I need your mechanical expertize. - Page 2 - PeachParts Mercedes-Benz Forum

#16 05-08-2002, 07:19 PM

Well, the new injectors (including the cold start injector), did not improve cold starting a bit, and low idle is still there.
I had the engine on the scope at MB dealer. Paid $550.00 of diagnostic time at the dealer for nothing.
I have the fuel accumulator and fuel line check valve on order ( to be installed Friday.) The check valve has been replaced a few weeks ago but maybe, just maybe, it could also be deffective.
Why did Mercedes built such a complex fuel management system?
I had some fuel management problems with my old Vette last year. I ordered a new Edlebrock Q-Jet carburator for less than $200.00, used a 1/2in. wrench and the problem was solved in an hour. I guess the german do not beleive in the KISS system....
Thanks for your help. I'll report on the results
JackD

Gilly · #17 05-08-2002, 11:27 PM

It's a Bosch system. Many European manufacturers used this system.
MB started using fuel injection in a car well before anyone else did, even while they were still offering cars with carburetors.
The injection system has lots more to offer in terms of mixture control and fuel distribution.
To solve the mixture control issues, and therefore emissions, the carburetor was becoming just too complex. The only thing they could figure out how to adjust mixture to was an O2 sensor, and even then those feedback carbs were a real nightmare. With OBD2 emission laws, you have to be able to shut off fuel to a cylinder with misfires, you can't (hardly) do that with a carb. You can't with this CIS injection system either, but at least it was a step in the right direction. I have wondered why they couldn't use the CIS injection system with a shut-off valve at each injector.
Even if the mixture issue could be fixed, you still have the distribution concern. You can control the mixture to each cylinder better with port injection like this, where each cylinder receives a dedicated amount of fuel, rather than a carb where all the fuel is mixed at a central location, then allowed to go where ever it wants. The closer cylinders receive a greater amount than the cylinders farther away, so then you have to make the mixture richer so the far away cylinders don't run too lean and misfire, which of course means the closer cylinders are running too rich.
Gilly

haasman · #18 05-09-2002, 01:46 AM

Jack

I just wanted to acknowledge your perseverance though all of this. There are a lot of us who REALLY want to know why your car is doing this AND what cures it.

Thanks for keeping the faith and for keeping us informed.

Hang in there.

#19 05-09-2002, 09:43 PM

Progress report on my low idle speed and hard cold starting.
I spent most of the day at the shop trying to find the cause of the problems.
Fuel pressure and leak down test show no problem.
new fuel pump relay installed, Not positive result.
New idle control valve replaced: No positive result.
New OVP installed: No positive result. Battery checked at 14.3 volts, fully charged. Alternator OK
Checked spark plugs (new 1000mi. ago) All clean and gap on spec. Compression test: low 155, high 167. No problem there.
Cap and rotor (new 1000mi ago) Still in new condition.
Check ignition wires resistance: None.
New coil installed: No positive result.
Checked all vacuum lines, replaced two suspect lines (the one going to the transmission modulator and the one going to the air filter box. No positive result.
next: A new fuel accumulator, check valve and fuel filter will be replaced tomorrow.
So far, I have spent well over $2,000. on this problem with NIL result. But I don't give up (yet). I'm gonna find it and let you know.
JackD

haasman · #20 05-09-2002, 11:34 PM

Go Jack Go!

Gilly · #21 05-09-2002, 11:51 PM

On the starting problem, has anyone made sure the cold-start injector is actually working? I know you replaced it, maybe no signal to it? I believe you replaced the temp sensor already, that's what controls how long the cold start injector runs, but maybe a wiring or ECM problem is preventing it from working. What they can do is remove the cold start injector, then reconnect the fuel line and electrical connector. Then, using a resistance substitution box simulate a cold engine, MB has a spec for what resistance simulates what temp, and at that particular temp, how long the cold start valve should operate (usually I think it's only in the 1 to 5 second range, so you shouldn't get too much gas sprayed out, in case you're worried about fuel all over the engine.
On the idle, there is a test for the idle control system that they should be doing, it is very cut and dried, shouldn't need to continue throwing parts at the problem. I know it's easy for me to "talk" sitting here in front of my computer, but geez I hate to see parts constantly thrown at a problem like this. Too many part replacers in this world now, not enough mechanics.
If I remember the test correctly, it should be either the valve (which has been done), the ECM (I don't believe this has a seperate idle controller module,it's the CIS control module), or the wiring, but there is an actual idle control test that can and should be done.
Why replace the accumulator, check valve and filter if it passed the pressure and leakdown test? Did they do the volume test too? Good pressure does not automatically indicate good volume! That's like saying that because your battery has 13 volts that it HAS to be able to start your engine. Not true! Sorry if you don't understand the comparison.
Let us know how it's going. I've recently been diagnosed as being "abrasive", so sorry if I seem a little abrasive. I'd really like your your car to operate to your satisfaction as well.
Gilly
ps Go Jack Go!

euro 287 · #22 05-09-2002, 11:54 PM

I have read all the replies on the post. We have had many ( hard start) problem cars that everyone has gave up on and we get stuck with them. One of the main things that comes to mind on this is how the fuel distributor is set up. Whenever replacing or doing repairs on the fuel distributor you are supposed to set it up , ( setting plunger) It covers it in the bosch cd's and microfiche. I have had many that were not set up correctly (even my own car when I first bought it ) . It will make a differance in how the car starts and also how it runs. This is just a suggestion to what looks like a ongoing problem. If you would like I could fax the procedure. Let me know.

#23 05-10-2002, 10:32 PM

The miracle has happened.
Today, my stubborn independant mechanic said: ''Let,s get our of here when the problem is fixed. Not a minute before that'' It was 8:00AM.
First: Let's try a new fuel accumulator: No result.
Let's try a new fuel pressure regulator: No result.
Let's try a new start injector. with a new temp. sensor. No result.
let's check this, and that, and maybe this. Let's do this test, and that one. No time for lunch. It's 1:00o'clock and the d*** thing is still not operating properly.
And finally::::::::::::::::::
Jiglling with the wiring harness with the ignition switch on, we heard the sound of sparks.
Open-up the wiring harness and voila:;;;; 3 contacts were very loose at a connector, making intermittent bad/no contact., leading to the temp. sensor.
A good clean-up of the contacts, little soldering, heavy tape wrapping over the new tight connections and the baby fired right up by only showing it the key.
We let it cool down a few hours (over a beer or two), and fired the baby again. The engine fired without turning more than 1/10 revolution. Shut it down, start a again. and again, and again.....
It now starts like a Honda does.
And the low idle problem is solved.
Gillybenztech: I like your abrasiveness. Keep it up.
Thanks you all for your help and recommendations
Like GillybenzTech said: parts replacers will never replace a good mechanic.
I left the shop at 7:00PM (11 hours work), and was only charged for 6 hours labour. All new parts (Non-necessary)were removed from the car and the old non-defective ones put back.
I think I'll wake up at 3:00 in the morning just to try it again.
JackD

suginami · #24 05-10-2002, 10:46 PM

Excellent result!

It just shows what can happen when you have a good technician who is very tenacious.

We're too hard on technicians a lot because we expect them to be miracle workers and get things right on the first try.

It sounds like he had a methodical approach, finally found the problem, and was more than fair in charging you for labor.

haasman · #25 05-11-2002, 01:08 AM

Jack

YES! I am so glad you not only found the problem but that you chronicled for us. Wow ... what a nightmare. The wires at the switch! It is indeed sometimes the not very elegant problems that bring about the greatest solutions.

You are very lucky to know a true technician.

Gilly · #26 05-11-2002, 01:29 AM

OK, here's where the abrasiveness comes in.
First, I am glad the car is fixed to your satisfaction, OK?
But here's the rub, and if any of the other techs reading this would like to give they're view, please do.
This is NO way to repair a car. This is called "throwing parts" at a problem. "replaced this:nope, tried putting this on:nope", etc etc ad nauseum. OH! Found a wiring problem, so we took all the parts off. Sheeesh!
The fuel pressure and leakdown was supposedly already tested, so why all the bothering with the accumulator and so forth? Doesn't trust the test? And he even proved that it wasn't related to the problem.
To relate this also to your problem, i outlined the EXACT test that would have led to this diagnosis, with NO extra work involved, and that was where I mentioned: Using resistance substitution box to simulate a cold engine (substitution box plugs in in place of the coolant temp sensor) then remove the cold start injector, turn key on and time how long the cold start injector operates. it will work a specified period of time depending on what temp is simulated. This would have tested bad in this case, and then what? You TEST the temp sensor, and if it tests good, then what? Check the wires between the control module and sensor. Hey! Isn't that what the problem was? THIS is what a mechanic does. PARTS REPLACERS throw parts at a car until it's fixed, which is more or less what this guy was doing until good fortune fell on his left foot and he "wiggled a wire". I think the term there is "dumb luck".
His royal abrasiveness Gilly

suginami · #27 05-11-2002, 01:10 PM

Fwiw, I don't find you abrasive at all.

Really.

I'd say that you are strong in your convictions.

It's what makes you, you.

You could also change your signature to:

Convicted since 1961. lol

And you could sign your posts:

His Royal Convictedness...

#28 05-11-2002, 09:05 PM

Dan, you were right on the money. I also hate ''parts replacers'' but I was to the point of throwing the car in the river. My super-qualified-super-equiped-computer-aided-knowledgeble-expensive Mercedes dealer (where 3 different mechanics looked at the car)spent 8 hours of diagnostic time (without replacing a single part) trying to isolate the problem He ran all the tests on the book (some twice) without finding the cause of the problem. 8 hours of testing (@$90.00 an hour) to tell me ''That's the way those cars were designed''
My independant mechanic also ran the tests, hoping to find one that the dealer misses. All tests demonstrated ''no problem''
Contrary to the Benz dealer, my mechanic did not throw the towel. He kept at it. That's when he started to replace parts in hope of.......
The real problem never showed in any tests. It was most certainly one of those intermitent problem, one of those almost impossible to find except by luck.
I get your point and I fully agree. Parts should be replaced when tested/proven to be defective.
It was one of those cases where it takes what it takes to take the problem away. I'm a little poorer now but much happier with the Benz.
JackD

stevebfl · #29 05-11-2002, 09:20 PM

How about a little more abrasion for the learning exercise. I agree with Dan. Nothing more frustrating than to give a bunch of good advice only to have the shot gun used anyway.

I am not trying to be hard on this problem or tech but this should be a learning moment.

What makes this frustrating is that good technicians almost hate a shotgun fix worse than no fix. It can often leave one not knowing what really was happening.

When dealing with these kind of problems one must find out what is missing or added to the proper equation.. Let me give an example of a current car in my shop at the moment unfixed,

The customer says the cars starts and as it is driven off the thing stumbles and can possibly stall. The first test drive brings nothing so a preliminary scope test for available voltage (coil/rotor problems) and/or other ignition irregularity. No prpblems present. Next closed loop operation was checked at x11 left fender. Pegged at 100%, now here is something. I adjust the mixture to 40-45% and drive again. During one of the early road tests the car had just briefly hesitated and now the car does well and I feel there is a good chance the problem is solved. An hour later the service writer wants to call the customer and I drive it one more time. Out the drive and at the street I almost get run over as the car bogs baddly studders as I head for the parking lane. I try again to enter the street and it dies but instantly restarts. Call the customer and tell them that we now have really experienced the problem but won't get done that afternoon.

I put on a fuel pressure gauge suspecting a pressure drop (possible fuel pump or relay problem) and I drive it a few times. Its back to running perfectly. On the third attempt it starts doing the problem and I am in the parking lot. The fuel pressure is constant at 6.5 bar. Its not fuel pressure drop. The car is continueing to screw up and it clears periodically like a switch is pressed. Further observation shows that trying to rev to motor causes great clouds of black smoke. Well now we are getting somewhere. This IS a mixture problem ....not caused by over fuel pressure.

The point to all my tests are to find the condition that exists so that I then can hypothesize a failure that can cause such; which will then be tested. Since system fuel pressure isn't the problem the gauge is removed. The next thought is that the car could be electronically enriched; either that or the mechanism of electronic control is acting without command.

The fuel gauge goes on the lower chamber pressure and the ammeter goes on the EHA and knowing it has been beaten the problem quits hiding. The next start I see my problem in full glory. After normal start-up enrichment the EHA current drops to 3-4ma and all of a sudden it goes to 67ma and the lower chamber pressure drops a whole bar. Now all of system control is usually done within a tenth of a bar or two. This IS my problem.

Thats where I left it on a busy Friday afternoon. I have a used KE controller that we will probably try but I didn't do that on Friday because I want to look at the start input to the controller to see if there is a reason for it to go to starting enrichment control levels.

The point to all this wasted bandwidth is that I almost never go fishing with parts. I seek what is missing or added and start with the basics. In the car in question, something WAS missing due to the poor connection. Untill the conditioned is labeled all efforts should go to monitoring fuel and ignition. One was missing or both. It would have been found within one or two events. The need for more than one event is that one must start somewhere. In my example we started with the concept of reduced fuel and found just the opposite. We could just as easily been monitoring primary ignition (which is what I assume was lacking due to the poor connection - although it could also have been a lack of electricity to the fuel pump relay). I often drive the car monitoring both fuel pressure and primary ignition. If its a steady problem, I'll do it on my dyno so I can watch the scope and not the road.

Matt565 · #30 05-12-2002, 01:16 AM

Jack,
My 88 260E is doing the same thing that yours was. Could you tell me where that harness is and how to get to it so I can check mine too?

Thanks,
Matt