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.

1 Answer 1


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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