Low gas pressure in 96 sunfire. Replaced the oxygen sensor, vacuum hose, fuel pump and fuel filter. Fixed the ignition regulator. When I shut off the car it sometimes fires right up right away. It used to fire up right away when shut off for less than 10 minutes. This happens even when it is cold out.

If you have checked the ignition system, replaced the fuel pumps and fuel filter, and the TPS voltage is stable when driving, there are a few other potential causes of your 1988 Bronco 2 2.9's issue:

1. Check the fuel pressure regulator: A faulty fuel pressure regulator can cause a lack of power and poor performance. Check the fuel pressure at the fuel rail and make sure it is within the manufacturer's recommended range.
2. Check the mass air flow sensor (MAF): A dirty or faulty MAF can cause the engine to run poorly. Remove the MAF and clean it with a MAF cleaner, or replace it if necessary.
3. Check the oxygen sensor: A bad oxygen sensor can cause the engine to run poorly and result in decreased fuel efficiency. Check the oxygen sensor and replace if necessary.
4. Check for vacuum leaks: Vacuum leaks can cause a variety of issues with the engine's performance. Check all vacuum hoses for cracks, breaks, or loose connections.
5. Check the catalytic converter: A clogged or damaged catalytic converter can cause a lack of power and poor performance. Check the exhaust flow and replace the catalytic converter if necessary.

If these steps do not resolve the issue, it may be necessary to take the Bronco to a professional mechanic for further diagnosis and repair.

oxygen sensors can't be cleaned. They're porous. If they're silled with soot, you have to replace them. Plus, O2 sensors don't caused lean codes, they only report them. Stop looking at the oxygen sensors and look for a vacuum leak, low fuel pressure or clogged fuel injectors.

You should have a test port on the Fuel Supply rail, use a tool from a local auto parts "Tool Loaner program" where you can borrow tools for free,w/a deposit of course,then follow the steps provided;

MPI Fuel System Pressure Test

The MPI fuel system used in vehicles equipped with a 4.OL engine employs a vacuum balanced pressure regulator. Fuel pressure should be approximately 55-69 kPa (8-10 psi) lower with the vacuum line attached to the regulator than with the vacuum line disconnected. System fuel should be 214 kPa (31 psi) with the vacuum line connected to the regulator and 269 kPa (39 psi) with the vacuum line disconnected. CAUTION: Some fuel may be discharged when connecting fuel gauge to fuel rail.

1. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to test port pressure fitting on fuel rail (Fig. 7).
2. Remove vacuum line from pressure regulator.
3. Start the vehicle.
4. Note gauge reading. With vacuum line disconnected, fuel pressure should be approximately 269 kPa (39 psi).
5. Connect vacuum line to pressure regulator. Note gauge reading. Fuel pressure should be approximately 214 kPa (31 psi).
6. If fuel pressure is not approximately 55-69 kPa (8-10 psi) higher with vacuum line removed from regulator, inspect pressure regulator vacuum line for leaks, kinks or blockage. CAUTION: Fuel pressure will rise to as much as 655 kPa (95 psi) when the fuel return tine is pinched shut, shut engine down immediately after pinching oft fuel return line.
7. If fuel pressure is low, momentarily pinch shut the hose section of the fuel return line. If fuel pressure remains low, inspect the fuel supply line, fuel filter, and fuel rail inlet for blockage. If fuel pressure rises replace fuel pressure regulator.
8. If fuel pressure is above specifications, inspect the fuel return line for kinks and blockage.

Capacity Test

1. Remove the cap from the pressure test port in the fuel rail.
2. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to the pressure fitting on the fuel rail (Fig. 7).
3. Start the vehicle. Pressure should be approxi- mately 214 kPa (31 psi) with the vacuum hose connected to the pressure regulator and 269 kPa (39 psi) with the vacuum hose removed from the pressure regulator.
4. If the pressure is not to specification, check the following before replacing the fuel pressure regulator:

• 4a - Inspect the fuel supply and return lines/hoses for kinks or restricting bends
• 4b - Check the fuel pump flow rate. A good fuel pump will deliver at least 1 liter of fuel per minute with the fuel return line pinched off. If the fuel pump does not pump adequately, then inspect the fuel system for a plugged fuel filter or fuel pump inlet filter (sock). Fuel pump flow rate can be done by connecting one end of an old A/C gauge hose to the fuel test port on the fuel rail and inserting the other end of the hose into a container of at least 1 liter capacity. Run the fuel pump by installing a jumper wire into diagnostic connector terminals D1-5 and D1-6. Be sure to pinch off the fuel return line or most of the fuel will be returned to the fuel tank.

P1131--Lack of HO2S-11 Switch,Sensor Indicates Lean

Front O2 Sensor -- at converter inlet,pass side (Bank #1)

Could be ten things

Check that you have no vacuum leaks anywhere,including
the exhaust manifold & system

Check air filter cover & ducting for leaks

I doubt you have experience or test equip to test
the O2 Sensors, so replace both front ones, if you
have dual exhaust

going what you say here i would try a coolant sensor get it from the dealor its better.

CHECK THE JETS , YOU HAVE GAS PRESSER BUT YOU COULD HAVE MAYBE JET PROBLEMS AND CHECK AIR HOSE'S.

------------
GAS-------INTO-------JETS---into---------ENGINE-----LOW RPM
-------------

SOUND LIKE VACUUM LEAK AT INTAKE MANIFOLD LOOK FOR STUCK OPEN PCV VALVE OR LEAKING EGR VALVE GASKET.CHECK MAP SENSOR VACUUM HOSE MAKE SURE ITS CONNECTED AND GETTING VACUUM OR CHECK FOR A DISCONNECTED ELECTRICAL CONNECTOR AT MAP SENSOR.IF ALL LOOK GOOD CHECK FUEL PRESSURE SHOULD BE 40 - 50 PSI FOR 98 TO 2001 CADILLACS WITH 4.6 ENGINES CADILLACS 92 TO 97 MODELS WITH ENGINES 4.9 TO 3.8 FUEL PRESSURE 41 - 47 PSI. THATS YOUR FUEL PRESSURES WITH NEW FUEL FILTERS.IF FUEL PRESSURE WAY LOW FUEL FUEL PUMP WEAK.IF FUEL PRESSURE GOES HIGHER THAN NORMAL OR SEE GAS IN FUEL PRESSURE REGULATOR VACUUM LINE.FUEL PRESSURE REGULATOR IS FAULTY.WEAK IGNITION COIL OR COILS BAD PLUGS WORN DISTRIBUTOR CAP AND ROTOR WILL CAUSE SPUTTERING.

When you have an engine that is hard to start or the engine takes longer than normal to start, with a fuel injected engine it will normally be caused by a fuel problem. Another problem would be slow cranking of the engine because of a low battery, I would check all of the fuel related problems if the engine seems to crank normally. There are a few things to check. First pull the fuel filter off and wipe it off so you don't get gas in your mouth and try to blow through one of the fuel connections on the filter. If you can't blow through it the filter is pluged and needs to be replaced. A plugged fuel filter can cause hard starting and can also damage your fuel pump. The next thing to do when everything is put back on the car is to check the fuel system for bleed down. You need to locate the fuel pressure test connection on the engine. Connect a fuel pressure gauge to the connection and start the engine, then turn the ignition off. With the engine off the pressure should read and stay between 30psi and 40psi, to be sure of the pressure you will have get the spec's on the engine you have. The main thing you will be looking for is to make sure the pressure doesn't start bleeding down in to direction of zero after a few minutes or maybe even immediately. If you see the pressure start to bleed down you have a problem. There are two problems that normally cause the pressure to bleed down. One is a bad check valve in the fuel pump, the other is a bad fuel pressure regulator. The main thing that happens with a fuel pressure regulator is the diaphram inside starts leaking. When that happens sometimes it will leak fuel into the intake manifold through the vaccuum hose connection to the intake manifold. To check for a fuel leak through the vacuum hose connection, locate the vacuum hose on the fuel pressure regulator and pull the hose from either the manifold connection or from the connection at the fuel reguator. If you see any gas at all the fuel regulator is leaking and must be replaced. If it is a slow leak from the regulator you might have to start the engine with the vacuum hose disconnected and look for a leak from the hose. If you don't find anything wrong with the regulator the next problem area would be fuel pressure bleeding back into the gas tank because of a bad check valve in the fuel pump. If this is the problem the fuel pump would have to be replaced. My first guess as to what is causing your problem would be the fuel pressure regualtor although I would definately want to make sure the fuel filter is not plugged. (Please Note) The fuel pressure regulator is located in the intake manifold area of the engine. The fuel pump is located in the gas tank. The fuel filter is located usually somewhere under the car.

sound like intake leak. get a scanner to see if egr valve not staying open . check map sensor + make sure the vacuum line didnt come off it . check coolant sensor. oxygen sensor .check fuel pressure regulator. check vacuum line that goes to fuel pressur e regulator . make sure there is no gas in it. make sure its getting vacuum. check pvc valve.shake it make sure it rattle .