D2 Cranks, No Start. Seems "Fuel Cut Off Strategy" is Enabled

[lifestyler]

Hi Everyone

Thought I'd see if there's any guru's here to help solve this PITA issue.

Anyhow, here's the basics:

1999 D2

Symptoms
Does crank
Does have spark
Does run if I spray starter down the throttle body
No DTC's

How it died
On the freeway and put my foot down. At the lights it was spluttering but recovered. After two stops later (10 minutes each stop and around an hour all up), I then started it up again. I put it in reverse and about 10m/30ft later while reversing, it came to a halt with lots of spluttering and it seemed it ran out of fuel. I still have half a tank of fuel.

What's happening:
The ECM is supplying a 5.5V to one side of the Fuel Pump Relay energizing coil, so no fuel pressure
The ECM is supplying a 5.5V to one side of the Injectors, so they're not firing

Conclusion
The Motronic ECM has "fuel cut off strategy" enabled and will not supply 0V to the Fuel Pump Relay and, as such, no fuel pressure. Also, the injectors are not being fired as a result of this "fuel cut off" strategy as well.

The Body Control Unit follows this procedure and it's here I believe is where the issue is:

When the engine is cranking, the ECM looks for a coded signal from the BCU. If the signal is not received within one second of cranking, the fuel supply to the engine is stopped and the injectors are disabled. This also prevents unburned fuel from entering the catalyst.

What I have done:
1) I checked for a spark & all OK
2) I could not hear the fuel pump so I checked for fuel pressure and no pressure
3) I checked the voltage at the fuel pump and it read 0V
4) I checked the Fuel Pump Relay and all OK
5) I found out about "fuel cut off strategy"
6) I checked and even bypassed Inertia Switch
7) I replaced the CKP Sensor
8) I replaced the MAF
9) I supplied 0V to the Fuel Pump relay so I had fuel pressure. Still no start due to injectors

What I'm doing now
1) Getting pissed off
2) Finding out what else the ECM takes into account to trigger the "fuel cut off strategy"

If anyone has any ideas, your input would be much appreciated.

Cheers

Erron

 

[JohnB]

Do you use the factory key fob to unlock and lock your truck?

 

[lifestyler]

Do you use the factory key fob to unlock and lock your truck?

Yes. I actually thought about trying the spare one but didn't. Looking right now for the procedures to do it manually.

 

[JohnB]

If its working then not the problem. Do you see the gear that your truck is in on your cluster?

 

[lifestyler]

If its working then not the problem. Do you see the gear that your truck is in on your cluster?

Yes. Shifted through all gears as well and it indicates the correct gear accordingly.

 

[JohnB]

Then I would replace them cam sensor since you already did the crank. Seems like the only other option.
Cam sensor or crank usually will no throw a code since the engine is not running.

 

[lifestyler]

Then I would replace them cam sensor since you already did the crank. Seems like the only other option.
Cam sensor or crank usually will no throw a code since the engine is not running.

I have an oscilloscope, so I'll connect that and see what signal I'm getting from the camshaft sensor.

Cheers

 

[lifestyler]

Well, I just checked the signal from the camshaft sensor and I'd probably get a better signal if I just let it drag loose on the ground.

It looks like I have to take the crankshaft pulley off to access the bloody thing.

Anyone does this job easily before and have any tips?

 

[listerdiesel]

Just do a resistance check, that will tell you if the coil is OK, there's not much to go amiss with it, it's just a coil wound around a bar magnet.

I don't think that's the issue here though.

Peter

 

[lifestyler]

Hi Peter

Maybe it's not the camshaft sensor, but the signal I'm getting on the oscilloscope definitely isn't a sine wave...or a square wave for that matter. It's a very very noisy signal.

I'm going to try and disconnect the sensor and clean everything up as there's oil everywhere down near the sensor...at least the ECM will be working with the right signals.

I'm still curious if anyone knows what can actually trigger a "fuel cutoff strategy".

Cheers


Erron

Just do a resistance check, that will tell you if the coil is OK, there's not much to go amiss with it, it's just a coil wound around a bar magnet.

I don't think that's the issue here though.

Peter

 

[ptschram]

If it really is a fuel cut-off issue, it is unlikely that you'd have spark as the immobilization of the DII shuts everything off.

IIRC, the fuel pump runs on a modulated square wave to run the pump (yeah, I gotta check the book). Try providing a full 12 volts to the pump and see if it will start. If it runs, at least we're that much further ahead with the process.

 

[seventyfive]

Then I would replace them cam sensor since you already did the crank. Seems like the only other option.
Cam sensor or crank usually will no throw a code since the engine is not running.

cam sensors do throw a fault and the truck will run fine on a D2. ask anyone that has done a gems bottom end swap and forgot to swap the Bosch cam gear.

you can jump the fuel pump relay, but without pulsing the ground signal to the injectors, the engine won't run.

check the main engine relay, in the engine compartment fuse box. the main engine relay supplies 12 volts to the air mass meter, fuel injectors, and fuel pump relay. the printed board, in the engine compartment fuse box, gets dry sockets in the solder (where the relay base is soldered to the board). if you're getting 5 volts to the hot side of the fuel pump relay and injectors, check power at the air mass meter and see if it's 12 or 5 volts as well.

 

[lifestyler]

Hi Paul

I'm probably calling it the wrong thing...maybe it should be called a secondary fuel cut-off

The quote I mentioned above:

"...the ECM looks for a coded signal from the BCU. If the signal is not received within one second of cranking, the fuel supply to the engine is stopped and the injectors are disabled. This also prevents unburned fuel from entering the catalyst."

is pulled from the following link on the BCU:

http://www.discoweb.org/forums/showthread.php?t=82111&highlight=ECM+coded+signal+BCU

I did supply a direct GND to the other side of the fuel supply relay coil (R9) and the relay kicked in and the fuel pump worked fine.

It seems the ECM is being notified by the BCU that all isn't well at this 1 second point after a crank is started (as referenced above) and fuel supply is cut off.

...though when I turn on the key to position II, 5.5V is being fed to the fuel pump relay coil from the ECM (the other side of the coil has 12V from the main relay), indicating the ECM isn't happy at this point in time either.

Cheers


Erron

If it really is a fuel cut-off issue, it is unlikely that you'd have spark as the immobilization of the DII shuts everything off.

IIRC, the fuel pump runs on a modulated square wave to run the pump (yeah, I gotta check the book). Try providing a full 12 volts to the pump and see if it will start. If it runs, at least we're that much further ahead with the process.

 

[lifestyler]

Hi Mike

I pulled all relays and checked them by supplying each relay coil with 12V and they're switching fine, however I haven't checked the MAF for a 12V supply.

I did test at least one other relay's hot side of the coil (not the switch) and it was 12V, however at least one other relay is indicating a 5.5V line voltage on the other side of the coil. I assumed that this relay was also receiving a 5.5V signal from the ECM as well, instead of the "all is OK" GND supply.

I'll check the fuse box to make sure 12V is being supplied where necessary.

Is there any component/sensor that, when faulty, the BCU would detect this failure and would then notify the ECM that all isn't well and the ECM then goes into the "fuel cut off" strategy due to a possible explosion of my disco?

Cheers


Erron

cam sensors do throw a fault and the truck will run fine on a D2. ask anyone that has done a gems bottom end swap and forgot to swap the Bosch cam gear.

you can jump the fuel pump relay, but without pulsing the ground signal to the injectors, the engine won't run.

check the main engine relay, in the engine compartment fuse box. the main engine relay supplies 12 volts to the air mass meter, fuel injectors, and fuel pump relay. the printed board, in the engine compartment fuse box, gets dry sockets in the solder (where the relay base is soldered to the board). if you're getting 5 volts to the hot side of the fuel pump relay and injectors, check power at the air mass meter and see if it's 12 or 5 volts as well.

 

[jafir]

"...the ECM looks for a coded signal from the BCU. If the signal is not received within one second of cranking, the fuel supply to the engine is stopped and the injectors are disabled. This also prevents unburned fuel from entering the catalyst."

If this were the case it would throw a code for the BCU serial link. It would also most likely start and then immediately die.

Are you sure that you got the crank sensor installed correctly when you repaced it?

 

[seventyfive]

I would first verify every output and input in the fuel supply/preparation circuit, is getting 12 volts with key in accessory position. If the fuel pump relay, maf, and hot side of injectors are all getting the same voltage then I would look at the source of that 12 volt.
Other than the alarm circuit which is a ground signal fed from bcu to ecu during cranking, I'd have to look at the wiring diagram.

I'm not a big fan of shot gunning parts but do you have another engine compartment fuse box? Personally I have two of everything for my D2's, just in case. 4 screws, and unclip a handful of connectors and the two battery positives.

Have you jumped the main engine relay and tried cranking? Only reason I'm stuck on the engine fuse/relay box is due to one of my D2's and a couple of customer trucks have had similar issues you're having. They all turned out to be the same problem.

 

[seventyfive]

main relay coil is fed 12 volts via inertia switch (fuse 13). verify the blu/red ground wire has a good ground (it is the ground side of the main relay coil).

main relay contact feeds 12 volts to Fuse1, Fuse2, and the hot side of the coil for the fuel pump relay, aux fan relay, and the AC compressor clutch relay.

Fuse1 (gets 12 volts from the contact side of main relay) gives 12 volts to the injectors, input to ECU, and idle control valve.

Fuse2 (gets 12 volts from the contact side of main relay) gives 12 volts to maf, EVAP canister, oxygen sensors, cam sensor, and purge valve.

it seems as though you know what you are doing so you know how the inputs scale voltage for the cam sensor, maf, etc.

if you are definitely getting battery voltage on the potential side of the main engine relay (contact and coil) you should be able to jump the main relay (contact not coil) to supply 12 volts, then measure if you're getting 12 volts to what that relay controls.

 

[seventyfive]

Is there any component/sensor that, when faulty, the BCU would detect this failure and would then notify the ECM that all isn't well and the ECM then goes into the "fuel cut off" strategy due to a possible explosion of my disco?

other than alarm circuit and inertia switch i don't think so. the low emission trucks will cut fuel to injectors the cylinder is reporting a misfire on, but non emission trucks are pretty straight forward. just to be sure you do have a non emission truck right? here in the states we see even '99's with air pumps (they were california trucks that migrated via auction to the east coast).

 

[JohnB]

I was under the assumption that power is supplied to the injector then grounded by the DME to operate the injector.
For that matter all the relays are operated via a ground signal. Odd if you are used to working on cars that relays are positve activated.

 

[seventyfive]

youre correct, there is 12 volts present and the DME supplies the ground.