Smooth9883

After many months of trying to understand I think I have taken a giant step forward.

Ever since my fuel pump burned out the beast has felt a little under powered. It would still perform but not nearly to what is normally does. I have submitted multiple posts on the forum with great advice and learned so much about my car.

It wasn't until a few weeks ago when I ran out of gas in my pathfinder that I discovered a band aide.

First I diagnosed the pathfinders problem. My gas gauge told me I had 3/8 of a tank left when it left me stranded at the side of the road. The dealer told me my fuel pump burned out because I ran out of gas in the vett. I told them I had just above 1/8 of a tank left when the pump died. Since both cars recently started to have fuel system problems in the last several months I came to one conclusion.

The problem appears to be BAD GAS! I have always purchased my gas from the shell station down the road. I have tried others but shell makes a noticeable difference. I didn't start having these problems until I moved 8 months ago and had to change the shell station I used.

So here is my Gregory House diagnoses. Let me know if you think it is sound or if I'm full of bull.

Both cars had false fuel indications because the fuel sensors were gummed up. With the pathfinder I pulled over right away and had no problems. With the vett however I had to drive down the road much longer to pull over at a safe distance. This long drive could have allowed enough time for the fuel pump to burn out since there was no fuel to cool it. At the same time I was driving down the road the engine was still trying to run. It was sucking every bit of fuel it could from the tank but in the process the check engine light flashed rapidly for several seconds. As this was happening the doors of the car almost fell off from the severe vibration. From my understanding this is engine knock in it's purist form.

The car was towed to the dealer and the dealer told me I ran out of gas. I told them BS due to the fact that the gauge read just above 1/8 of a tank and the light didn't come on. I got the car back and noticed it didn't seem to have the guts that it normally does. It would have to downshift much earlier to accelerate at higher speeds since it didn't have the power. Just today I was looking in how to correct a possible octane problem from the shell station and I read and learned all about octane. I also read that running a lower octane could cause engine knock, and whenever engine knock occurs your fuel system changes the fuel trim to a low octane setting.

Solution! (kinda) I turned the ignition to on but didn't start the engine. I pulled fuses 16 and 23 then shut the car off. I then replaced the fuses, started the car, reset the codes that fired from me reseting the PCM and took it out for a test drive. WOW, the power was back to wear it had been before. at 45 MPH no longer did the transmission have to shift to accelerate. IT appears to be where I want it.

That to me was a temporary solution to a bigger problem. That solution might also be BS.

Here are my thoughts and questions.
1) The computer should have automatically reverted back to the normal fuel trim table after a couple tanks of gas. I had gone through about 10 so this should have occurred. Is it possible the fuel trims would not reset to the high octane setting?
2) If the fuel trims were staying at the low octane setting what could cause this? Could it be the bad gas? I put 91 which is the highest we can get in Denver.
3) Could a bad O2 sensor be messing with my fuel trims? I have a lose heat shield around my O2 sensor that vibrates horribly and I'm wondering if there could be a problem with the sensor that is messing with my fuel trims.
4) How can I truly prove the shell station is selling bad gas? I've had two cars show faulty gauge indications after buying there. I've tried different stations since the problems but I think the damage has been done.
5) How do I clean my fuel system if in-fact it is bad gas? Is Sea-foam the best product?
6) Bill Curley, be brutally honest with me and tell me if my theory has any validity, if not, let me know if I'm on the right track and what direction you would go.

Thanks for listening to the longest single post in CF history!

lucky131969

Smooth9883

Is the theory sound??

Bill Curlee

My first attempt to post comments directly into the the OPs post didnt work out correctly. See the post below.

Bill Curlee

Wow. I read this post 3-4 times in an attempt to understand it and find the best way to respond. There are 3-4 things here and some misconceptions. So,,,I will try to answer each section of the post.

First,,,,What is your understanding of the term BAD GAS?? "IMHO" Fuel quality is pretty consistent. Most of the fuel in this country is clean and represents the correct octane that its advertised at. There are exceptions and mistakes, but there pretty rare.

BAD FUEL. It is either contaminated with water or particulate matter or accidently combined with diesel fuel.

After many months of trying to understand I think I have taken a giant step forward.

Ever since my fuel pump burned out the beast has felt a little under powered. It would still perform but not nearly to what is normally does. I have submitted multiple posts on the forum with great advice and learned so much about my car.

It wasn't until a few weeks ago when I ran out of gas in my pathfinder that I discovered a band aide. Cant comment on the pathfinder. Could be Murphy’s law.

First I diagnosed the pathfinders problem. My gas gauge told me I had 3/8 of a tank left when it left me stranded at the side of the road. The dealer told me my fuel pump burned out because I ran out of gas in the vett. I told them I had just above 1/8 of a tank left when the pump died. Since both cars recently started to have fuel system problems in the last several months I came to one conclusion.

- Most fuels today are TOP TEIR fuels and there specifically engineered to burn clean, help prevent deposits and not damage fuel systems. SHELL is a Top Tier fuel.
The fuel gage issue normally occurs due to SULPHER deposits on the sending unit. The addition of Chevron Techron PLUS in a few tanks of fuel seems to clear that issue up. Occasional treatments help keep it from returning.
There are sending unit failures where the deposits are bad enough that it requires mechanical cleaning or sending unit replacement.

I use SHELL fuel 95% of the time and have NOT had any fuel system issues.

The problem appears to be BAD GAS! I have always purchased my gas from the shell station down the road. I have tried others but shell makes a noticeable difference. I didn't start having these problems until I moved 8 months ago and had to change the shell station I used.

-Can one station have a poor fuel tank condition over another. YES. If you suspect poor fuel from that station, find out if there is some sor of local inspection agency that you can complain to and have the fuel inspected.

So here is my Gregory House diagnoses. Let me know if you think it is sound or if I'm full of bull.

Both cars had false fuel indications because the fuel sensors were gummed up. With the pathfinder I pulled over right away and had no problems. With the vett however I had to drive down the road much longer to pull over at a safe distance. This long drive could have allowed enough time for the fuel pump to burn out since there was no fuel to cool it. At the same time I was driving down the road the engine was still trying to run. It was sucking every bit of fuel it could from the tank but in the process the check engine light flashed rapidly for several seconds. As this was happening the doors of the car almost fell off from the severe vibration. From my understanding this is engine knock in it's purist form.

-When you have a flashing CEL indication, that means the engine is MISSING. Its most likely missing from improper air/fuel ratio. The cause: IT RAN OUT OF FUEL! Was the pump loosing pressure because it was sucking zero fuel OR because it was pumping against dead head (CLOGGED FUEL FILTER)

Is the fuel pump & fuel system able to flow the correct GPH of fuel?

Conduct a FUEL FLOW check. Make sure that your fuel pump and system components provide the CORRECT VOLUME of fuel to maintain the correct fuel pressure.


If I was in your shoes, Do a fuel flow test then I would replace my fuel filter and run the test again. Cut the old filter apart and examine what’s in the filter. That would justify your theory of contaminated fuel if it full of crap. If there are significant particulate debris in the element, that would justify you poor fuel theory from that station. Take pictures for evidence and submit the evidence to local fuel quality people and or file charges on the station for damages if it is bad fuel.

The car was towed to the dealer and the dealer told me I ran out of gas. I told them BS due to the fact that the gauge read just above 1/8 of a tank and the light didn't come on. I got the car back and noticed it didn't seem to have the guts that it normally does. It would have to downshift much earlier to accelerate at higher speeds since it didn't have the power. Just today I was looking in how to correct a possible octane problem from the shell station and I read and learned all about octane. I also read that running a lower octane could cause engine knock, and whenever engine knock occurs your fuel system changes the fuel trim to a low octane setting.

-If the engine sees KNOCK,,it goes into Knock Retard timing reduction. If the PCM reduces timing in the timing tables and the knock continues, it drops into the LOW OCTANE TIMING TABLES.

The LONG TERM FUEL TRIMS are just that. Adjustments to the fuel trims over a long period of time. Just adding 100 octane to the fuel or correcting an issue that cause a 25% increase or 25% decrease to these tables does not get them back to correct trims. That takes time. YES, removing the PCM fuses resets them to neutral and they relearn from that point.

Data log your engine and look at the STFTs and see what there doing to the LTFTs If there causing them to spike significantly one way or the other, you still have some sort of issue.


Solution! (kinda) I turned the ignition to on but didn't start the engine. I pulled fuses 16 and 23 then shut the car off. I then replaced the fuses, started the car, reset the codes that fired from me reseting the PCM and took it out for a test drive. WOW, the power was back to wear it had been before. at 45 MPH no longer did the transmission have to shift to accelerate. IT appears to be where I want it.

Transmission shift points. Shifting normally? I have never owned a AUTOMATIC C5,,,,so,,,,,,heres my best shot at a guess from work. I would have to read the SERVICE MANUAL to properly summarize what’s all used to make a dynamic shift point. If your engine is not running up to spec, your pressing the accelerator more to get the same throttle response that you desire. Trans shift points take in to account several inputs to determine proper shift point:
- Throttle Position
- MAP value
- coolant temp.
- could be more???

Is the tranny just responding to an improperly operating engine?


That to me was a temporary solution to a bigger problem. That solution might also be BS.

YEP.. I agree!
Here are my thoughts and questions.
1) The computer should have automatically reverted back to the normal fuel trim table after a couple tanks of gas. I had gone through about 10 so this should have occurred. Is it possible the fuel trims would not reset to the high octane setting?

Data LOG and see what the PCM is seeing for LTFTs, STFT, KR, O2 sensor operation.. That will be TRUTH!


Remember. Data Logging with EFI Live or HP tuners is FREE! You just need to find someone with the equipment in your area who is willing to do it for you .

2) If the fuel trims were staying at the low octane setting what could cause this? Could it be the bad gas? I put 91 which is the highest we can get in Denver.

Data LOG and see what the PCM is seeing for LTFTs, STFT, KR, O2 sensor operation..

3) Could a bad O2 sensor be messing with my fuel trims? I have a lose heat shield around my O2 sensor that vibrates horribly and I'm wondering if there could be a problem with the sensor that is messing with my fuel trims.

-Data LOG and see what the PCM is seeing for LTFTs, STFT, KR, O2 sensor operation..


4) How can I truly prove the shell station is selling bad gas? I've had two cars show faulty gauge indications after buying there. I've tried different stations since the problems but I think the damage has been done.

Test the fuel, cut open your old fuel filter.

5) How do I clean my fuel system if in-fact it is bad gas? Is Sea-foam the best product?

Chevron Techron Fuel System PLUS, Seafoam...


6) Bill Curley, be brutally honest with me and tell me if my theory has any validity, if not, let me know if I'm on the right track and what direction you would go.

-As honest as I can get. Data LOG and see what your PCM is telling you.

Conduct a FUEL FLOW check. Make sure that your fuel pump and system components provide the CORRECT VOLUME of FUEL to maintain the correct fuel pressure under all load conditions.
Thanks for listening to the longest single post in CF history!


YES IT WAS!

LUCKY. COMMENTS???????????????

Bill C

FL_Dave

Bill - Another post showing why so many of us appreciate your participation in this forum.

Smooth - I use to have the fuel problem and had the sender replaced before having the problem again. As Bill said, Techron.

lucky131969

Well Bill, as usual, you've covered the bases. With respect to fuel trims, I'm not sure I've experienced the octane of the fuel causing an issue. Typically the following will:

-Vacuum leaks
-MAF issues
-Coolant temp
-Fuel pressure
-O2's
-Injectors

That being the case, getting hooked up to tuning software is the best bet.

To the OP: What was the fix on the Pathfinder? Was the sending unit contaminated, and if so, can you determine the nature?

Smooth9883

As of the now the fix on the pathfinder is dont let the gauge drop below 1/4 of a tank! I haven't had time to bring it in to the dealer yet, but i'm hoping to do so soon.

Bill Curlee

Lucky

You are ABSOLUTLY correct. I was trying to do three things at once. WORK, FORUM and answer a long post.
A/F ratio has the MOST effect on LTFTs so,, anything that you do to the AFR to correct LTFT, will take a long period of time to average out the current reading unless you command reset them with tuning software or pull fuses. Thanks for the back up.

Bill

herbgriff

I just installed long tube headers. Car runs great. My water temp gage pegs after startup. Water feels warm not hot. Help.