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Discussion Starter #1 (Edited)
Hi All,

After I did the head gasket replacement, fired up the 94 E320 (M104.99) and it ran nicely. Took it for a drive -had two several second bouts of high reving, but they seemed to correct themselves.

It worked well for a few miles - couple of short trips around town.

The next morning after rain and cool temps, it started hard and missed badly. Not drivable. After the weather dried up and warmed up, I tried again and had the same result when I could get it to run at all.

I checked the engine harness (which I already suspected) and it was full of dust and bits of cracked insulation as I expected. I completely rewired the harness.

Now I get no start. It cranks but will not start. I can pull the injector wires off and it sounds fine when cranking continuously, so I don't think it's mechanical.

I have re-checked my harness wiring with a meter and everything tests good. Coils and injectors ohm out within spec. Fuel pump fuse is good, all other fuses look good. Can't detect any shorts in my wiring job. I did delete the air pump coil connector, as the pump was removed it from the system, but can't see how that could be in play.

I have not yet looked at the ETA wiring. Could a bad ETA harness cause a no start like this? I know that it could be the cause of the surging I had on the first test drive.

Any other ideas?

I posted up on Peachparts as well - need to get running so I can return the rental before I end up having to sell the car to pay the bill :)
 

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So did you rewire your old harness yourself, are you using a used harness, or are you using a brand new harness??? There were many running changes during W124, and hence different harnesses between the different M104 motors. The best option with the fewest question is to get a (new) harness that is VIN coded to your vehicle & engine#.

Doing the headgasket job is pretty much the kiss of death for the original eco kamikaze wiring harness.

Your symptoms definitely appear to be electrical in nature, with the ETA being high on the list if it is still original.
 

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Discussion Starter #3
Rewired my harness - a good 8 hour job.

More testing - ABS goes out after key on so probably not OVP?

Fuel problem - can't hear FP running 4 out of 5 turns of the key to On position (not start) no fuel spurt from schraeder valve unless I hear pump. I am guessing fuel problem - wiring to fuel pump? FP relay? poor connection under pass side rear seat?
 

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If it were my car, I'd get a new harness. Expensive, yes, but the only true solution to get rid of electrical issues.

Recommend using a new OVP relay whenever a new harness is installed.

Trying a new fuel pump relay can't hurt, but should be done after engine wiring issues (ETA & all 3 engine harnesses) are under control. Since you can hear the pump run, the relay is working.

The wiring inside the car and outside the engine bay are usually not affected. Never seen any signs in those areas on any W124s, including the late ones with the eco wiring.
 

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Discussion Starter #5
Still cranking with no start, occasional hiccup like it might catch.

I disassembled the FP and OVP relays. The relays all test good and click nicely with a 12 volt source. I resoldered all connections and sprayed relay contacts with contact cleaner and reassembled.

I have 12 volts at the fuel pump connector in the back seat for 2 seconds at key on, 10 volts continuous while cranking. FP's running while cranking with good fuel spray out of test valve. (planning on picking up a tester to get a number)

What else to check?

I saw a no-start post from someone talking about vacuum problems or air tube to idle control causing cranking with no start, but I think it was a 103.
 

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Throttle internal wiring needs repair just like the harness. It shorts out also, ASR or not. Did we mention coil packs also? Id bet they are original my coils were.

Good Luck.
 

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Resoldering a relay only buys you a little bit of time. In case of the OVP, it's the components that go bad rather than just the solder joints.
 

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Discussion Starter #8
Coils measure good with a dmm, impedence within spec on primary and secondary and all 3 have almost exactly the same readings.

Would bad throttle wiring keep it from even catching on startup?

I did not measure any bad components or find any stuck relays on the FP or OVP, I checked them, cleaned them, and refreshed the solder joints as a precaution.

I did find a sticky relay in the multi-purpose relay block with the turn signals that is now cleaned and working, but all I can do at this point is sit in my driveway pretending I'm going to turn left.
 

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Discussion Starter #9
If I disco the throttle wiring connector (14 pin round connector?), should I get a change in behaviour on cranking or will it not fire up at all when unplugged?
 

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Think of the OVP as a surge protector for your car. Just because the unit is still passing through electricity does not necessarily mean it is still a surge protector.

A new OVP relay has cured many a W124 when it comes to electrical troubleshooting.
 

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Discussion Starter #11 (Edited)
I have now re-tested a number of things to confirm.

- I have fuel (pressure at rail, injectors running, plugs wet after cranking)
- I have spark at the plugs - looks hot enough
- All wiring in my harness tests good with no shorts.
- Battery fully charged (again)
- have tried cranking with/without MAS and IAT sensors connected - no diff.
- I can see varying resistance from the cam sensor, but my scope is broken and my dmm has horribly slow response, so I can't see any more than that. (I guess i could crank it by hand) Voltage between the pins on the connector from the harness is .25 volts. Seems a bit low - or is it normal? I can't find a reference to this.

- OVP relay to swap in to test is on the way.

I am becoming despondent.
 

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Discussion Starter #12
more testing today - new OVP had no effect

plugs are all getting wet with cranking

all three coils tested again have good spark

I still think it must be timing related somehow - any idea on the cam sensor question? I measure the harness lead and it reads .25 volts with key on or cranking. The sensor has varying resistance while cranking.
 

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Discussion Starter #13
Couple of people suggesting CPS - Would not a bad CPS give me no fuel and no spark? I have lots of both.

I read up on that cam sensor - my mistake on looking for voltage. I was reading posts on later model years with hall effect sensors. I realize now that This sensor generates an AC signal and does not require supplied voltage. I also read thgat it should still start with a bad Cam sensor.

Still not running......
 

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Discussion Starter #14
Well, I found the problem.

First problem was definitely the wire harness, which I rebuilt, but got a no-start condition afterwards.

The answer is - when doing wiring and encountering a problem, don't just test once or twice, test at least 3 times. I had swapped pins 9 and 10 at the 44 pin engine harness connector block. This reversed my wires for the #1 and #2 coils.

Found the error with more continuity testing - started right up after i fixed it.

I feel like a boob - an entire wasted week.
 
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