I have a Pontiac LeMans, 1989 year of manufacture, engine 1.6 with Rochester TBI 700.

I think that I have a problem with a fuel pressure. Engine idling is bad. Engine idle has 800 rpm with fluctuation +/- 120 rpm and it uses a lot of gasoline. Spark plugs are black with feathery carbon deposit.

I tested fuel delivery pressure with manometer.

Engine not running:
When the ignition is placed in the run position, the fuel pump works for two seconds.
1. The fuel pump works two seconds. I'm reading pressure: 0.8 bar (11.6 psi).
2. The fuel pump stoped. I'm reading pressure: 0.7 bar (10.2 psi).

Engine running:
3. The throttle is closed: 0.9 bar (13 psi) with minimal fluctuation +/- 0.01 bar (0.14 psi).
4. The throttle is wide open: 0.9 bar (13 psi) with minimal fluctuation +/- 0.01 bar (0.14 psi) - the pressure is not falling off.

Well, does anyone have any suggestion?

Thank you for your help in advance.


There is evidence of overfuelling from the fouled plugs and excessive consumption. As you have shown, the fuel pressure is not changing which could be an indication of a faulty fuel pressure regulator.

You would expect the fuel pressure to increase as the RPM increases, to maintain a consistent air-fuel ratio, as higher fuel pressure should deliver more fuel.

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