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rallysteve



Member Since: 10 Feb 2014
Location: South Yorks
Posts: 1656

United Kingdom 1984 Defender 90 V8 Petrol PU Caledonian Blue
Cause of 3.9EFi rich running (14CUX)

All,
I am having some issues with the 3.9Efi in my 90 project and have run out of ideas. It is running a non-CAT map (map 2 tune) with tubular exhaust headers and obviously no cats.

The idle is fine when its cold but as soon as the engine is upto temp it starts to fluctuate and often just stalls itself. I have had it hooked up to Rovergauge and no errors shown, all readings seem in the right ballpark.

Put a CO analyser on it this weekend and we were getting readings of 10%. Struggle to get it down less than 6% even with the AFM CO trim screw turned right down.

It has had:
New plugs, dizzy cap and rotor arm, new coil, injectors cleaned and tested,new air and fuel filters etc and just fitted a new TVR idle control valve.

We have also tried a different AFM and ECU with some small changes but not good enough still.

We put a pressure gauge on the fuel rail and i am sure it was showing high 30s (psi) without the running and mid 30s at idle. This seems maybe a little high?

Cheers Steve 02' 110 TD5 Double Cab Rebuild Thread
84' 90 3.9 V8 Caged Pickup Build Thread


Mobile Diesel Heater Build Thread

Post #765270 25th Mar 2019 8:37am
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oneten110



Member Since: 02 Jul 2011
Location: Wish I was still in France
Posts: 741

United Kingdom 

Might be worth your while to talk to Mark Adams.
http://www.tornadosystems.com It is not a Defender, it is a One_Ten

Post #765276 25th Mar 2019 9:23am
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drakes



Member Since: 09 Oct 2009
Location: Hexham
Posts: 95

United Kingdom 2004 Defender 90 Td5 HT Auto Belize Green

I would also vote for Mark Adams, he sorted out the 3.9efi I had about 20 years ago, he is a genius with rover V8s

Post #765342 25th Mar 2019 6:16pm
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diesel_jim



Member Since: 13 Oct 2008
Location: hiding
Posts: 5267

United Kingdom 2006 Defender 110 Td5 SW Epsom Green

Sounds like the temparature sensor is up the duff? (if it works OK when it's cold).

my old 3.9 had two sensors, one in the inlet manifold (i think) and one on the thermostat housing.. one ran the guage on the dash, the other ran the ECU

Post #765344 25th Mar 2019 6:18pm
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V8GPC



Member Since: 18 Jul 2016
Location: Manchester
Posts: 289

United Kingdom 

http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm

Really informative, the following info is at the bottom of the page (copy and pasted below)

Looking at the info resistance goes up as temperate goes down, the fuel is enriched when cold (open circuit or bad contact would show as high resistance) meaning ecu thinks engine is cold - enriches the fuel. (10K or higher)

At 80C the resistance would be 300 ohms

Also from the GEMS manual (slightly different - but similar) Engine fuel temperature (EFT) sensor

The EFT sensor is located on the fuel rail. This sensor measures temperature of the rail rather than the fuel. The resistance varies with changes in temperature. The signal is used to increase the injection pulse time when undergoing hot restarts.

When the fuel is hot, vapourisation occurs in the rail which may result in the formation of bubbles in the injectors. Increasing the pulse time helps flush the bubbles away and cools the fuel rail with fuel from the tank.







Engine Coolant Temperature Sensor (aka: "thermistor" or "thermal resistor")

The Engine Coolant Temperature Sensor is threaded into a boss on the intake manifold. Note: this sensor contacts the coolant fluid, and thus its threads need to be sealed appropriately. When the engine is "cold", as determined by this sensor, the ECU richens the fuel mixture by lengthening the time injectors stay open. The ECU reduces the length of fuel pulses as the engine reaches normal operating temperature.

The Coolant Temperature Sensor should change resistance with heat, per the following specs.
10C (14°F) 9100-9300 Ohms
0C (32°F) 5700-5900 Ohms
20C (68°F) 2400-2600 Ohms
40C (104°F) 1100-1300 Ohms
60C (140°F) 500-700 Ohms
80C (176°F) 300-400 Ohms
100C (212°F) 150-200 Ohms

The Engine Coolant Temperature Sensor on our example system is marked "73355A", "Lucas", and "Made in UK". It has a 2-pin integral sealed connector. My local Auto Zone lists this sensor as part number SU5133 at $26.99, and they keep it in stock. Although I haven't been able to verify it, I've also been told this sensor is interchangeable with the sensor in a late 1980's VW Golf.

I'm told that these sensors are a relatively frequent cause of trouble on older Rover fuel injection systems. One installer told me he replaces the Engine Coolant Temperature Sensor whenever he does an engine swap.

Fuel Temperature Sensor (aka: "thermistor" or "thermally sensitive resistor") (see fuel rail photo above)

The Fuel Temperature Sensor is threaded into a boss on the fuel rail, forward of the plenum. (See the fuel rail photograph above.) Note: this sensor does NOT contact fuel, and thus it can be removed without gasoline leakage. The information provided by this sensor is mainly of interest when the engine is being started. If the fuel in the fuel rail is already hot, the ECU "knows" a hot engine is being re-started, and can adjust the mixture accordingly.

Post #765483 26th Mar 2019 3:27pm
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rallysteve



Member Since: 10 Feb 2014
Location: South Yorks
Posts: 1656

United Kingdom 1984 Defender 90 V8 Petrol PU Caledonian Blue

Thanks for the info. Should have mentioned; I have it connected upto the rovergauge software on the laptop which shows the coolant and fuel temperature sensors are behaving as expected (88deg coolant temp and 25deg fuel temp when up and running).

I will check them again to make sure.

I have a proper fuel pressure gauge and vacuum gauge to check the FPR is working correctly as it seems to be the most likely candidate. Will report back.

Cheers,
Steve 02' 110 TD5 Double Cab Rebuild Thread
84' 90 3.9 V8 Caged Pickup Build Thread


Mobile Diesel Heater Build Thread

Post #765494 26th Mar 2019 4:22pm
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