PAUL T Posted October 18, 2008 Report Share Posted October 18, 2008 My 97 Deville has been throwing intermittent codes P0151 & P0174. Car has had hard cold starts which got a little better after I replaced the air filter. I have also noticed a few mpg drop lately. I am suspecting a bad front O2 sensor or wire. I have checked the FPR and all is dry. Anything else I need to check? Link to comment Share on other sites More sharing options...
Cadillac Jim Posted October 18, 2008 Report Share Posted October 18, 2008 P0151 Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 2 Sensor 1 P0174 Fuel Trim System Lean Bank 2 The hard starts when cold tell me that it's not the oxygen sensor; the oxygen sensors don't have anything to do with the engine until it has run a couple of minutes. Bank 2 is the front bank of cylinders, so you're in luck if it does turn out to be an oxygen sensor. The first thing I would do is check the wiring and connector for the oxygen sensor on the front bank. It's low on the manifold just before the flange for the crossover pipe. You didn't say whether either of these was Current or History. If the MIL (check engine light) is on, one of the codes is Current, or was Current within the last three drive cycles. It's likely a vacuum leak. Check for vacuum leaks, such as a PCV valve stuck open, loose or cracked vacuum hoses, or loose intake manifold bolts. Make sure that the engine oil dipstick is there, and all the way down, and that the oil filler cap is tight. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted October 19, 2008 Report Share Posted October 19, 2008 P0174 Fuel Trim System Lean Bank 2 Yup, look for a vacuum leak. Particularly near the front bank. Link to comment Share on other sites More sharing options...
PAUL T Posted October 27, 2008 Author Report Share Posted October 27, 2008 O.k. guys here is an update. I am still getting the P0151 & P0174 codes. Also with those codes I got a P0171. I am noticing now that these codes come up only after filling the gas tank. Last night it just really did not want to run after filling the tank. I also could really smell a lean mix at the time of the codes which does explain the codes. I have checked for vacuum leaks and so far have not found any. I also checked the PCV and it is clicking o.k. when I shake it. To remind everyone, the air filter was just changed. It just did not seem to be getting enough air when I was stumbling. After a few miles it finally cleared up. I have not checked the throttle body yet. Also, this morning I noticed that there was no hard cold start that usually occurs. Is it possible I may have some water in the tank that causes this after a fill up? Gas last night was $2.499 at Sam's Club, at this price I might be able to start driving my Excursion again. Link to comment Share on other sites More sharing options...
Cadillac Jim Posted October 27, 2008 Report Share Posted October 27, 2008 P0171 Fuel Trim System Lean Bank 1 What P0171 and P0174 mean is that the fuel injectors can't provide enough fuel to make the mixture right. Also, if you keep getting P0151 you have a problem with the oxygen sensor on Bank 1 (connector, wiring, or the sensor itself). A clogged air cleaner can cause P0171 and P0174. Look at the new air cleaner element and see if you think it has ever been wet, that it's inserted properly, etc. If there is any doubt, get a new one. AC/Delco have been shown in dyno tests to be better than K&N overall, right here on Caddyinfo. Be sure and check your oil filler cap and dipstick. If they aren't all the way down and tight you vacuum leak is there. Poke around on your vacuum hoses. Some years ago I looked at a 1973 Eldorado with the 500 cid engine because the owner said that it was running rough. It turned out that all the vacuum hoses had rotted out where they contacted the valve covers and such because the oil was there, but the looked OK until you pulled them up with a pencil and looked at them. A trip to NAPA for some new neoprene hoses and twenty minutes of work did wonders for the idle and general driveability of that fine car. Then, she felt so good about the car that she tried to kick sand in my face while I was driving my 427 cid Chevrolet station wagon... -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted October 27, 2008 Report Share Posted October 27, 2008 Have you checked the fuel pressure? Link to comment Share on other sites More sharing options...
PAUL T Posted October 27, 2008 Author Report Share Posted October 27, 2008 Have you checked the fuel pressure? Not yet, I will have to find my gage first. I did poke around the vacuum hoses and did not find anything unusual. I am going to check the air cleaner tonight to see if I somehow got it in wrong. I checked the oil dipstick and filler cap and they were on correctly. I put some dry gas in the full tank this morning before my wife took it to work. How hard is it to get to the front O2 sensor? Do I have to get under it? Link to comment Share on other sites More sharing options...
Ranger Posted October 27, 2008 Report Share Posted October 27, 2008 The air filter would have nothing to do with it. even if you put it in wrong it may draw unfiltered air, but the filter is upstream of the TB so it won't created a lean condition. Link to comment Share on other sites More sharing options...
Cadillac Jim Posted October 28, 2008 Report Share Posted October 28, 2008 Ranger -- If it's clogged it would force a rich condition, not a lean condition. You're right. But, I once read that a lean bank code could be caused by a bad air cleaner element. Perhaps a torn one, and not on a Cadillac. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted October 28, 2008 Report Share Posted October 28, 2008 No, it won't force a rich condition Jim. On a carbureted engine it would, but on a computer controlled, fuel injected engine the MAF will report less air flow and the PCM will compensate accordingly. It would have to be clogged almost to the point of no flow to force a rich condition. Link to comment Share on other sites More sharing options...
JohnnyG Posted October 28, 2008 Report Share Posted October 28, 2008 How about a clogged fuel filter? Also, do these cars still have the charcoal canister somewhere? Vacuum leaks on the hoses leading to that location should be checked as well. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
JohnnyG Posted October 28, 2008 Report Share Posted October 28, 2008 Also, the erratic nature of the driveability issues lead me to suspect the tank or sock filter. I do realize that problems from filter issues tend to show up in high fuel demand situations. What does the car do if you drive up a hill agressively? On ramps? Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
Ranger Posted October 28, 2008 Report Share Posted October 28, 2008 How about a clogged fuel filter? Also, do these cars still have the charcoal canister somewhere? Vacuum leaks on the hoses leading to that location should be checked as well. Yes they do. Link to comment Share on other sites More sharing options...
Cadillac Jim Posted October 28, 2008 Report Share Posted October 28, 2008 No, it won't force a rich condition Jim. On a carbureted engine it would, but on a computer controlled, fuel injected engine the MAF will report less air flow and the PCM will compensate accordingly. It would have to be clogged almost to the point of no flow to force a rich condition.A clogged air cleaner would produce low manifold pressure relative to atmospheric pressure, which would be compensated by the DFI as you say. Wouldn't the DFI trying to lean the mixture past a sanity check threshold based on the known barometric pressure throw a fuel trim code? -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted October 28, 2008 Report Share Posted October 28, 2008 Well I suspect it might throw a code of some sort (not sure what) if like I I said, it was REALLY, REALLY clogged bad. All I am saying is that a dirty air filter is no where near as critical as it was in the old days. That is why the owners manual says change it every 30K. Remember the old days? I think it said 1 yr or 10K if I remember correctly. Link to comment Share on other sites More sharing options...
PAUL T Posted October 28, 2008 Author Report Share Posted October 28, 2008 I change my air filter when I can't see the sun through it. According to my manual P0171 & P0174 can be caused by a bad air filter, that is why I changed it first. Another hard start this morning and a P0151. After it runs a few miles there are no drivability issues. I am going to concentrate on the P0151 for now because it seems to occur more often. I am going to get a new fuel filter just to rule it out though. I will just have to track down the wire to the front O2 sensor. Oil cap & dipstick are o.k.. I still need to check the Throttle body and I am going to take out the air box and reinstall it also. I will check the lines to the charcoal filter. Link to comment Share on other sites More sharing options...
PAUL T Posted November 1, 2008 Author Report Share Posted November 1, 2008 Well I went to change the fuel filter today, easy job right? I inspected the screw fitting end and it was very rusty, so I sprayed it down with liquid wrench. I figured I would probably round out the fitting so when I did I resorted to the vice grips. I tried as hard as I could to get the fitting loose but it would not budge. I have never had a fitting like this that I could not bust until now. I even tried, very carefully, to heat it and still no luck. I finally quit before I really did some damage and while I had some pride left. My only resort now is to cut the fuel line and splice a section back in. Rockauto has a splice kit for it, so it must be something of a problem. Has anyone else ever had this problem? Link to comment Share on other sites More sharing options...
Cadillac Jim Posted November 1, 2008 Report Share Posted November 1, 2008 The fuel filter has a quick disconnect fitting. The fitting that you are trying to unscrew is probably part of the filter. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
PAUL T Posted November 1, 2008 Author Report Share Posted November 1, 2008 The fuel filter has a quick disconnect fitting. The fitting that you are trying to unscrew is probably part of the filter. The quick release is on the end that connects to the plastic line that runs to the tank. The other end has a fitting on the metal line that screws into the filter, similar to a brake line. I just called a local parts store and they have the repair kit, so I am off to get that. Link to comment Share on other sites More sharing options...
PAUL T Posted November 2, 2008 Author Report Share Posted November 2, 2008 I am not having a good day. Well I got the kit to splice the fuel line to put a new fuel filter in and it went o.k. until I went to take off the bracket that holds the emergency brake line, the fuel, and brake lines up under the car. As I ever so carefully twisted on the bolts they snapped off rather easily leaving me with having to minority construct the bracket back on thru a third mounting hole. After I made sure everything was back together and no leaks were present I found my fuel pressure gage and went to check the fuel pressure. Well the gage only registered 30 psi and is supposed to be about 45 psi. This explains the cold hard starts. I also checked for a vacuum leak at the charcoal canister and did not find one. Could a bad FPR cause a low fuel pressure, I have checked the vacuum side and no gas is present? Should I change the FPR or save up for a new fuel pump? Link to comment Share on other sites More sharing options...
Ranger Posted November 2, 2008 Report Share Posted November 2, 2008 If there is no fuel leaking from the FPR nipple, then it is good (you did check it with the ignition on or the engine at idle, didn't you?). Save for a fuel pump. Link to comment Share on other sites More sharing options...
PAUL T Posted November 2, 2008 Author Report Share Posted November 2, 2008 If there is no fuel leaking from the FPR nipple, then it is good (you did check it with the ignition on or the engine at idle, didn't you?). Save for a fuel pump. Yes I have checked the FPR both ways. I know sometimes it could still be bad and not be leaking. I may go ahead and change it while I am saving up for a new Fuel pump. Link to comment Share on other sites More sharing options...
PAUL T Posted November 5, 2008 Author Report Share Posted November 5, 2008 UPDATE!! I just got through having the 97 Deville towed home. My wife was about 50 miles from home and it would not start for her. When I got there it would not start for me either. It had the same codes P0151, P0171, P0174, & P1599. After I got it home I put the fuel pressure gage on it and with the key on I went to 10lbs.. After I started it, yes it started, it registered 30lbs. and stayed there. I had ordered a front O2 sensor that I plan to put on this weekend. It looks like I might be putting on a new fuel pump soon also. Does anyone know if a bad O2 sensor would cause low fuel pressure? Link to comment Share on other sites More sharing options...
JimD Posted November 5, 2008 Report Share Posted November 5, 2008 ....Does anyone know if a bad O2 sensor would cause low fuel pressure? O2 sensors have nothing to do with fuel pressure. It is remotely possible your fuel pump relay is causing the low pressure. Temporarily swap in a known good relay and see if the pressure changes. Most likely, you are looking at a new pump. Your P0171 and P0174 could be pointing at a vacuum leak. Check/listen for bad hoses at the throttle body, brake booster, and PVC plumbing. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
PAUL T Posted November 5, 2008 Author Report Share Posted November 5, 2008 I have checked for vacuum leaks twice already and no luck. I also swapped the fuel pump relay with another and no change. I might try a new FPR before I get the pump, I know I am grasping at straws. Link to comment Share on other sites More sharing options...
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