Hi,

So I still have the P0171 from a couple of months ago happening on a daily basis. It only happens under load while driving. No issues at idle or even high revs at idle so doesn't look like a vacuum leak.

I have 3 attachments. The first shows the error code freeze frame, the second live data while driving and the third an O2 sensor check. Freeze frame points to a bank 1 issue. Live data points to both banks. O2 sensor shows the possibility of a bad sensor.

Any experienced Autoenginuity users out there who can point me in the right directions please?

 

Both banks have high LTFT so you may as well regard it as P0174 as well.

What are LTFTs at idle, hot engine (drive it before parking, it must be hot), and again if you rev it to about 2500rpm?

 

Hi JagV8,

LTFTs at idle don't go over 7 even hot and at high idle (3000).
It only happens under driving conditions that I get the P0171.
Any thoughts on the O2 sensor test results? Could running the car with a misfire for a couple of weeks have damaged an O2 sensor?

 

Hi Revere, you might want to check that lower IMT seal first. Then check the torque settings on the rear bolts of the intake manifold. Next, try checking the gaskets on the manifold, especially the lower ones.

 

Hi JagV8,

IMT seals have been replaced. Valve cover gaskets have been replaced. Other gaskets were fine (like new). This doesn't look like a vacuum leak because the LTFT is fine until I drive the car. In a vacuum leak situation the LTFT should be high at idle and close to 0 at load. I have the situation where at idle the FT is close to 0, at 3000 RPM idle FT moves to 7, at driving down the road FT is 20.
Now I'm thinking either an O2 sensor is misreporting, the fuel pump is failing or the cats are failing.
Do these make sense to anyone or am I missing something?

Oh, just to add, the car drives as well as ever even with the error codes. No misfire or leaks.

 

How's the graph for fuel pressure looking?

 

So not a leak at idle.

Quite high Load so could be poor fuel supply - blocked filter / failing pump.

 

So I did a picture of what the fuel pressure, intake manifold pressure, Load and throttle position looks like under driving and accelerating (which normally leads to the high LTFT issues)

Thanks Barnter for the question. I hope you guys can diagnose a bit more from this.

 

In the middle there, did you blip the throttle three times? My interpretation is the fuel pressure drops at those times.

 

From the graph the fuel pressure is stable when I am going full throttle and releasing. The one that drops and increases is the manifold pressure.
Fuel pressure only really drops when I take my foot off the accelerator but this may be normal behaviour. I will do some research on what to expect from fuel pressure.

 

I would interpret the yellow line as fuel pressure. 40-55 psig seems reasonable. To me, fuel pressure fluctuates, and there's a possible discontinuity in three places.

 

Make sure whether it was changing gear as then it may well back off the throttle etc.

 

I may have fixed the issue. It was pretty obvious but I didn't do the job properly the first time!
So if you are getting high LTFT on acceleration but not on idle then your culprits are normally dirty MAF sensor or bad fuel delivery (pump, filter, pressure). I cleaned the MAF at the beginning of this issue but I didn't know that there are 2 hidden "hot" wires further inside the MAF. So all I cleaned was the temperature wire and not the important host wires (the ones with resistors). After watching a few videos I properly cleaned the MAF yesterday and so far the SFTF is going negative when the LTFT is going high so the car is hopefully adjusting to get correct information from the MAF.
Thanks for all the help!

 

It's amazing at times, how little can throw these cars off. Whether it's low battery volts, or a poorly locked gas cap etc. Nothing beats getting it fixed, especially when you find the solution yourself. Enjoy!

 

Give it a bit of time and it should relearn. Or you can do a hard reset (disconnect the battery) to clear the learned values.

It should get back to sane LTFTs and not have to compensate using STFTs.

 

I know this is an old thread, but I wanted to say that I had the same exact issue and solution as Revere. I would get P0171 and "no cruise / no above 3000 RPM" only under load while driving, never while parked. I replaced all the usual suspects including the brake booster hose which had totally deteriorated. I even cleaned the MAF sensor. But after re-reading this thread I decided to clean the MAF sensor a second time with particular attention to the hidden hot wires Revere mentioned. Sure enough my codes cleared and haven't come back in over 3 months so far.
Big Thanks to everyone!

 

Hey there CatFan, how do you clean the hidden hot wires in the MAF? I pulled mine and cleaned the red bead that is easily visible looking down the tube. I used a swab with isopropyl alcohol. I was unaware of the hot wires tho.

I currently have P0174, P0171, lean in both banks and no rev above 3K rpms. The funny thing is that the limp mode mentioned is very intermittent. Comes and goes randomly. The engine light is always on, but the limp mode/No Cruise comes and goes. When not in Limp mode, the motor sounds great and revs up to red line.

Thanks!

 

Patterson, I used Mass Air Flow Sensor Cleaner spray you can find in any auto parts store or Amazon. It designed not to damage the sensor. I stuck the little red spray tube into the sensor unit and "flooded" it with cleaner a few times. Also sprayed all exposed areas too. Then just let it dry. Be sure the o-ring on the sensor is not damaged or missing either. Mine broke off and I had to find a replacement at ACE Hardware for a few cents.

My limp home symptoms were similar to yours. On the surface streets, no issues. But on the highway to/from work on the 101 (I'm in AZ too BTW), it would give a big thunk and I'd have to stay in the slow lane. But once I slowed down enough on the off ramp, it cleared. Very annoying.

 

Well, I cleaned the hot wires in the MAF (after I learned what they are) and I bought a new Duralast MAF for $80 at Autozone. I cleaned the old MAF, but I'll keep the new MAF on hand in case I need it. I can return it as long as I don't install it. I also have a new fuel filter to be installed tomorrow. I did the fuel filter 5 years ago, it was a mess.

I'm taking it in to a new shop I found near work.

Richards Auto Clinic - expert auto repair - Phoenix, AZ 85008


I hope cleaning the MAF works and so I don't get the No Cruise light tomorrow, but, my luck so far has been zero. While the car is still drivable and has not left me stranded, I happen to have an emissions test due this month.

After this I'm setting my sights on a leaky brake booster diaphragm. My brake pedal hisses when I press it at a stop light. It's been that way for a long time b4 the CEL so I haven't got into that. That said, I know my brakes basically need a rebuild from the ground up. My ABS system is probably working, but rotors, pads, and even calipers are pretty banged up and worn. I bought this car in 2010 and I've been driving it payment free for 5 years now, so I don't mind the cost of repairs if I can get them at a fair price. I'm pretty good at parts installing, but I'm no mechanic.

 

Keep us updated on the status. I was pushing up against emissions too and lucked out with that second cleaning of the MAF sensor. I also changed the fuel filter. Although what looked like mud came out of it, it didn't fix the original issue. BTW that's really easy to replace yourself. I pulled the fuse on the fuel pump however to get rid of most of the pressure.

As for a local shop, I use to take my X-Type to Eurotechs in Tempe. The owner Jerry was a Jag tech in N. Scottsdale and started his own shop. Really great guy. But he has since closed shop and now works for Lesueur Car Company as a service tech. I haven't needed any work lately however, but it could be worth it to schedule time for him to check out your car. He knows his stuff.