Hi Michael
This is quite a common problem for the PI's. What I suspect is happening is
one of your injectors is either dirty or has an airlock.
There is a first simple test which will help narrow down to whether this is
an electronics or PI problem.
Take the car for a drive and get it up to normal temperature. When it is
missing, drive at say 30MPH in 3rd, pull out the cold start and put your
foot flat on the floor for a couple of seconds. This will dump something
like 300% fuel through the injectors and a big puff of black smoke out the
back. This is often enough to remove an airlock or clear a very small
blockage. Do this a couple of times. If after the 2nd or third time, the car
stops missing, you know you have a PI related problem. If there is no change
there is likely no problem with the PI system.
Just a comment on the ignition side of things, I have had great success
using Lumenition with PI motors. On the earlier 2500 saloon cars, a common
problem was coking up the plugs especially if they were only driven around
town. A stronger spark afforded by the lumenition solves this problem. As a
byproduct, you will also find the car has a lot more toke in the upper rev
range (from 3500~5000) you will notice a BIG difference.
I have also had a lot of trouble with spark plugs in the past. I find the
best brand is champion. I have had bosche and ND fail on me several times.
To clear an airlock:
Essentially we want to remove the injectors one by one while the motor is
running and ensure they are making the correct conical shaped spray cone.
Note there is some fire risk in this as we are playing with fuel spray. To
that end make sure you do this outside and have a suitable fire extinguisher
nearby (just in case!).
Here's what to do:
1. Loosen all the injector brackets so the injectors can be pulled out.
Depending on your car, you may need to remove the injector pipe clamp on top
of the tappet cover if your car has one of these. At this stage, remove each
injector without the motor running and inspect the tips. You may find there
is a bit of gunk holding one of them open.
2. Make up a small blanking plate big enough to cover the injector hole.
This will stop the idle of the car running away when you remove the
injector.
3. Get a dark coloured rag (I find navy blue works well) and lay across the
injector manifolds. This is what you squirt each injector on and look at the
spray pattern.
4. Start the car as normal. Pull each injector individually and squirt on
the rag. You are looking for a complete spray circle. It should only take 2
or 3 seconds to check each injector.
Be careful to keep the spray away from your eyes and also the exhaust.
If you find a cone of spray is not correct, rotate that injector so the tip
is the highest point. It will gradually fill as the injector expels the
airlock with each pulse.
Note that the injectors on the PI system work in pairs. My money is on #2
being the problem which will also affect #5.
I hope this is helpful. Please be careful if you choose to do the injector
bleeding yourself. Fuel spray can be very dangerous.
Best of Luck!
Bernard Robbins
'71 2500PI
'73 TR6 PI
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