1996 ford ranger 2.3 4x2 odometer stopped working at 199k

bought this truck about a year ago seemed to run pretty good but noticed gas mileage was pretty bad and it would smell of gas from time to time. So I decided to hook a scanner up to it and shows the code p0172 looked at live data and fule trims were pretty high. At idle would range from -6 to -10 and once you start driving that number would climb to as high as -25 so I look at the 02 sensors and they seem pretty lazy so I changed them. Made no difference fuel trims stayed the same. So I pulled all the plugs and did a leaky injector test. All plugs looked good nothing really standing out and don’t seem to have leaky injectors. Had a mechanic take a look and he suspected a bad maf sensor. Even though the maf seemed to be reading right I changed it anyway. After I clear codes and drive it about 120 miles before hooking the scanner back up. P0172 is still there but fuel trims are at 0 but both my o2 sensors are reading constant voltage. Upstream reading from 0.80 to 0.90 and downstream tends to stay at 0.88. Every once in a while on the highway they will start to work if I’m accelerating or decelerating and my trims will go really rich to -15 to -20 and once I hold at a constant speed the o2 sensors will flat line and fuel trims will go to 0 to +6
also has a slight stumble at idle. Any help at all would be appreciated thank!

 

Welcome to the forum

Good testing

P0172 System too Rich (Bank 1)

Did you check the Fuel Pressure Regulator(FPR)?
Its on the engine
It has a Vacuum Hose attached and the Return fuel line, looks like a small "can"
If the FPR leaks internally then raw fuel is sucked into the intake via that vacuum line, remove that hose and check it for fuel, replace FPR if found

Also test fuel pressure, engine running, 1986 thru 1997 Rangers use 30-40psi running pressure, FPR is set for 43psi
Fuel pump is capable of 80psi, so if FPR isn't working that would sure cause Rich running

O2 voltage is generated by the O2 sensor, but only after it is heated above 600degF
0.1v is high oxygen and called Lean
0.9v is low oxygen and called Rich
But Lean and Rich are related to fuel, O2 just sees Oxygen, NOT fuel, lol

Downstream O2 voltage should be 0.8v, 0.75-0.85v is expected
O2s can only see Oxygen, and a working Cat converter should burn up/use up almost all the oxygen in the exhaust when cleaning the exhaust
But it should be a fairly stable 0.8v, shouldn't jump around like an upstream O2

Upstream O2 sees raw exhaust, and computer uses injector open time to try and keep O2 voltage at 0.4 average, so 0.2v to 0.6v would be range you would see
Fuel Trims are injector open time
Computer calculates STFT 0 then opens the injectors, if O2 shows 0.1v then computer open injector 2% longer, STFT 2%, if still 0.1v then STFT 4%, if O2 shows 0.9v then STFT -2%, then -4%, ect
So -25% means computers calculations were way off, OR there is a mechanical problem out of the computers control


Some times people think fuel injectors are the same as Jets in a carbeurator, they ARE NOT, lol
So they put in bigger injectors.....................and you get what you got now
Computer calculates the amount of fuel to add to the engine based on pre-programmed fuel pressure(35psi) flowing out of say 12lb/hr injectors
If fuel pressure was 80psi or injectors were 21lb/hr then too much fuel is flowing out when an injector is opened so Rich code and -25% STFT

 

Checked the vacuum line on the fpr, no fuel is leaking into the hose. I haven’t checked fuel pressure but will do that asap. Driving to work today watching live data truck is running lean now +5 to +15 and both o2 sensors giving me a pretty steady reading of 0.98. Before I changed the maf sensor the o2 sensors were acting normal fluctuating within a normal range then once I changed the maf sensor it’s running lean with weird o2 readings. Also fuel mileage was horrible. Maybe bad wiring?

 

Probably not wiring
Change MAF sensor back, "new" parts are a pain now-a-days, "new" means NEVER EVER tested, not "tested and works"
We are now the FREE quality control for parts makers
If its a Motorcraft(Ford) MAF then it probably is OK, 3rd party are the ones in doubt

Its looking more and more like a computer issue
Or over sized fuel injectors, if fuel pressure is OK

 

So tomorrow I’ll get a fuel pressure tester to make sure that’s good. Before leaving work cleared codes andi swapped my old maf sensor back in. While driving home which is 70 miles, there’s was really no change fuel trims reading close to 0 and o2 sensors reading pretty much a constant voltage. Got home checked codes and no longer have p0172 but have a p1132.. also the smell of fuel is coming from the fuel filter under the driver side of the cab idk if that helps but figured ide mention it. But I’ll update once I check fuel pressure and make sure it has the proper injectors. . Just seems odd how for a week I’ve have really high fuel trims and what seemed to be good o2 sensors to all of a sudden having normal fuel trims but weird o2 readings. I mean if fuel trims are good and truck seems to run ok does it matter what the o2 sensors read? Lol

 

So I checked fuel pressure. Key on engine off is 60psi and idleis is 85 psi. So that means bad fpr?

 

Yes, FPR is bad
1996 should be 30-40psi engine running, usually holds at 20psi or so key off
1986 thru 1997 FPR is rated as 43psi maximum

FPR is connected to the Return line to the gas tank, this is an open line no valves, if this line was blocked it would act the same as bad FPR as fuel can't flow back to the tank
So after taking off this line/hose blow thru it and air should flow thru it and bubble up in the tank, end of this line is at the bottom of the tank,so if tank is full it will be harder to blow thru, lol
Blocked return line is a long shot but not a "no shot"

gas tank/Fuel pump----->>---------filter----------->>---------------fuel rail->>--FPR---------------->>----------------------------gas tank

 

So the return line was indeed clogged, cleared it all out now I don’t have enough pressure. At idle it’s around 10 and running it’s about 20 lol bad fuel pump?

 

Yes, or FPR

I would suspect FPR stuck open because the pump was generating 80+ psi before, so is more than capable of doing 30-40psi

 

I changed the fpr and still showing low pressure. I’m gonna change the fuel filter and see if it helps. Bright side is it’s a small truck so the bed is easy to take off to access the fuel pump lol

 

So, I'm curious how this worked out for you. Give us an update if you are ever back on here.

Thanks