14 CUX Over fuelling

[mikanel]

I have a rebuilt 400 Chim motor fitted in a Wedge but I am having problems with over fuelling. The motor starts OK but as it warms up becomes progressively richer. An ecumate gave fault codes with :

No tune resistor
Faults on Lambda A and B sensors
Limp home mode selected

The motor is from a precat Chim and has no cats in the Wedge, and the 14cux and engine loom came from an early precat Griff. The specified green tune resistor is fitted and measures correctly at the ecu connector, as do the coolant and fuel temperature sensors, where both both hot and cold readings look correct. Fuel pressure is 40 psi, AFM readings look OK at low revs and timing is set at 8 btdc. I have tried an ecu from another car with the same results, and the Wedge ecu runs fine on another car also. Getting a bit frustrated at not being able to sort this, any ideas welcomed as to why the ecu is apparently not recognising the tune resistor and selecting the correct fuel map, before I seek help from someone who knows these ecu's.

Thanks Mike

[O mage]

Did the other car it ran ok have lambda inputs? I think this problem can happen if the chip is waiting to see input then dosn't so it goes into limp.

[mikanel]

Yes it did, but should the ecu not look at the tune resistor first to select one of the maps?

[Belle427]

Not sure if this helps.
https://www.pistonheads.com/gassing/topic.asp?h=0&...

[mikanel]

The ecu pins all look typically 30 years old so although I can't see any damage I will give them a clean.

[O mage]

It cant select the right map if its in limp and the limp tune is the catalyst tune so it will make a green tune over fuel and the diagnostic side will be compromised to compound things even more. Try changing the chip.

[blaze_away]

First and easiest thing do a hard ecu reset ie disconnect the battery the reconnect it.

[blitzracing]

The ECU will go onto the catalyst map by default if the tune resistor is open circuit, and look for the lambda probes and flag limp home If they are missing, it will register a lambda fault as there are no voltages, and this will make the car run rich as it tries to get the probes to produce a voltage. If you do want to run an non catalyst fuel map, ie the green tune resistor, you do need the correct map, as by default the green tune is still a Range Rover map, so it's likely to run lean at higher RPM. Don't forget your mixture has to be set with the screw on the side of the AFM on green. From your description it has to be connectivity to the ECU from the tune resistor as you are assuming.

Edited by blitzracing on Wednesday 29th July 07:10

[Penelope Stopit]

mikanel said:

The specified green tune resistor is fitted and measures correctly at the ecu connector

Mmmm that killed it for me, was going to suggest open circuit resistor or wiring

I don't know what happens to the resistors value when the looms plugged into the ECU and the resistance is measured at the rear of the ECU plug

Might be worth checking the above.......the problem is that there will be a voltage across the resistor when it's connected to the ECU and a voltage measurement would need to be taken and compared with another known good vehicle

What I'm trying to point out is that although the resistor value is seen at the disconnected ECU plug........Is that value still there when the ECU plug is connected to the ECU?

Also trying to point out that although it's a resistor.......It's doubtful that it's true resistance value can be measured when it's connected to the ECU due to a voltage from the ECU being applied to it........Multimeters set to ohms don't like the idea of measuring volts

Short version........Is the voltage across or resistance of the tune resistor correct when the ECU is connected

I don't know what the reading should be between pins 5 and 27 when the ECU is connected

I know you've checked the loom through but..........There is always the possibility of an intermittent earth fault at pin 27 or elsewhere

There is also the possibility that I'm not even close to what's going wrong

[blitzracing]

You missed the bit he said it was working in another car, so the resistor supply from the ECU must be good.

[blitzracing]

For reference the connected voltage across the resistor on green is 1.62 volts, while white is just under 5 volts. Open circuit is 5 volts so it makes sense it drops to the cat map. I does not make sense in straight forward as potential divider, as the voltage difference would be greater between the white tune and open circuit unless my cat map resistor is open circuit. Better check that out.

Edited by blitzracing on Wednesday 29th July 10:03

[Penelope Stopit]

blitzracing said:

You missed the bit he said it was working in another car, so the resistor supply from the ECU must be good.

Where have I mentioned anything about a possible problem with the resistor supply?

You've misunderstood something

[Penelope Stopit]

blitzracing said:

I'll nip out and do an open / connected voltage check on mine.

Nice

Now you've surely understood

[Penelope Stopit]

blitzracing said:

For reference the connected voltage across the resistor on green is 1.62 volts

Nicely done, you're the man

OP's got something to work on now, not much but there's a chance

[Penelope Stopit]

Forgetting fault codes for a moment

Is this the problem????????????????????????? see below

The most common fault here is to swap the Coolant Temperature and Water Temperature sensor connectors. Symptoms of this problem are usually that the car starts fine from cold, but progressively gets richer as the car warms up. This is because the fuel temperature should always be a lot cooler than the coolant temperature. Note that this particular fault does not show up on a fault code reader or cause a fault code to be set in the ECU, because both values are still within a reasonable range.

Taken from here https://www.actproducts.co.uk/2011/lucas-14cux-fue...

Scroll down the page to Fuel Injection Connectors

[Penelope Stopit]

Also from the same page

Should the Tune Resistor be changed or disturbed for any reason, the ECU should be reset afterwards by disconnecting it for ten seconds. Failure to do this may cause the ECU to select the default tune.

[blitzracing]

That bits not quite right, it runs map 5, but flags a fault code. I've yet to see an ECU run the limp home map, even with the MIL light on, so there must be some very specific failures that cause it.The OP has a ECU mate, so he can see the map its running, and I believe it will display the lambda probe outputs if they are being used. With no probes, it will be stuck at 0 or 255 depending on hows its measured by the ECU mate. In terms of swapped sensors making it run rich, it would cause the lambda voltage to be too high, but I dont think this flags a lambda fault as that a 0 volt situation

Edited by blitzracing on Wednesday 29th July 14:02

[mikanel]

I've just checked out the voltage across pins 5 and 27 with the ignition on its 4.93V

[Penelope Stopit]

Possibly getting somewhere then

[Penelope Stopit]

Something breaking down when connected to the ECU?

As long as the following is correct, you're definitely now onto something

blitzracing said:

For reference the connected voltage across the resistor on green is 1.62 volts

Are you able to measure the voltage at the ECU of another car running on a green resistor?

Edited by Penelope Stopit on Wednesday 29th July 17:21