> I am trying to solve an issue with a 1987 fuel
> injected, gas powered Morgan Plus 8. The problem is
> that at moderate rpm's there is a surging of rpm's up
> and down. This problem goes away at higher rpm's and
> speeds.
>
> Have checked the ECU, but am at a loss.
> RAL
Hi "RAL"
For a Morgan fueling system that is not supposed to exist in the US, I
sure seem to running across them frequently lately. (smile) I just
finishing dealing with another with Graham Fuller over at Cantab.
For the year and car you mention, you should be sporting a "flapper"
ECU, the name given to the Bosch L-Jetronic airflow meter with a Lucas
analogue ECU (the "4CU Fuel Control"). This system was first offered as
an pricey option only on a few cars in 1984-1986 and then became a
standard Plus 8 feature until the switch to the Hotwire system. In its
Morgan setup it is not normally US emission compliant for 1989.
To cut to the chase, you are displaying the classic symptoms of a
"flapper" ECU problem. However, it is best to check other things before
getting there.
Firstly, check the resistance at the flap potentiometer (or flap
position sensor) which is the round black plastic item attached to the
plenum nose opposite the throttle. The reading between the right and
green wires should be .335 v. If it isn't, loose the holding screws and
turn until it is then retighten the screws.
Second, you should verify your fuel pressure (28lbs and rising on
acceleration). If there is a problem there, come back to me...there is a
fuel pressure regulator out now that can vastly improve your car's
performance.
Third, get a can of spray ether (QuickStart) , and lightly spray you
vacuum hoses to see if you have a leak. If you spray slightly and the
engine revs change you have one..)
(To check the following, the easy way is having a known good unit about
and switching it..but we can try to work around that.
Fourth, (I am assuming you have a good clean air filter), check the
airfuel mixture. This must be done with a CO2 gas analyzer, Many garages
have them or you can buy one out of the Whitney catalogue for 100 USD.
It is the only way to tune this system. Hook up the tester to your
exhaust pipe and check the reading..it should be between 1.5 and 2.5%.
Insert a Allen key into the adjustment screw on the airflow meter and
mark the spot. Turn the key once or twice and see if there is a
reaction. If there is none..you airflow meter has gone bye bye.
http://www.gomog.com/articles/EFIflap.html
The only two items left are your ECU and your coolant temperature
sensor...unless this problem is only occurring when the engine is
cold...? The ECUs can and do deteriorate over a long time. The analogue
ECUs are pretty hearty and simple..more like old time radios than the
digital ECUs of today. Like any old radio...the soldered connections get
brittle and the signal becomes imprecise. You can replace it or have a
radio man simply mildly reheat and reflow the solder. That works most
often.
Here are further checking specifics on your system including the correct
resistance on each component and the ECU connections.
http://www.landroverclub.net//Club/HTML/ECU_check.htm
Here is a diagram of your entire injection system.
http://www.gomog.com/mi/GoMoG/images/Plus8mapuk.jpg
And I would peruse through the GoMoG Plus 8 page in the Injection
Specific section.
at http://www.gomog.com/plus8.html
If you need more help...ask. There is some solid expertise on the eMOG
discussion group at http://www.gomog.com/emog/emog.html
Good luck!
Lorne
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