w124 e320 wont start immobilser, ecu or wiring loom

[boomtings]

I recently made a post in the electronics section about my cars fuel pump. I forgot to put w124 in the title.

The car is a 320 coupe that ive had the good fortune to own for a week. last week I started the car and 5 seconds later it cut out, after that it crancks but does not fire up. I suspected the fuel pump as I could not hear them.

After testing the fuel pump relay socket I see that its only getting a 1.8v signal from the ecu
Im not sure what I should test next.

Ideally id like to check if im getting spark as when I bypassed the fuel relay and ran the fuel pumps the car still did not start.

Ive tried swapping the ovp relay already.


Can the ignition barrel cause this? All lights appear normal on key and engine cranks.

The car does have a IR immobiliser. Should I bypass this to eliminate it.

I tried to read engine fault codes but the blink tester just remained with the led dimmly lit. I was able to test other systems normally. Is my ecu dead?

Anybody have any advice.

 

[RBYCC]

Immobiliser, at least factory, will not allow the engine to crank, much like the neutral safety switch.
Did you confirm that you have fuel?
Test for spark at the plug leads?
Fuel, spark and air should allow start unless the crankshaft position sensor isn't outputting a signal to the engine controller.
Of course if you have a bad engine bay wiring harness then it's very problematic.

Start with the basics, pull your spark plug leads, one by one from the spark coils.
Crank the engine and see if you get a spark to earth.
Pull a plug while your there and see the color or if it is wet...wet would indicate fuel with weak or no spark. Cranking the engine and not firing yet remaining dry may indicate no fuel supply.

 

[tintinmt]

As above, its unlikely to be immobiliser. Check for spark at each plug. Check distributor and rotor arm.

 

[bolide]

Start with the basics

^^^ what he said

One step at a time!

Nick Froome

 

[scillyisles]

UK cars were often fitted with MBSS which was tied into the infra red locking system. This immobiliser allows the starter motor to crank the engine and thengine might fire and run for a second or two with the fuel already in the fuel lines but then it cuts out because the imobiliser cuts out the fuel pump.
Are the red and green lights on your door and boot both working?

 

[scillyisles]

As above, its unlikely to be immobiliser. Check for spark at each plug. Check distributor and rotor arm.

He will have difficulty checking his distributor and rotor arm. The E320 with HFM does not have a distributor or rotor arm.

 

[grober]

Immobiliser or ignition switch. UK dealer fitted alarms often disabled the FPR and OVP relays but not the starter motor! So don't take cranking as a sign the immobiliser is OK! check for spark - you have already got the fuel pumps to work by shorting the FPR. Make sure you use an old spark plug earthed to the block as a dummy load on any HT LEADS as the coil output stages wont appreciate a direct short!

 

[boomtings]

I tried to reply last night and my phone died just before a submitted the post.

Ill confirm tommorow if im getting spark. Thanks for the advice so far.

Grober I do hope its ignition or immobilser and not loom/ecu related.

 

[boomtings]

Tested this morning and I can confirm that I also have no spark.

If I sit in the car and use the ir key to lock it, when I attempt to start it the starter is also locked.

On the bright side the suns out.

 

[Dec]

What kind of remote fob do you have and is it working ok?

Dec

 

[boomtings]

The locks work fine. I have the single button ir key fob like above.

 

[grober]

Right no spark may mean the ECU is not getting its 12v supply- this might be due to the immobiliser, the OVP relay or the ignition switch. You need to determine which pin/s on the ECU connector should have 12v on them with the ignition on-- and test it for 12v presence with a DVM details here --- ECU shematics(pinouts) needed!!! - Benzworld.org - Mercedes-Benz Discussion Forum --- the pdf at post #3

pins A27 and A39 as far as I can make out from the OVP

 

[RBYCC]

Tested this morning and I can confirm that I also have no spark.

If I sit in the car and use the ir key to lock it, when I attempt to start it the starter is also locked.

On the bright side the suns out.

+1^

It appears the immobiliser is working as you indicate.
Doubtful all three spark coils have failed.
Also do a visual check of the engine bay harness.
Look at areas/connection points where the wiring leaves the loom and see if the insulation is intact, particularly at the ECU.

 

[boomtings]

So ive had some chores to do and then ive stripped away the lower part of the dash. I found the ignition barrel but could not really access the wires. Ive pulled out the instrument cluster with just fingers and loosend the speedo cable. Ive tugged at the key loom a little to find not much slack.

So I sit there for two minutes just turning key on and off then I thought I heared a relay sound from either battery area or psx footplate. Turned key and the b!tch started gracefully. To scared to switch it off.

Whats the verdict on possible causes.

Any ideas

What should I do next.

 

[Dec]

Don’t use the button on the remote fob for a few days to lock the car until you can see if the fault comes back again.

When you unlock the car with the fob you also disable the immobiliser.
When you lock the car with the fob you enable the immobiliser, so for now don’t lock the car with the fob, use the key blade in the door instead.

Dec

 

[boomtings]

Now im back at square 1 it wont start again.

 

[Dec]

Did you press the fob button at any time since it last started?

Dec

 

[boomtings]

Switched it off , went to give a see it works demonstration to the wife and it never started.

But it is starting now again.

Im pretty sure the ir and immobiliser can be eliminated as possible reasons for failure. The only wires ive totouched are the ignition loom and a bunch of earth wires. Its either them or an intermittent problem somewhere else that decided to work all of a sudden.

I think for now its a good time to put everything back together.

 

[IRISH E55]

I remember a good few years ago I had a problem with a customers 124! Can't remember exactly but I think there were corroded/broken wires under or around the battery!!!
Sorry for being so vague,hope this might help.

 

[boomtings]

Just to update everyone.

The car now starts regularly, however it idles above 1000 rpm and cruise control has stopped.

I now have a isc related fault (code8) on pin 8 of the diagnostic port.
Cruise worked before as I used it . It seems like this maybe throttle body wiring related.