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Cannot seem to get this code to go away. Also a sight surge under light acceleration. New to me truck, (96 F150 4x4, 5.0, automatic), so I went through and changed all vacuum lines, new plugs, wires, cap, rotor, pcv, fuel filter, cleaned MAF. Smoke test found no leaks, sprayed water around intake and injectors as much as I could get to, even small hose up to my ear could find no sound of a leak anywhere. Starting to get frustrated, so I turn to the FTE experts or at least someone else that has experienced the same issues.
Have you tested the fuel pressure at the shrader valve on the fuel rail?
Those were the codes that eventually lead to my '96 4.9 I6 F150 going to a shop, where the intake manifold gaskets had to be replaced.. for what it's worth. I wasn't about to tackle those with my schedule. You've definitely done a lot of the best diagnostics for basic issues. Maybe spray some brake cleaner to look for leaks? Good luck.
haynes says OBDII -thats your left and right o2 sensor telling you engine lean, how many miles on truck? any mods done when you did tune-up (e.g. sixliter tune-up) what is base timing set at? what was/is fuel pressure on both tanks? Did you check for exhaust leak both sides? Check that both sensor are tight in bungs(not worked loose)? It would be doubtful that both went out at same time (see pic below posted by 96blackford) to check them before just buying 2.
Done the carb cleaner trick multiple times and found nothing, may have to get a pressure gauge. Any idea what the pressure should be?
You need to check fuel pressure to do any further diagnosis, definitely get a gauge.
Looking for 39-40 psi with no vacuum supplied to the regular, and somewhere north of 30 psi at idle with the vacuum line hooked up to the regulator. My 5.8L sits at 32 psi at idle with vacuum, 40 psi under heavy load (or vacuum supply removed from regulator). Pressure must rise under load (decreasing vacuum), and never drop under continuous load.
87000 miles. Timing @ 10 degrees, no modification, plugs gapped to .054. I have an ELM to iPhone and can see O2 sensors working going down the road. Possible they are not switching fast enough. STFT bank 1 over 10, bank 2 just about 8, LTFT bank 1 pegged at 25, bank 2 23. Haven't found anything loose yet. I can hear a slight exhaust tick while driving. Have to stop by and rent a fuel gauge.
87000 miles. Timing @ 10 degrees, no modification, plugs gapped to .054. I have an ELM to iPhone and can see O2 sensors working going down the road. Possible they are not switching fast enough. STFT bank 1 over 10, bank 2 just about 8, LTFT bank 1 pegged at 25, bank 2 23. Haven't found anything loose yet. I can hear a slight exhaust tick while driving. Have to stop by and rent a fuel gauge.
The switching sounds good for normal closed loop operation. What happens to the oxygen sensor voltages under sustained heavy load? Pcm should go open loop and maintain near 0.9V, no switching, just run rich. If they fall off over time, especially during the surge, I bet fuel pressure is low.
Results of fuel pressure test. KOEO pressure 35, stays constant for 5+ minutes, KOER pressure 31, revving engine pressure goes up 1-2 psi and then goes right back to 31, vacuum disconnected from regulator pressure rises to 40 and back to 31 as soon as vacuum applied. All seems to be within spec. Not sure what to look at next. Is a road test while monitoring pressure needed?
Driving test showed no change in pressure at any RPM, O2 voltages changed with throttle change. MAF changes like it should, coolant temp good.
No fuel pressure change while driving? Clarify that statement. Does it remain at 31 psi even under load? What is the pressure while the shuddering (edit: surge, not shudder) occurs?
Can you graph the oxygen sensor voltages? In torque, I am able to plot this over time, along with other parameters like percent engine load. Do your voltages peg high voltage under load? Drop is deceleration. Normal closed loop rich/lean switching. high load. Note Bank 2 was a touch richer than Bank 1.
If I remember right I was comparing switching speed of an old (bank 1) and new (bank 2) sensor in the above. Anyway, that's the kind of behavior you should see.
Correct, stays at 31psi while driving even under load. Didn't go very fast but worked the engine a bit with 4L and in first gear driving in a field. Hard to have the gauge where I can read it and drive down the highway. Didn't get to see the surge cause RPM's were too high. The surge is only at very light throttle when starting up a hill and about 1500-1800 RPM, in or out of OD and only by about 100 RPM. Quick blip up then back to normal, every 10 to 20 seconds unless it downshifts. Don't think I can post pics of my O2 readouts yet (not enough posts) but I do see voltage go up to .7v when on accelerator and down to .3v when I let off. I know, not very scientific. Bank 1 is a little higher than bank 2 on STFT.
0.7V is pretty low for the "rich" end and 0.3V is pretty high for the "lean" end. Are these original O2 sensors? If they are, they should probably be replaced. Maximum I see is about 0.95V, lowest being 0.05V or so. If your sensors are old and worn, they may not be capable of accurately telling the PCM how rich or lean the engine is actually running, causing fueling to be off, or even if it is correct the PCM can't accurately see that and will trigger a code. I believe there is a "slow switching" code in these EEC-V OBDII trucks, but may be mis-remembering.
It's okay about posting the readouts of the sensor voltages. I posted mine just so you'd know what is normal operation.
It is tricky to read the gauge safely. If you can round up someone to sit in the passenger seat and do the reading for you that's more ideal, or have them drive while you observe. The trouble is 4L in 1st gear isn't much more engine load than an idle or free rev' in park (unless climbing a steep hill or dragging something heavy), so manifold vacuum will remain high and bring fuel pressure down, as designed. It's just such a deep final drive that not much fuel is needed. Lugging the engine up a hill in 2H will be a high load (high injector duty cycle) low vacuum situation and give you a better idea of if the fuel pump can keep up with fuel demands.
It's hard to say if you have two worn out oxygen sensors or potentially low fuel pressure until pressure is verified to reach ~40 psi under a high load/low vacuum situation. If I were guessing based on what you've posted, I'd say the sensors are bad.
Did driving test again, fuel pressure goes up to 38 psi under load and back to 30 when not. I see b1o2 and b2o2 cycle back and forth from .1v to .9v. B1 sensor 2 (I assume this is the final o2) stay at about 0v until I give it gas. Then it goes up to about .8v then back to about 0v and stays there. The freeze frame data shows error 171, closed loop, 62% load, 177 degrees coolant, fuel trims-st1 11, lt1 25, st2 7.8, lt2 25 @1459 rpm and 34 mph. Did test again later and results near same 36% load, 187 degrees, st1 10.1, lt1 25, st2 5.4, lt2 25 @ 1407 rpm and 48 mph
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