Running Rich, p0172 p0175

2002 Taurus SE vulcan v6 3.0 - not flex fuel - returnless fuel system
Completely stumped on what the cause is
All 6 Fuel Injectors
EVAP canister purge control valve(on the firewall passenger side)
Catalytic converters
Fuel pump(fuel pressure sensor works fine, compared its’ reading to a mechanical gauge, both read the same)
MAF sensor
Both upstream O2 sensors
Both ECT sensors

Both banks’ LTFT read -20% and worse at idle
Both banks’ LTFT read around -10% cruising at 60 mph
Fuel pressure normally reads 40 psi, sometimes reading higher right after startup, about 50 to 60 psi.

Have you checked for vacuum leaks? Exhaust leaks? Leaks in the intake tube between the MAF and engine? Is the engine coming up to the proper temp?

Vacuum leaks would have the opposite effect; make the car run lean.

Both catalytic converters were part of a big Y pipe that connected both banks exhaust to a single pipe, so that whole Y pipe was replaced along with the gaskets.

When I replaced the head gaskets two winters ago (due to overheating) I also replaced the gaskets between the exhaust manifolds and the cylinder heads.

The computer says the coolant gets to anywhere between 195f to 210f.

No leaks that I could find or hear, whilst having taken off and on the intake manifold multiple times trying to find the issue.

Have you checked the car with a vacuum gauge? Normally I’d agree that vacuum leaks should show a lean mix, not rich, but you’ve already spent more on parts than an 02 Taurus would normally be worth so all bases need to be covered.

Have you considered the fuel pump drive module have gone bad? With the on-board pressure sensor, you’d think Ford would use a closed loop control for injector pulse but maybe things are beyond the range of control.

The car hasn’t been checked with a vacuum gauge.

Wouldn’t the FPDM being faulty cause the fuel pressure to be way off?

It may be a softer failure than “way off.” Your fuel trims are off, for sure, but not way off. Off enough to throw a code but the car still runs.

That brings up another thought. Where did you get the replacement fuel pump?

I ask this because the cheap replacement pump in my truck can’t keep up with demand. LTFT is near 0 at idle but +17 on the highway and the performance is off by a few horsepower.

Consider the flip side… too much pump output… flow, not pressure… the ECU is trying to compensate, but it can’t and then codes are thrown. Maybe the occasional 50 -60 psi at idle is a clue. Returnless systems would tend to be more sensitive to these things.

My dad is the one who ordered the fuel pump, I think in 2016. It’s from rockauto, but you can still get some crap parts if you order from the economy section. (I just know he got the pump from rockauto)

Is it never normal for pumps to spike the pressure at startup?

I won;t say never… but the return systems have a regulator that prevents that. Steady fuel pressure is important to the proper running of the engine. A returnless system has the regulator essentially at the pump side but the FPDM controls the amount of current to the pump so it doesn’t consume too much power. It is a fuel economy thing. If the FPDM can’t steady the pressure for some reason the pressure would spike. But it shouldn’t. An oversized pump, failing internal regulator or bad FPDM might be the issue. Since the pump is 4 years old (and ??? miles on the pump?) I’d be looking a bit harder at the pump.

The car has put on 28000 miles since it was purchased in 2016. So the pump might have something like 23k miles on it. As far as I know, the FPDM hasn’t been touched.

I would suspect the fuel pump drive module is the problem.



Alright, I’ll shoot for that part next. Any brand recommendations?

Replaced the fuel pump drive module today with an ultra-power unit - no change in fuel trims.

Something to note:
LTFT’s are maxed -25% at idle, also at idle the STFT’s are +10% or greater.

Just replaced the egr valve, and now cylinders 4&5 are missfiring…
Considering just selling the car :upside_down_face: