How to do a compression test - 405 1.8 TD

I assume i've got to pull the injectors out to do this but i'm a bit
sceptical since I dont want to disturb the metal pipes.

I'm sure you'll ask why - really just a bit of a health check but also
it is not getting the MPG I think it could get - gets 40 driven v e r y
slowly and 60 on the motorway - I think it should get 50. Also it
drinks fuel if you go fast (90).

So has anyone else done this - any advice / tips thanks

Ian

 

I seem to remember doing a compression test years ago. My father had a
little piece of kit but I only tested it on a petrol engine, don't know if
the principle's the same for diesels.

You had to remove the spark plug, replace it with the unit and I'm sure I
had to remove the positive cable from the coil whilst testing. Memory's a
little hazy but it sounds right.


A

 

A spark plug is easy to remove and replace - I'm unsure about the
diesel injectors.

You have mentioned another problem though - how do i stop it from
firing!

I think the fuel pump may have a stop lever... maybe I can force that
shut?

 

Workshop job really....unless you've already got a suitable pressure gauge
and adaptor which is unlikely!

I suspect that if the engine's so worn that you have a compression loss
you'd be burning engine oil at a high rate and leaving clouds of smoke
behind you. Is this the case? Have you tried just flushing the injectors
first?

 

You would need a special compression tester made for diesel engines, the
normal type will not read the high pressures.
The tester fits into the glow plug holes, so you don't need to remove the
injectors, and as long as you have the ignition off, it will not fire as the
fuel cut-off solenoid prevents this.
What are you tryig to prove, if the compression is low you will have
problems stating, and the cost of rpair is quite high.
You can get a reasonable idea of the state of the engine by jacking up one
front wheel, put it into 5th gear (with ignition off) and turn the engine
over with the wheel. It is about one rev of the wheel to one rev (two
compression strokes) of the engine.
If the engine is hot, you should have a real problem turning it over
compression. You can also check that all 4 cylenders feel the same.
Have you checked the valve clearances? If they have tightened up, you will
lose compression there, and it is a relatively easy check and also easy to
correct if they are out.
I assume you have checked the air filter is clean, and put some injector
cleaner in the fuel. Then go out and floor the accellerator in second, till
it hits the limiter, and keep it there for a few seconds. You will probably
see a cloud of black smoke which will then clear. This has removed all the
build up of soot in the exhaust, and amkes it run much better.
It is also a mistake to run the engine too slowly, you must be on the turbo
to get the best efficiency.

 

OK so a glow plug tester would be easy to use! (as long as the glow
plugs come out)

I have noticed the starting is not as good as my 205 whose engine was
excellent. (could be glow plugs or compression I guess)

I have not checked valve clearances yet - I expect they will be out - i
dont think the previous owner would have checked them - I was hoping a
compression test may point out if they were out though (or other
mechanical issue e.g. worn rings). If the compression was good I was
going to leave everything. If it was not good I may do the valve
clearances and if that doesn't improve it consider what to do with the
car (sell it?). I did the valve clearances on my 205 and several
exhaust ports were a long way out some had no clearance when cold! But
changing them made no difference to the running or fuel consumption
that I noticed.

If the ignition is not on I can't crank the car unless I short the
starter motor which I dont think is a good idea so perhaps I can jam
the solenoid shut?

Yes clean air filter, new oil.

Have you noticed a difference using injector cleaner - I used a batch
in my 205 and I noticed a slight difference it would run a bit smoother
at very low revs but made no difference anywhere else or with fuel
consumption so I was thinking it was a waste of £20.

I can try and clear the exhaust out - I do occasionally thrash it to
5,000 rpm on the road but not that often most runing is less then 2500
rpm.

As for low speed running is it really more efficient to have higher
revs and be using the turbo - mine starts to kick in at 2,000 rpm where
a lot of time I cruise at 30 - 40 mph at 1,500 rpm?

Thanks in advance for the advice.

 

I have noticed the starting is not as good as my 205 whose engine was

What about hot starting?

It can make a difference if the valves are not closing properly. It can also
make hot starting poor on some of the PSA engines, it did on my 106 1.5D
Yes I know that the clearance should increase as the engine heats up, but
not it appears on the 1.5D
To do the job properly, you also have to grind in the badly seating valves
which of course, means taking the head off.

You just disconnect the wire to the solenoid, it's the big nut with a
connector on it just above where the high pressure pipes come out.

It will only make a difference if the injectors need cleaning. This is
normally indicated by the sound of one pot knocking (the injector dripping),
ie. an uneven beat.

Depends on how much accelleration you want. You can do a test, with the
engine at say 1500 in perhaps 3rd gear, put your foot to the floor, then
slowly bring it back up, and see at what point the accelleration decreases.
All that movement further down than that point is just burning fuel for no
gain.
If you do the same thing once the turbo is working, you will get more
useable throttle, and less unburnt fuel, though you still can get too much
fuel if you put your foot down too far at given revs.

 

I've got a 405 1.8 estate with 100,000miles and got 46mpg on a closely
monitored 800 mile run, mainly motorway here and France, 70-80. Comments
here put that or just a little higher about right. If you've no smoke
I'd be inclined to put this in the category of "If it ain't broke ..."
since apart from coolant problems these engines seem to go on and on ...

Cheers

 

I think I would get 40mpg at 80mph. There is grey smoke on startup and
heavy acceleration (quite a lot)...

Ian

 

I sometimes get grey smoke on startup and heavy acceleration as well. It
gets less during periods when the car is doing long runs. I don't
worry about it, because oil consumption is negligible ...

 

Try and give the car a oil change and filter.also air filter change. i
have done this on many cars before M.O.T. and they always pass. so try
and change the oil plus filters.

 

A little grey smoke on startup is quite normal on these.
Smoke on heavy accelleration is common especially when the car has been
driven relatively slowly round town for a bit. The remedy is to go to a
quiet open road, put it in second and floor the pedal for about 15 - 20
seconds. Rev it to the limiter. You will see a load of grey/black smoke out
the back, which will clear. Take your foot off when it has. Most of that is
soot which has built up in the engine/exhaust.
I do this immediately before all MOTs, and it works. I normally get very low
emmissions readings. (so do the cars)!
Obviously you also need to check that the air filter is clean too, but as
long as you keep to the correct regime on oil changes, I would not change
the oil just for an MOT.

 

Yes oil is changed every 6k miles with filter and air filter is clean
and 6 months old.

So the grey smoke is nothing to worry about but I was wondering if it
was a symptom of a problem e.g. poor combustion which could also
explain the mpg?

If black smoke is unburnt fuel (perhaps the fuel is not mixed well
enough in the cylinder - clogged injectors maybe or under hard
acceleration when it runs rich for max power) and white smoke is water
vapor then what is grey smoke - inparticular why would I get it at
start-up?

Ian

 

I think we're gently trying to tell you most of what you describe is
common. The mpg is acceptable. Given the 1769 was the early engine, like
us you probably have an older high mileage car which no longer has a
great street value. I do try to change oil and filters at under 5k, but
if the engine runs and accelerates ok, why worry?

Cheers ...