Pontiac LeMans 1.6 TBI - fuel pressure problems?

[autominus]

Hi all,
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:

1. The throttle is closed: 0.9 bar (13 psi) with minimal fluctuation +/- 0.01 bar (0.14 psi).
2. 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.

 

[92 Sunbird LE]

Pressure reads good from what I found online ( 9 -13 psi on the 1.6 LeMans TBI)

Have you checked your IAC? ( Idle Air Control valve)? They get dirty and the port it sits in on the throttle body. It's a big nut on the side of the body with a wire connector. Just needs to be unscrewed, cleaned with throttle body spray , and the port on the body also.


When dirty, your idle will go up and down, when cleaned it will take a few days to relearn idle .

Also try unpluging your map sensor if after cleaning the IAC it still acts up.

Could also be the small rubber hose that connects the fuel pump to the steel line inside the tank. It gets old and splits and you lose fuel pressure.

Try the upper things above first, more easier to do than dropping the tank.

Doug in P.R.

 

[autominus]

Pressure reads good from what I found online ( 9 -13 psi on the 1.6 LeMans TBI)

This is a wide pressure range of values.

Have you checked your IAC? ( Idle Air Control valve)?

Okay, I'll check the IAC.

Try the upper things above first, more easier to do than dropping the tank.

I have easily access to the fuel pump by removing the bottom, of the back seat.

It gets old and splits and you lose fuel pressure.

I started the engine for a few minutes. But at runtime, I'm reading pressure: 0.9 bar (13 psi). When I stopped the engine, pressure's down to 0.7 bar (10.2 psi).
After a few hours I'm reading pressure 0.7 bar (10.2 psi). This pressure holds where the engine not running.

Has the fuel pressure shouldn't be constantly at all times? - both when the engine is running and turned off.

 

[92 Sunbird LE]

No , pressure drops out the return line when the car is shut off, these cars run on pulse type pump that only runs when demand is needed. Newer cars pumps run all the time.If your pressure regulator is bad , then you would of lost more pressure when you checked it after the 2 hours.

My 90 tbi Chevy pickup bleeds most of the fuel out when shut down. My 90 mpfi Sunbird has a primer solenoid that primes the fuel rail when the key is turned . So that pump only comes on for a split second. The truck take a few cranks to start. The Sunbird starts instantly.

I still suspect the IAC in your case....

Doug in P.R.

______________________________

 

[autominus]

I still suspect the IAC in your case....

The IAC seems to be working. I measured the distance that the valve is extended and it has 28 mm. This distance of pintle extension is correct. Signal from an ECU is okay - I did test an IAC valve as instructed.



One year ago has been replaced a fuel pump. This supply pump has sign on the casing: maximum pressure 3 bar. Its catalogue number isn't known.
However, the old pump has OEM part number: AC 6441376. So, I've decided for the purchase of the new supply pump.
Well, yesterday, I replaced the fuel pump for a new. New the pump has sign on the casting: operating pressure 0,8 [bar], flow rate 80 [l/h]. Its catalogue number is in line with original part of the GM 6441376.

Now when I tested fuel delivery pressure with manometer, I have results:

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: 0.715 bar (10.37 psi).
2. The fuel pump stopped. I'm reading pressure: 0.615 bar (8.91 psi).

​

I watching manometer and... waiting, at least ten minutes. At that time I observed that fuel pressure's down to 0.4 bar (5.8 psi).
So I did some tests and the fuel pressure falls slowly in one instance or quickly in another.



I haven't fired up the engine, because I need to clean the spark plugs from carbon deposit.

Well, does anyone have any suggestion?

 

[92 Sunbird LE]

Hopefully you cleaned the IAC while you had it out.

Did you check the fuel pressure regulator be on the throttle body? Some times the little spring breaks or the gasket leaks.

Try some Seafoam in the tank.


Fuel filter changed?(every 3rd oil change)

Is a fuel line kinked under the car?

Plug up the hose to the EGR valve, see if the idle improves.
.

Look for vacumn leaks.

Change plugs to Autolite platinum, they burn better in oil or rich conditions.



Doug in P.R.