Pontiac G8 Forum banner
1 - 19 of 19 Posts

·
Registered
Joined
·
91 Posts
Discussion Starter · #1 ·
Hello guys my name is Tyler as i just introduced myself over in the Newbie/Introduction Forum.

As i have stated over in that forum, my car has been in a wreck and im slowly repairing the issues that the 2nd owner didnt fix from the 1st owners wreck. The car is solid, just cosmetic like the driver fender and back bumper, driver side door is slightly lower then driver side second door. Car runs all day everyday and the hell that i put her thru from time to time, never any hiccups from the fuel system.

Ever since i got the car after filling it up and even past after it clicks off the fuel gauge would always read 3/4 full. It would just sit there for a few days and then it would start reading and slowly fall off 3/4 but not just all at once. Then after owning it a while it would still read 3/4 after refueling but the next day it would read between full and the small mark.

As of lately when i go to the track or do hard launches the fuel gauge will fly up to almost full. Normally i can do this and after it sits overnight its fine the next day. The other day i went to power brake and the brakes were cold and the tires really just hooked so the brakes didnt hold and the car jumped forward. This was on a saturday, the gauge was messed up saturday doing home, sunday, monday, tuesday i didnt leave the house, still messed up on wednesday, then going to work thursday it fell down to 3/4, and then a couple miles later it fell so far that the low fuel came on.

My problem is it doesnt effect the car at all but once i get it supercharged, any little goose of the gas and im afraid that ill never know what my gas level is and i dont want to run out.

Livernois Motorsports is going to be doing the build up and they have never heard of this issue, so im trying to sort this out before they do the work. The reason why i think this will be the most difficult challenge is that ive read a little on the fuel system. 2 tanks, 2 sending units, 2 fuel pumps, sensors...etc. i dont have any idea where to start?

My buddy was asking whether or not this system runs on ohms readings? He figured we could take readings at full, half, and low fuel. With 2 sending units maybe we could take readings from both and then get it to mess up and see what sending unit/ float it is?

Livernois Motorsports recommended replacing the pump so i was going to replace the entire fuel pump unit but after reading about all the components i didnt want to just throw a new pump at it, even though its a good investment for the mods to come.

It seems that maybe the float is messed up or bend from the wreck? any ideas? will the ohmns reading work or at least point us to the right side of the tank. Any pictures and where to measure or what to do is greatly appreciated. Thanks guys
 

·
Premium Member
Joined
·
4,637 Posts
Well some things are right, but there is only *1* fuel tank, *1* fuel pump (with check valve, strainer/filter and 2 jet pump actions and sender) within the housing and a 2nd fuel level sender within its own housing. The tank has a saddle design, requiring the 2 fuel level sending units. Which means a fuel transfer pipe is used to get the fuel from one side to the other (hence the jet pump action) It forces the fuel level to remain as balanced as possible at all times.
Yes, both sender units are variable resistance type (using a little float and wiper arm action) to send out their signals to the ECM. Yes, you can access 2 different connectors between the tank and ECM, to read *each sensor units value at any given time. They say you should see a reading of *less* than 41 ohms at one extreme and *over* 119 ohms at the other extreme. Which way is which, I don't know. But I would think that whatever reading you get, at any given time, should be about the same from both sender units.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #3 ·
Well some things are right, but there is only *1* fuel tank, *1* fuel pump (with check valve, strainer/filter and 2 jet pump actions and sender) within the housing and a 2nd fuel level sender within its own housing. The tank has a saddle design, requiring the 2 fuel level sending units. Which means a fuel transfer pipe is used to get the fuel from one side to the other (hence the jet pump action) It forces the fuel level to remain as balanced as possible at all times.
Yes, both sender units are variable resistance type (using a little float and wiper arm action) to send out their signals to the ECM. Yes, you can access 2 different connectors between the tank and ECM, to read *each sensor units value at any given time. They say you should see a reading of *less* than 41 ohms at one extreme and *over* 119 ohms at the other extreme. Which way is which, I don't know. But I would think that whatever reading you get, at any given time, should be about the same from both sender units.
So does it sound like a float is getting stuck to you? Would be much cheaper yo buy another float versus a whole new pump.

Anyone have any other ideas/pictures?
 

·
Premium Member
Joined
·
4,637 Posts
The service manual does show that the fuel level sensors can be replaced within the tank modules. But I thought you said you wanted to read the value of the sensors if possible (to try to find out which one might be at fault), an you can. But if you've changed your mind, go for it an buy 1.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #5 ·
The service manual does show that the fuel level sensors can be replaced within the tank modules. But I thought you said you wanted to read the value of the sensors if possible (to try to find out which one might be at fault), an you can. But if you've changed your mind, go for it an buy 1.
Well yeah i want to read them first to help me locate at least what side of the tank is messing up so i can replace it. Are the fuel level sensors the same thing as the floats? i read that once one goes bad, that the system defaults to always reading low fuel and mines not doing that? so im not sure what that means?

Not sure what i said to make you think i changed my mind? The fact i was going to replace the entire pump assembly vs just the sensor? Well if the pump is in good shape then there is no need to replace it, its $100 vs $450 for a new pump assembly.
does the service manual state anything about what tests can be performed to make sure the fuel pump is adequate and this sensor is the only thing that will need replacing? If i going as far as taking the tank down then i only want to take it down once, so if i need a new pump ill do it but if the sensor is all thats needed then ill do that, but i dont want to reassemble and realize that the pump is getting weak and it needed to be done.
 

·
every village has one
Joined
·
2,371 Posts
If you plan on serious mods in the future, look into a better pump/aftermarket fuel system.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #7 ·
If you plan on serious mods in the future, look into a better pump/aftermarket fuel system.

Well its going to be pretty serious for me 600+ hp and 500+ tq at the engine from 9 pounds of boost. Livernois said they could upgrade me to a return style system but using the OEM pump and a boost a pump unit is defiantly the cheaper way and will still work great. I doubt i ever have any plans further then that
 

·
Car RamRod
Joined
·
1,795 Posts
it does "sound" like one of the 2 sensors is sticking, but I would think that the difference would throw the big red X and contact dealer message.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #9 · (Edited)
it does "sound" like one of the 2 sensors is sticking, but I would think that the difference would throw the big red X and contact dealer message.
The difference in the 2 values coming the sensors you mean? Only time ive ever seen the red X was letting the fuel get to low and thats it. It hasnt came on due to the hard launches
 

·
Premium Member
Joined
·
4,637 Posts
All the wiring from within the fuel tank, goes to a 14 pin (black) disconnect connector. If labeled, it should read X305 and is located on the right side (passenger) of the fuel tank on the frame rail. The primary side sensor uses pins E to P and the secondary sensor uses pins F to P. (P) is the common ground return wire to the ECM from both sensors. At a time when you suspect the indication is incorrect, that would be a good time to meter read the 2 sensors. If they disagree with each other, trying to figure out which reading is wrong might be a problem. You may have to do it at several fuel levels to get an idea which side may be at fault (if that's the source of the indication problem).
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #11 ·
All the wiring from within the fuel tank, goes to a 14 pin (black) disconnect connector. If labeled, it should read X305 and is located on the right side (passenger) of the fuel tank on the frame rail. The primary side sensor uses pins E to P and the secondary sensor uses pins F to P. (P) is the common ground return wire to the ECM from both sensors. At a time when you suspect the indication is incorrect, that would be a good time to meter read the 2 sensors. If they disagree with each other, trying to figure out which reading is wrong might be a problem. You may have to do it at several fuel levels to get an idea which side may be at fault (if that's the source of the indication problem).
Great info, thanks. Im pretty sure it has to be the float/ fuel level sensor.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #12 ·
All the wiring from within the fuel tank, goes to a 14 pin (black) disconnect connector. If labeled, it should read X305 and is located on the right side (passenger) of the fuel tank on the frame rail. The primary side sensor uses pins E to P and the secondary sensor uses pins F to P. (P) is the common ground return wire to the ECM from both sensors. At a time when you suspect the indication is incorrect, that would be a good time to meter read the 2 sensors. If they disagree with each other, trying to figure out which reading is wrong might be a problem. You may have to do it at several fuel levels to get an idea which side may be at fault (if that's the source of the indication problem).
Do you happen to have the page number or a picture of the connector? I'm pretty sure I've found it but there is only 9 pins inside. The connector isn't labeled and the pins don't seem to have any labels on the inside or outside. I have the service manuals and I can't find the end connector view for that connector anywhere.
 

·
Premium Member
Joined
·
4,637 Posts
It sounds like your at the correct connector. It says it uses 9 of the 14 pin positions. Since you have the books, look at page 11-388. In my manual, this is page showing the X305 connector with the wire colors used, as well as what they do to.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #14 ·
Hum that's weird. To be on page 11-388 I need to be in the volume 3 book of 4. That page only shows troubleshooting for a specific trouble code.

OK I found it, I thought it would be listed with the fuel, its listed under x and then the ### near the back. Page 11-354 for me.
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #17 ·
They say you should see a reading of *less* than 41 ohms at one extreme and *over* 119 ohms at the other extreme. Which way is which, I don't know. But I would think that whatever reading you get, at any given time, should be about the same from both sender units.
Well I have got some #s and a pattern has started to emerge as well as a possible culprit.

Full Tank
Primary: 40.8 ohms Secondary: 115 ohms

1/2 Tank
Primary: 140.4 ohms Secondary: 195.8 ohms

Low Fuel Light
Primary: 170 ohms Secondary: 249 ohms

* full tank is not full on the gauge, for me the highest it ever shows is the small hash mark before the long full line.

* after I fill the car up it shows 3/4 and then after a day later, or if I have to travel a good distance then it reads slightly higher
 

·
Premium Member
Joined
·
4,637 Posts
Trying to understand the manual, I believe it says that the TOTAL resistance that the indicator wants and expects to see is about 40 ohms for the max full reading, and about 250 ohms for a total empty reading. That's cumulative between the 2 level sensors, (meaning that each one should read between about 20 to 125 ohms or so) for a perfect unit. An that info, could be somewhat incorrect. But if it is correct, it kinda makes both sides look like they have a problem. But the secondary side #s look like crap.
This of course is assuming that the jet pump action that takes place within the tank, is indeed moving the required amount of fuel from the secondary side over to the primary side at the correct rate (for fuel tank balance)
 

·
Registered
Joined
·
91 Posts
Discussion Starter · #19 ·
The tank is absolutely full and bc of that the primary side #s look within specs to me. The secondary #s are absolute crap. It makes me think that bc the secondary #s are so off that it fluctuates the average between the 2 and pulls the average down and makes the gauge read the way it does.

I imagine its suppose to read what the specs are for each sensor not adding both of them equals 40 or 250. Someone with a working system care to take readings on their system
 
1 - 19 of 19 Posts
Top