MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - Still having issues with my fuel injection

After a two week hiatus due to cold weather and a fuel leak, I played with my fuel injection system again today and here's what I found:

I set the air flow meter to the suggested 1.2 volts between the sensor wires.

I also hooked up my fuel pressure tester inline right at the fuel rail so I could monitor fuel pressure as the motor ran.

I also ran air down the return line and was getting bubbles in the fuel cell, so I know that's working too.

When I first hooked everything back up and primed the fuel injection system, it didn't want to start. I yanked 2 plugs and they were pretty soaked in gas. Eventually I got it to start and warm up the plugs enough to run and I began watching my fuel pressure. When priming the system (no vacuum on the FP regulator) I had 50 lbs of pressure. When running it dropped to 42, and when I revved the gas it would momentarily drop to about 38-40, but as the rpm's dropped the pressure would rise back up to 42 and sit there. When I pulled the vacuum line from the fp regulator it instantly jumped back up to 50, so I know the thing is at least working.

Not enough vacuum?

I have too much fuel pressure. That's now a proven issue. Rover prescribes it should be between 34-37 lbs and I have 42 lbs which is roughly 15% above the max. Is that enough to cause the kind of poor mileage I'm seeing, or is this merely another factor in the equation?

I still need to figure out a good way to tell if the afm is bunk, but I don't think that would cause all my issues. If the plugs are soaked in gas after repeated cranking, then I'm getting way too much fuel in the cylinders. I'm starting to think that running excessively rich could cause starting problems. (More fuel then it can handle?)

Input?
Justin
Justin

These two websites seem to have pretty comprehensive troubleshooting and testing procedures. Have a look -

http://www.roversd1club.net/pdf/Article-EfiTestAdjust.pdf

http://www.pixeltechnology.co.uk/wedge/wedge_epistles_mk2.pdf

I believe they refer to the same system as you are using.

Regards,
Wayne
Wayne Pearson

Justin,

I've had one AFM fail...that gave excessive fuelling before it died.

I've found fuel pressure critical to correct mixture.....do you have an adjustable rising rate regulator, or are you using the standard hotwire fixed regulator ?

With the rising rate regulator and an exhaust gas analyser, you can adjust the mixture very easily.

The TVR service manual recommends fuel rail pressure of 36-40 psi with engine running and vac pipe dis-connected, so your regulator seems to be OK, I had to knock mine up a couple of psi to get it right, but I've got big bore throttle and trumpets from a TVR setup, which could be the reason.

The AFM should read 0.3-0.6 volts with the ignition on, you should be able to see a voltage change when you turn the adjuster, maybe this is out of range ?

Mike
M Barnfather

Hi,

I too have had an afm fail, as Mike B. will remember. I caused intermittant idle problems, very annoying! When I replaced the afm, not only did it cure the idle fault, but the mpg has improved no end, can't remember last time I filled up with fuel! So if you can borrow a afm from someone at least you could eliminate it?

Mike
m clemas

Justin, your running rover EFI or Ford?? I thought you had a Ford 5.0??
Larry Embrey

I looked very seriously at switching to a 5.0 or doing a supercharged 4.2L Rover, but took a 75% paycut last year when I switched to being self employed. I have to pick my battles, and spending money on the car isn't one of them!

Justin
Justin

This is pretty vague I'm sorry but I have a recollection of trying 1.2 and getting terrible fuel economy (it went with more zing though) I think (vague again) about 0.7V.
I'll have go out and have a look later.
Peter

Yes Wayne that's a thought.....we are talking about the hotwire 14CUX system, and the airflow meter is a Lucas (Hitachi)3AM or Lucas 5AM I assume ?


Mike
M Barnfather

Yes 14cux system 3AM airflow meter.

I set the airflow meter in accordance with rpi's recommendations.

Justin
Justin

Justin,
I also set as per that RPI site. Then after using huge amounts of fuel returned settings to orrigional settings. The wiring colour coding is different to the haines manual (and the RPI site) so some establishing of which wire is what is required.
Standing on Left hand side of car, With the electrical socket pointing at me/you, square plastic wire housing with printed info' on top and adjuster screw on top on engine side). Air flow going from left (front of car) to right (engine).
The four Wires from left to right are;
(1)Red/black wire then (2)Blue wire then (3)Brown/orange wire then (4)Blue/red wire.
The Brown orange wire is the power (I guess)and all the others are 12 volts compared to it.

Between Red/black (1)and the blue/red (4)is 0.20 Volts
Between Red/black (1)and Blue(2) is 0.36V
Between Blue(2) and Blue/red (4)is 0.15Volts.

This is with the ignition on but the engine not running.
I'm not sure which wire does what (if someone knows please tell) but this is how I found it and it gives good fuel ecconomy. Better suggestions will be gratefully recieved.

The engine is a 3.9 hot wire. No oxygen sensors and with a non cat' tune resistor (if that makes a difference, which I doubt)
At least this gives you are starting point.
Peter

I played around more yester and while I was cranking it over I had someone shoot carb cleaner through a vacuum line, and the motor started right up! I visited my uncles sports car shop today and he gave me a cold start injector from a nissan and the associated wiring bits for it. There is a boss on my upper plenum for the rover cold start injector, so I'm going to tap into there and install it. I'll wire it up with the starter solenoid relay so it only sprays gas while the car is starting. I 'think' that should solve some of my cold start problems.

I'm thinking I have a few separate, unrelated problems. Lack of fuel at startup, and rich mixtures when running. I'm going to solve one problem at a time.

While at my uncles he traded me a hardtop in pretty darn good condition for a kingpin reamer that I only used once and has sat for 3 years! Great trade!

Justin
Justin

This thread was discussed between 06/05/2005 and 08/05/2005

MG MGB GT V8 Factory Originals Technical index

This thread is from the archives. Join the live MG MGB GT V8 Factory Originals Technical BBS now