chris-g
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| posted on 25/4/12 at 04:45 PM |
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Volvo engine. Help needed please.
Hello. I went to visit a friend this afternoon, he has a 1991 Volvo 740 estate. Some weeks ago it blew the dipstick out and covered the engine bay in
oil. He seemed to think that the rings had let go on cylinder No. 1 so he bought a second hand engine which he is having problems with. Th car has an
LPG conversion which piggybacks the injectors and a control box then controls some sort of solenoid valve on the gas inlet. The gas is piped into the
inlet manifold before the plenum. The gas kit was fitted while the old engine was in working order. The new engine is type 20f and the existing ecu
and inlet manifold, injectors and rail were retained. The new engine will hardly run on petrol or gas, its starts after a some cranking but dies
within a few seconds. With the gas solenoid valve bypassed the engine will run but doesn't have much power, therefore the ignition would seem to
be ok. The MAF sensor is faulty, the platinum wire has snapped off one of the terminals and disconnecting it makes no difference. It seems to me that
the injectors are not firing or not getting a signal to fire which would explain the gas valve also not working correctly. Would failure of the MAF
sensor cause this sort of fault or is there another issue? Any help would be greatly appreciated as my friend is from the carburettor era and is
losing patience with this modern technology.
Thanks. Chris.
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T66
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| posted on 25/4/12 at 05:15 PM |
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If theres no wire in your airflow meter, the engine cannot do it sums inside the ecu with the injector fuelling. It needs to know how much air the
engine is flowing using that wire. If its not it cannot.
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mark chandler
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| posted on 25/4/12 at 05:22 PM |
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Those volvo's had a habit of blowing oil everywhere when the crank ventilation system became blocked, they threw it everywhere !!!
Hope you have not been wasting your time.
Back to the original question, engines will not run with gas and petrol together (unless you have a modern system that allows it), essentially you
flood the engine and kill the spark.
If a old venturi gas system it will have it's own ECU which controls a gas flow meter that looks like an old bosch idle control valve, when LPG
is engaged all injectors should then be disabled and emulators trip in to fool the ECU that everything looks okay.
Gas is let into the engine before the throttle butterfly with this system.
So first question really, injection system or venturi ?
Regards Mark
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Volvorsport
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| posted on 25/4/12 at 06:13 PM |
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drill the breather out on the inlet manifold , and clean the one on the block , that normally sorts the dipstick blowing oil issue ......
what engine did it have and what engine has it got in there now ?
if it was a B200 'E' then that was kjet
if it was a B200 'F' then that was LH 2.4 two different injection systems and sensors , ,and more importantly holes in the cylinderhead
for injectors .
engine will run with a nackered MAF .
www.dbsmotorsport.co.uk
getting dirty under a bus
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chris-g
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| posted on 25/4/12 at 06:35 PM |
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Thanks for the input chaps. The gas system was fitted by professional conversion company and the old engine ran fine on gas and petrol before the
exploding dipstick. As far as I am aware, the new engine is the same as the old one except it came out of a 940 and everything went back together ok.
Not too sure if its a B200 F or B200 E, my mate just said it was a 2 litre 20F engine.
I had assumed that the ecu would just go into a get you home mode if the MAF was faulty and allow the engine to still run. I should have been more
specific about the gas by pass. With the servo valve removed altogether and the two pieces of pipe connected strait through so that a constant supply
of gas is entering the inlet manifold, the engine runs. It seems to me that the injectors never get a signal or if they do, they are on for too
shorter time period or are firing at the wrong time. There is fuel pressure at the rail, slackening off the nut securing the supply pipe causes fuel
to squirt out.
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rusty nuts
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| posted on 25/4/12 at 07:24 PM |
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Easy to check if the injectors are firing with a Noid light which just plugs onto the injector plug , crank the engine and the light should flash . If
the engine has been standing the injectors may be sticking ? Might also be worth checking the coolant temperature sensor , a faulty one may cause the
engine to run very weak. If the flywheel was removed or changed was it refitted in the correct position ? It is possible to fit the flywheel in the
wrong position which will upset the ignition timing
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mark chandler
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| posted on 25/4/12 at 09:33 PM |
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I should have been more specific about the gas by pass. With the servo valve removed altogether and the two pieces of pipe connected strait through so
that a constant supply of gas is entering the inlet manifold, the engine runs. It seems to me that the injectors never get a signal or if they do,
they are on for too shorter time period or are firing at the wrong time. There is fuel pressure at the rail, slackening off the nut securing the
supply pipe causes fuel to squirt out.
Servo valve removed, are you refering to the gas vaporiser here (looks like a servo) and the gas regulator that sits in line with the gas Venturi and
one 1/2" pipe to the inlet manifold before the throttle butterfly but after the MAF sensor.
Injectors, it sounds like you are talking about petrol injectors not gas injectors?
If I am correct then if it runs with the gas regulating valve removed and the petrol injectors not working then this is correct for an early LPG
system, as it is running on gas in which case has disabled and spoofed the cars injectors.
If you trace the car injection harness back it will arrive at a emulation box, this is basically some 25ohm resistors and a relay in a box so
switches the injectors on or off. It may even just be a relay switching the power off to the petrol injectors.
Pull the fuse for the LPG system, it will then drop the relay and the petrol injectors will then be energised and try and run just on petrol.
LPG cars will run from cold but as the mapping on these early system is very basic it will be very poorly until hot enough to run properly.
Regards Mark
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chris-g
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| posted on 26/4/12 at 02:38 PM |
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The noid light has to be the next thing to look into, and is strait forward to do. I assume there is crank position sensor somewhere within vicinity
of the flywheel. Any idea how we can test this with a multimeter and ascertain if it is being triggered at the the correct time? Is it likely to just
be a magnetically operated switch?
Mark. From what I remember your description of the LPG system is accurate. The down side is that the battery was not on the car when I was at my
friends, he had to take the battery off another car to start the Volvo. So in theory the relays should already have switched back to petrol mode. I
guess its worth checking the wiring to make sure the relay isn't being energised all the time and turning the petrol injectors off.
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