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2002 chevy tahoe 5.3 flex fuel
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Al1120
Novice
Jan 23, 2015, 8:23 PM
Post #1 of 15
(4950 views)
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2002 chevy tahoe 5.3 flex fuel
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My service engine light is on and i had it checked and it has the code P0178 flex fuel sensor and now its shutting off while im driving. I changed the crankshaft position sensor noticed it was soaked in oil drained some oil and installed the new one and its still shutting off while driving can someone help me solve this problem has 200,000 miles
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 8:29 PM
Post #2 of 15
(4946 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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The crank sensor head is going to get oil on the end of it from the interrupter throwing oil on it. Was the oil in the sensor connector cavity or leaking on the outside of the block around the crank sensor? Make sure your oil level is correct according to your dipstick. Draining some oil isn't going to keep the crank sensor from getting oiled on the business end.
Does it shut off at stops, while cruising, or both?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Al1120
Novice
Jan 23, 2015, 8:32 PM
Post #3 of 15
(4942 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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It was soaked in oil and when i checked the dipstick it was 3qts too much. It only shuts off while driving could the flex fuel sensor do that?
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 8:39 PM
Post #4 of 15
(4935 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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Those engines are oil leakers, so don't be surprised if your sensor is covered in oil again.
I've seen fuel compensation sensors fail and cause that code to set, but haven't seen a failed sensor cause an intermittent stalling concern as of yet. Now, something that is related to your stalling could be causing the fuel compensation sensor to fail. Maybe trouble shooting the fuel compensation code may lead to the cause of both the code and the stalling concern. Especially if they both showed up at the same time.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 23, 2015, 8:41 PM)
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Al1120
Novice
Jan 23, 2015, 8:44 PM
Post #5 of 15
(4931 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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I just looked under the vehicle at the fuel filter and saw that the fuel filter is connected but bypassing the flex fuel sensor could that be a problem? do i need to reconnect it to get the P0178 flex fuel sensor gone? Maybe thats the problem?
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 8:51 PM
Post #6 of 15
(4929 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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How long have you had this vehicle? Are you running E85?
Is the sensor's connector plugged in? Wonder why it was bypassed? Connecting the fuel system back up to the sensor may not cause your code to go away if the sensor is faulty or if you have some circuit issue going on. Fuel sensors were common failure items and are very expensive to replace on those. Driers and methanol would take them out.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Al1120
Novice
Jan 23, 2015, 8:56 PM
Post #7 of 15
(4925 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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the connector is still plugged in and the only code im getting is the fuel sensor. not running e83 what steps should i take to resolve the shutting off issue troubleshooting wise?
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 9:04 PM
Post #8 of 15
(4922 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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The key to figuring out why it is stalling is to be monitoring the right system at the right time. You stated in the PM that it wouldn't start for 10 secs after it stalled. That means you have 10 secs to figure out why it won't start.
Engine needs fuel, spark, proper spark/fuel events, and good compression (breathing) to run.
You'll need to monitor fuel pressure during the stall and no start to see if you have proper fuel pressure. You'll have to monitor injector activity and spark using appropriate tools. You may also need to monitor scan data to be sure your PCM is communicating with your scan tool when it doesn't want to start. Driveability problems can be really hard to figure out for DIY due to complexity, knowledge, and the tooling necessary on these modern vehicles. Sure you can throw parts at it and guess, but troubleshooting in the long run is cheaper and saves a lot of heartache.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 23, 2015, 9:04 PM)
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Al1120
Novice
Jan 23, 2015, 9:10 PM
Post #9 of 15
(4918 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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ok but when your driving you really cant troubleshoot when your trying to get out of the road can you give me an idea of what tools i need to get to be able to do this? I greatly appreciate it for all the help im gonna buy a new fuel filter tomorrow. I just bought the truck 4 days ago for 1900.
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 9:19 PM
Post #10 of 15
(4912 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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Do a good visual inspection under the hood. Check electrical harnesses for proper routing. Look for anything out of the ordinary. While the engine is running wiggle harnesses and wiring around to see if you can induce a fault. If everything looks good, the easiest thing you can check is fuel pressure. You can probably rent a fuel pressure gauge from one of the parts stores. Run the gauge out the hood and mount it to your windshield. Make absolutely sure the hose and connections are not leaking and you don't pinch the line with hood closed. Carry an extinguisher with you just encase. Take it on a test drive and see if it acts up. Watch the pressure to see what it does during the stall. That would be a good start. Let us know what you find out so we can advise you on the next step.
I am going to tell you right now that monitoring spark and injector activity is going to be really difficult using anything other than a lab scope during a test drive, so hopefully fuel pressure is the culprit.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Al1120
Novice
Jan 23, 2015, 9:29 PM
Post #11 of 15
(4908 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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Thank you so much for all your help ive been to alot of forums and this by far is the best one ive been to do you think i should buy a chilton manual to see what else i can find out?
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 9:40 PM
Post #12 of 15
(4899 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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Going to be honest with you on the Chiltons or Haynes manuals. That are ok for minor maintenance and repairs, but the wiring diagrams and troubleshooting procedures have a lot to be desired. Check out AlldataDIY for good service info if your interested. I think $25 for a yearly vehicle subscription is a good deal if you want to do repairs and troubleshooting on your own and need good service info.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 23, 2015, 10:50 PM
Post #13 of 15
(4889 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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Just reading and may not be back for this. Just noted reading thread and Quote from several posts back ">>It was soaked in oil and when i checked the dipstick it was 3qts too much. It only shuts off while driving could the flex fuel sensor do that?<<"
What the heck was with that? 3 quarts too full! IMO that would have to cause problems.......... T
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Al1120
Novice
Feb 7, 2015, 6:41 PM
Post #14 of 15
(4827 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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I wanted to say thank you for helping I fixed the problem it was the fuel pump. I started the car took out the pump relay tried to start it then sprayed starting fluid in the intake and it started and ran for a while that let me know it was getting air and spark. problem solved. thanks for the fuel air spark advice
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Discretesignals
Ultimate Carjunky
/ Moderator
Feb 7, 2015, 7:48 PM
Post #15 of 15
(4822 views)
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Re: 2002 chevy tahoe 5.3 flex fuel
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Great to hear you got it figured out and fixed  Thank you for the follow up on this. Can be reopened upon request. Closed as solved.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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