Help with Fuel Pressure Issue
Posted in the Toyota Corolla Forum
#1 Nov 27, 2010
I have a 1997 1.8L (4 cyl) Corolla DX. I have had trouble with slow acceleration for some time now, but the other night the car would not start. I suspected a fuel delivery problem, because it would crank and fire, but would not run. Well, now the car is running again (without me doing anything to it), but the acceleration problem is still there, so I thought I'd try to get to the bottom of it and avoid it not starting again when it might leave my daughter stranded somewhere. I hooked up a fuel pressure gauage and here are some results I could use some help interpreting.
1. When I turn the car on without starting it, I'm supposed to be able to hear the fuel pump engage for a couple of seconds. However, I hear nothing of the sort (I know the sound a fuel pump usually makes). I have tried this numerous times, including with the rear seat and fuel pump access plate removed. Odd, given that the car starts and runs reasonably well except for poor acceleration.
2. When I turn the ignition on, but don't start the car, the fuel pressure reads zero. The repair manual I have (Chiltons) says it should read between 38 and 44 psi when the key is switched on without the engine running. I have run this test numerous times, always with the same result.
3. Starting the car causes the fuel pressure to jumps up to 40 to 44 psi. That is in the range specified by the repair manual (38-44 psi).
4. Removing the vacuum line from the fuel regulator causes the psi to jump to 50-52 psi.
5. Pinching the return fuel line (as specified in the manual) causes the fuel pressure to go crazy high (much beyond the 60 max the manual says I should allow).
6. I took the car out for a drive around the block with the fuel pressure sensor readable as I drove. When the car sputtered upon attempted acceleration, the fuel pressure was up near 50. When the car settled and ran smoothly, both at higher and lower the speeds, the psi was close to 40.
Q1.a. It seems like the fuel regulator may be faulty (based on items 4, 5, & 6), but would that explain the complete lack of pressure when the ignition is turned on?
Q1.b. What sure fire tests are there to tell if the fuel regulator is faulty (I'd prefer not to spend the $100 to replace it if it doesn't need to be).
Q2.a. The fuel pump is obviously currently working to some extent or the car wouldn't run, so why can't I hear it engage when the ignition is turned on?
Q2.b. Are there other tests I should run to see if the zero pressure when turning the key on (with the car not running) is due to a faulty fuel pump?
Thanks in advance for any help offered.
#2 Nov 28, 2010
IMO, the "key" point is-key on, engine off-you should read pressure and you don't. How about ignition switch issues?
#3 Nov 28, 2010
I don't think there is a problem with the ignition itself, because it functions in all other ways correctly. However, you got me thinking it could be related to that, such as a relay. If the relay that keeps the fuel pump from running with key on, engine off were malfunctioning, would that account for the symptoms I hav (i.e.,#1 and 2 in my original post)?
#4 Nov 29, 2010
I suppose it could. Why not go to the simple stuff....voltmeter the fuel pump at the pump connector, KE EO, and work back from there.
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