'79 242 running roughly, poor fuel economy

My brother's car has started acting up lately, according to him it happened
gradually. The engine is a B21F with K-jet and Lambda, idles very rough and
doesn't have much power (not that it was ever a hotrod but I've driven it
before and it used to be quite perky compared to now), and the fuel economy
has dropped dramatically. Just put new plug wires on since the old ones were
pretty ratty, no change. Hoses look ok, air cleaner is clean, cap and rotor
are fine, frequency valve is buzzing, timing belt appears to be ok though
it's hard to see the crank pully mark without really tearing into things.
What should I do next? Compression test? Check the fuel pressure?

 

Check for air leaks, particularly at the injector seats. Trickle water
over them while the engine is running and listen for a change in
speed, or even for it to stall.

Does a car of that age have points ignition? If so and they are pitted
change them. If you see much of a spark between them if you open them
manually (ignition on) change the condenser. Set the points gap (or
dwell angle) and check the timing. Also replace the spark plugs if
here is any doubt about them.

It's unlikely to be a slipped timing belt if this has come on
gradually.

A compression test may tell you something.

If all that checks out OK, move to the fuel system. Make sure the cold
start injector isn't leaking. Check the spray patterns of the
injectors into a jam jar (be aware that the fuel pressure is several
bar).

Check the air flow meter flap is unobstructed, and check the spray
patterns change when you move it.

We didn't get K-Jet with the lambda upgrade in the UK, but this could
be a likely candidate, too. I'd say that a failed lambda probe is more
likely than any other part of the system, but don't know what symptoms
it would produce.

The warm up regulator can go bad. Check for a voltage at the
connector, and make sure the internal heater coil has not gone open
circuit.

Similarly, the thermo-time switch (looks like a temperature sensor at
the rear of the engine, under the last leg of the inlet maniforld).
This should be open circuit if the engine is warm, or if the starter
has been operated for more than a few seconds. There should also be a
voltage at the connector.

After this, you need to think of pressure testing the system.

--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name

 

Obviously, if the engine is in poor shape (compression) then the
following will probably be a waste of time.

The number one problem with K-Jet is vacuum leaks. Assuming that there
are none, then the next step is to measure the fuel pressures - line
pressure and control pressure. Control pressure is controlled by the
Control Pressure Regulator, aka Warm Up regulator. It's the pressure on
the center fuel line connected to the fuel distributor, and greatly
affects the mixture. It should be about 25 psi at cold start, and about
55 psi when the engine is fully warm. Also water in the fuel can cause
rust and sticking inside the fuel distributor.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

If the car is fitted with a catalytic converter make sure it's not
plugged. I was having this problem until the we bored-out the cat and
then she flew. If there is no cat then still consider the possibility
of a partial blockage in the exhaust and check this out.

Your solution (and your cost) may be surprisingly low-tech.

blurp

 

I tried spraying some WD-40 around the injectors and on hoses, didn't seem
to make a change, I'll try water though so I can get in more places without
making such a mess.

Nope, it's fully electronic with a pickup coil in the distributor. Timing is
adjustable but no points to mess with.

That was my thought too, though knowing my brother it's hard to say exactly
how/what happened, I seem to have gotten all the mechanical aptitude and he
got the art/music ability.

I guess I may as well do this since I have access to the equipment, the
engine has around 230k miles on it but it doesn't make any nasty mechanical
sounds and ran strong well past 200k.

The Lambda system doesn't kick in until the O2 sensor has warmed up anyway
and it idles very poorly even when cold so I'm thinking this is probably ok
or at least not the cause of all the problems.

The warmup regulator has been a source of trouble on my 240 Turbo as well,
it's a bit of a black box, nobody seems to know how to diagnose or repair
them. I'm hoping it's ok but another thing to check I suppose.

I've got a list of things to check, now to find some time to deal with it.
Thanks.

 

I know it is a long shot, but I had a 145 that started running very badly in
the winter. It turned out the thermostat was sticking partly open - maybe
only a mm, but it prevented the engine from warming up. If you have a
temperature guage you can rule that out, but if not....

Mike

 

It has a temperature guage and warms up in a normal amount of time. Even
when cold it should run fine though.

 

I remember another fault that can *apparently* occur with these units.
The underside of the unit has a hole in it (some versions vary) so
that it is open to atmospheric pressure, and somewhere between the
unit and the mounting bracket, it gets blocked.

Inside is a bi-metallic strip that is heated by an electric coil as
well as by ambient temperature. The purpose of this strip is to push
against a spring, countering the effect it has upon a fuel valve port,
restricting the flow, and consequently affecting the system's control
pressure. When the strip is cold, the spring is restrained, and a
richer mixture results for cold running. As the strip warms up, it
moves away from the spring, which can then bear harder upon the valve,
reducing the mixture for normal running. Have a look here for diagrams
and further detail about K-Jet http://www.auto-solve.com/mech_inj.htm

If the strip doesn't lift off the spring retainer (for example, if the
heater coil has failed), the car will start normally from cold, and
then gradually behave as if the mixture was over rich. If the strip is
damaged, and is permanently away from the spring, it will be hard to
start, but behave normally when warm. If the valve port is blocked it
will be harder to start, and may show signs of a weak mixture when
warm. If the spring is weakened, then a permanently enriched mixture
will result.

In practice, the bimetallic strip doesn't move more than a few
millimeters, and this can be checked on the bench by opening the unit
and connecting the heater coil to a 12v battery.

I have repaired a warm-up regulator, but other than re-solder a broken
wire to the heater, you are very limited with what you can do. It is
possible to alter the position of the bimetallic strip inside by
whacking it's mounting post with a hammer (I've done it), but this is
hardly precision adjustment. Easier by far to replace.



--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name

 

Check the fuel filter?


Gary

 

Well the compression test told us just about all we needed to know. The plug
on #3 was siezed so we couldn't check, but
the compression on 1, 2, and 4 was 8 (yes, 8), 120, 120. Leakdown test on 1
and 4 revealed badly leaking exhaust valves, spark plug in #1 was gummed up
black and #4 was white with bubbles in the insulator, #2 looked pretty
normal. I'm guessing either the injectors partially clogged or the whole
system was running too lean. At any rate it looks as though it's time for an
engine swap, might be a good excuse to drop in a B23E for a bit more kick.
Thanks all for the tips.

 

That is a beautifully informative web page. Thanks James!

blurp

 

CORRECTION!

Well thanks for everything else, James, but thanks to Stewart for that
link!

blurp

 

No need to thank me for anything, all I did was ask a question