W202 C180 1994MY - Won't start

Page may contain affiliate links. Please see terms for details.

julianps

New Member
Joined
Jul 2, 2009
Messages
18
Hi, gone to my car this evening and it won't start.

Normally, when I turn the key to position 2, I hear the fuel pump run up to pressure then stop. At that point I start the car.

Now the fuel pump is just running and running.

There is fuel in the tank.

My understanding is that the only things under the car are a fuel pump and a fuel filter but I can't remember is there's a pressure storage thingy; there was on old Volvo's.

I was thinking if the pump failed it wouldn't create pressure so wouldn't know when to stop pumping; anyone buy that idea?
 
The system seems to use and fuel and ignition module to drive a fuel pump relay, throttle body idle controller, ignition coils and fuel injectors. Most of the inputs to this are electronic sensors but there's a vacuum pipe passing absolute pressure data (there's no MAF on the M111.920) to the ignition module too.

When the ignition is turned on and without the engine running one of two modules send a pseudo signal to the fuel pump relay. This tells the pump to do a pre-flight run and pressurise the fuel rail(s). After a preset period this ends and, if the engine's not running, the FPR stops the pump.

What's happening here is that pre-flight isn't stopping; this is pretty much the same as bridging the FPR and forcing the pump to run always-on (as a diagnostic test). This would suggest that whatever module is responsible sending the kill signal to the FPR either thinks the engine is running (a pretty odd sensor failure given that it's a pulsed signal) or is itself compromised.

If the module thought the engine was running there's no reason it shouldn't allow the engine to (re)start (as it would, say, in a stall/bump-start) so that suggests it's not a sensor but a module that is compromised (open circuit, closed circuit or unit failure).

Sadly I've no wiring diagrams to know how these systems are set-up and no pulse-reader to examine the OBD ... ho-hum.

Question; These Phase0 cars (the one's without passenger airbag) also have the dreaded overload protection relay (OVP) on a carrier next to the fuelling unit (PMS). Could it be as simple as that died?
 
Could be any number of things. No way to tell until you test some of this stuff & start eliminating components.

To test the PMS module unplug each ignition lead (at the spark plug end) in turn being careful not to pull them apart. Then stick an old spark in the end & crank the engine. Make sure the body of the test spark plug is sitting out in the open & is earthed to the engine block. Just sitting on the block with a small gap usually works. A screwdriver also works.

A spark = good, no spark = problem with your PMS unit.

You can do this yourself watching through the gap of your raised bonnet for the spark, just don't shock yourself.
 
Could be any number of things. No way to tell until you test some of this stuff & start eliminating components.

To test the PMS module unplug each ignition lead (at the spark plug end) in turn being careful not to pull them apart. Then stick an old spark in the end & crank the engine. Make sure the body of the test spark plug is sitting out in the open & is earthed to the engine block. Just sitting on the block with a small gap usually works. A screwdriver also works.

A spark = good, no spark = problem with your PMS unit.

You can do this yourself watching through the gap of your raised bonnet for the spark, just don't shock yourself.
I have an old timing light that has +/- and an inductive pickup. Attach to #1 lead, if it flashes I have ignition ... much safer that your, equally effective, alternative ... :thumb:

As to the unit being dead, I can find a part for £170 and received the following from a German repairer;

Unfortunately, I cannot quarantee that this unit is repairable, however I see a real chance and would like to offer you a repair. Please send us your engine control unit for check and repair if you are fine with that.

We only need the engine control unit itself (no immobiliser or key).

Current approximate repair time is 4-5 working days in our workshop.

The cost for repair would be as follows (price for consumer):

350,00 € (£243,98 *) repair engine control unit
20,00 € (£13,94 *) handling and shipping to United Kingdom
70,30 € (£49,01 *) 19% VAT
440,30 € (£306,93 *) total cost of your repair
* Invoicing in EUR, no warranty on exchange rate changes. Base is the current FX rate of 0.6971.

That's more than the car's worth!
 
Replacing all four tyres with new premium ones is more than the car is worth. You have to decide whether you want to keep the reliable, old car you know or start with a different one you don't.

Anyway, you're getting ahead of yourself here, you don't know what needs replacing yet.

If it turns out to be the PMS unit I would say read the thread linked in post 2. IME these are not repairable & you would be wasting your money going down that route.
 
Replacing all four tyres with new premium ones is more than the car is worth. You have to decide whether you want to keep the reliable, old car you know or start with a different one you don't.

Anyway, you're getting ahead of yourself here, you don't know what needs replacing yet.

If it turns out to be the PMS unit I would say read the thread linked in post 2. IME these are not repairable & you would be wasting your money going down that route.

Yeah; true. but this one needs diagnostics and work on the clutch and prop-shaft work and new parking brakes and there's no-one I trust out here in tractor-territory to do the work so I'd need to be able to drive it to Shrewsbury and my guess is that by this point I'm £1,000 in.

And it needs 4 new tyres ... :doh:

Shame, because the body is rust-free and it still has it's original exhaust system. In a perfect world it's a keeper. I'm just not sure it's worth this much effort even though I\'m sure it has 10 years left in it.
 
Did you figure out what was responsible for the non starting?
 
Could be any number of things. No way to tell until you test some of this stuff & start eliminating components.

To test the PMS module unplug each ignition lead (at the spark plug end) in turn being careful not to pull them apart. Then stick an old spark in the end & crank the engine. Make sure the body of the test spark plug is sitting out in the open & is earthed to the engine block. Just sitting on the block with a small gap usually works. A screwdriver also works.

A spark = good, no spark = problem with your PMS unit.

You can do this yourself watching through the gap of your raised bonnet for the spark, just don't shock yourself.

A slightly safer way to test for HT to the spark plug is to plug a strobe light in between the end of the HT lead and the plug :thumb:

Edit , replied before reading the next post :doh:

Just been through the same thing diagnosing my W201
 

Users who are viewing this thread

Back
Top Bottom