CIS Problem?--AGAIN!!!

[Cody Forbes]

L DC wrote:
> I have a few Qs based on your response Ben.
>
> +++++
>
> Ben wrote:
>
> You have a fuel leakdown, sounds like you need to
> solve that problem since it is only leading to other
> problems.. You need to find the source of leakdown -
> my bet is you need new injectors, as the problem you
> describe indicates that is where the leakdown is.  Bet
> you spend the $250 or so replacing them and the
> starting issues go away - that is if your wiring is
> undamaged.
>
> +++++
>
> How does a fuel leak-down come about/develop,
> specially on an injector of this type?
>
> I take this as fuel being leaked into the combustion
> chamber, and if so, shouldn't it ignite when cranking
> engine given there's spark as I did?
>
> These injectors go bad, just like that? I mean they
> were working fine 3 or 4 weeks ago, or so I thought
> so.
> Also, from what I can see these type of injectors,
> unlike EFI, are nothing more nozzle sprayers?
>
> If they leak, does that mean they have some kind of
> internal seal that has gone bad?
>
> I'm sorry for all the Qs, just curious to know a bit
> more about these injector failures based on real world
> experience.

CIS injectors are presssure operated. They are spring loaded to stay closed
until a specific pressure reaches them (I think something like 1.5bar on our
cars). When they get old the spring tension won't be high enough and they
can leak a bit at lower pressures, such as whats left over when you shut the
engine off. If they are indeed bad they didn't go bad overnight, they just
got worse then before, and before they didn't leak enough to cause an issue.

You are correct on leaking fuel into the combustion chaber, which is why I
don't think you have bad injectors. Other possible pressure leakdowns occur
at the check valve on the fuel pump, and the pressure accumulator in front
of the right rear wheel under the car.

>
> +++++
>
> Ben wrote:
> I recommend relaying your fuel pump at this time -
> positioning the relay under the seat near the battery.
> This will alleviate some of the load from the pump.
> Although the 5000 wiring was better than the earlier
> models, benefits are always gained by moving the
> switching nearer to the load which is in this case
> conveniently located near the power source.
>
> +++++
>
> I take it you have performed this task before and if
> so, how much disassembling, chasing/tracing of wiring
> harness and or trim does it involved?
>
> Can one simply take the connections from the fuse box
> involving fuel pump wiring harness and migrate it back
> near the battery, making the necessary wire
> trimming/replacing?
>

It's not too bad of a job. Use a standard Radio Shack 4 pin naturally off
relay (SPST). Remove the rear seat bottom, find the fuel pump wires on the
drivers side. You should be looking for a green wire with yellow stripe
according to my Bentley wiring diagram. On the relay you have 2 coil wires
to energise the relay, then 2 wires that go through the switched portion of
the relay. Heres a link to a quick diagram I drew up.

http://jcforbes.com/jcfpics/codysaudi/relay_fuel_pump

You have a few choices to make.
Option 1:
Key on power. You can just make the fuel pump turn on any time the key is
turned on. To do this just find a nearby wire that goes hot when they key is
in both start and run positions, and run it to the part of the relay I
labeled as "Key On Power".

Option 2:
Factory wiring. You can use the much safer method of using the factory
wiring so the pump automatically turns off if the engine stops (ie. in event
of an accident). This is the most simple method, but it does leave the OEM
fuel pump fuse and relay in the way in case they go bad. For this method
follow the diagram I made exactly.

Option 3:
Direct to ECU. You can run a whole new wire all the way to the ECU. It's
alot more work, but I recomend the second choice.With this choice it's
actually slightly different then the wire diagram I made. The ECU turns the
GROUND on and off, not the positive, so you have to run the wire from the
ECU to the new relay (where I labeled "from green and yellow wire), then the
other wire from the coil of the relay (where I labeled "Chassis Ground")
goes to the battery positive. The other two go exactly how I did the
diagram. The pin on the ECU connector is pin #21
(http://www.sjmautotechnik.com/trouble_shooting/pinout.html#ten).

When you use any of these options make sure to install a fuse between the
relay and battery. Use the same amperage as the factory fuel pump fuse. This
way if the fuel pump shorts or the relay goes bad you don't end up with a
fire. To protect the relay you could install a second fuse between the relay
and fuel pump if you want.

-Cody Forbes
http://www.5000tq.com
'86 5ktq
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