2.5L ('98-'01) LTFT Rich and poor mpg.

[Sloryd66]

Anyone good with LTFT diagnosis? My long term is running in the -20 range points to a rich condition and I’ve begun getting horrible fuel mileage again. I’m thinking a possibility is a leaking injector. MAF is recent, O2’s appear to be working properly based on the varying voltage while driving but I ordered them just in case. No vacuum leaks which would present as the opposite and show the ecm adding fuel instead of subtracting it like it’s doing. Clean K&N that’s not over oiled. New exhaust from the cat back. No codes pending either. I’m going to pull the plugs when it cools down….just looking for ideas of what else I should probably look at.

 

[RonD]

Do the Clear Flooded engine test to see if an injector is leaking

Key on
Press gas pedal down to the floor all the way and hold it down
Crank engine over
It should NOT start, fuel injectors are OFF
If it doesn't start/fire then injectors are not leaking, but Fuel Pressure Regulator in the gas tank is bad, fuel pump can do 80+psi, the FPR should keep it at 50-60psi
If fuel pressure is above 70psi then you will get RICH codes because too much fuel is flowing out when an injector is open, Rangers never had fuel pressure sensors, 1998 and up computers expect 55psi average that's how they calculate how long to open an injector

If it does start, then an injector is leaking, but one more test
Warm up engine, or do this first after you get home one day
Turn engine off
Cycle key on and off 3 times then key OFF
Take off the big air hose from throttle body and open the throttle, smell the air inside the intake
If it smells like gasoline then for sure a leaking injector

When you turn off a running engine the spark and injectors are turned off instantly, but engine is at, say 750rpm idle, so any gasoline smell would be sucked out and into exhaust as the engine winds down to 0 RPMs
Turning key on and off 3 times is turning fuel pump on and off 3 times so a leaking injector would leak that fuel into the warm intake making is a vapor(smell-able)


Clear flooded engine
ALL fuel injection computers have this, not a Ford thing
With key on, computer is on
If you press gas pedal down to the floor the computer see WOT(wide open throttle) from TPS(throttle sensor)
When computer sees WOT and RPMs are 0 it will enter "Clear Flooded Engine" mode, which means it will not pulse the fuel injectors UNTIL TPS is no longer at WOT

I use this every morning to start my high mile 4.0l, I press gas pedal to the floor and crank the engine for about 5 seconds, to pump oil thru the engine, I then release gas pedal and it starts

 

[55trucker]

Try removing the K&N filter & run the snorkel wide open in front of the MAF, keep your scanner running, note if there's a change to the short term which would lead to a LT change.

 

[Sloryd66]

Thanks guys. I’ve tried the flooded engine start procedure and it didn’t start. However I don’t completely trust that test simply because if it’s a single injector that’s sticking/leaking it probably wouldn’t start on one cylinder anyway. I’m going to try the sniff test and also run it without the K&N. My MAF data looked fine when I used that data set earlier with the fuel trim. What gets me is my short term looks okay….however that isn’t conclusive enough because the LT is what the fuel map table will refer to over an extended period of time from my understanding. ST is only trying to make small adjustments whereas LT shows the true problem and will cut or add fuel based on the map. It’s weird because it stays around the same -14 to -20 range at idle and throughout the rpm ranges. That’s why I ordered the O2 sensors to rule out a bad signal reading rich all the time. I’ll have more time Saturday to really dig into it because by the time I got home last night, pulling all the plugs wasn’t a good option.

 

[RonD]

The one cylinder would fire, for sure, so you would hear that

And cranking speed is 200rpm, the Computer will exit "Clear Flooded engine" if RPMs exceed 400rpms, one cylinder firing would cause momentary 400+ RPM usually so all injectors would start working

Check fuel pressure

 

[Sloryd66]

UPDATE:
Another member has a post up about poor fuel mileage so I replied there and figured I’d copy and paste what I tried so far.

“I’ll chime in because I’m chasing the same problem on my 2.5l 4. Just did the following below last weekend.
New MAF - no difference
New Autolite Plugs - no difference
New wires - no difference
Drove it this past week with a bottle of Techron FI cleaner. No difference.

Yesterday I changed out all 4 injectors, temp sensor* and replaced my K&N with a regular paper filter.

*My gauge now reads right in the middle whereas it never went above 1/4 before.
There are 2 sensors but the ecm sensor reads 89c through my OBD reader so that one appears to be working properly.

I’ll see what I get out of this tank for average. It’s been around 14-15mpg and I literally baby it and do 80% highway miles daily when I drive it to work. My commute is 52 miles round trip with the majority being on the highway and it’s been using just over a quarter tank per day.
I don’t think I mentioned I got this truck for free with 130k last August and have recently put about $350 or so in the new parts trying to improve the poor fuel mileage which I don’t mind. Truck runs and drives perfect otherwise with no codes present or pending. My LTFT is running at -18 to -20 so it definitely running rich for whatever reason and I’m sure that’s why I’m getting the less than ideal fuel economy and the ecm is telling the injectors to cut fuel. I thought perhaps a sticking injector so this upcoming drive cycle will rule that out if the mileage doesn’t improve. The LTFT should point it out as well.
I have a new upstream O2 sensor on the bench…I’ve been trying one thing at a time to eliminate the problem…this way once I notice the change, I’ll be better able to pinpoint what it was and can share that if another member is having the same issue.”

 

[Sloryd66]

Figured I'd update this since I've fixed my poor mileage after throwing a bunch of parts at it. In the end, it was the MAF sensor which I should've troubleshot first. My MAF was reading up in the 7.8-8.4 g/s at idle. This was the tell since the general rule of thumb is it should be x.x g/s for your particular sized engine in liters. So mine should've been at 2.5 or so and I missed that completely. I was too focused on why my ecm was telling the injectors to pull fuel since it was seeing a rich condition, so i was poking around it possibly being a lazy O2, leaking/stuck injector, old plugs not burning the fuel efficiently etc. Things I did in order which made no difference until I finally changed the MAF.

Autolite Dbl Plat plugs and Duralast wires $88 - No difference
STP Paper Filter replacing my K&N - $12 - No difference
Ultra-Power Fuel Injectors $98 - No difference
Denso Upstream O2 $24 - CEL P0172 Arggggggh.

This is when I threw the Foxwell back on there to check the MAF since that's what the suggested issue could be and noticed the high incoming air reading which was adding a bunch more fuel to get it to 14:1 stoichiometric, which the O2 was reporting still rich and cutting the injector pulse time to a -20 on the LTFT.

Duralast MAF including the alum housing $89 - Fixed

Went from 14mpg mixed driving to 21.6mpg on this recent tank. In the end I spent some unnecessary money on injectors, wires, plugs etc but the extra $225 spent left me with peace of mind knowing those items don't need to be addressed anytime soon. Not having to do the intake side plugs again is worth it alone, lol. Truck runs great (actually ran fine before other than the poor mpg) and figuring out the issue will eventually pay for itself on the improved mpg savings. $60 in fuel every 3 days was adding up quickly.

 

[Jazzer]

Glad you got it done!, and thanks for taking the time to add to the TRS body of knowledge.

-Jazzer