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MG MGB GT V8 Factory Originals Technical - EFI Help Needed

I am in the process of getting my V8 running and have run into some problems with the fuel injection.

Specifically, the engine runs well at higher RPM levels but "thrashes" at idle and lower RPMs. The Throttle Position Sensor tests clean and nearly all of the sensors are new.

Advancing the distributor leads to the engine smoothing out and acceleration is good, however, the engine will not start with it at that state of advancement. When the distrubutor is retarded from that point the engine easily starts, but thrashes and stalls. I am currently using a Mallory, non vacuum advance distributor unit.

The ECU warning light is now illuminated, however, I do not have a computer to read the codes. The harness has the older style diagnostic plug.

Any assistance is appreciated.

Regards,

Scott Miller
Scott Miller

Some quick clarifiers...14CUX ECU, comprehensive rebuild including new fuel regulator, stepper motor, sensors, O2 sensors, and injectors. The harness was painstakingly rebuild using a RV8 wiring diagram. I am not sure of the Mass Airflow model number. I am not running cats.

Scott
Scott Miller

You haven't said, but have you gone through the procedures to set the TP voltage, then disconnected the idle compensating stepper, to set the TB butterfly and set the base idle?

For the 14cux hot wire system, there is much trouble-shooting information in the Haynes Range Rover 1970 to 1992 Manual.

It may also matter which tune resistor you have installed.

That said, there are often idle issues without the speed sensor connected, but they can overcome with tweaking from a good baseline.
Edd Weninger

Proper way to set the idle:

Step 1) Get the car so it will stay at least running on its own

Step 2) shut off the car, and disconnect the hose leading into the stepper motor on the back side of the plennum.

Step 3) Put a piece of ductape over the fitting that you just took the hose off of and then refit the hose (this way air can't enter the plenum through this hose)

Step 4) Start up the car and adjust the idle with a 3/16" allen wrench. If you don't know where the idle adjustment screw is, it's on the top side of the plenum, to the right of the main inlet.

Step 5) Blip the throttle a few times and make sure the idle is as low as it can go without stalling.

Step 6) shut off the car, remove the ductape and reconnect the hose leading into the stepper motor on the rear side of the plenum

Step 7) Drive.

If you have any air leaks in the system, that will mess with your idle in a bad way. The most common air leak for a new conversion is the four bolts that used to hold the coolant lines right below the main inlet into the plenum. Make sure you seal those off very very well!

The existence (or lack thereof) of cats does not negate the need for oxygen sensors. Use a 470 ohm resistor for the tune select resistor, and a heated oxygen sensor in each exhaust manifold. There are aftermarket O2 sensors that are WAY cheaper then what rover wants for them. (Comes off of a nissan, check http://www.rangie.com for more info)

Hope that helps!
Justin
Justin

Jason ,I had always thought the O2 sensors were entirely an emmissions contol. Do the sensors improve the power significantly. If they do I'll add some.
Off a nissan you say?
Sorry to jump in Scott.
Just a thought, is you TDC mark OK?. I changed balancers (I used a SD1 with the long neck ) and had to move the timeing mark quite a long way.
Peter

Thanks for the feedback. The TP sensor seems to be in good working order.

Does the fuel injection system require the use of a vacuum advance distributor. I currently have a Mallory mechanical advance in it?

Scott
Scott

The fuel injection doesn't require a vacuum advance distributor. It is pretty independent of the ignition system.

O2 sensors are required all the time. It's part of how the fuel injection knows what is happening in the combustion chambers and adjusts air/fuel mixtures accordingly.

O2 sensor info:
Nissan part number 22690-88G01
Bosh part number 13021
NTK part number 24005

All of those are around $55.00 each but have generic plugs which would require cutting and replacing to match the rover plugs.

You can get direct fit (no need to change the plug to match the rovers) for about $95.00. Info on that can be found here too: http://www.rangerovers.net/rrpartsv.htm#osensor

Justin
Justin

Justin-

The O2 sensors are installed.


Could you drop me a line with you number? I would like to talk with you on your findings.

Scott
Scott

This thread was discussed on 13/05/2005

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