• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

240 with fuel pressure problem.

H

hessam69

Well-known member
Joined
Jun 19, 2009
Location
Sydney, Australia
I have a 1989 240 with LH2.4.

In hot weather, it would drive for 10-15 minutes before it would start losing fuel pressure to the point of being undrivable.

In cooler temperatures, it drives fine for about half an hour then loses fuel pressure, but only in high load high rpm conditions. The fuel pressure loss is up to 20-25psi at its worst. During cruising and at idle, the pressure stays constantly at 35-40psi.

What I found was that shutting the engine down and restarting it immediately resulted in a perfect running engine with correct fuel pressure, for about five minutes, until the fuel pressure starts dropping again.

Fuel level was at full during this test.

Both fuel pumps and fuel filters are new.

Is there something going on with the fuel tank or it’s ability to vent?

Thanks to everyone for any and all help.
 
What about fuel regulator on the rail? It's working good? Are u sure it's correct one with good pressure rating? Fuel pattern of injectors?
 
Are you sure the in tank pump is running the correct direction? What is the fuel pressure reading with just the in tank pump running? Just disconnect one of the leads to the main pump and cycle the key a few times to build system pressure.
 
2manyturbos said:
Are you sure the in tank pump is running the correct direction? What is the fuel pressure reading with just the in tank pump running? Just disconnect one of the leads to the main pump and cycle the key a few times to build system pressure.
Click to expand...
I thought about exactly that, and I disconnected the tank pump and the pressure drop occurred sooner.

Reconnected and pressure improved.

I have not tried running the engine only with the tank pump operating.

This would present a problem all of the time though if it were backwards wired?
 
I’ve had 2, 7, 9 series cars with dead in tank pumps that didn’t affect the pressure readings at all. It sounds like you’ve already ruled out the pump running backwards. It sounds to me like the pumps are keeping up until the fuel demand becomes high enough to cause a problem, thus, the pressure drop. In other words, there must be something restricting the uptake of fuel from the tank.
 
2manyturbos said:
I’ve had 2, 7, 9 series cars with dead in tank pumps that didn’t affect the pressure readings at all. It sounds like you’ve already ruled out the pump running backwards. It sounds to me like the pumps are keeping up until the fuel demand becomes high enough to cause a problem, thus, the pressure drop. In other words, there must be something restricting the uptake of fuel from the tank.
Click to expand...
Yes you’re definitely right.

On really hot days the car can only be driven for about 15 minutes.

It feels like excessive pressure builds in the tank, stopping the pump from doing its job.

Turning the engine off seems to neutralise the pressure, then another five minutes and it’s too high again.

Cold weather is not as bad.

No other drivability issues.
 
Take the fuel tank cap off and drive the car. Pressure in the tank would only help the fuel pumps to pump fuel. In other words, you would not get a drop in pressure that you could see on a fuel pressure tester. If pressure in the tank made it more difficult for the return line to dump fuel in the tank you would see a pressure rise on a gauge, not a drop.
 
2manyturbos said:
Take the fuel tank cap off and drive the car. Pressure in the tank would only help the fuel pumps to pump fuel. In other words, you would not get a drop in pressure that you could see on a fuel pressure tester. If pressure in the tank made it more difficult for the return line to dump fuel in the tank you would see a pressure rise on a gauge, not a drop.
Click to expand...
Interesting. I will try that.

What about if vacuum in the tank was too excessive?

Thank you for your help.
 
Vacuum would not have much effect on the ability for the of the pump to pump the fuel because you have the weight of the fuel column. IOW, gravity.
 
2manyturbos said:
Vacuum would not have much effect on the ability for the of the pump to pump the fuel because you have the weight of the fuel column. IOW, gravity.
Click to expand...
It’s definitely a heat related issue.

Just cannot think of what particularly causes the heat to drop the fuel pressure.

I will remove the fuel cap and test.
 
hessam69 said:
It’s definitely a heat related issue.

Just cannot think of what particularly causes the heat to drop the fuel pressure.

I will remove the fuel cap and test.
Click to expand...
sounds like exactly the symptoms of vapor lock.

have you tried plugging both vacuum lines going to the charcoal canister? loop them into each other at the manifold
 
check the computer temp sensor in the head.

do you have an actual temp gauge or the stupid compensator stock water gauge?
is there a chance your car is running hotter than you think it is?

do you have the plastic bellypan installed in your car?

pull your spark plugs and see how they look

fuel pump relay getting hot?
 
Last edited:
240 240 said:
sounds like exactly the symptoms of vapor lock.

have you tried plugging both vacuum lines going to the charcoal canister? loop them into each other at the manifold
Click to expand...
That’s interesting what you’re describing.

What does doing that achieve? Someone else did mention a possible problem involving the charcoal canister.
 
240 240 said:
check the computer temp sensor in the head.

do you have an actual temp gauge or the stupid compensator stock water gauge?
is there a chance your car is running hotter than you think it is?

do you have the plastic bellypan installed in your car?

pull your spark plugs and see how they look

fuel pump relay getting hot?
Click to expand...
The car is 100% standard with no modifications. The standard temp gauge is working as it should.

I did consider a possible fault involving the temp sensor. I tested it and the output was correct. I even disconnected it and drove the car to rule it out, no change.

There is no plastic protection panel fitted.

I haven’t removed the spark plugs yet.

I did test the fuel pump relay. Yes, it was getting warm, but so was the brand new one I tested. No change.

Something is definitely telling me the problem relates to something going on with the fuel tank, the lines, or the charcoal canister and it’s lines.

Someone else told me that’s where I should look first.

I also wanted to drive the car with no gas cap, something I will test tomorrow.
 
hessam69 said:
The car is 100% standard with no modifications. The standard temp gauge is working as it should.

I did consider a possible fault involving the temp sensor. I tested it and the output was correct. I even disconnected it and drove the car to rule it out, no change.

There is no plastic protection panel fitted.

I haven’t removed the spark plugs yet.

I did test the fuel pump relay. Yes, it was getting warm, but so was the brand new one I tested. No change.

Something is definitely telling me the problem relates to something going on with the fuel tank, the lines, or the charcoal canister and it’s lines.

Someone else told me that’s where I should look first.

I also wanted to drive the car with no gas cap, something I will test tomorrow.
Click to expand...
eh, dont be so sure of your "testing" and assuming that temp gauge is working correctly. What coolant cap are you using? which temp tstat? do your hoses get hard when you lose pressure?

disconnecting the temp sensor doesn't rule it out. did you test current at the computer and the actual sensor?

put the belly pan on. its that important. it controls the flow of air to cool down the engine bay.

lean burn conditions, too hot thermostat or overheating engine, heat soak, clogged vapor canister, bad injectors, etc etc can lead to the car being overworked and thus overheating the fuel.
a clogged cat or bad o2 sensor can also affect this
 
240 240 said:
eh, dont be so sure of your "testing" and assuming that temp gauge is working correctly. What coolant cap are you using? which temp tstat? do your hoses get hard when you lose pressure?

disconnecting the temp sensor doesn't rule it out. did you test current at the computer and the actual sensor?

put the belly pan on. its that important. it controls the flow of air to cool down the engine bay.

lean burn conditions, too hot thermostat or overheating engine, heat soak, clogged vapor canister, bad injectors, etc etc can lead to the car being overworked and thus overheating the fuel.
a clogged cat or bad o2 sensor can also affect this
Click to expand...
All of your advice is important regarding diagnosing this issue.

About the coolant temp, I have a thermal imaging camera which I can use to tell me the exact temperature once I get the engine hot enough.

The cooling system has been already done on this car, and I have no valid reason to believe it is overheating. It’s had a recent radiator, water pump and an 87° thermostat. It doesn’t show any sign of overheating, but I will test the actual temp as you recommended. I will also check the temp sensor once the engine is hot (not just cold like I tested before).

There is no catalytic converter (been deleted).

I will keep testing, in the meantime as I drive the car, I will test the fuel pressure with no fuel cap and or disconnected lines to the charcoal canister.

Thank you for your help this far.
 
You must log in or register to reply here.
Back
Top