So much for my hearing or lack thereof. I'm hearing MAF sensor when it was MAP sensor. A new Manifold Absolute Pressure (MAP) sensor and replacement of the two upstream oxygen sensors has fixed the lean fuel errors. I'm back up and running, the new engine feels and sounds like new. This was an expensive learning experience. Live readings of the Long Term Fuel Trim now show a range from near or slightly below zero at around town speed (<80mph) to 17.6 which is what I likely read while I had the stalling issues last weekend. The service writer said that it needed to stay under 10 to keep from triggering the engine light. I haven't found anything specific to the 150 XKR regarding proper range. It's possible that the replacements fixed the stalling, but it also seems possible that in the diagnostic process something that was loose was tightened or stopped leaking (repair by accident). For now, the car is telling me thanks for the surgery, let's have some fun.

 

 

....and just when you thought this saga was over... Check engine light came back on after about 90 miles, same P0171 and P0174 lean errors. Long Term Fuel Trim (LTFT) is up to 19.5% at idle or when my foot is off the gas. The engine feels better, just a hint of leanness when I take off from a stop or accelerate quickly - I'm not stalling. The last round of attempted repair ran another $700 for the MAP and upstream oxygen sensors. I can't pass Maryland emissions with active engine warnings and without 30 warmups and turning off of the engine. One of the lessons I'd pass on for your consideration is making sure to request all the old parts be held. This didn't happen with the bits that came off the 21,000 mile engine. Now I've allowed myself to be put into a position where I'm paying for new parts with jacked up prices that may or may not fix the underlying problem. I have run a tankful of gas through the engine with SeaFoam to hopefully clean the injectors and fuel lines. It didn't seem to help with the lean issue, but I'd hope it improved something somewhere. I'll confirm tomorrow that the MAF sensors were both cleaned and the seals were rechecked. Thoughts? Suggestions? Laughter?

 

Save me wading through another 80 posts. What are the 4 trims, hot engine parked at idle? And the 4 when you then rev to about 2500 and let them settle?

There are a few sensors you can figure out quite easily (ECT, IAT,...) - do they have plausible values and behave sanely from cold (meaning engine off long enough to cool properly e.g. overnight))?

 

Thanks for trying to help. Here goes:
At Idle with engine hot:
LTFT 1: 19.5%
LTFT 2: 19.5%
STFT 1: 10.4%
STFT 2: 10.9%
STFT (B1-S2) -1.6 to .8%
STFT (B2-S2) -1.6 to .8%
Fuel Rail Pressure: 47 psi
HLV: 18.4
CLV: 20%
CEP: 7.8%
IMAP: 12.9 inHg
Fuel/Air Commanded Equivalence Ratio: .98
Air flow rate from MAF: .7 lb/min
Coolant temp: 197 degrees F
Ambient air temp: 95 degrees F

At 2500 rpm
LTFT (both) 0.8%
STFT (both) 10.9%
After revving to 2500 rpm all numbers almost immediately go to the idle numbers above.

... and the check engine light came on again.

 

I"ll still throw money at a vacuum leak after the throttle plate (PCV system, etc). It's a much larger component of the A/F at idle versus 2500 rpm and that's why the fuel trims are changing so dramatically. MAP replacement was a poor diagnosis because they didn't believe the reading. Pick up an absolute vacuum gauge and install it on this port.



It should match the MAP #'s if you can convert the numbers. An even cheaper troubleshooting tool is to hit the engine with a couple squirts of starting fluid to see if the idle bumps up. If it does you've managed to get starting fluid to the intake path. I'd spray a lot around the throttle body and intake tubing. Just stay downwind of the air filters.

Mine from my Icarsoft LRII. Our tools don't talk the same language for some of the readings but here's the ones that matched up.
At Idle (652 rpm) with engine hot versus / 2500 rpm
LTFT 1: -1.56% / 7%
LTFT 2: 1.56% / 6.25%
STFT 1: 0% / 0%
STFT 2: 0.% / 0%

MAP V 1.16 vdc / .90 vdc
MAP: 6.96 psi / 4.6 psi

Air flow rate from MAF: 10-11K gram / hour / 32-34k g/h

 

Fuel trim can be a valuable diagnostic tool - Eastern Manufacturing

From the above webpage:
"Diagnostic Tip:

For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak."

 

1. The new MAP and oxygen sensors did not change the readings or address the fuel trim issues.
2. Checking for vacuum leaks is a necessary basic primary test that must be conducted prior to replacing sensors.
3. The logical diagnostic steps have either not been taken or they were not performed effectively.

From the article above: "Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter."

I'll reengage in the morning. Thanks!

 

I'd go for Ranchero's suggestion and use a can of engine starter spray to find the leak, finding it by eye is difficult.

 

Looks like an air (aka vacuum, i.e. into vacuum) leak.

Usually you'll find it as you spray close to each possible place for a leak (at idle). (The exception is where you miss the place e.g. due to it being inaccessible.)

STFTs go mad when you find the place, as the car has to suddenly cope with weird fuel/air mix. (Sometimes you can hear the revs change but the STFTs are far more sensitive.)

 

If you don't want to spray starting fluid all over the place, you can also hook up any vacuum line to a Smoke Generator and watch for little wisps of smoke to come out of any leaks.
I've found leaks using both methods, the Spray Fluid finds out IF there is a leak quicker, and the smoke locates the leak more precisely.

 

They say they did both the smoke test and the starting fluid routine before. They didn't take the car for an extended drive before I got it back on Friday and the numbers don't show while the engine is cold. I told them I'd take it for the weekend to monitor the numbers and performance. It' s back once more to the shop. Stay tuned.

 

Costs what, $3 for a can of starting fluid? At certain point you either start troubleshooting the simple stuff or suffer the consequences. I'm not sure what my schedule is later this week but I might be able to stop down.

 

Smoke tested - nothing found. All vacuum related connections were pulled, resealed with dielectric lube, the MAP sensor may have had a pinch in the seal. Bottom line is the fuel trim is now correct. LTFT ranges from zero at normal load to 5.5 % at no load/idle. Big difference from 19.5% yesterday. STFT was okay too. It only takes a very small leak to screw things up. Looks like I'm good to go for now. Thanks to all for your interest and help.

 

Fingers crossed, Pete - crap like that, you do not need.

 

Yeah, vacuum ain't pressure so the pressurized smoke test would only find really bad leaks. Silly kids should know better.

Good to hear it's rolling happy.