BX Time - '89 16v project

The Electrical gremlins just don’t give up. This weeks problem is the engine won’t start. Cranks over fine and fires but it refuses to continue running. Almost like an immobiliser kicks in and shuts everything down. Only thing is, this car doesn’t have an immobiliser that I know of.

Definitely getting fuel to the rail and it feels like the fuel pump relay is working properly. Just in case I’ve tried swapping the fuel and injection relays for new ones with the same result.

Do I need to go hunting for a crank angle sensor or
 
There is usually two circuits for a fuel pump, the start and run. Is the fuel pump stopping once you let the key off ? (in a CX this is usually the tachometric relay wiring).
 
Not sure about that TBH Shane. I’ve been through the wiring diagrams and it doesn’t look like motronic uses a tachymeteic relay. Just a fuel pump and main power relay. I’ll go hunting though
 
There isn't a tachometric relay as you have found out, but there may be a fault in the ignition switch that is cutting power to the ECU in the run position after it has it in the start position.

What is the ECU light doing? When you switch ignition on, the ECU light should come on and go off once the engine starts. If the engine stops, does the ECU light come back on?

You can get error codes out of the ECU using the ECU light to flash out the codes. I'll try to find an article that explains how to get the codes.

Cheers, Ken
 
Faulksy,

Here is an excerpt from the BX Do It Yourself website. You have a Motronic M1.3 ECU in the 16V. The Diagnostic Connector is the green two terminal connector over on the drivers side next to the two power relays that has nothing connected to it.

Full website address is

Testing the EFI & EMS components | Citroën BX do-it-yourself

This site was originally dedicated to Citroën's upper middle category cars, the BX series of automobiles, from the point of view of those owners who are not afraid of tackling some maintenance and repair work on their car themselves. As years have passed, more and more pages of its larger...
citroen.tramontana.co.hu citroen.tramontana.co.hu

Below is an Aussiefrogs Thread that speaks to reading the codes as well if not better than the text below. The TZi also uses the M1.3 ECU but without a knock sensor.

Citroen BX TZi ECU diagnostic codes

I'm having the 'engine autodiagnostic lamp' coming on for up to 10 minutes at a time. Car still runs fine, but I know it is trying to tell me something. It's got a Motronic ECU, does anyone know how to get the diagnostic codes out of it? Does it need a special reader, or is there a simple...
www.aussiefrogs.com

EMS error codes​


When the EMS warning light (symbolizing a transistor, similar to a letter K) lights up on the instrument panel, don't wait too long. Unless the failure is permanent, after twenty engine starts the fault flag will be automatically cleared. Not all errors that store an error code in the computer will light up the warning light, less serious and passing errors do not.


The fault codes are easily retrieved by a Fault Code Reader, a special diagnostic equipment. At least they are supposed to be special but it is very easy to rig such an equipment. First of all, many systems only need a single switch to operate the diagnostic readout, the codes will be displayed using the mentioned warning light on the dashboard. Some other systems will use a LED in the diagnostic equipment itself (you might prefer this solution even if your system can use the dashboard lamp as this spares you the trouble of finding a long wire so that you can sit back behind the steering wheel to see the lamp). The circuit diagram shows how utterly simple such a "specialized diagnostic equipment" looks like.


Once you have the reader connected to the green Self Diagnosis plug and the ground, switch on the ignition. Close the switch for three seconds (the LED or the dashboard lamp should stay off), then open it. The LED will flash n times, then pause for 1.5 seconds, then flash m times. The code the system tries to tell you is 10n+m. Wait three seconds before you repeat the procedure.


The first code you receive will be 12, meaning Test Start. The last one will be 11, Test End. If there are no other codes between these two, the ECU has nothing to say. Otherwise, check the meaning of the codes in the following table (not all code numbers can appear on all systems):



CodeFailure at...
11Test End
12Test Start
13Air temperature sensor
14Coolant temperature sensor
15Fuel pump relay feed
21Throttle switch, idle contact
22Idle speed control valve/motor feed
23Idle speed control valve/motor
25Variable inlet resonance L valve
26Variable inlet resonance C valve
27Vehicle speed sensor
31, 32Wrong fuel/air mixture
33Air flow or MAP sensor
Throttle potentiometer (Mono-Jetronic)
34Canister purge electrovalve
35Throttle switch, full load contact
36Oxygen sensor heating
41Crank angle sensor
42Injector
CodeFailure at...
43Anti-knock control
44Knock sensor #1
45Ignition coil #1
46Turbo pressure valve
47Turbo pressure regulator
51Oxygen sensor #1
52Oxygen sensor system control
53Battery voltage
54ECU
55CO mixture potentiometer
56Coded alarm system
57Ignition coil #2
62Knock sensor #2
63Oxygen sensor #2
64Fuel/air mixture control B
65Cylinder sensor
71-76Injector #1-#6
91Injectors feed
After you obtained the Test End code, you can repeat the whole procedure from the beginning.


Note that the computer cannot actually check the sensors themselves, only the input it is fed with. An error code means that there is (was) some malfunction in the circuit mentioned but that can be (and most of the time it is) caused by an error in the wiring between the sensor and the ECU, or a bad contact in the several connectors between the two end points. Thus, start with checking the wiring and only then the sensor itself.


If you just peeked at the codes to see what to tell the workshop, don't clear the codes so that they will also have a chance to see them. However, if you did correct the fault yourself, reset the fault codes by performing the previous reading test until you receive the code 11, then close the switch for more than ten seconds. The warning lamp should stay off.


On some systems, the injectors and the idle speed control valve can also be checked using the unit: close the switch, turn on the ignition (without starting the engine), and wait for three seconds. You can observe the injectors functioning by their vibration and clicking. Open the switch quickly to avoid any greater quantity of excess fuel to enter the engine. If you repeat the test by closing the accessory switch once more for three seconds, the ISCV will operate shortly this time.

Cheers, Ken
 
Our BX assuredly had a "factory" immobiliser fitted before the car was sold new. There was a tiny push-button over-ride hidden in the glove box. Can't remember how it worked but I needed it once or twice.
 
But it wouldn’t start with an immobiliser fitted. My guess is fuel pump issue. Just a guess
 
It certainly seems to be an electrical problem. There’s a lot to go through in that link Ken which is great.

I’ve never noticed the ECU light come on but I’ve also never checked the bulb works.
 
faulksy said:
It certainly seems to be an electrical problem. There’s a lot to go through in that link Ken which is great.

I’ve never noticed the ECU light come on but I’ve also never checked the bulb works.
Click to expand...
Faulksy, one of the fundamental of the Otto 4 cycle is, give it fuel, give it a spark at the right time and whether you like it or not it will fire. That is why you do not touch aircraft propellers and must remove spark plug lead of lawn mowers before doing anything underneath- they both operate on a magneto and they not require 12 volts from a battery. They must be deemed live as they can be with a very small rotation of the magneto!
So may I suggest that you connect a fuel pressure gauge to the fuel rail to confirm that the fuel is available upon cranking over,
Then if it is, then continue with your further analysis.
I'm will be undertaking exactly the same process with my XM when I've overcome my D issues and have it registered on the Club Permit scheme.
John
 
There are 2 relays attached to the inside of the drivers side mudguard near/aft of the LHM tank. These are sometimes in a plastic bag cover. They are in the fuel pump and ignition Cct. Make sure they activate with the ignition switch - you can feel/hear them working.
 
Those relays were first on the hit list. both seemed to be working but I swapped in another relay as a test and got the same result.

Would a faulty TDC sensor cause the symptoms I’m getting?

I’ll get a pressure gauge onto the fuel rail over the weekend. Does anyone know what pressure the EFI system runs at?
 
does a 16valve have a flywheel sensor? The 19tri we used ot have had a dizzie..... when it started playing up I foudn the cap and rotor so burnt away I was amazed it had run at all!
 
faulksy said:
I’ll get a pressure gauge onto the fuel rail over the weekend. Does anyone know what pressure the EFI system runs at?
Click to expand...
PM me your email address and I'll send you the Mi16 Motronic 1.3 manual. It's the same engine, wiring and ecu. It has great fault finding instructions.
 
The 16V does have a flywheel sensor that sends pulses to the ECU for spark timing and engine speed.

I keep coming back to either that sensor as being the problem or something stupid like a blocked fuel filter. I'll get back into it this weekend and report back. It would be nice to drive it to a workshop for clutch work rather than tow it.
 
A spray of "Start Ya Bastard" down the throttle body will help you confirm the crank angle sensor, or other problem. Like this:
 

Attachments

  • 322925499_4360781570712502_8864209029717087857_n.mp4
    1.8 MB
faulksy said:
The 16V does have a flywheel sensor that sends pulses to the ECU for spark timing and engine speed.

I keep coming back to either that sensor as being the problem or something stupid like a blocked fuel filter. I'll get back into it this weekend and report back. It would be nice to drive it to a workshop for clutch work rather than tow it.
Click to expand...
Michael. I have a cx sensor that I keep in the glovebox for the inevitable. It may fit yours if you want to check
 
If it will keep running with lots of throttle, it could be the idle control system not supplying any air because it is jammed shut or disconnected. Guess how I know that one.

My memory of fuel pump operation is that the ECU cycles the pump for a second when the ignition is turned on, then the ECU waits for a good CAS signal before it will turn on the fuel pump again and power the ignition coil and the injectors through the two relays.

I can remember having to hot wire the fuel pump system on Daves original 16V to get him home from Supercheap one afternoon. Boy I wish I was still quick enough to be able to do that sort of thing on the spot.

Cheers, Ken
 
After much poking around with a multimeter and the workshop manuals it’s now up and running!!!! Thanks guys for all the suggestions. I now know far more about Motronic than I ever wanted to.

In the end giving the fuel pump a good smack was all it needed. Probably a sign that a new pump is in order but for now it’s happily purring away and revs up to the redline quite happily.
 
faulksy said:
After much poking around with a multimeter and the workshop manuals it’s now up and running!!!! Thanks guys for all the suggestions. I now know far more about Motronic than I ever wanted to.

In the end giving the fuel pump a good smack was all it needed. Probably a sign that a new pump is in order but for now it’s happily purring away and revs up to the redline quite happily.
Click to expand...
And what fuel pressure did you end up with Michael?
 
Haven’t a clue John, I didn’t get as far as putting a gauge on the fuel rail. Motronic M1.3 is meant to run at around 3bar though.
 
You must log in or register to reply here.
Top