The fuel trim at -28 indicates that it is running way too rich. normal is +5 to -5. The computer is trying to lean it out. Goes back to engine vacuum is not acting on the fuel pressure regulator to reduce fuel pressure. See if the fuel trim improves with a hand vacuum pump at around 18" to the FPR at idle Block off the engine vacuum source for this. With the lower fuel pressure the fuel trim should run around zero.
The first o2 sensor should fluctuate between .1 and .8 volts fairly regularly, on an oscilloscope a nice sine wave pattern, on the scanner you just see the voltage go up and down regularly. It reads oxygen. .1 volt is lots of o2. .8 volt is little oxygen.
The second o2 sensor is to measure catalyst efficiency code p0300.. It should read fairly steady around .8 volts but will vary depending on acceleration and other loads. A very low reading constant (.1 volt steady) indicates an air leak in the exhaust between the two sensors. Look at the cat to tailpipe gasket. If it varies the same as o2s1 the cat may be worn out. Yours appears good.
catalyst efficiency is code p0420. p0300 is running rich. sorry.
You're map sensor is reading good. 20" Hg = 1.2v and it varies so that is good. But that doesn't match what you were getting with the vacuum gauge from earlier. Is your Fuel pressure regulator connected to the right port? Try a t connection to the map vacuum line and the FPR and block off the other.
I hooked up the vacuum pump to the FPR, applied 18ins of vacuum and it did bring the STFT down to around -9.4% at its best and LTFT to a negative-2.3%. The MAP Sensor doesn’t have a vacuum line to it, looks like it plugs directly into the upper intake.
Can you do a picture of the vacuum lines and the emission label if it still exists. I suspect the FPR is plugged into the hole for the EGR and vice versa. Swap them and see what happens. The EGR would be ported, meaning no vacuum at idle (closed throttle). The fuel pressure regulator wants full manifold vacuum at idle for lower fuel pressure so it won't run rich and under acceleration the manifold vacuum drops thereby increasing fuel pressure (more gas per injector squirt). The EGR should have no vacuum at idle, EGR is there to allow exhaust gas into the cylinder to cool the walls to help reduce knock and NO3 production. If you have full vacuum to the EGR and the EGR solenoid is not closing entirely it could cause the EGR to open a little and cause stalling. Hook your vacuum gauge in place of the EGR valve and see if there is vacuum all the time. If so the EGR solenoid is leaking. Hook the vacuum gauge in place of the FPR or T it in. You should have full manifold vacuum the same as the MAP sensor. The EGR valve could also be carboned up and letting exhaust gas leak by when it shouldn't, causing intermittent stalling. The fuel trim responded to the vacuum so you are on the right track.
The EGR doesn’t have a vacuum line attached to it I don’t believe, just an electrical plug that goes into the top. All the vacuum lines run together and connect into a plastic piece that snaps on top of the throttle body. I cleaned the EGR when I first got the truck and it did have some build up, would there be a way you can check to see if it is functioning correctly?
The EGR would set the check engine light with code P0401. You cleaned it and it isn't setting a code so not likely to be an issue. When you checked vacuum with the gauge you said you have 6", but the MAP sensor says you have 20". Somewhere between the throttle body and the FPR you are losing vacuum. If your vacuum lines are plastic, you might find a cracked line. The FPR works with the rubber hose from the hand pump but not with the factory connection to the throttle body. Or the plastic piece that snaps on the throttle body is not sealing.
Ok, when I got home I’ll check that plastic piece on top of the TB. I know it has 4 little rubber feet that plug into the top of the throttle body, they looked a little worn. I will see if I possibly have a leak coming from those feet.
I went home and checked the vacuum harness on top of the TB for leaks. I used some starting fluid while it was running to see if the RPMS would go up and it didn’t. While I was going it I was using my scan tool to monitor the fuel trims. When you first start the truck up it will go to like -24 on the short term, but within 30 seconds it brought its self back down to around -3/-10 and would fluctuate around there. The engine load was around 63% - 70% the whole time, is that normal for a truck that’s in park and idling?
Short term fuel trim is considered normal to fluctuate between -5/5. It will be richer when cold open loop. Long term fuel trim compensates to bring short term into range. For example if stftr is -15 the ltftr will move negative (computer attempting to lean the mixture) so the stftr moves toward zero. Actually the fact that you went from -28 to -10 to +10. means you fixed something.. A happy computer will be ltftr close to zero and stftr varies between -5 and +5, but -10 to +10 is not bad. Probably safe to assume the FPR high pressure issue is resolved. What is MAF (mass air flow), at idle and 2000 rpm? The long term and short term fuel trims, o2 sensors 1 and 2, also at idle and 2000 rpm. o2s1 in closed loop will fluctuate. o2s2 should be around fairly steady around .7 volts o2s2 is only there to monitor the cat efficiency. Nothing to do with the current issues. Throttle position sensor should move smoothly between .5 and 4.5 volts approximately. The TPS is like the volume control on old transistor radios, sometimes they get bad spots. Temp sensor hot and cold? MAP should approach barometric pressure 0" Hg and should be the same as at the FPR with wide open throttle under load. Tricky to do with a manual trans. Automatic trans just put in gear with the brake on. Be safe. Visually inspect that fuel pressure vacuum line. It could have tiny cracks that you semi-fixed when you moved it. Mine had a intermittent air leak at the resonator box of the air intake, by the upper radiator hose. The gasket is not available so I resealed the original gasket with RTV Red and afterwards I thought it idled better. Never paid any attention to engine load, I don't what it is measuring, but later I'll go see what mine is. RPM 800 to 1000 could be AC compressor kicking in and out? An old battery they can rot internally and intermittently short a cell, or loose terminals can cause wacky things to happen that defy understanding. A new battery solved my intermittent security system problem. Does it still stall out? You didn't mention. How is the fuel pressure steady when the idle fluctuates? I'm going to cook some gluten free Ronsoni spaghetti for dinner. Good luck with the clue hunt. Post the numbers.
I wish I had some but my engine has been pretty much trouble free... for a while mine would act like it wanted to die when first starting up and coming to a stop, but I just cleaned the idle air control valve out and problem solved.
You could take it for about an hour test drive before you go crazy to give the computer a chance to relearn with the new parts and the battery was disconnected so it's running on default program map for mixture and timing. Clear the plugs fouled from all the over rich running. Maybe just needs some gentle exercise.
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Hi. New to the forum, long-time gearhead. Recently purchased 2003 Regular Cab Short Box 2.2l 5-speed 38948 original miles.
Been driving for about a month noticed temp gauge will be at 210 quite often and oil pressure is always high 40 psi at idle 80 psi under load at 3000 rpms.
Truck runs great...