3.9 efi problem

[Grumpy2]

HI sorry to be a leech on a first post but I'm stuck and stumbled in this forum which seems full of very detailed advice.

I have a 94 Morgan 3.9 injection with the 14CUX eco. it start and drives great but occasionally cuts out at idle. its been like this for about 18 months but its getting worse and not cuts out regularly.

I have rover gauge which had lead me down several false trails and I've fitted a variety of parts following 'advice' but the problem persists. I've fitted 3 stepper motors original, cheap Chinese and Britpart. The stalling continues. I've tried two MAFs original and eBay special (runs rough on this), still cuts out. I've set base idle, replaced fuel temp sensor (ouch!) and fitted new dissy cap leads and rotor arm (all from Morgan) and cleaned out the road speed sensor in the speedo cable.

Rover gauge points to this issues Stepper motor, speed sensor and error 69 NEUTRAL SWITCH. now I've eliminated stepper motor and speed sensor so Im left with the neutral switch which I understand on a manual is connected to ground via a 520 ohm resistor.

so ..

a) where would I find this resistor as I can't locate it or its orange/black wiring

and b) does anyone have any other suggestions as this sensor seems to be clutching at straws a little

thanks

Gary

[r2d2hp]

Not sure where you find the resistor but I have written down add 510 ohm resistor between pin 34 and ground orange/black wire when doing my conversion

not sure if that helps

[Grumpy2]

thats the thing - cant really get my head around what it does. I guess I could strip back the loom cover a little to find the wire and connect it to earth via a 510 ohm resistor if all else fails. Instead not as well.

[Ian Anderson]

I had a similar thing happen in my GT40.

From memory the resistor was used on auto only and stopped the engine stalling when in drive. Not needed in neutral.

The only thing I never tried was the road speed sensor, as this not only should stop the dying at idle but would limit top speed, which I certainly did not want

There are posts on this forum about it.

Ian

[ChrisJC]

Is it possible to eliminate some of the basics?, for example:
Ignition low tension definitely OK? (does the tacho plummet to 0 before it stops?, or does it always remain accurate)
Fuel pressure?

Is the system open loop or closed loop?, by which I mean does it have lambda sensors. Maybe they are measuring AFR incorrectly and it's choking or leaning out at idle.

Chris.

[Grumpy2]

yes it has the lambda sensors in the exhausts and a speed sensor in the speedo cable. don't know how to check fuel pressure although it had a new filter last year in an attempt to cure the problem

Tacho drops with engine not before, sometimes I can tell when its about happen as the idle hunts a little first, perhaps 1 maybe 2 seconds. More often it just stops as I'm approaching a junction with the clutch in can see the tech drop to 800rpm then as I come to a standstill it cuts out.

[Grumpy2]

OK a little update - not that I'm expecting folks to be on the edge of their seats! I replaced both the MAF and Stepper motor back to original and immediately the idle became smoother and pick up from idle more assured.

Also the lambda reading dropped fluctuating around 40-60%.

However I'm now on the trail of fault code 69 - the orange/black wire with a 510 ohm resistor that goes to earth.

I can't locate the resistor but having disconnected the ECU and located the orange/black wire at the ECU connector end I get a reading close to zero ohms on a DVM. This must mean that there is either a direct to earth connection or the resistor has failed as short circuit.

Given that every failed resistor I've encountered before this one has failed open circuit I con only assume there is no resistor or there's a short to earth in the circuit.

As I've ordered 5 x 510 ohm resistors I intend to cut the wire and make my own connection to earth via the resistorMine reads zero ohms so I'm going to try to rig up a second wire with a known good resistor. eek!

[Ian Anderson]

The resistor on mine was wrapped in the wiring loom….. a total bugger to find!

Ian

[GDCobra]

yes it has the lambda sensors in the exhausts and a speed sensor in the speedo cable. don't know how to check fuel pressure although it had a new filter last year in an attempt to cure the problem

Tacho drops with engine not before, sometimes I can tell when its about happen as the idle hunts a little first, perhaps 1 maybe 2 seconds. More often it just stops as I'm approaching a junction with the clutch in can see the tech drop to 800rpm then as I come to a standstill it cuts out.

Don't know if this is your only problem but the section I've highlighted above is what you tend to get if the system is not getting a road speed reading, only just skim read the above posts (it's a bit late) so may have missed it but did you run the car with RG attached and if so were you getting a road speed reading? The reading doesn't have to be exact, but it does need to indicate when the car is moving. I believe TVR used a system which came in wtih a constant speed reading at about 3MPH basically telling the system "moving or not" and that still worked.

You may have come across this information
https://www.actproducts.co.uk/2011/luca ... tic-notes/
About 1/3 of the way down the page there is a section on the road speed sensor which explains why this may happen.


The Neutral signal to the 14CUX is a little odd as it adds an idle speed offset to the basic idle, typically about 100RPM so you may have a basic idle of 700RPM but when this signal is sensed it will rise to 800 or something similar. The strange thing is how this works (or why it exists) is the signal is when the gearbox is in neutral or park, in these conditions you get the higher idle speed which seems the opposite way to what I would have expected.

Obviously this is not important as you are using a manual box so you should have the 510ohm resistor permanently attached in this case you would get the offset RPM always in effect hence the higher idle speed.

I've actually made a modification to my system using a pressure switch on the clutch in place of the auto gearbox switch. In this case I get the elevated idle speed with the clutch pressed and the 100RPM lower speed when it is released, this means I can have a slower idle (and hopefully lower underbonnet temperature) when the car is sitting idling out of gear but a higher speed when I put it in gear to as an aid against stalling, particularly useful when reversing.

When the car is fully warm what does RG indicate as your target idle speed? Also what did you set your base idle to?

EDIT
I just looked at your screen grab, looks like you have a target idle of 700 (engine up to temp) and it's registering in park/neutral so presumably the gearbox switch is grounded and you are getting the basic idle speed (presumably 600) and the elevated idle combined.

[Grumpy2]

Thanks for taking the time to reply. I have previously driven the car with RG connected and it does show road speed so I assume it’s working. Mind you I also assumed the 510 ohm resistor was in place as RG suggests but measuring with a dvm suggests otherwise.

I have been reading the website you mention and it’s very clear and informative.

I still intend to try the replacement 510 resistor but while I’m waiting I’ll check out the road speed indicator which on my car is located between two short speedo cables on the bulkhead.

Cheers

[GDCobra]

Thanks for taking the time to reply. I have previously driven the car with RG connected and it does show road speed so I assume it’s working. Mind you I also assumed the 510 ohm resistor was in place as RG suggests but measuring with a dvm suggests otherwise.

I have been reading the website you mention and it’s very clear and informative.

I still intend to try the replacement 510 resistor but while I’m waiting I’ll check out the road speed indicator which on my car is located between two short speedo cables on the bulkhead.

Cheers

Sound similar to what I have in mine, I just remembered that mine failed last year and I had to replace it. Was about 12 years old but had not done much in the way of miles. It did get tempramental for a while before it failed completely with similar symptoms to what you have mentioned.

[Grumpy2]

Bench tested and generating a signal fine. All nice a clean inside with no defective wiring. Where did you get a replacement from?

[r2d2hp]

You might find this useful https://www.actproducts.co.uk/2011/luca ... tic-notes/

[Grumpy2]

You might find this useful https://www.actproducts.co.uk/2011/luca ... tic-notes/

Yep I’ve seen that. Very informative. Waiting for a resistor to arrive then I’m going to recheck the timing and base idle. All out of ideas after that. I’ve checked everything I can check I think.

Frustrating.

[r2d2hp]

Have you checked the TPS and made sure its setup correctly and functions with no strange behaviour