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Any K-Jet experts? Starting issue needs diagnosis!

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Old Jun 12th, 2020, 00:05   #1
Vakito
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Default Any K-Jet experts? Starting issue needs diagnosis!

Hi all, I own a 1988 240 Saloon with the 2.0L K-Jetronic engine.

Once started the engine runs perfectly, pulls a strong 20"Hg vacuum at 1000rpm idle and eats up thousands upon thousands of miles without a care in the world. However all my time owning it I have had troubles starting it and to make things worse this is an intermittent fault. This really puts a lot of stress on my recently replaced engine mounts. Here's what I've observed:

- When starting the engine feels like it's firing on 3 and sometimes 2 cylinders, the throttle feels slightly more delayed and you have to rev it to about ~1500rpm for a few seconds before everything smooths out
- Sometimes it will start and immediately stall, sometimes it will start and run down over a few seconds until it stalls.
- It it stalls, the engine takes a bit of cranking to get it going again, unless you anticipate this quick enough and turn the key back to zero before it stalls, in which case it will very often surprisingly start back up immediately with no issues.
- This whole starting issue affects probably 20% of cold starts and 90% of warm/hot starts.
- I have not noticed any correlation between this problem and weather conditions
- Once started like I said, engine runs perfectly with no issues whatsoever.

Here's what I have currently done, with no success in curing the problem.

- New plugs, leads, distributor cap and fixed type rotor arm.
- New fuel pump relay
- New fuel filter
- Thorough cleaning of fuel injectors with new O-rings
- Cleaned throttle body
- Polishing of distributor and rotor arm contacts every few thousand miles
- Replacement of all cracked vacuum lines

I believe the problem may lie with either the fuel accumulator, the one way valve on the fuel pump, the ignition coil or god forbid the K-Jet metering unit but before I go throwing more money at the problem has anybody else had this experience and any success in curing it?

Thanks

Last edited by Vakito; Jun 12th, 2020 at 00:22.
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Old Jun 12th, 2020, 00:53   #2
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Hi,

In all honesty these problems all sound familiar to what I have had over the past decade with my own 1989 K-jet 2.0.

Check the condition of the six connections in the plug that the fuel pump relay plugs into I ended up replacing the six female spade connections in that plug and starting/running improved greatly.

Also replace the vacuum line that runs from the throttle body to the distributor this had perished on mine and went unnoticed for years once replaced behaviour improved.

Hope this may be of use.

Scott
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Old Jun 12th, 2020, 02:45   #3
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Hi Scott, thanks for the advice

Yeah it looks like it's a fairly common problem but the solutions seem to widely vary between each individual.

Sorry I forgot to mention that I cleaned the spades and replaced the plastic connector on the fuel pump relay since it had actually melted due to the main pump drawing excessive amps during the time before I replaced the broken in tank pump. I have now also got the output of the new fuel pump relay going into the solenoid of a separate generic 40A relay to take the load off it.

As for the vacuum line, I have replaced all the old cracked rubber hoses with silicone vacuum hoses. However, a previous owner had fitted what looks like some kind of air filter although I'm not sure on the large vacuum hose going into the brake servo. I have no idea what purpose it serves and I have been meaning to swap it out for a standard piece of hose all the way for a while now but the engine still pulls a nice strong vacuum.

Another thing I haven't checked yet are the fuses, probably benefit from polishing the contacts

Peter
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Old Jun 12th, 2020, 09:54   #4
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Ok,

The additional relay may not be helping it's usually best to strip a circuit back to as original as possible.

The main pump drawing too much current isn't good is it noisy when the engine runs?

Is the in tank pump working properly? When this fails it gives the main pump far more work to do especially on start up there is also a short rubber hose that joins the fuel pickup in the sender unit to the in tank pump.

Out of interest how many miles had your Volvo covered so far?

Also the fuse boxes on these cars are pants I'm forever having to clean the fuse holders with a small piece of wet and dry paper.

Scott
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Old Jun 12th, 2020, 14:17   #5
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Hi Scott

I replaced the in tank pump months ago but yes before that the main pump was being excessively noisy which is how I realised it needed replacing, I replaced the rubber hoses in the sender unit too. All is okay with that now.

I'd say around ~210,000 miles ish. I'm saying that because it currently reads 190,000 miles but the previous owner said the odometer was broken for years.

Peter
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Old Oct 19th, 2020, 19:46   #6
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Quote:
Originally Posted by Vakito View Post
Hi all, I own a 1988 240 Saloon with the 2.0L K-Jetronic engine.

Once started the engine runs perfectly, pulls a strong 20"Hg vacuum at 1000rpm idle and eats up thousands upon thousands of miles without a care in the world. However all my time owning it I have had troubles starting it and to make things worse this is an intermittent fault. This really puts a lot of stress on my recently replaced engine mounts. Here's what I've observed:

- When starting the engine feels like it's firing on 3 and sometimes 2 cylinders, the throttle feels slightly more delayed and you have to rev it to about ~1500rpm for a few seconds before everything smooths out
- Sometimes it will start and immediately stall, sometimes it will start and run down over a few seconds until it stalls.
- It it stalls, the engine takes a bit of cranking to get it going again, unless you anticipate this quick enough and turn the key back to zero before it stalls, in which case it will very often surprisingly start back up immediately with no issues.
- This whole starting issue affects probably 20% of cold starts and 90% of warm/hot starts.
- I have not noticed any correlation between this problem and weather conditions
- Once started like I said, engine runs perfectly with no issues whatsoever.

Here's what I have currently done, with no success in curing the problem.

- New plugs, leads, distributor cap and fixed type rotor arm.
- New fuel pump relay
- New fuel filter
- Thorough cleaning of fuel injectors with new O-rings
- Cleaned throttle body
- Polishing of distributor and rotor arm contacts every few thousand miles
- Replacement of all cracked vacuum lines

I believe the problem may lie with either the fuel accumulator, the one way valve on the fuel pump, the ignition coil or god forbid the K-Jet metering unit but before I go throwing more money at the problem has anybody else had this experience and any success in curing it?

Thanks
Right then, My money is on a faulty warm up regulator or auxiliary air valve.

Assuming you have checked and sorted out ignition problems,( you have) and the relay is not faulty(replaced with a new one)

The first thing to do is check all the pipes for vacuum leaks you can snip off the end of the vacuum lines lines and refit them
if the lines are long enough and a push fit just cut off the tip that is wider than the rest of the pipe

secondly check all the pipes that feed air from the metering unit for splits cracks etc and are not leaking between the metering unit and the throttle body,leaks here will reduce the pull on the metering plate screwing up the mixture for starting and once running will cause a weaker mixture when these leaks open up to atmosphere

from your description I think you have the following problems these are caused by the control pressure regulator being faulty or there is a leak in the lines to it, check fuel and vacuum if you have vacuum depending on which one you have.

The control pressure is managed by the control pressure regulator during warm up and also acceleration if a vacuum connection is present
Behind the larger of the 2 unions is a metal gauze filter. If this gets blocked, it causes the warm up regulator to remain closed, causing very bad flat spots and poor acceleration during the warm up, its like driving with the choke in. It can be cleaned using clean petrol. It also has a vacuum connection to it.This is for full load enrichment.
At full load,the engine vacuum is low, which opens the valve slightly, reducing the pressure on the control plunger and giving a slightly richer mixture exactly like an accelerator pump in a carburettor

Inside the main fuel feed line to the metering head is a small mesh type filter which you should remove and either clean thoroughly or replace it, see a manual how to do this
they are cheap and available on ebay but be careful replacing it as you may need new seals for the banjo bolts etc

check the smoothness of the air flow sensor plate it should not be jerky just smooth and easy.

Also sometimes the Auxiliary air valve sticks closed and does not open test this as follows

Cold Operation.

Test the auxiliary air valve first with the engine cold (not run for several hours, preferably overnight).
Disconnect the electric plug from the auxiliary air valve and from the control pressure regulator.
Remove both air hoses from the auxiliary air valve.Using a torch and a mirror, look through the valve When the engine is cold, the valve must be open. If not, the auxiliary air valve is knackered also check the voltage at the plug should be 11.5 volts minimum

Warm Operation.

Disconnect the electrical connection plug to the auxiliary air valve. feed 12v to the auxiliary air valve pins observing the correct polarity, you will know which way around it is from the previous test, the valve must be completely closed within about 10 minutes.
If the auxiliary air valve does not completely close within about 10 minutes, it's knackered.

The cold start injector is only squirting fuel when the starter motor is active but a dribbling injector will cause a rich mixture

some of the faults you describe make me think its these listed below

Engine stalls immediately after starting(warm)

1)Warm control pressure
If the warm control pressure is too high,the
air-fuel ratio will be very lean,causing the engine
to die.
2)System pressure
If the system pressure is too high or too low,the
air-fuel ratio will be incorrect.Incorrect fuel
pressure can result in either a rich or lean running
engine.Either one can cause the engine to stall
after start up.

Engine stalls immediately after starting(warm)
1)Warm control pressure
If the warm control pressure is too high,the
air-fuel ratio will be very lean,causing the engine
to die.

2)System pressure
If the system pressure is too high or too low,the
air-fuel ratio will be incorrect.Incorrect fuel
pressure can result in either a rich or lean running
engine.Either one can cause the engine to stall
after start up.

for those who don't know ....

The Auxiliary air valve looks like this

http://www.bosch-classic.com/media/b...ll_gb_w734.jpg

The warm-up regulator, also called the control pressure regulator, looks like this

http://www.bosch-classic.com/media/b...er_gb_w734.jpg

hope this helps
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Old Oct 20th, 2020, 14:57   #7
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I have a 740 with similar symptoms however always starts. I suspect a leak on the injection pipes but in my 20 years of ownership I haven't checked them properly lol

TBF I only came up with the theory recently after actually sitting down and working the system out, it seems to work very similar to a diesel in that it needs pressure to make the injectors "pop" therefore a slight leak allows pressure to drop in the line thus not allowing that injector to fire until pressure is regained. MY other theory is a leaking injector which is washing the cylinder walls and taking away compression until the oil is replaced.
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Old Oct 23rd, 2020, 01:16   #8
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Quote:
Originally Posted by NI_Volvo_Nut View Post
I have a 740 with similar symptoms however always starts. I suspect a leak on the injection pipes but in my 20 years of ownership I haven't checked them properly lol

TBF I only came up with the theory recently after actually sitting down and working the system out, it seems to work very similar to a diesel in that it needs pressure to make the injectors "pop" therefore a slight leak allows pressure to drop in the line thus not allowing that injector to fire until pressure is regained. MY other theory is a leaking injector which is washing the cylinder walls and taking away compression until the oil is replaced.
The fuel injectors don't work like diesel ones which crack open under a typical injection pressure pulse of between 1000 to 2200 bar or 14503.77 psi to 31908.3 psi pressure in mechanical diesel pump arrangements, or opened electrically in modern electronic systems at the correct timing.

the K jetronic injector feed line pressure has got to be 3.3 bar or 47.8 psi to open the injectors and once the engine is running the injectors are open continuously spraying fuel onto the back of the inlet valves all the time.
The pressure at the injector will go up depending on the throttle position to around 4.5 bar.
If the injector line was leaking you would see fuel spraying out at 3.3 bar or more and probably catching fire quickly, you would certainly smell fuel if it was leaking at the very least.

its more likely that the injector is sticking closed reducing the available fuel to the cylinder, you would notice a misfire possibly intermittent, also a leaking injector would not cause a problem while driving because of the normal fuel delivery is greater than the leak and once the engine is stopped the control pressure is reduced and the line pressure drops in the injector lines below 3.3 bar and the injectors close if you suspect a leaking injector you can test them with jam jars and the offending injector will need replacing/cleaning.

Also the cylinder that may have a leaking injector will cause the idle CO reading to go up depending on how much extra fuel its giving out at idle and if its leaking into the cylinder that would be intermittent due to the inlet valve on that cylinder either being open or closed when the engine stops and letting the fuel run in until the line pressure has gone down this might cause starting issues but may not be noticeable due to the choke effect on starting depending on how bad the leak is, normally if there is a leaky injector its the cold start injector that leaks a dribble that evaporates before the next starting up.

The cold start injector is electrically opened on starting to richen the mix like pulling the choke on a carburettor by power supplied to it during the cranking of the starter motor

The fuel pressure fed to the metering head is more than enough to cope with a small pressure drop from the lines leaking hence the huge fuel leak you might see a huge fire ball to confirm a leak while driving

If your engine has low compression and needs oil to hold the compression in the cylinder your engine needs
to be rebuilt due to worn piston rings

Hope this helps with your 740's diagnosis

Andy
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Old Oct 23rd, 2020, 01:36   #9
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Quote:
Originally Posted by Vakito View Post
Hi all, I own a 1988 240 Saloon with the 2.0L K-Jetronic engine.

Once started the engine runs perfectly, pulls a strong 20"Hg vacuum at 1000rpm idle and eats up thousands upon thousands of miles without a care in the world. However all my time owning it I have had troubles starting it and to make things worse this is an intermittent fault. This really puts a lot of stress on my recently replaced engine mounts. Here's what I've observed:

- When starting the engine feels like it's firing on 3 and sometimes 2 cylinders, the throttle feels slightly more delayed and you have to rev it to about ~1500rpm for a few seconds before everything smooths out
- Sometimes it will start and immediately stall, sometimes it will start and run down over a few seconds until it stalls.
- It it stalls, the engine takes a bit of cranking to get it going again, unless you anticipate this quick enough and turn the key back to zero before it stalls, in which case it will very often surprisingly start back up immediately with no issues.
- This whole starting issue affects probably 20% of cold starts and 90% of warm/hot starts.
- I have not noticed any correlation between this problem and weather conditions
- Once started like I said, engine runs perfectly with no issues whatsoever.

Here's what I have currently done, with no success in curing the problem.

- New plugs, leads, distributor cap and fixed type rotor arm.
- New fuel pump relay
- New fuel filter
- Thorough cleaning of fuel injectors with new O-rings
- Cleaned throttle body
- Polishing of distributor and rotor arm contacts every few thousand miles
- Replacement of all cracked vacuum lines

I believe the problem may lie with either the fuel accumulator, the one way valve on the fuel pump, the ignition coil or god forbid the K-Jet metering unit but before I go throwing more money at the problem has anybody else had this experience and any success in curing it?

Thanks
OOh Vakito,

thinking about it and posting the info above I have just realised you need to check this as well it could be helpful too the relevant bit is below regarding the misfire bit of your original description

its more likely that the injector is sticking closed reducing the available fuel to the cylinder, you would notice a misfire possibly intermittent, also a leaking injector would not cause a problem while driving because of the normal fuel delivery is greater than the leak and once the engine is stopped the control pressure is reduced and the line pressure drops in the injector lines below 3.3 bar and the injectors close if you suspect a leaking injector you can test them with jam jars and the offending injector will need replacing/cleaning.
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Old Oct 23rd, 2020, 11:01   #10
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Quote:
Originally Posted by AndrewBrown View Post
The fuel injectors don't work like diesel ones which crack open under a typical injection pressure pulse of between 1000 to 2200 bar or 14503.77 psi to 31908.3 psi pressure in mechanical diesel pump arrangements, or opened electrically in modern electronic systems at the correct timing.

the K jetronic injector feed line pressure has got to be 3.3 bar or 47.8 psi to open the injectors and once the engine is running the injectors are open continuously spraying fuel onto the back of the inlet valves all the time.
The pressure at the injector will go up depending on the throttle position to around 4.5 bar.
If the injector line was leaking you would see fuel spraying out at 3.3 bar or more and probably catching fire quickly, you would certainly smell fuel if it was leaking at the very least.

its more likely that the injector is sticking closed reducing the available fuel to the cylinder, you would notice a misfire possibly intermittent, also a leaking injector would not cause a problem while driving because of the normal fuel delivery is greater than the leak and once the engine is stopped the control pressure is reduced and the line pressure drops in the injector lines below 3.3 bar and the injectors close if you suspect a leaking injector you can test them with jam jars and the offending injector will need replacing/cleaning.

Also the cylinder that may have a leaking injector will cause the idle CO reading to go up depending on how much extra fuel its giving out at idle and if its leaking into the cylinder that would be intermittent due to the inlet valve on that cylinder either being open or closed when the engine stops and letting the fuel run in until the line pressure has gone down this might cause starting issues but may not be noticeable due to the choke effect on starting depending on how bad the leak is, normally if there is a leaky injector its the cold start injector that leaks a dribble that evaporates before the next starting up.

The cold start injector is electrically opened on starting to richen the mix like pulling the choke on a carburettor by power supplied to it during the cranking of the starter motor

The fuel pressure fed to the metering head is more than enough to cope with a small pressure drop from the lines leaking hence the huge fuel leak you might see a huge fire ball to confirm a leak while driving

If your engine has low compression and needs oil to hold the compression in the cylinder your engine needs
to be rebuilt due to worn piston rings

Hope this helps with your 740's diagnosis

Andy
Thanks for this. The issue I have mainly occurs after a long drive or a period of heavy work - towing a trailer for example, so whatever it is - it is heat related. It does have a slight misfire which I have never gotten to the bottom of, compression test is good and wet test is as expected. Because it is so intermittent I have never had a opportunity to pull a plug lead to determine which cylinder is the cause, but really until I do that I can't go much further. I did change the injectors a few years ago with set from a car with no issues which made no difference. A few years ago I restored a 740 which was off a cylinder one day returning from work which turned out to be a split injector pipe which is were I developed my theory of how the injectors work. I need to do the PCV and I want to clean the injection / air metering unit while I'm down that far so will inspect joints and pipes at that time.
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