P0171

Thanks for asking... seems like I may have had multiple problems and replacing the IAC fixed one of them.

I thought LTFT might update after I drove it a while, but it's probably been 25 miles and it's holding at 0% while STFT is now pretty consistently at 19.5% whether I'm driving or idling. I'm not sure why, but sometimes the STFT kicks in right away when I start it up and other times I have to drive it a mile or so with really low power and a couple mild backfires before the ECM adjusts. Basically, it acts like I disconnected the battery even when I didn't, which is one reason I expected LTFT to adjust. That doesn't seem normal but maybe I'm right at some trim threshold where the ECM is evaluating whether to set LTFT each time and decides against it, IDK.

Replaced the fuel pressure regulator, but that didn't seem to do anything. I ordered some 505 CRF treatment to see if maybe there's just some stubborn carbon deposits but if that doesn't work I suppose I need to either replace the injectors or the fuel pump? I think the IAC may have been the vacuum issue, so I'm not sure what else would be left....

Any thoughts or ideas would be greatly appreciated.

 

The entire system revolves around the correct fuel amount of fuel getting squirted in at the right time. There is some wiggle room for built into the stratgey in the PCM. I'll bet that your fuel pump is on the lower end of pressure and or volume. I had a buddys F150 not too long ago that was doing similar things, mechanically the motor was sound, no vacuum leaks, no exhaust leaks, but a P0171 and P0300 and other P0300 codes and "not running right". Fuel pressure was ok, then not ok, then it would shut off going down the road, then one morning when I started her, I heard it... it sure sounds like fuel is hitting the inside of the fuel tank and it runs like crap. Take the bed off, take the module out and sure enough the oneway valve was split. Ford and maybe others also use a rubber bladder valve in bewteen the pump and the outlet to smooth out fuel pressue pulsations. Replaced the module and checked the pressure, inital prime pegged my fuel pressure gauge at 100 psi, it dropped to normal after it starts. Fuel trims immediatly went to 0 after closed loop. This truck has 200k on the motor btw.

Why am I telling you this story... keep at the diagnosis, unfortunatly you threw parts at it hoping for a magic bullet fix. The P0300 codes were a symptom of low fuel pressure and the misfire counters for those cylinders were related and random... why would it be cylinder #1 and #5 and next drive cycle it would be #4 and #2, thats just how this one was. I did not go down the rabbit trail chasing misfire codes.

As an afterthough, I am assuming that the valves are adjusted?

 

Yeah at this point I kinda wish I wouldn't have dropped so many unnecessary parts into, but they weren't too expensive so not a huge deal. I'm basically a novice so it's taught me a lot about vehicles that I had no clue about before so I suppose that's a plus.

Anyway, it seems like I'm good to go on the vacuum side, so yeah it looks like I'm gonna need to pull the fuel tank down to check the pump and the lines and whatever else is in there.

I took a look at the valve adjustment procedure and even bought some feeler gauges but then I decided it seemed a little time consuming and over my head, so no I haven't done that. I thought I read somewhere after I'd given up that the 2.4L 2RZ-FE engines are self-adjusting anyway... is that not the case?

 

No they re not self adjusting. It isnt that difficult to check the clearances. You will see the lobe on the camshaft, have it pointing up and away from the shim/bucket and slide the feeler gauge in there. Looser than spec by a few thousanths is no big deal but tighter can be an issue. Adjusting them is the problem, this all depends on the tools in your toolbox and the avalibility of shims.

 

Thanks I'll take a look when I get a chance. Appreciate the help.

 

OK I need a sanity check. I checked the fuel pressure and I'm getting 45psi, which I believe it just slightly on the high side? Seems like that would rule out the fuel pump, correct?

One question though... I installed a banjo bolt with a female NPT on top, a 90 degree elbow, then screwed the gauge directly into that. The holes in this banjo were much smaller than the stock bolt though... wouldn't that affect the pressure?

I suppose I could drive it like this and see what my trim readings are but it was tough to install and I had to have the gauge facing up, so I'm a little concerned about leaks. I'll probably still try, but if I find out the smaller hole did increase the pressure and everything seems good wouldn't that just be masking another problem? Like a weak fuel pump?

Thanks

 

While she is running disconnect the vaccum line to the fuel pressure regulator and see if the pressure changes slightly.

A problem with OBDII is how the data you are looking at is given to you. Various codes such as the P0171 are "calculated" by inputs of the various sensors and the readings are compared to an internal set of tables inside the PCM and if the readings are off over a period of test cycles a code is generated. The lean codes wont be tripped until the fuel trims exceed 25%.

Check the g/sec of air flow at idle, the industry standard is 1 g/sec of air flow per liter of displcement so yours should show 2.2 to 3 ish at idle. This is not a hard and fast rule, more of a guideline. If your shows 7 g/sec at idle, there is a problem.

TnTroubleshooters comment is accurate. Watch your g/sec air flow at idle and slowly raise the rpms and hold at each new level and observe the reading. It should increase. Do the same thing and observe the STFT it should get better, meaning a +17% should slowly go lower if there is a vaccum leak in the motor. There could be an air leak in the tube between the MAF and the motor too. At idle a motor will generate a vacuum of ~ 18" of vacuum. Atmosperic pressure is + 14.7, that is a 32" of difference between the outside of the motor and the inside. as the throttle opens this starts to equalize, the engine vacuum starts to travel up the tube (pressure differental) and if there is a hole, a split in the tube, false (unmetered) air will be introduced. A 1/16 ID vacuum line off can induce a P0171, thats how sensative the system is.

Sorry for a long winded post.

'

 

Thanks Glamisman. No worries about the long-wind... I appreciate every detail I can get.

I'll disconnect the fuel pressure regulator vacuum and see what happens... what will that tell me?

That makes sense about the lean codes not tripping until 25%. When I was getting the P0171, LTFT was locked-in around 40% and STFT was 19.5% at idle and would steadily drop to around 0% as RPMs increased. I know now that most likely indicates a vacuum leak, but I believe I fixed the vacuum issue (or at least one of them) when I replaced the IAC valve. Since then, I've been at a constant LTFT-0%/STFT-19.5%.

I could probably deal with those trims and call it a day since I'm not getting any codes, but from what I've read that's not great for the engine. More importantly, pretty much every time I start the truck now it putters along for a mile or two until STFT is re-learned and then it jumps to a normal power level. Would I be correct to assume that is happening because the 25% threshold is also where STFT changes to LTFT? For example, I'm guessing if I was at LTFT 0%/STFT 28%, after a certain number of test cycles that would change to LTFT 28%/STFT 0% and the trim would be saved and be active immediately when I start the truck. Is that an accurate assumption?

MAF at idle is .5 lb/min or so, which I believe converts to around 3.8 g/s... so fairly close I think. It increases with the RPMs... the sensor says it's been as high as 7.7 lb/min (58 g/s), but I've only seen it go to 2.7 lb/min (20.4 g/s) at 2800 RPMs. Not sure if that's normal or not.

Thanks!!

 

If the fuel pressure changes with the vacuum line removed the FPR is working. An often over looked vacuum leak is the seal at the brake master cylinder/brake booster, just pinch off that large line and see if the STFT changes.

As to your puttering when cold. See if there is a PID on the BlueDriver App for Open loop or closed loop opperation. Monitor this the next time you start her cold when she doesnt run "right". Open loop operation is when the PCM is running the motor off of stored values in the PCM and closed loop is when the sensors are modifying how the motor runs. I am curious if the change in how she runs cold is due to open loop or closed loop status.

One other thing to look at is the engine coolant temp as reported by the scan tool.

You can change the readings from imperial to metric in settings on the Bluedriver app.