ECU Problems

[JackFitz]

Hi! I bought a 2001 redbull blue 4.0l Tuscan in September as a project. The engine had oil pressure problems so I rebuilt it over the last few months and I'm now trying to start it. The engine ran ok in October before I dismantled it.

The problem I have now is it won't start. I've got no fuel pump (relay doesn't trip, replaced with a new one), no spark and the injectors aren't firing. The laptop won't even connect to the ECU. I've bypassed the immobiliser and I'm getting 11.7v to pin 52 on the ECU plug with the ignition on.

All ground pins on the ECU plug are showing no resistance to the battery.

Very very occasionally when turning the ignition key on, the fuel pump relay will trip and the ECU momentarily connects to the laptop. Within 1 second everything is dead again.

I'm completely lost now. Does anyone have any other suggestions?

Edited by JackFitz on Thursday 13th January 14:27

[spitfire4v8]

Did you remember to refit the 8mm ring terminal to earth .. goes onto one of the top bellhousing bolts.

[JackFitz]

Have double checked that earth point. I'm going to buy a new battery as this one seems to have discharged quite fast, hopefully that might work.

[JackFitz]

New battery didn't help unfortunately. Is it common for the ECU's to fail? This is one of the early blue ones.

Update:
On closer inspection, there is a Racelogic traction control system installed. Could this cause some issues?

Edited by JackFitz on Thursday 13th January 18:10

[so called]

It may be as simple as corrosion on connector pins.
They can be a pain when a car has been standing, especially this time of year.

[JackFitz]

I removed every single fuse and relay and there were no signs of corrosion. I also removed every connection to the fusebox and again it all looked fine. Today I'm going to remove the traction control unit, put the wiring back to normal and see if that makes any difference.

[spitfire4v8]

The racelogic system i fitted went on the outputs from the ecu to the coils .. so that wouldn't stop the ecu powering up, and you should be able to see sensor readouts etc on the diags software. Something else is amiss.

[Penelope Stopit]

JackFitz said:

The laptop won't even connect to the ECU. I've bypassed the immobiliser and I'm getting 11.7v to pin 52 on the ECU plug with the ignition on.

Was the above voltage measured with the ECU Connected?

JackFitz said:

All ground pins on the ECU plug are showing no resistance to the battery.

Measuring the resistance won't find many faults due there being no loads on any measured circuits

Better to measure the voltage with the ECU Connected or disconnect the ECU and load each cable in turn with a 21 watt bulb and then measure the voltage while the circuit is under a close to 2 Amp load

With ECU connected
Measure the voltage from ECU Plug Terminal 52 ignition positive to ECU Plug Earth Terminals 7, 26, 50 and 51, then check diagnostic plug terminal 1 earth in the same way

JackFitz said:

Very very occasionally when turning the ignition key on, the fuel pump relay will trip and the ECU momentarily connects to the laptop. Within 1 second everything is dead again

This fault does point to a breakdown of supply voltage and if proven not to be, there is a possibility of a short circuit to the ECU forcing it to switch off, the thing is I don't know how the ECU behaves if a lambda sensor or any other component for that matter goes short circuit but you could disconnect them to test (if lamda sensors are being used)

[JackFitz]

Penelope Stopit said:

This fault does point to a breakdown of supply voltage and if proven not to be, there is a possibility of a short circuit to the ECU forcing it to switch off, the thing is I don't know how the ECU behaves if a lambda sensor or any other component for that matter goes short circuit but you could disconnect them to test (if lamda sensors are being used)

I checked the voltage with the ECU connected so it should've been under load. I will check terminal 52 to the ground pins and see what I find.

I'm also wondering if there is a short circuit somewhere that is tripping the ECU. There is an absolute mess of wire splices in the footwell including into the main engine harness. I'm slowly going through and removing them so I've got a clean slate. I'm taking the racelogic unit out too just to eliminate it as a possible cause.

[Oneball]

From memory both the alarm and the immobiliser work separately so it could be the alarm.

Try disconnecting the battery, and then hold down the keyfob for 5-10seconds whilst reconnecting the battery

Edited by Oneball on Friday 14th January 19:33

[JackFitz]

Oneball said:

From memory both the alarm and the immobiliser work separately so it could be the alarm.

Try disconnecting the battery, and then hold down the keyfob for 5-10seconds whilst reconnecting the battery

Edited by Oneball on Friday 14th January 19:33

I tried holding the key down while reconnecting. Sadly it didn't work. I thought it would just be the immobiliser that stops the engine from starting?

[Penelope Stopit]

You will know if there is anything immobilising the ECU 12 volt supply once you've correctly checked the voltages

[JackFitz]

So I've hooked the ECU directly up to a 12v power supply. Pin 52 to 12v, pin 50 to ground. I'm not sure if there needs to be any other inputs active but upon hooking up the power, pin 25 is not producing any power for the fuel pump to prime.

Bridging pin 36 (producing a 5v signal) and 49, which I think should simulate a very high engine coolant temperature is not triggering any output from pins 6 or 41 (the cooling fans).

The laptop still isn't connecting.

There's also a very very faint high-pitched electrical whine coming from the board.

It's not looking good...

[Penelope Stopit]

Mmmm, time to open the ECU up as you may see something

JackFitz said:

I'm also wondering if there is a short circuit somewhere that is tripping the ECU

Have you now proven this not be the case?

[spitfire4v8]

Not sure if this will help as my paperwork refers to the ajp8 ecu, though they're based on the same system so you wouldn't think main pins would change, but double check to be sure before using any of this info ...


7, 26, 50 and 51 are system earths on my paperwork.

52 is 12v in.

Fuel pump pin 25 is a switched to earth signal not a power out.

Pin 48 is the 5v out on my paperwork not pin 49

[PetrolHeadPete]

Another simple test...with ecu open find the main crystal for the mcu. Use your dmm in ac rms mode and measure both ends to gnd. If either end has something like 1 or 2v on the end them mcu is running (probably)
I'm guessing you don't have a scope?

[JackFitz]

Thank you for the help everyone. I decided to have it tested by TVR Power since they are just up the road from me. I'll update you all once I have their verdict.

[JackFitz]

To follow up... The ECU is completely dead. Apparently there is corrosion to the pins of the processor, these probably shorted. It was probably caused by the damp from when it was sat for the last few months in the rain... I'd better get some new seals!

I have purchased a secondhand tested ECU, I need to make a new cable for the diagnostics as the new ECU does not have a serial connector. Hopefully this will all work!

[Penelope Stopit]

Nicely proven

Pain of a fault

https://www.amazon.co.uk/Raytech-Magic-Gel-300-bot...

Edited by Penelope Stopit on Thursday 20th January 16:00

[JackFitz]

New ECU fitted, everything works as it should, fuel pump primes and laptop connects. Fingers crossed tomorrow it will rumble into life!