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1997 E420
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68 Posts
Discussion Starter #1
I decided to repost my issue now that I know the issue is electrical. Sorry for those that have all ready read this.

I have been having a problem getting no fuel from the injectors. Used a little test light and confirmed that I am getting no power to the fuel injectors. From a different site it sounds like the IFI controls the fuel injectors. I also heard that a lot of electronics run through the K40. Does anyone know if the power to the fuel injectors passes through it? Also I would like to pull the IFI and inspect it. It sounds like the IFI is a major computer component. Would it cause any problems if I pull it out? Anyone know if I am even headed in the right direction?
 

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1996 210.020
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3,972 Posts
I believe that the K40 module does supply the power to the injection computer.

As long as you are careful to get the connections out without damage and inserted completely, you should have no trouble removing and reinstalling the computer. Of course, disconnect the battery before you disconnect anything and don't reconnect it until everything is in place.

Don't worry about this repost. Sometimes it is the best thing to do, and this is one of those times.
 

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1997 E420
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68 Posts
Discussion Starter #3
All right I am totally lost again. After looking through wiring diagrams and the forums all day. I found all the lines that directly connected to the fuel injectors.

On one side MAF, camshaft hall effect sensor, and the K40

On the other side Engine control module, checked and secured all connections tested wires on the MAF, camshaft, k40 side for shorts. All wiires tested O.K. reassembled.

Now I am getting power to the fuel injectors right at about 5 volts. Is that enough?

Still the car won't start. After researching more on the fuel system, figured I am just not getting enough pressure to open the fuel injectors. Got a new connection to test the fuel pressure. I knew I had some pressure but figured it wasn't enough. At first the pressure went up to about 55 PSI when cranking and when I stopped it woud drop right back down to 0 after about the 3rd or 4th time cranking it would go up to about 40-45 PSI. Still wouldn't start, but now the pressure is maintaining. It has been about 15 minutes and the pressure is holding steady at 40 PSI. Just can't figure where to go from here. Everything I have read says that the fuel injectors should open at 30 PSI. haven't tried it since a member recommended not to. But the car would start with starter fluid. I think I would be fine if I could just get fuel through the damn injectors. In case it makes any difference this is a project car it was sitting for quite a while without running. Thanks to everyone who has helped so far!
 

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1997 E420
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68 Posts
Discussion Starter #5
Yeah I don't get any, but I don't think it will throw codes unless the motor turns over right?
 

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1996 210.020
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3,972 Posts
You can get codes during a starting attempt. Too bad that you didn't.

I'm not sure how much voltage the injectors need. I've never looked into it because I lack such parts in my engine. Hopefully others will see this and recognize something that may help. I'm somewhat surprised that nobody else has chimed in yet.
 

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1997 E420
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68 Posts
Discussion Starter #7
Unfortunately it doesn't show any codes. But I did find the following does anyone know if this would apply? I assume that mercedes injectors would require the same voltage as any others. I am getting about 5 volts. Any ideas?

Injectors
The injector is an electromechanical device, which is fed by a 12 volt supply from either the fuel injection relay or the ECM. The voltage is present only when the engine is cranking or running, because it is controlled by a tachometric relay. The injector is supplied with fuel from a common fuel rail. The injector pulse width dependson the input signals seen by the ECM from its various engine sensors, and varies to compensate for cold engine starting and warm-up periods, the initial wide pulse getting narrower as the engine warms to operating temperature. The pulse width also expands under acceleration and contracts under light load conditions.

The injector has constant voltage supply while the engine is running and the earth path is switched via the ECM. An example of a typical waveform is shown below in Fig 1.3.

image won't display.
 

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1997 E420
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68 Posts
Discussion Starter #8
Can anyone tell me which way this system works? Does the power come from the K40 and is grounded by the ECU to create the pulse. OR does the ECU send the power. Replaced the battery and still only getting about 5-6 volts to the injectors. thinking maybe I have a weak connection in the K40 and its not able to send enough voltage if that is the way that the system works.
 

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2003 Mercedes Benz E500
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668 Posts
A subscription...

to AllData DIY would most like be a good idea at your stage in this problem. I believe the subscription is less than $30/yr.

A guess is the K-40 may be the problem; this is only a "guess" based upon a good number of anecdotal reports of K-40 related problems with early W210 cars, in that this module reportedly causes a good number of faults relating to engine management systems.

The part is not all that expensive, and if you follow the mechanic's mantra of "always replace the least expensive part first," this may be the way to go as a next step.

Good luck,

JR
 

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1997 E420
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Discussion Starter #10
Thanks. That was my thinking also, I am glad to hear that coming from someone with more experience. I actually ordered the K40 from Autohausaz yesterday following your line of thinking. I will post an update tomorrow or the day after when I receive it. I will check out the site above. The more info the better! FYI my post above with the section labeled injectors got part of it cut out. I read this when doing some research on fuel systems in general. I was actually trying to ask if that is the way this fuel system works. Sounds like the system actually sends a constant power signal and then the computer grounds the injectors to create the spray or pulse signal. Sorry newbie still learning how to post. :(
 

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1997 E420
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Discussion Starter #11
:banghead: Received the new K40 today. Absolutely no change to the fuel injector voltage. I am more than happy to get a new ECU if I knew that was what was wrong. Anyone know if MB can or will test the ECU without it being in the car? Also I heard that the computers integrate after a period of time. Would I need MB to reprogram a new computer? Would they need the car or could they just use the VIN number? Thanks
 
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