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So I have a 1996 f150 with a 4.9 in it. I'm getting codes for P0174 and P0171. I've checked for vaccum leaks and can't find any. I replaced the maf sensor not that long ago and I'm getting a 0.7 lb/min at idle and 16.1 on the TPS. Is this normal? Any suggestions?
16.1 TPS for throttle % opening? That's pretty close to what I see in my '96 with a 5.8L, best I can recall I'm at 17.5% opening at idle. Also, the maximum is ~95%. It's just the way the App normalizes the voltage (I wish it also gave the raw voltage instead of just a percent).
Being a '96, this is OBDII. Are you using something like the Torque app to read codes? You should be able to monitor and record the upstream oxygen sensor voltage(s) while driving. Do they switch rich/lean under light throttle cruise, and then peg rich under high load? Rich is over 0.45V, lean is under 0.45V. If it doesn't peg rich under high load, check your fuel pressure.
16.1 TPS for throttle % opening? That's pretty close to what I see in my '96 with a 5.8L, best I can recall I'm at 17.5% opening at idle. Also, the maximum is ~95%. It's just the way the App normalizes the voltage (I wish it also gave the raw voltage instead of just a percent).
Being a '96, this is OBDII. Are you using something like the Torque app to read codes? You should be able to monitor and record the upstream oxygen sensor voltage(s) while driving. Do they switch rich/lean under light throttle cruise, and then peg rich under high load? Rich is over 0.45V, lean is under 0.45V. If it doesn't peg rich under high load, check your fuel pressure.
I'm using an Inova scan tool. I'm more concerned about the maf and if those numbers would cause lean codes.
0.7lb/minute is 5.3 grams/second. My 5.8L at idle reads between 5-7g/sec. So you're ballpark there.
I would be looking at fuel pressure, and the ability of the fuel system to provide enough fuel under load. Monitoring oxygen sensor voltages and fuel pressure during a few driving conditions is an excellent diagnostic.
When was the last time you replaced the fuel filter?
I just replaced the fuel filter a few weeks ago. And it does it with both tanks so either both pumps are bad at the same time or its not the pump. I also did the fuel pressure regulator, maf, iac and some other things.
Did you check fuel pressure? Since lean is either a lack of fuel or surplus of air, makes good sense to not assume anything in terms of fuel supply without actually measuring it. While I agree that things are probably OK on that end, you could have a voltage supply issue to the pumps, and that could effect both tanks, no matter how many other parts you replace.
How many miles on the truck? Is the idle elevated at all? While I've not ran into it, I've heard of high mile trucks having so much wear in the throttle bodies that there is a leak through the blade bushings.
Are the two codes you listed the only codes present? I ask because sometimes posters think codes aren't related to their issue, and don't mention them..
What other things have you replaced? Be careful throwing parts at a problem. New doesn't always mean good, and you can confound the diagnosis doing this without evidence based reason.
What's the general state of maintenance here: new to you truck with unknown history, had it since new & keep up on regular maintenance, somewhere in the middle? By this I mean, how many miles on plugs, cap, rotor, wires, air filter? Battery terminals all clean & tight. Oxygen sensors ever been replaced? Any mods?
Sorry for all the questions. I don't always know the answer but the more information the forum has, the more likely someone who does can help you. On top of that, most of the guys on here are accustomed to dealing with EEC-IV PCM logic, not the EEC-V/OBD-II, so there's potentially less knowledge base applicable to the '96 half tons & some of their quirks.
I have to go get a pressure gauge to check the fuel pressure. So I may do that tomorrow. What should it be at? So it's a 1996 f150. It has 109000 miles on it. I have had it for a little over a year now. PO took good care of the truck. He did a lot to it. It has new distributor plugs and wires as of when I bought it. It's got a two inch leveling kit with 33s. K&n cold air intake, magnaflow high flow cat and cherry bomb muffler. I recently pulled the plugs and they aren't fouled. They're all nice a tight. I have replaced a bunch of vacuum lines, maf, egr, egr pressure sensor, brand new battery, all new front end and steering box and lines, New water pump and fan clutch, crankshaft position sensor, New radiator core support and headlights. And probably other things that I'm forgetting. And yes those are the only codes. And I also did all three o2 sensors
These lean codes can be associated with a Dirty/Contaminated MAF sensor. I know you said you have a replaced it in the past.
Using K&Ns' less pleated, oil filled sponge of an air filter can contaminate and/or damage the sensor.
I highly recommend you find the stock air filter housing and use a quality filter.
A malfunctioning EGR/DPFE sensor can also trigger lean codes. It wouldn't take much as OBD2 vehicles are stringent on vacuum, intake leaks and they create havoc you have found.
Fuel pressure on your 4.9 should be between 50-60 PSI. If yours is in range then perhaps the injectors are dirty causing a lean condition. If you have time please describe exactly what symptoms your truck is doing that is abnormal other than codes. That may help diagnose the cause.. At this point we only know you have codes. Sandy
I have a rough idle, poor fuel economy, and the engine bogs down and doesn't have enough power (slow to accelerate).
Thanks. Maybe rla will have ideas based on this info. I know you have your own gauge without the proper adapter, but If you have a auto parts store handy you could rent a pressure gauge with full refund rather than wait for the Amazon order.
