Engine issues, bad fuel pump or injectors?
Thread Starter
Junior Member
Joined: Sep 2007
Posts: 10
Likes: 0
From: Kalamazoo, MI
Car: 1987 IROC-Z28
Engine: 350 TPI
Engine issues, bad fuel pump or injectors?
This has been a frustrating problem so far. The car is an 87 350 tpi generally stock except a PO put slightly larger injectors on it, 24s I think.
The problem is that sometimes the car will bog down when accelerating at low rpm. It sputters and goes nowhere, and adding more throttle makes the engine knock and run worse. After a little bit it will usually catch and then I have to keep the rpms above about 1700 or it will have problems regardless of what gear its in. The rest of the time the car runs great plenty of power and idles and sounds fine.
It has new spark plug wires, tps sensor and 02 sensor and I've popped in a second identical ecm and same problem. When it is messing up the 02 readings go to 4.44 mv and stay there the entire time it is missing, then goes back to normal readings.
The weirdest thing is the fuel pressure. There is a gauge mounted on the fuel rail. At normal idle it will go to about 43 psi, then fall down to about 40 after a second or two, then bounce between about 35 and 40 rapidly, like engine speed fast and repeat. At some throttle the pressure goes up and the gauge starts bouncing in a larger range centered in the 40s, at about engine speed. When it starts missing the gauge starts bouncing all the way from 50 to 0 and will do that the entire time its missing.
This makes me think that the problem is fuel related, but does this sound like injectors or the fuel pump? All injectors passed resistance testing 16.3-17 ohms.
Sorry for the long post, its been difficult problem to nail down so far. Any thoughts?
The problem is that sometimes the car will bog down when accelerating at low rpm. It sputters and goes nowhere, and adding more throttle makes the engine knock and run worse. After a little bit it will usually catch and then I have to keep the rpms above about 1700 or it will have problems regardless of what gear its in. The rest of the time the car runs great plenty of power and idles and sounds fine.
It has new spark plug wires, tps sensor and 02 sensor and I've popped in a second identical ecm and same problem. When it is messing up the 02 readings go to 4.44 mv and stay there the entire time it is missing, then goes back to normal readings.
The weirdest thing is the fuel pressure. There is a gauge mounted on the fuel rail. At normal idle it will go to about 43 psi, then fall down to about 40 after a second or two, then bounce between about 35 and 40 rapidly, like engine speed fast and repeat. At some throttle the pressure goes up and the gauge starts bouncing in a larger range centered in the 40s, at about engine speed. When it starts missing the gauge starts bouncing all the way from 50 to 0 and will do that the entire time its missing.
This makes me think that the problem is fuel related, but does this sound like injectors or the fuel pump? All injectors passed resistance testing 16.3-17 ohms.
Sorry for the long post, its been difficult problem to nail down so far. Any thoughts?
Thread Starter
Junior Member
Joined: Sep 2007
Posts: 10
Likes: 0
From: Kalamazoo, MI
Car: 1987 IROC-Z28
Engine: 350 TPI
Re: Engine issues, bad fuel pump or injectors?
Well I just changed the pressure regulator, no change. Fuel pressure still still oscillating like crazy, 0-50 when its missing
Thread Starter
Junior Member
Joined: Sep 2007
Posts: 10
Likes: 0
From: Kalamazoo, MI
Car: 1987 IROC-Z28
Engine: 350 TPI
Re: Engine issues, bad fuel pump or injectors?
Well problem is fixed. Turns out I had a bad fuel pressure gauge and a bad pump. Changing the gauge showed me my fuel pressure was only getting up in the 20s. So after a minor battle the pump is changed and pressure is back up where it needs to be. Drives like a whole new car
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