I'm having trouble with my Lucas Injection - I think.
My car has Lucas Injection and is experiencing horrible rough running. It
sounds like only 4 out of 6 cylinders are producing power. It sounds quite
reasonable at idle and given that I have a lumpy cam I think it's probably
normal. Whilst under load it feels weak and runs rough. It can be pushed
up to high revs but continues to be rough and low on power. It sounds like a
shitty old volkswagen or a lawn mower when out on the road under power. It
also backfires quite a bit - just small random pops.
The car was running fine and had been working fine (albeit a little rich and
occasionally showing black soot around the threads of plugs 5 and or 6) but
a couple of weeks ago it was very low on fuel and I had plans to store it
for a month. I reversed it up a slope to a spot where I was parking it
(tail a lot higher than the front) and as I pulled the handbrake it
spluttered and stopped. It had obviously ran out of fuel and given the
slope I assumed the bosch pump was not getting any fuel pushed down to it
from the tank as the angle would have placed the pump slightly higher than
the low (almost empty) fuel level in the tank. I was happy it had stopped
where I needed to leave it so thought nothing of it.
Just recently (after 5 weeks of it sitting there) I put some fuel in the
tank (about 3lt from an old jerry can) and tried to fire it up - it took
ages on the starter motor and about three or four goes cranking it for a
long time before I got it to fire and run for a little. I figured that it
was just getting fuel up to the injectors. Eventually it ran but sounded
really rough - like that horrible rich misfire sound you get when you pull
the choke out too far. As I tried to drive off I noticed it was completly
gutless and needed heaps of throttle with the choke wide out and riding the
clutch to get it to move without conking out.
------------
The progress and checks so far:
I assumed the fuel was old and dodgy so I put in 20L of fresh premium
unleaded and tried again. It sounded better but when I took it out for a
run the rough running was still there under all throttle positions.
I figured the fuel filter (before the bosch fuel pump) may have become
clogged since running out of fuel and was perhaps now dirty and limiting
flow. I disconnected the pump side of the filter and fuel poored out via
the filter just by gravity push alone at an incredible rate - filling a
takeaway food container in only seconds. So I am convinced that plenty of
fuel is getting to the pump via the filter.
I thought perhaps something was going on with the ignition system so I
checked engine noise by seperately removing plug leads one at a time to
check for change in engine note. Each lead seemed to have a fairly similar
impact on engine note so I am quite sure I'm getting a good spark to each
plug. Plugs 5 and six didn't seem to make as much difference to engine note
though. I'm getting a solid 12.4V at the coil. This makes me think that
the rough running is not cylinder specific but randomly across all cylinders
although possibly more pronounced at 5 and 6.
I have a manifold vacuum gauge which prior to the problem showed a
reasonably steady 8.5-9 In Hg of vacuum at idle and it used to move steadily
and smoothly up as you opened the throttle. Now the gauge flickers wildly
between 7.5 and 10 at idle and continues to flicker as you open the
throttle. I have checked for manifold leaks and cannot find any.
I thought that perhaps we weren't getting fuel satisfactorily to the
injectors and perhaps there was an air lock - this would make sense seeing
as it ran out of fuel prior to the problem. I checked for a pulse at the
injectors and noticed 5&6 felt weaker than 1&2 - but 3&4 felt really light.
I individually removed each injector with the motor running and checked for
the correct cone shape of spray. Each injector showed the correct shape.
Whilst each injector was out (with engine running) I pointed it up and away
from the motor into a container to attempt to push out any air locks in the
individual lines as has been suggested with rough running PI's. The idle
seemed to smooth out a bit after that but there has been no change in the
'on-road' condition - it still runs rough.
I have also checked that the fuel return line is not blocked.
I checked the plug leads for spark leakage using a lead tester and all leads
showed only minimal leakage - as per new leads (which they are).
I have double checked all the throttle linkages and made sure the choke and
throttle cables aren't sticking. Everything to do with linkages is as the
text book states.
After another road test with horrible rough running I quickly cut the motor
and removed every one of the spark plugs. 1,2,3,4 were all the same colour -
a milk chocolate brown electrode and tip with plenty of black soot on the
threads. 5 and 6 were both dry black all over the threads, the electrode and
the tips. By this I assume all plugs are showing a rich condition but 1
thru 4 are on the edge of being acceptable whilst 5 and 6 are totally rich.
I assume the state of 5&6 is due to over-fueling or poor sparking and
fouling terribly. This suggests to me that the metering unit is failing in
some way on 5 and 6 - or a difference in throttle linkages is making the
rear throttle body not open enough or as early as the other cylinders thus
providing less air to cyl 5 and 6 resulting in too rich a mixture. I have
of course checked the linkages though and found nothing wrong.
I fail to see how anything valve related could have happened after sitting
the car still for a few weeks.
I figure it has to be the metering unit or plugs 5&6 have gotten so badly
fouled that they need to be cleaned and tried again.
-------
My plan now is to check fuel pressure at the metering unit. I am going to
clean plugs 5&6 and then put the plugs back in in a different order to how
they were. I will also check for a loss of vacuum at the rear throttle body
(which is where the brake booster is connected). I will also check metering
unit timing.
-------
This one has really got me stumped. - Remember nothing has changed on the
motor - it simply ran out of fuel and was never the same again.
Glen Johnson
[Site Designer]
TRIUMPH OWNERS TASMANIA CLUB
www.triumphowners.com
1977 2500 S (INJECTED)
http://www.triumphowners.com/registry.cgi?sectionID=111014&vehicleID=5
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