E320 Cranks but won't start - PeachParts Mercedes-Benz Forum

#1 12-19-2002, 11:55 AM

My 1995 E320 still will not start occationally. I brought it to the dealer and of course the car started for them. They replaced the OVP relay as I had the older version. They also replaced the Fuel Pressure Regulator because of a leak down condition.

This morning the car will not start. Any ideas? The repair bill is starting to grow.

Thanks in advance.

Mick J · #2 12-19-2002, 02:03 PM

Could be faulty fuel pump relay. Give it a sharp tap with the handle of a screwdriver next time it plays up and see if starts.

#3 12-19-2002, 02:21 PM

I am told that it is not a fuel problem. Apparently there is not power to all three coils when this condition appears.

suginami · #4 12-19-2002, 02:31 PM

You may have an engine wiring harness problem.

All wiring harnesses are bad on M104 engines from '93 to '95.

Do a search on "wiring harness" and you'll have enough to read to keep you up all day and night.

Arthur Dalton · #5 12-19-2002, 03:35 PM

Quote:

Originally posted by dwooding
I am told that it is not a fuel problem. Apparently there is not power to all three coils when this condition appears.

Power to the coils [ positive 12 v.] comes from fuse # 6 and goes through the OVP.
When it will not start, give fuse #6 a light twist in its holder
and retry....
The way the coils fire is a switched ground. This is controlled by the ecu circuit [ with the crank sensor signal, etc.]
This ecu ground completes the coil circuit on the Neg side of the circuit.

But if you have no Positive 12 v to the coils [ all 3 positive feeds are tied together [parallel], then the feed fuse /ovp circuit can be the fault. This can be tested with a simple meter/test lamp at the coils input wire for 12v+. [ w/key on]
I have read that the coil feed wire on the later 104s has had bad solder connection where the 3 wires solder to the main feed for distribution to each coil in the harness...[ and possible bad harness, though I would think that the have already looked at that]

I also think that when they tell you there is no power to the coils , they are more likely talking the complete circuit , vs power feed.....but if it is just feed ,a power test for intermittent fuse
connection is a possibility... [ or ovp/fuse/ign sw. ]

#6 12-19-2002, 08:20 PM

I tried twisting and replacing fuse no. 6 and still no start. I am reading about the wiring harness and it seems to have a lot of problems. Can the dealer test the harness without replacing it?

I talked to an indendant shop and he is suggesting the HFM unit for $1200. What is the HFM and is it likely to produce this intermittent electrical problem?

Thanks,

suginami · #7 12-19-2002, 08:31 PM

The HFM unit (hot film management) is the mass air flow sensor.

The usual symptoms of a bad mass air sensor is an uneven idle that fluctuates up and down, kinda like the engine is hunting for the right idle speed and can't find it.

There are many places to check the wiring harness to see if the insulation is flaking off. One place is right at the the terminations on the thermostat housing you'll see the insulation at the ends coming off. Another place is where the wires in the plug to the intake cam advance magnet are. It may be necessary to remove the plastic connector from the wires to see the insulation.

#8 12-19-2002, 09:11 PM

I check wiring in locations indicated above. There are no obvious signs for deterioration. I will do some testing with the volt meter.

Arthur Dalton · #9 12-19-2002, 10:02 PM

The HFM management unit is the ECU module that is used for both ignition and fuel management. [ N3/4- control module]
It is actually the HFM-SFI control unit. This is the unit he is referring to and it controls the ignition switching I mentioned along with fuel injector durations.
The MAS sensor is of the hot film design, [ changed from the earlier hot wire design, LH-SFI systems] and is one of the sensors that influences the HFM control unit , but is not referred to as the HFM unit, but simply the MAS ....
[ B2/5- mass air sensor] .

It is probable that the HFM-SFI unit is electrical faulty, but
the power feeds to and from the unit should be checked first...

joe p · #10 12-20-2002, 08:20 AM

You do know that HFM needs to see a reference signal prior to firing the coils right? Check for crank signal from the CKP located under the oil filter housing. I also have seen 1 (only 1) electrical part of a ign switch that would not light up circuit 15 to the OVP on occasion.

Basic trail for diagnosis.

failed condition
fuel pressure increase on crank
15 power to ovp
power out of ovp
crank signal from flywheel

Joe

joe p · #11 12-20-2002, 08:23 AM

And another thing..... does the check engine light come on while cranking in a failed state? (short cut for circuit 15 power supply)

Joe

#12 12-20-2002, 11:41 AM

Yes, Check engine light does come on when cranking in failed condition.

joe p · #13 12-20-2002, 12:46 PM

Then follow the other steps and you shold find it.

Joe

#14 12-30-2002, 10:24 PM

I have my E320 and this thing has sucked the money out of me. I have a check engine light on and initialy the car would just not start one day and once you fidget with the neutral safety switch it would start and then that wouldn't do the trick and so I took it to a shop.

The guy changed, fuel filter, fuel pumps ( both of them!!), changed the wire harness, cranks sensor, three coils and that has just about done it for me.

He gave it back to me last friday and said he figured it out,...no way the darn thing is now stalling in the middle of the road with no warning signs, but guess what if you give it five seconds it will start right up after the whole Boston traffic has yelled and cussed at you.

Please help me zero in this problem too,...

suginami · #15 12-30-2002, 10:27 PM

Has he changed the OVP?

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