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E420 W210 97
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Discussion Starter · #4 ·
Check for water contamination at the ignition coils for those cylinders
thanks for answering.
I removed the coils and everything is dry.

out of curiosity when this failure started I checked the spark plugs and they were wet with fuel on the side where the cylinders fail.

i thought it was the maf sensor and i put a new maf and new spark plugs will no longer get wet with fuel. but the failure remains the same.
 

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W210 Section Moderator
1998 E320 base sedan @ 235K miles
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thanks for answering.
I removed the coils and everything is dry.

out of curiosity when this failure started I checked the spark plugs and they were wet with fuel on the side where the cylinders fail.

i thought it was the maf sensor and i put a new maf and new spark plugs will no longer get wet with fuel. but the failure remains the same.
I do not think it has anything to do with the MAF sensor. Swap the coil and spark plug from one of the misfiring cylinders, with one that is good. If the problem moves to the new cylinder, then replace the plug and the coil.
 

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Discussion Starter · #6 ·
I do not think it has anything to do with the MAF sensor. Swap the coil and spark plug from one of the misfiring cylinders, with one that is good. If the problem moves to the new cylinder, then replace the plug and the coil.
thank you very much for the contribution.

i changed the maf because it was already giving some symptoms of faulty maf idle at idle.

I changed the coils and cylinder 5 and 7 continue to fail
 

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Discussion Starter · #7 ·
thank you very much for the contribution.

i changed the maf because it was already giving some symptoms of faulty maf idle at idle.

I changed the coils and cylinder 5 and 7 continue to fail
a curiosity sometimes I have difficulty starting the start the pump relay does not fire I had to activate the pump relay manually,

could it be a low fuel pressure the cause of the failure?
 

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W210 Section Moderator
1998 E320 base sedan @ 235K miles
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You need to change the K40 fuse and relay module. That is where the fuel pump relay is. Or you can remove it and check where the problem is (bad relay contacts, cracked solder joints, cracked printed circuit traces, etc.

If it is related to fuel pump issue, then you would have problems with all cylinders, not two specific ones.

Have you done compression testing on the cylinders ?


Did this problem start after doing some maintenance?

You also need to find someone who can connect a scope to the ignition coil lines from the ECU for cylinders 5 and 7. It may be related to a bad ECU / connector / wiring.
 

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Discussion Starter · #9 ·
You need to change the K40 fuse and relay module. That is where the fuel pump relay is. Or you can remove it and check where the problem is (bad relay contacts, cracked solder joints, cracked printed circuit traces, etc.

If it is related to fuel pump issue, then you would have problems with all cylinders, not two specific ones.

Have you done compression testing on the cylinders ?


Did this problem start after doing some maintenance?

You also need to find someone who can connect a scope to the ignition coil lines from the ECU for cylinders 5 and 7. It may be related to a bad ECU / connector / wiring.
yes I believe the fuel pump relay is not working well but maybe it is another problem.
I didn't do the compression test,
I don't javé the tool to do it,
I'll have to buy it, but I believe that if the cylinder is dead, the fault should continue even when I accelerate?

I didn't do any maintenance, the car was running fine. a curiosity is that this failure started gradually. I was at the post at the car meeting and she was having difficulty starting, failing a little when I got home the failure was much worse.

there is 12v in the coil socket. Where is the ECU that controls the coils located?
 

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W210 Section Moderator
1998 E320 base sedan @ 235K miles
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You need to describe the problem a bit more clearly. It appears from the misfire codes that both of them are type B, meaning TWC (Catalytic converter damaging). This means there are a lot of misfires compared to type A. For type B misfires, the check engine light flashes.

Are you saying that when you accelerate the misfires go away, and the check engine light stops flashing and go away? It could be a case of bad injectors for those cylinders.

If you have an OBD2 scanner, you should be able to obtain the freeze frame data which may give you clues regarding under what conditions the problem occurs.

The ECU is in the module box at the passenger side, where the K40 relay module is. The ECU applies ground to the other lead of the coil primary o create spark at the plugs.
 

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Discussion Starter · #11 ·
You need to describe the problem a bit more clearly. It appears from the misfire codes that both of them are type B, meaning TWC (Catalytic converter damaging). This means there are a lot of misfires compared to type A. For type B misfires, the check engine light flashes.

Are you saying that when you accelerate the misfires go away, and the check engine light stops flashing and go away? It could be a case of bad injectors for those cylinders.

If you have an OBD2 scanner, you should be able to obtain the freeze frame data which may give you clues regarding under what conditions the problem occurs.

The ECU is in the module box at the passenger side, where the K40 relay module is. The ECU applies ground to the other lead of the coil primary o create spark at the plugs.
Thank you very much for replying.

Check light does not appear on the dashboard.

I removed the injectors and had them checked,

they are all working fine. When I accelerate the glitches decrease a lot but not disappear completely.
 

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W210 Section Moderator
1998 E320 base sedan @ 235K miles
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When I passed the scanner I cleared the codes, started the engine and the same codes appeared again
Then you have a problem with the ECU or Instrument cluster (which you have a code for it already).

The check engine light should start blinking with the codes you have immediately. Have a look at the description below.

It is important to obtain the freeze frame data. I am sure your scanner supports this.

You should get the K40 relay replaced / fixed as something else may be going on with that (apart from the fuel pump relay). Also you should check the connections on the Instrument cluster. Obviously there is a comm problem over the CAN bus. The Check engine light should come on when the key is in position 2 (run) prior to starting the engine.
 

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Discussion Starter · #15 ·
Then you have a problem with the ECU or Instrument cluster (which you have a code for it already).

The check engine light should start blinking with the codes you have immediately. Have a look at the description below.

It is important to obtain the freeze frame data. I am sure your scanner supports this.

You should get the K40 relay replaced / fixed as something else may be going on with that (apart from the fuel pump relay). Also you should check the connections on the Instrument cluster. Obviously there is a comm problem over the CAN bus. The Check engine light should come on when the key is in position 2 (run) prior to starting the engine.
with the key in position 2 the panel looks like this

Speedometer Car Motor vehicle Tachometer Automotive design
 

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Discussion Starter · #16 ·
Then you have a problem with the ECU or Instrument cluster (which you have a code for it already).

The check engine light should start blinking with the codes you have immediately. Have a look at the description below.

It is important to obtain the freeze frame data. I am sure your scanner supports this.

You should get the K40 relay replaced / fixed as something else may be going on with that (apart from the fuel pump relay). Also you should check the connections on the Instrument cluster. Obviously there is a comm problem over the CAN bus. The Check engine light should come on when the key is in position 2 (run) prior to starting the engine.
thank you very much for the contribution.

about the k40 relay is there any test with a multimeter that I can do before taking it to a technician?
 

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W210 Section Moderator
1998 E320 base sedan @ 235K miles
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10,576 Posts
Don't worry about the dash side fuse panel. It has nothing to do with fuel pump or misfires. It is for lights mostly, and you will not have power on them with key out. The key needs to be in position 2.

You have to remove K40 and inspect the relays, tracks, solder joints visually. Fuise 5 powers the fuel pump through K1 relay contacts. Measure voltage on fuse 5 against chassis ground. It should have 12V on both sides when measured at the top test tabs. If it does, then, it is likely the relay contacts are pitted and not making low resistance contact to start the fuel pump. You can follow the trace from fuse 5 to the relay. One side goes to the connector B pin 1 (12V from the battery), the other, to the relay contact. The other side of the relay contact goes to connector B pin 3, and wired to the fuel pump.
 

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W210 Section Moderator
1998 E320 base sedan @ 235K miles
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10,576 Posts
with the key in position 2 the panel looks like this

View attachment 2782342
It appears that your cluster is missing few bulbs. Check engine light is above the SRS light. If everything else works (speedometer, tachometer, odometer). it is likely burnt bulbs or someone removed them.
Brown Speedometer Gauge Tachometer Measuring instrument
 

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Discussion Starter · #20 ·
Don't worry about the dash side fuse panel. It has nothing to do with fuel pump or misfires. It is for lights mostly, and you will not have power on them with key out. The key needs to be in position 2.

You have to remove K40 and inspect the relays, tracks, solder joints visually. Fuise 5 powers the fuel pump through K1 relay contacts. Measure voltage on fuse 5 against chassis ground. It should have 12V on both sides when measured at the top test tabs. If it does, then, it is likely the relay contacts are pitted and not making low resistance contact to start the fuel pump. You can follow the trace from fuse 5 to the relay. One side goes to the connector B pin 1 (12V from the battery), the other, to the relay contact. The other side of the relay contact goes to connector B pin 3, and wired to the fuel pump.
I tested the K40 relay outputs are all with 12V,

but the relay that arms the fuel pump seems to have a problem, when the car starts the relay arms and should disarm but it remains armed,
drowning the engine but it doesn't always happen.

this photo of the K40 relay seems to me that the welds have rust spots, could this be causing all these problems?

pin 20 of the 38-pin socket is 5.9V is this normal?
Gauge Measuring instrument Gas Auto part Audio equipment

Circuit component Audio equipment Netbook Electronic engineering Hardware programmer
 
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