Get the codes read and cleared at most auto parts stores. AutoZone will do it for free. Be sure and look at the code reader display yourself so you can write down exactly what it says.

I usually have to request they clear the codes and once had to show the guy what button to push to clear them.

Might save you a few dollars??
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dont confuse cleared codes with erasing volatile codes, or turning off the cel light. You can get a cel off on some codes with key cycles too. But the code is always there. Especially any odb2 codes. Which are p codes primarily p0430 p0300. Etc this is to keep people from disconnecting the battery or using a paperclip between 2 terminals on the obd1 connector to erase them and running to get the car state inspected without fixing the car. This was days of old and al changed with obd2 requirments and laws. So anyone that said they did this was mistaken. If the light is off it does not meen there are no codes

 

Well this is for sure a myth buster busted. I tried and engine light still on as I wished it wasnt but had to try. Anyway I have no way of hard clearing as suggested here except dealer, but I did do the tests again and recieved similar results
st1 4.7/16.4
St2 -1.6/12.5
Lt1 17.2/.8
Lt2 15.6/2.3

 

Hang on there. Your LTFTs should have gone to near zero. Then they'd gradually increase (assuming the leak is still there). You touched the disconnected battery leads together?

Please remind what year & engine your car is.

 

I don't know what it was supposed to do after clearing the codes but I can say that yes I did disconnect both battery cables and held them together for roughly 30 seconds. Upon which I restarted car and still observed the engine light . At that point and I do understand according to Brutal that I really need to Hard clear(dealer for me) the codes, I cleared the codes with what Autozone would typically use and the light turn off. I than shut off and restarted the car after 30 seconds and with no light evident proceeded to reread the codes P0171 & P0174 come right up without a light on the dash.

Its clear at this point I have a vacuum leak. I just need to locate it and I wont be able to do that till Tuesday as im getting ready for alittle R&R.

My car is a 2004 Jaguar XJR which is a 4.2 Supercharged V8. Only engine mod is a drop in K&N airfilter which has been there for 42,000miles(and kept clean). I wish I was able to say were the leak was today, but it will have to wait.

 

Oh, sorry. I only know what S-Types do. You've a different car but are in the S-Type forum. Now I'm really confused!

 

You are correct I came and intruded your posts, but the topic was relevant and from what I understand here in the states the s-type R which ive owned in the past was and is the same engine...no? I do still own an S-type if that counts just not the same motor(3.0 V6). But, I am sorry for the confusion. The S type R and XJR share the same engine and Transmission last I looked so I felt it was all relevant to the original posts and current same issues with the 4.2 SC

 

The common leakers on the 4.2 sc engine are
1) intercooler ducts on top of engine
2) brake booster pipe where it goes into the induction elbow below the throttle body. Theres a oring in there that is behind the plastic release ring. Jag only sells the induction elbow. That oring is always brittle and in piece and is a big source for vacuum leaks
3) the plastic piping and rubber vacuum lines

 

Im back again. I wanted to at least let you know what I have done and that I was able to rectify my air leak code. I grabbed a full intake and MAF as well as a CCV from a donor S-Type R. After replacing the CCV (Crank Case Valve) and clearing codes I have yet to go back into a limp mode. Its been a couple of days and I was used to seeing it every morning and afternoon come and go. CCV for those who dont know is located on a 4.2 Supercharged( I assume the same for NA) on the pass. side valve cover. I noticed it sounded like air sucking alittle to much. So a quick swap confirmed my problem though I haven't gone back to check my LTFT's I feel pretty confident her problem is solved. Now at least I have a good MAF and intake if needed as extra and only cost me $40.00. Thank you for your kind advise on what to look for as always and regardless of which part of the forum the help is tremendous.

 

Hi Guys,,
After a long battle, testings, maf cleaner, smoke test for vacuum leaks, any others I have found that a common problem with jaguars 4.2 supercharged engines is the EGR valve which leaks. I have just took mine off, inspected, clearly show that doesn't close properly, ordered a new one (£250 gbp) and the restrict perform codes p0171 and p0174 are gone.

 

If you are changing the EGR valve be sure and change the metal tube too.

Several people have had this rust out and it's hard to change. It's in the same area so a good time to do both.

No point in swapping the EGR valve and then getting a leak in the EGR tube!
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It is all sorted, the big cat roars again up the red line, eml and restricted perform is gone 4ever!

 

I had the same codes P0171, and P0174 in my 1998 XJ-8. One of the easiest and smartest things to try FIRST is to connect a fuel pressure gage to the fuel rail. If it shows a pressure lower than 38psi when your car is at idle, you have a fuel pressure problem. When I say a lower pressure, I am talking 25-30psi. I spent a lot of time looking at the MAF, checking for vacuum leaks and buying a scanner and finally discovered low fuel pressure was causing the car's computer to run high numbers on both the LTFT and STFT to keep enought fuel going into each cylinder. Now, every car is different and you might still have a vacuum leak or bad MAF, but it is not likely that all these will occur all of a sudden. You can borrow a fuel pressure gage at Autozone for free. Good luck....

 

Mine is doing this right now too, restricted performance, P0171 P0174 codes, lean both banks.

ONLY does this on start up, warm or cold start, doesnt matter, at which point I clear the codes, the restricted performance goes away tooo, and any subsequent driving, cruising, idling, etc, does not throw the lean codes again...

Wonder if it is some valve get cycled only at start up that causes a leak...

Only had the car out twice since taking it out of storage this past week, so haven't had too much time to troubleshoot...

edit: found the cause of this to have been a vacuum leak due to cracked PCV hose... fixed.

 

Ok so here is my night mare story with P0171 & P0174 codes, back in December car started to miss restricted performance light flashing, CEL comes on and then it starts flashing as well. Pulled out my OBD2 reader and found I had the above codes. After a good search of this forum I get a bunch of solutions to the dash disco light issues and determined that at 176KM maybe its time for some plugs. Well I go to Napa and get everything I need, upper and lower intake gaskets, 6 new coils, 6 new plugs and procede to perform the repairs. Get her all back together take it out for a test drive runs like a top. Go to go out that night and don't go more than 2 blocks bang back on is the CEL and it drops flat on its face with a huge miss and stutter in the engine. Great next morning hook up my scanner and find that 171 & 174 are back. Start checking and found the small vaccum hose for the injector management valve I believe its called has pulled out of the 90* rubber boot. Awesome put it back into the elbow out for another test drive runs great. Finish putting the cowling and wiper back on go to out again that night instant replay jump on the gas stutters then falls on its face and back is the CEL. Ok out come the propane bottle and check everywhere that one can for a vaccum leak none found. At this point gas inside the car with a match is looking like a great addition to the car. So find out my scanner will not do fuel trims so I buy an Elm 327 and find that my fuel trims are very high, I dont have my laptop with me so I don't have the numbers. Anyways it confirms vaccum leak. So only thing not changed are the "o" rings for the VMT's I believe they are called. Before I can get to change them the car starts having cardiac arrest, the a/c ditital display starts blinking on and off same for the radio, the CEL and restricted performance light are back and again and now the CEL is flashing like mad. Back to the scanner pul out P0351, cyl #1 miss, P0171 & P0174 great this just gets better all the time. Back to searching the forums for the electrical gremlins, everyone recommends a new battery around 5-6 years, mine seems ok at 11 years car was parked in a garage every night must have helped somewhat. Anyways buy a new battery put it in and end up changing cyl #1 coil, still had my old coils on the bench. Clear all the codes, fire her up and low and behold all of my codes including 171 & 174 are gone car runs great. I have not checked the fuel trims yet but the CEL has been out for over a week, no restricked performance message and no engine miss or stumble so far. Took me a while but got all of the issues solved and I still have some hair left on my head.

 

Your paragraph is in need of some formatting, but from what I gather, battery and coil packs were your issue?

 

Yep pretty much it lol, I type like I talk long winded. Only issue left to fix is the DSC

 

I don't want to burst your bubble, but I seriously doubt that plugs and a battery were your problem. I had a similar experience with my 98 xj-8 that lasted off and on for about 6 months until I finally replaced the fuel pump. Codes p0171 and p0174 show that you have a lean running problem on both banks of cylinders on your v-8 engine. A lean condition means too much air or not enough fuel getting to the combustion chamber. Here's what happened to me: I could not find any vacuum leak problems, so I purchased a fuel pressure gage....the best 50 bucks I ever spent ! My fuel pressure was only about 24 psi on the fuel rail instead of the 39-41 psi it was supposed to be. My car seemed to run just fine because the fuel trims were running very high trying to keep the fuel/ air at the proper ratio. I could sometimes drive 500 or more miles before the CEL would light up. When I removed the fuel pump, the connector was badly burned around the wires going in to the fuel pump. This connector is too small, IMO, for the amount of current passing through these terminals. I have read numerous accounts of similar damage on other jaguar fuel pumps. So, if you have any more issues, drive to Autozone and borrow their fuel gage and see if your pressure is low. Good luck...

 

One more thing: the internet is a wonderful thing, but it can also send you on a wild goose chase if you do not fully understand what these CEL codes mean. Codes p0171 and p0174 tell you that you have a lean running problem on both banks of cylinders...period ! This might be a vacuum leak or a fuel supply problem or even an intake gasket leak, but with both codes p0171 and p0174, the problem exists on both right and left banks of cylinders. So your intake gasket would have to be leaking on both sides to throw both codes. I almost took my car to an "expert" for repair, but he wanted to install new intake gaskets before even looking at my car....I don't think so ! Use your head and ask questions that might save you a lot of money. If you don't find a vacuum leak, check fuel pressure next. You might have a clogged fuel filter. A fuel filter only takes a few minutes to change and eliminates the possibility of a clog when it is changed.

 

Well all I know is last week I put a battery in the car and changed out cyl #1 coil pack and since then knock on my wooden head I have not had any codes return and the car is running great.

I agree with you that having both codes does indicate that the engine is running lean on both banks. I have not had a chance to recheck my fuel trims as I am in the middle of moving but once I am settled I will hook up the laptop and check them and report back here my findings