Fuel Trim Questions

[MAS Tequila]

Ok, here is one for you.

2000 Mountaineer 5.0 4WD.

New plugs and wires, fuel filter, and MSD coil packs were installed less than 1000 miles ago after lean codes were being thrown, in order to try to smooth out the idle stumble.

A brand new alternator is putting out 14.4 volts.

The front O2 sensors have been replaced with Bosch direct fit units within the last 1500 miles.

The ltft's are both right at 1.0%.

Bank 1 stft bounces from .97% to 1.02%, I believe this to be in the acceptable range as the dog chases it's tail.

Bank 2 stft upon start up goes right up to 1.29%, 30% rich, one cycle it went to .70% or 30% lean.

It will stay there as long as the engine idles, but once the throttle gets to about (?) 40% Bank 2 stft starts functioning correctly and pretty much mirrors Bank 1, then returns to 30% rich as the throttle is depressed less to maintain speed.

Any serious ideas?

 

[Blown]

It may be a bad injector(s) or wiring to them. How many miles on them?

I think I would swap injectors from side to side, inspect the wiring as I went, and then see if Bank 1 is now rich.
.

 

[MAS Tequila]

It's not that it's actually running rich.

It is going into a closed loop mode which defaults into a setting which richens the mixture on those 4 cylinders.

It acts like the pre heater on the new O2 sensor stopped functioning.

Once everything is up to operating temperature bank 2 functions just like bank 1.

The long term fuel trims are right at 1.0, maybe .99 or 1.01, but never further out than that.

So it really can't be anything other than electronic.

Now I just need to find the receipt, pull the sensor, and go get another and put in.

Then see what happens down the road.

 

[SWIGIN]

Are your cats open?

We had a work truck with a come and go miss that turned into a full time thing. After replacing everything you did my boss took it to Ford and said fix it.

Turns out the cats were partially clogged and a few injectors were acting up.

 

[MAS Tequila]

I only have the two front ones.

I haven't checked them, but would they cause this issue when cold?

 

[SWIGIN]

Ours did it all the time.

And I cant remember if the injectors were lean or rich acting but thy said the injectors are what caused the cats to clog.

 

[Turdle]

Do you mean going into open loop mode? Closed loop is good.
I too suspect the bank 2 injectors, if the o2 sensor is good.

 

[VR4]

First thing I would do is ditch those Bosch units and get denso sensors.

No exhaust leaks?

 

[MAS Tequila]

OK, last night I re-cleaned the MAF and the IAC, then checked both with the meter, both are good.

I unplugged the O2 sensor for bank 2 and no change.

So either the sensor has gone bad, or there is an issue with the wiring, or the PCM is bad.

The sensor is covered for 1 year and is the easiest to check by changing.

So I'll be trying a new O2 sensor this evening.

I'm thinking the sensor since it has thrown the no upstream heat switching code.

 

[97-5.0]

Ford o2's from rockauto are your best option......

I took a peak at my cats my unhooking mid pipe from manifold....passengers side honeycomb inside cat has melted in the centre.....I suspect the cause was my egr tube was cracked for over a year.

Fixed tube but I always have a stumble miss from a stop....cats and injectors are next for me

 

[delexploder]

Keep us posted

 

[MAS Tequila]

Ok, I ordered a pair of Motorcraft O2 sensors and put them in last night.

So far the problem is solved.

I guess the Bosch unit just failed quickly.

It's running just as smooth as can be now.

 

[delexploder]

I'm running NGK junk in mine , they act up all the time , I've had a set of motorcraft on the shelf just waiting for the next time I drop the front exhaust , should be soon

 

[97-5.0]

on the shelf just waiting for the next time I drop the front exhaust , should be soon

Dude, there is a hole in the floor from factory, your working too hard!

 

[delexploder]

Lol my exhaust is all stainless and comes apart very easy, im gonna be in there doing other stuff soon , thats how i work on it , gonna be changing front diff, torsion bars , every thing on the front , and the manifolds back to cast iron from the tubular ones , i figure ill do it then

 

[97-5.0]

Ouuu all stainless, was that a kit or custom made?

 

[MAS Tequila]

Still running just like before all of this started, or maybe even a little better.

When they're hitting on all eight, they sure can be sweet.

 

[delexploder]

that's great news!

 

[delexploder]

My cats are 2.5 in direct fit ( for the V8 ) i used ball flanges for the connection to the dual in/out muffler step band clamps and a set off ranger dual tail pipes with some modification , its all magnaflow