'88 300SEL stalls when accelerating
 

I'm not sure if I have just one problem, or if it's a combination of problems. The first symptom was the car stalling at idle. I checked the distributor cap and cleaned the rotor and that problem seemed to disappear. The cap and rotor (and plugs and wires) have about 10,000 miles on them. The fuel injectors, seals, and holders are about the same age also.

The next (and current) symptom is the car bucking (missing?) and stalling on acceleration. I changed the fuel filter and fuel pump and the problem is a lot less pronounced, but is still there. The car doesn't buck as much, but it does still stall on acceleration most of the time. I drained and replaced the gas also. I thought maybe I had some bad gas.

I tried to attach my fuel pressure gauge, but I don't seem to have enough clearance at the lower chamber plug. The smaller fuel line from the distributer to the fuel pressure regulator is in the way.

I don't know if this makes any difference, but when I had the air cleaner off and tried to start the car, white smoke was coming out of the breather hose that connects the valve cover to the air cleaner. Not a lot, just a little.

I pulled all of the plugs and none of them were fouled. They also didn't look tan like the old set of plugs. They weren't wet either. They seemed to be a cross between tan and black. They are Bosch H9DC0. I'm thinking about replacing the plugs, but I don't think that is the cause of the problem.

At this point, I'm somewhat at a loss. I can't seem to connect the fuel pressure gauge to help diagnose and I'm not sure what else to do. Any ideas?

Thanks

The first thing to do is to verify that you have closed loop control. From this you will also know your basic mixture and be able to see if fuel control is continuous.

OK, I made a harness for the EHA and decided to try it out on my 560SL first, to see what good readings would look like. I don't know which pin is neutral and which is hot, but I put red on pin 2 and black on pin 1.

I'm using the Sears 82139 digital multimeter (with duty cycle). I've got it on the mA setting and I'm reading 0 mA at all times, from startup through about a 5 mile drive. If I switch it over to VDC, I get constant change in the voltage, but I can't seem to get a current reading. The 560SL is not hard to start. It needs new engine mounts and has a noisy lifter when cold, but is otherwise running fine.

Why would I not get a current reading?

It is my best guess that you don't have your meter set up properly. Most meters don't read amps and volts with the wires plugged to the same holes.

As far as current goes polarity matters for point of view but not quantity. You should get 20ma with the key on and engine off. Also, to measure current the meter must be in series with the circuit. Voltage readings are read parallel to the circuit. This means that to read EHA current you must remove the two pin connection. The ammeter will then be connected from one terminal of the harness to one terminal of the EHA. The other terminal then must be jumpered from the EHA to the other harness pin. In this configuration current flows through one leg of the harness through the instrument, through the EHA, through the jumper into the orginal harness and back to the controller.

Thanks, I didn't have it in series. I'll correct that right now.

OK, I'm now in series with pin #1 on the EHA. Key on, engine off, I'm getting 1.12 mA. Driving around, I consistently get from 0.64 mA to 0.72 mA when at idle or giving throttle. When I release throttle, I get ~ -1.50 mA until I return to idle again. At 2000 rpm, I'm getting 0.71 or 0.72 mA.

Does this look reasonable? Is there a problem with the difference at Key on Engine off?

This is all on the 560SL, which appears to be running fine.

Your values are way to small. The point to the key on engine off numbers is to calibrate or correct your testing to a standard. Almost all KE cars are 20ma KOEO. There are exceptions but they are 10ma and maybe 50ma but no 1.12ma. Do you have the right scale setting.

Another way to try your tool is to measure the idle air valve. It will have between 600 and 900ma. Much higher, but another point of reference.

Another way to check it is to go under the carpet on the passengers side and disconnect the O2 sensor (large green wire). Jump the part that goes to the computer to ground. This will drive the current idling to 12-15ma. This will make a difference in the way it runs. View it with your meter disconnected first! Then disconnect the EHA while running. It should make a difference. Now do the same thing with your ammeter in the circuit. Like I said you should see 12-15ma. After the car has finished richening out disconnect the circuit again. Does it again make a difference. The point of this is to determine if the meter is carrying the circuit or not. Most meters have a fuse inside and they blow quite regularly causing useless readings.

plugs
 

I dont necessarily think it is your only problem but the plugs you have in there are the large electrode model (0 on the end, 9dc0). I dont know your car but for mine (84 380sl) a w9dc0 spark plug caused a number of problems with the car, mainly a jolting hard miss at idle. I pulled them out and put w9dc in there (versus w9dc0) and the problem instantly went away. To verify I put them back in and problem came back. Even used multiple different sets of the. It was a real problem. For cleaning your fuel system, I highly recommend Chevron Techron, the big bottle. Put it in there on an empty tank, fill up, drive hard. For what it is worth (probably not much) my first reaction to your problem was bad fuel distributor (I think your car has one like mine). A rebuilt distributor for a 380sl not rebuilt by bosch (they are expensive) is $500, mine works great. It is a relatively easy thing to change on my car. Be sure to replace all rubber<gaskets with new ones and lubricate them. There seems to be either a fuel pressure drop in your system at acceleration or a bad vacuum leak. Also you can check your air flow sensor (I think your car has that?) to make sure it is moving freely and smoothly. Again if not, fuel distributor.

I have three amp settings on my multimeter. A, mA and (mu)A where mu is the Greek letter. The last two seem to differ by a factor of 10, where 1 mA is 10 (mu)A. So 1.12 mA would be 11.2 (mu)A. But that would move all the other measurements up by a factor of 10 also.

Anyway, I must be doing something wrong because I hooked up to the 300SEL and KOEO measurement was 0.76 mA.

ericgr, the plugs I have are the recommended plugs for my engine. at least according to the EPC. And the 300SEL saw a lot of Techron before I replaced the fuel injectors a year and a half ago.

This is my multimeter. The current setting are at 3 o'clock (in red). I'm using the middle one.

http://content.sears.com/data/produc...139000-dlv.jpg

recommended versus original, bosch versus mb and my experience
 

I do not know what epc stands for, if it stands for electronic parts catalog then I believe you are putting your faith potentially in a system with errors as I found (read on). It is what your original manual recommended that matters. Also I assume you have the correct Bosch/MB wires so that resistance is correct. By the way, I did not read all of the previous posts but make sure your multimeter is high impedance or you may damage something, I use a fluke 88 with 10 Megaohm impedance.

I did a post focused on this plug issuea few months ago. Mercedes, in their parts system, also recommended w9dc0. However that is NOT the original part for the car nor the plug the car previously used. I called Bosch and they agreed with me and did not recommend the plug for the car. I called MB America and they were arrogant and would not address Bosch's or my comments. To this day, MBs parts system still says w9dc0 despite the fact that Bosch does not recommend it and it is not the original plug for the car. Several mechanics I spoke with also,agreed with me. Since my posts here and on another group I have received mixed responses-- it solved some peoples problems and did nothing for others. Some engines are probably more sensitive to this style of plug which I believe is colder.

Funny that your name is Heath and you have a multimeter.

(Heathkit for all us old guys)