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95 Pathy intermittent loss of power


Burco
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My 95 V-6 Pathy either runs perfectly, or loses power to the point where it will only reach 25 mph.  Always idles smoothly. Fuel pressure is 32 lbs. with Fuel pressure regulator  connected, 43 with it disconnected. The pressure goes to zero immediatly when engine is killed. ( Not sure if that is normal ) It takes a few seconds to start, which may be related to the loss of fuel pressure. I have a check engine light on, that sometimes dissappears.
 
  I recently changed timing belt and plugs.
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That seems like a low fuel pressure to me; I was thinking that the correct pressure was 43 at idle and 50+ above 2400 rpm.... someone correct me if I'm wrong!  That it idles fine but then runs like crap would maybe be a plugged filter in the engine bay? At least that's where I would start because those filters are cheap, eazay to get to and you only need a star screwdriver to get them off.

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Definitely wrong sir. No vacuum the fuel pressue will be about 43 PSI. With full vacuum it will be around 32 PSI. The only way it would exceed that is if it was boosted and the boost causing a little more pressure(my 1983 280zx did that). 

 

Personal recommendation, find out what the code is first. After that it will be easier to go to the right place.

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43 PSI with the vac line off, 34 with it connected (at idle) is correct. The pressure going to zero as soon as you turn it off is not. It will bleed down eventually, but normally you have to pull the fuel pump fuse and run the engine to bring the pressure down before you open the system, or you spray gas from hell to breakfast. It shouldn't just snap to zero when you turn the pump off. Sounds like fuel is getting out of the rail too easily, and the pump is having a hard time keeping up when the engine is under load. This would also explain why it's taking longer to start. You don't mention a puddle, a fuel smell, or being on fire, so I'm going to assume it's not leaking externally. Idling normally suggests it's not leaking through a bad injector. Sounds like a problem with the regulator to me, but it holds pressure all the way back to the tank on the high-pressure side, so it could be something in the pump assembly leaking back into the tank--though I'm not sure how that would come and go. A clogged filter can cause drop under load, but it wouldn't cause the pressure dropoff when you turn the pump off. 

 

Did you check fuel pressure while it was running normally, or while it was acting up? If you can catch it when it's falling on its face, that might give you a better idea of what's going on. +1 for running codes as well, on the off chance the computer has something useful.

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On 10/14/2022 at 5:37 PM, Slartibartfast said:

43 PSI with the vac line off, 34 with it connected (at idle) is correct. The pressure going to zero as soon as you turn it off is not. It will bleed down eventually, but normally you have to pull the fuel pump fuse and run the engine to bring the pressure down before you open the system, or you spray gas from hell to breakfast. It shouldn't just snap to zero when you turn the pump off. Sounds like fuel is getting out of the rail too easily, and the pump is having a hard time keeping up when the engine is under load. This would also explain why it's taking longer to start. You don't mention a puddle, a fuel smell, or being on fire, so I'm going to assume it's not leaking externally. Idling normally suggests it's not leaking through a bad injector. Sounds like a problem with the regulator to me, but it holds pressure all the way back to the tank on the high-pressure side, so it could be something in the pump assembly leaking back into the tank--though I'm not sure how that would come and go. A clogged filter can cause drop under load, but it wouldn't cause the pressure dropoff when you turn the pump off. 

 

Did you check fuel pressure while it was running normally, or while it was acting up? If you can catch it when it's falling on its face, that might give you a better idea of what's going on. +1 for running codes as well, on the off chance the computer has something useful.

  Yes, I did check the fuel pressure during power loss, and the pressure did not change. Update;  I was discussing it with a friend of mine and waiting for an answer about "fuel pressure loss immediatly after killing engine". The problem went away.  Has been gone for about a hundred miles and ten trips. I asked my friend if he did anything, and he mentioned shaking some electrical connections. I asked if he found any connections loose, and he said "No".  I still need to determine the loss of fuel pressure immediatly after killing the engine, and check the also intermittant check engine code.    Thank all of you for your valuable input. 

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On 10/14/2022 at 5:37 PM, Slartibartfast said:

43 PSI with the vac line off, 34 with it connected (at idle) is correct. The pressure going to zero as soon as you turn it off is not. It will bleed down eventually, but normally you have to pull the fuel pump fuse and run the engine to bring the pressure down before you open the system, or you spray gas from hell to breakfast. It shouldn't just snap to zero when you turn the pump off. Sounds like fuel is getting out of the rail too easily, and the pump is having a hard time keeping up when the engine is under load. This would also explain why it's taking longer to start. You don't mention a puddle, a fuel smell, or being on fire, so I'm going to assume it's not leaking externally. Idling normally suggests it's not leaking through a bad injector. Sounds like a problem with the regulator to me, but it holds pressure all the way back to the tank on the high-pressure side, so it could be something in the pump assembly leaking back into the tank--though I'm not sure how that would come and go. A clogged filter can cause drop under load, but it wouldn't cause the pressure dropoff when you turn the pump off. 

 

Did you check fuel pressure while it was running normally, or while it was acting up? If you can catch it when it's falling on its face, that might give you a better idea of what's going on. +1 for running codes as well, on the off chance the computer has something useful.

Isnt there a check valve to hold the pressure in the fuel rail?

 

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Yeah, if you're losing fuel pressure immediately, there's either a leak somewhere in the lines or the unit in the tank itself. I have seen on some vehicles the rubber hose connected to the pump inside the tank deteriorate over time causing this. But it usually comes with a really hard start condition too. 

 

The MAF wiring was a known issue on these trucks. Right at the connector and wiggling it did temporarily resolve it for a lot of people. So you might want to look there.

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