rwhite1

Afternoon,

I've searched and at this point am spinning my tires.

Vehicle: 2002 F150, 5.4L, automatic, 4WD, 178k miles. I'm using an OBD with Torque Pro for diagnostics.

Late last week check engine light popped - codes P0171 and P0174. Codes were accompanied by an underhood whistle. I searched and read - vacuum leak.

I replaced a couple of suspect vacuum connections, cleared the codes, cleaned the IAC and MAF. Short term fuel trims improved (vascillate between -5% to +3%). Long term trim remains +12-18%.

No start yesterday after driving to town (30 miles) and sitting for several hours. Started in the next couple of cranks and whistle returned on the way home. Codes have no reappeared and no codes are pending.

Short term fuel trim seems fine (-5% to +3%). Long term fuel trims seems high at idle (+13%) - but when throttle is applied, long term fuel trim comes to about +5%.

Everything seems to indicate a vacuum leak. Correct? But I'm unable to find the leak - I've used propane, carb cleaner, and felt every vacuum hose I can get my hand on. Nothing changes RPM. Any thoughts on how to further check for vacuum short of making a smoke tester?

Through all of this - 02 sensors jump together from .1 to .8 volts. At start up, vehicle idles around 1,000 RPM. After thorttle is applied - idles around 660-680 RPM. Normal?

Also - intake is 40*F and under during all of this. Ambient temp in shop is 20'isih, ambient outside is teens to subzero.

Finally - in the Torque app, there are the emissions DTC check - the only incomplete check is for the evaporative system. Based on my reading it's probably because of the cold temperatures but I'm open to insight.

Questions:

1) It seems I have a vacuum leak because of the high long term fuel trims. Correct?

2) How does cold affect fuel trims? Is the high fuel trim simply because of the temperature.

3) Best way to find the vacuum leak at this point?

4)Based on everyone's experience - am I not chasing a vacuum leak and something else is going on?

Thanks. If you have any questions, please ask.

mbb

Your pcm was programmed before ethanol put in gas. This makes a big difference.

As does fuel filter or injectors that are clogged.

Find a station that sells gas with no ethanol and prove diff to self. Station blend ethanol into gas with really poor control and if you get tank high in etoh, it makes really high trim. E20 might throw code.

The trim isnt amt of fuel...its injector duration relative to preprogrammed ideal fuel map. More air than MAF...yep it will call for more fuel. So poor maf can cause as well, also less fuel flow than expected due to clogged injector or filter or fuel pressure.

rwhite1

Thanks. I'll try and find a pump with no ethanol to try it.

With clogged injector/filter/low pressure because of dying/dead pump - I understand it would seem to cause a lean condition. Yet - how does that play into have a very rich long term trim reading?

In my mind if low fuel flow - lean condition - trims should also be lean, not rich.

I will certainly look at fuel issues and put a new fuel filter in (old one has 14K on it) and check fuel pressure. But fuel restriction doesn't seem to fit my rich fuel trim issue

mbb

RThe fuel trim is attempting to correct the lean by increasing the injector duration

It sounds like you think your rich, its not. the computer is attempting to add more fuel to correct the lean Condition it's still controlled by the oxygen sensor and OK. The oxygen sensor in front of the Cat Cycles rapidly as it controls the fuel your fluctuating voltage shows exactly what it's supposed to

Think of the fuel trim is how much time your injectors spend open relative to the ideal parameters they were designed to run at. Any restriction on the fuel side and they have to be open more time to pass the same amount of fuel

rwhite1

Got it. Thank you - that makes sense.

rwhite1

Back for more ideas.

Prior - vacuum connections were checked and replaced, new PCV, PCV tube, and connector on back of throttle body, IAC cleaned, MAF cleaned - couldn't get it right. I ended up taking the vehicle to the shop because I couldn't find an intake leak. Shop performed a smoke test - no intake leak. They cleaned the MAF (apparently better than I did) - and said that was my issue. Mileage - 174,788. Issue resolved, long term fuel trims were around zero.

Vehicle is now at 176,047 and counting - SES light returned 100 miles ago - again P0171/P0174. Fuel trims are high. At 175,800 I added a can of BG44 cleaner to the tank.

I've searched and have the workshop manual that I've read and looked through, especially related to fueling. Looking for ideas here.

I'll clean sensors again tonight or Thursday. Fuel pressure gauge is attached and idles at 30 psi - lower end of factory specs. I'm having my wife watch the gauge today while driving under load and will update with those findings.


Thoughts? Ideas? Looking for experience. Thanks everyone.

jprevat

iTrader: (1)

How exactly did you clean the maf? Rubbing alcohol and a q-tip or the spray? I have found the spray does nothing for me. Are you still using your factory intake?

rwhite1

fActory intake - MAF cleaned using the spray, I'm not sure how the dealer cleaned it.

jprevat

iTrader: (1)

Try it with a qtip and rubbing alcohol. Be real easy with those wires and it should clear it up. If not then I will see what I can do to help out.

rwhite1

I'll be working on it this evening. Thanks.