So Jackie the Jag needs some assistance in diagnosing problem please.
I have a check engine light, on and off restricted performance and lean fuel codes on both banks, P0171 and P0174. My ltft are running 5 at idle, 10 at around 30mph and 19 at hwy cruise speeds. I looked and did not see any obvious cracks causing an air leak. I put in a new air filter and cleaned the MAF. Fuel trims are still the same. I read that if the issue is an air leak that your fuel trims would initially go up high with acceleration and then slowly come back down, mine stay high steadily. Driving doesn't feel any different except a very subtle roughness at idle and not all the time while idling. Sometimes it idles fine other times I feel a slight shimmy so to speak. Twice in the last few days after initial start it didn't stay on, but I wasn't revving the engine, just turned key, initially caught then dies almost immediately. 2nd start I press on the gas a little to rev engine and it is fine. Am I looking at a bad MAF, O2 sensor or something else? Thanks for your help .

 

Did you check the brake vacuum going into the passenger side under the throttle body (its a hard plastic line coming from the drivers side)? It has an O-ring on it that may have dried up and let go. Also, check the MAP vacuum line coming from the driver side under the throttle body.

Here's a test for you:

The best way to check the oxygen sensors (the pre catalytic converter oxygen sensors) is to create a rich condition while observing your scan tool (in Live Data mode) to see if the oxygen sensor numbers go up to 800 millivolts (.800) to 1 Volt.

This is what you need to do (its a nice C&P, I shortened it from 4 pages to this):

1 With your scan tool still connected to the diagnostic connector and the engine running, scroll down to the oxygen sensor PIDs. These PIDs will be labeled O2S11 and O2S21.

2 Make sure the coolant temperature, as recorded on your scan tool, is still above 190° F (88° C).

3 While you observe the oxygen sensor values, have a helper spray a little bit of carburetor cleaner into the intake manifold via a small vacuum hose with the engine running.
I want to emphasize spraying carb cleaner spray into a small vacuum hose. You can not disconnect the intake air duct Hose (while the engine is running) from the Throttle Body to spray carb cleaner into the throttle while the engine is running.

4 If the oxygen sensors are working normally, as soon as the carburetor spray hits the inside of the intake manifold (via the vacuum hose), your scan tool should read 0.900 Volts for both O2S11 and O2S21.

Most common causes for a P0171 and P0174:
CAUSE 1: PCV Tube's rubber elbow (where it connects to the intake manifold) is torn open and causing a major vacuum leak.

CAUSE 2: intake manifold gaskets that are leaking vacuum.

CAUSE 3: fuel pump that's going BAD, but hasn't completely fried yet.

CAUSE 4: A dirty (contaminated) MAF sensor.

CAUSE 5: An exhaust leak right before the pre-catalytic converter oxygen sensors.

CAUSE 6: BAD pre-catalytic converter oxygen sensor.

Remember... the most important thing to consider (or keep in mind) when you're troubleshooting a P0171 or a P0174 trouble code is that whatever is causing it... is making the PCM think that too much unmetered air is entering the engine.

 

Sorry about this bad pic I scammed it off of ebay, (it was upside down, so I turned it for this purpose), but it will do the job. Ok, first you are looking at the neck under your throttle body going to the SC as if you were looking from your windshield. The marked line on the left is for your MAP and the one on the right is the insert hole for that plastic brake line for your booster.

 

Thank you for the reply and suggestions. Now I am about to make you slap your forehead and groan but please bear with me. I need a pic or a diagram showing me where on the intake manifold I should insert the short vacuum hose to do the test. Also, I will pick up some of the carb cleaner at the auto shop so will they also have a short vacuum hose I can buy and should I ask for a certain diameter?

 

Actually some of the carb cleaners come with a plastic tube attached.

The hard part with a Jag is you just can't spray it down the intake tube or you can nuke your MAF (if its good in this case), only MAF cleaner should be used on a MAF. The orange is where you need to get a shot of the carb cleaner into, the green is your MAF.
It will send a code, perhaps even stall it, but you can clear it, ...but the easiest way is to pull the MAP vacuum from under the MAP and give it a shot down it. On the AJ26 diagram, you can undo one of those vacuum leads (blue circles) and spray it in there.

 

Those are definitely the places to look, while you have the intake elbow off also take a close look at the two silencers on the elbow. They do separate/break/crack with age and you will get the po171/174 codes as well.

 

High LTFT at highway speed and stumbling at startup makes me wonder if a fuel pump is failing. I know the fuel filter was replaced, so that shouldn't be a problem.

 

My amateur reaction would be fuel pump also. In my understanding, a vacuum leak will get better under load (better fuel trims) whereas a fuel pressure problem would get worse under load, which seems to be what you are experiencing. Has the fuel pressure been checked?

 

Mostly air leaks, both banks. Try this overly simplistic approach first before tearing your the car apart.

On NA engines, usually some crack or break in the air tube on the right side and broken part load breather hose and leaking dipstick o-ring on the left.

Less knowledgeable about the SC units.


Fixing A Hesitating Car P0171 Code - YouTube

 

Jim,
Why would a air leak result in LTFT readings of 5 at idle and 19 at highway speed? That seems completely opposite what I have observed and read. Could the MAFS be defective without throwing a unique code?

It doesn't really seem likely that a fuel pump is at fault because the car accelerates well at full throttle, but she's going to pull the relays for a quick check.

 

I will defer to anyone with better experience with Long Term Fuel Trim diagnostics. Tho I wrote air leaks, I meant vacuum. So at 2500 RPM, if steady or decelerating, will yield a high vacuum. And the ECU enriches to compensate. One reason not to read the LTFT at road speed but at constant RPM in the driveway. Apparently high enough to set a CEL.

But again, this ain't my speciality. This is how we learn.

On my car (before I traded it) it was running +3.7 to +7.6 at idle; increasing to ~+10 at 2500, then would settle back a bit. New o-ring on dipstick helped; so did replacing the part load breather (the fitting was just an o-ring fit, since I broke the retainer on the cam cover fitting when doing the tensioners in 13. New tube fixed the problem on the left side. Never found anything on the right. The 5.0 liter in the RRS is dead on +1 both sides.

Would not know where to start on a supercharged unit.

 

Ok, pulled relays to check fuel pumps. Results are pump 1 runs nice and strong, car starts up and stays running no problem. Pump 2 the car starts but immediately dies. Rpms go down to zero unless revving and the car shuts off. My amateur reaction is this means fuel pump 2 is going bad. Would just one failing fuel pump cause my issues? As RJ mentioned my car does not hesitate upon acceleration at all.

 

The second fuel pump is used when you apply more throttle for the needs of the SC. It functions on startup only if pump #1 isn't functioning. It may take some cranking for the ECM to do the switch when it recognizes the fault. But you should get a code (P1230) then declaring fuel pump relay failure. If you don't get that code, it didn't recognize the lack of pump #1 and needs to be rolled more to get it to engage. If you do get the code and it doesn't start, then odds are very good its that pump.

 

Went and pulled codes, none pending. Repeated relay test. This time pump 2 would immediately die even if I tried revving on 1st try and subsequent tries would fail to turn over at all. Check engine light and restricted performance came on. Pulled codes, I did indeed have the P1230 under engine codes and under pending codes P1230 and P1671. So am I right in that my 2nd fuel pump is dead and the only reason it even initially turned over but couldn't stay running was because there was residual fuel pressure left over from the previous start?

 

That makes sense. Sounds like you have become a diagnostician.

 

Had both fuel pumps replaced, no change. Smoke test revealed a leak in the seal where the air intake pipe attaches to the top of the engine. Replaced rubber gasket seal, no more leaks anywhere but still no change in my fuel trims. I already tried cleaning the MAF sensor and no change. Other then a bad MAF that needs to be replaced altogether with a new one any ideas on what could cause high fuel trims of 19 on both banks at hwy cruise speeds?

 

Seems to me you've covered the bases & signs point to MAF.

 

A failing MAF could still be possible obviously, but how long have you driven since the pump replacement? If the battery was disconnected for that period (as it should have), you may need to drive it awhile (about 50-100 miles) for it to relearn again.

 

Fuel pumps replaced on Monday, mechanic did not disconnect battery. Driven over a 100 miles since.

 

Ok, that kicks that in the butt....
So, here's this...
The most common symptoms of a BAD MAF Sensor are:
1.A MAF sensor code.
2.Lean and/or Rich code(s).
3.Fuel Trim code(s).
4.A tremendous lack of power upon acceleration.
5.Black smoke coming from the tail-pipe.
6.Vehicle may idle rough and stall.
....to read the rest of it to see how to test it...http://easyautodiagnostics.com/misc-...-test-basics-1 ....
Here's the layout of intake system...http://www.jagrepair.com/images/Trai...ual-9-5-01.pdf