber tube along the valve cover that has outlets going into each cylinder. That's the breather hose.

[mbtjc]

That makes sense...I guess I didn't catch that! As far as the brass/steel...I think they used them after a certain year. I'm not sure, late 80s somewhere, so yours might have had them stock. I really don't know though.

With that inline filter...really good ones don't really seem to mess with fuel flow. My dad put a little one on his Harley and with the line disconnected, it just poured right out of the filter. Didn't dribble or anything. So I wouldn't be afraid to put on on...I'm just not sure where yet.

[Blu 420Sel]

Let me know what you find out, seems like a no brainer.

[ctaylor738]

The $75 was for the testing only. That is why I thought it made sense to spring for the extra $125 and replace them. Herr Fuchs told me that he has had injectors that spray tested OK and still did not idle well.