1984 500 SEL fuel injectors ? - PeachParts Mercedes-Benz Forum

dloveless · #1 06-07-2004, 12:16 PM

Although all new injectors, I've heard of getting defective one(s). Is there a test to determine if injector(s) are good??

History: Had car for 16 months. 130K miles. Did top end rebuild. Been chasing down idle problem (was too high now right rpm but really rough idle and quits eventually).

Did the following: installed rebuilt Fuel Distr, warm up reg, cold start valve, idle control valve, idle control module, air distrib hoses and vac lines and connectors, new throttle switch and coolant and oil temp sensors (and new injectors).

In short, hard to think of cause of rough idle problem.

the printed engine manual diagnosis keeps pointing me to "renew idle control module". I've put a rebuilt in and finally a new one. And checked for continuity from the Idle control module wires this past weekend. All OK.

Thanks in advance for any suggestions.

ctaylor738 · #2 06-07-2004, 01:15 PM

Is it a rough idle like it's missing, or a rough idle like the RPM's are rising and falling?

Is there any stumbling or hesitation when you increase the RPM's as you drive off?

What is the on/off ratio doing at idle and 2000 RPM?

dloveless · #3 06-07-2004, 02:15 PM

engine shakes ... like it is missing... rpms are around 750 warm.

When driven it seems to run better at higher rpms but there is a noticeable hesitation upon acceleration [behavior is like flooding out in a conventional engine- let up and nurse it and it gets better], if accelerate slowly there does not seem to be a problem with hesitation. Stumbling may be a better description than hesitation.

on/off ratio - testing #3 terminal on the diagnostic socket and ground with a Sears DMM with duty cycle gives me 59% plus or minus a half % at 2500 rpm and no change [absolutely no change] going to idle.

Thank you!

ctaylor738 · #4 06-07-2004, 02:39 PM

Hmm ...

I wonder if it is running rich and has fouled the plugs.

If you are getting 59%, your mixture is rich and the lambda system is trying to bring it down.

I would start by checking the cap and rotor, putting in a fresh set of plugs, and adjusting the mixture towards lean in small steps (1/4 turn at a time, ccw) to see if you can get the ratio around 50%.

dloveless · #5 06-07-2004, 03:36 PM

"Test on/off ratio at 2500 rpm and take average reading. Compare this reading with the idle speed, adjust if necessary. The average reading at idle speed must not vary by more than +/- 10 from the reading measured at 2500 rpm."

this is in footnote 2 in section 07.3-105 page 1 of the section.

the way I read this it does not matter if it is at 5 or 40 or 40 or 70 as long as it does not vary by more than 10.

Maybe reading this manual wrong?

thanks again.

other info: new [rebuilt] ignition distributor, new cap, new rotor, new plugs, new wires [Bosch].

Appreciate the info.

ctaylor738 · #6 06-07-2004, 04:21 PM

I think you are reading the manual wrong. Admittedly, I am working off my 380SL's info, but I believe that it is the same system. You should be seeing fluctuation around 50%, and your reading is telling you that your basic mixture is rich. How rich is unclear. IMHE, as you approach 60%, you are nearing the limit of correction. so you may be 'way rich, especially if you have a weak O2 sensor.

You have an impressive list of replaced parts and this was what stood out when I read your post.

You are getting fluctuation, I assume. If it is stuck on 59%, you may be seeing a fault code.

dloveless · #7 06-07-2004, 05:49 PM

either wrong format or too big of file to do the attachment of the page in my manual [it can't be the computer operator can it!?]... [can't attach a pdf file?] but appears the CD engine manual does differentiate between the a 1981/2 engine 116 and a 1983-1985 engine 117.

Let's say the reading is a steady 59% on my duty cycle DMM [not varying] ..... so if it is a fault reading instead of "on/off ratio" what would be my next step?

Thank you!

ctaylor738 · #8 06-08-2004, 12:13 AM

I have the same stuff on my CD.

A constant reading of 53-64% suggests that the oil temp switch is making the brain think that the engine is still cold and is therefore keeping the system in open loop. Try unplugging the oil temp sensor so the brain does not get a ground signal, and see if the ratio starts to move around after the engine warms up.

The full sequence of tests for the emissions system is on the CD in 14-100 under the intake/exhaust manifold section.

dloveless · #9 06-08-2004, 11:01 AM

should have time within a couple of days to run these tests. Looks like it should give me a clue as to problem.

Will try to report back with results.

dloveless · #10 06-11-2004, 10:56 AM

In the 14-100 section in the CD manual... when it states "control unit" is it referring to the ECU in the passenger footwell? Up to now I've been centering on the Idle Control Unit [between the two firewalls] but this section mentions a "terminal 15" in one of the tests and there is no terminal 15 on the ICU. Not very well marked on the ECU either. Just count from the "live" end of the plug in?

Also, when it refers to position 1 or position 2 on the "official" tester dial do those correspond to the socket number on the X11 diagnostic socket?

Thanks again. Sure do appreciate the information.

ctaylor738 · #11 06-11-2004, 11:38 AM

In the 14-100 section in the CD manual... when it states "control unit" is it referring to the ECU in the passenger footwell? YES

Also, when it refers to position 1 or position 2 on the "official" tester dial do those correspond to the socket number on the X11 diagnostic socket? NO. I THINK THE OFFICIAL TESTER IS A BREAKOUT BOX THAT PLUGS INTO THE CABLE TO THE ECU. WHEN THE DIAL IS TURNED TO DIFFERENT POSITIONS, YOU CAN MEASURE CURRENT ON SPECIFIC CIRCUITS.

dloveless · #12 06-11-2004, 08:02 PM

Appreciate it !

dloveless · #13 06-14-2004, 12:55 PM

In the manual there is some discussion on a "sudden pressure valve" [it is located right in front of the radiator overflow tank on the RH [passenger] fenderwell-- it has a 2 prong wire plug in on top and vacuum line out the bottom that goes to the top of the warm up regulator] .... manual says only on 1985 MY but for whatever reason I have one on my 1984.

Unplugged wire and shorted across and idle went to normal. Right now driving it that way until I get a replacement. I also had to plug off the warm up regulator vacuum line with a golf tee to get it to warm up.

Optimism is returning.

ctaylor738 · #14 06-15-2004, 09:30 AM

What controls the valve? Where do the wires go?

dloveless · #15 06-15-2004, 11:29 AM

attached is part of TSB 07.3 001 dated 01-01-85. I know it [the number of the TSB] appears it is part of manual but it was not in my manual. I found this on AllDATA data base under the Technical Service Bulletin list.

this is part of the TSB :
5. Connect the additional wiring harness to the 16~C temperature switch and the main wiring harness (Figure 5). Attach the ground wire to ground (W2 - at the head lamp assembly). Secure the additional wiring harness by tying to the main harness.
19 Temperature switch 16~C (Engine oil) 100 Acceleration
enrichment switch
a To main wiring harness
W2 Ground, right front(at headlamp assembly)
W5 Engine ground

In a quick look at my 500 I believe there are some incorrect vacuum connections also but I have not had time to get into it. I have both a red thermovalve and a white thermovalve- does anyone know which is the 50 degree C and which is the 70?

Appears the valve is controlled by vacuum from the warm up compensator- the vacuum port on the backside of the regualtor. mine was plugged into the top of the WU regulator. Is that just supposed to be plugged- the top -sometimes referred to as the vent?

Thanks. I'll report on results after I "re-arrange" the vacuum lines - maybe not a bad accel enrich switch after all just hooked up incorrectly.

Chuck, let me know if you want any more of the TSB and I'll email it to you.