1997 Pontiac Bonneville SSE fuel tank reading way over max pressure

Chris Owner/Technician Alabama Posted   Latest  
Updated
Electrical
Emissions
1997 Pontiac Bonneville SE 3.8L (1 L67) 4-spd (4T60-E)
Fuel Gauge Stuck
Fuel Tank Pressure Very High

So, this is a family members car. Went to work on it on site. It was bought new and has less than 30k on it. Been sitting. Would not start (would crank). So I make the 3 hour drive to check out the car, took my Tech1A and AutelElite. Some history codes, etc. Fuel showed ¾ full. Live Data confirmed 73 reading from sender. No fuel pressure when cranking, checked fuses and relay..no go. So I listened for the pump to run and I could hear it. So I decided to drop two gallons of fuel in it…fired right up. Went on a test drive and put 5 gallons in it, no movement on the gauge or the scan tool reading. So I know I need to drop the tank and replace sender (entire unit) . So I have the FSM, it mentions and shows a picture of a fuel pump module that seems to be located on the body of the car somewhere. I cannot find a location diagram in the FSM at all, can anyone help with the location of the module if it exists? Can't find it in the parts diagram either. Other thing is the fuel pressure inside the tank is extremely high, not sure where to start on that. And BTW I need to find the fuel module because there are two different senders to order depending on the code on the elusive module. All help is appreciated. 

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Interesting
Glenn Owner/Technician
Texas
Glenn
 

Fuel pump electrical module is in the left rear of the trunk, behind the seat. The tank pressure sensor is the top of the tank fuel pump sender unit pushed into a grommet. At this age and if it has been sitting, it may need a tank. Ethanol fuel left sitting is very destructive to any and all metal components and tank sensors. In All Data it is located under the Emission control system tab.

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Chris Owner/Technician
Alabama
Chris
   

I will put a tank in it if it looks bad or has rust. I Searched the PONTIAC dealer manual ( 2 volumes) for an hour. When you say behind the seat, in the trunk compartment. Can you be anymore specific. If not , thanks anyway, I will find it With what you gave me.

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Stephen Owner/Technician
California
Stephen
 

I would check the entire EVAP system for the high pressure issue. You likely have a clogged or stuck vent valve.

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Chris Owner/Technician
Alabama
Chris
 

I plan to check it all, any idea of a fuel module?

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Drew Mobile Technician
Pennsylvania
Drew
   

Going back in the memory bank so might be wrong, but fairly certain the fuel pump control module was only on the supercharged 3.8.

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Agree
Chris Owner/Technician
Alabama
Chris
 

Wondered about that as the ZR-1 from that time had two pumps and a secondary module unique to the DOHC LT5

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Kerry Mobile Technician
Ohio
Kerry
 

We had a trouble child last week on a 1997 Buick Lesabre....fuel gage not reading correctly. New pump/sender had been installed with no improvement. Did some digging and found that some Lesabres were built with the module you seem to be describing. Finally found it behind the glove compartment and up to the right....there was a bracket with space for 2 or 3 modules. Found a diag step that called…

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Chris Owner/Technician
Alabama
Chris
 

Thanks!!! I have UB3 RPO as well. It mentions there is a 3 letter code on the module you are describing to get the corresponding correct sender. How to did you fix the issue? Did you change out the sender to a new part# and were you using OEM sender or aftermarket? Did you reinstall the tank before you found the issue?

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Chris Owner/Technician
Alabama
Chris
 

I just found this online… This is from Summit racing that has the AC-Delco sender but it doesn't give me an option of different senders.?

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Timothy Owner/Technician
Wisconsin
Timothy
 

I'm not too clear on whether you're concerned about Evap pressure, or fuel pressure? Vehicle has two speed pump, controlled by the Fuel Pump Control Module. Pressure will be high when cranking, and then change to low speed operation for most driving, but raise pressure based on MAP and other inputs… Evap pressure is determined by the FTP sensor mounted on the fuel pump module itself, not the FSM.

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Chris Owner/Technician
Alabama
Chris
 

Not concerned with fuel pressure, it’s good and pump getting replaced anyway. My two immediate Issues are how do I order the correct sender to match FP(Module) and two the high fuel TANk pressure, not fuel line/rail pressure. Thanks for your help!

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Stephen Owner/Technician
California
Stephen
 

I think he means the vapors exhaust when taking the fuel cap off. At least that's how I read it, I could be wrong tho.

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Chris Owner/Technician
Alabama
Chris
 

I will post a screen shot, I’m reading the fuel tank pressure sensor showing tank pressure off the chart. May be a bad sensor, no fuel smell or change with fuel cap on or off. Thinking evap purge valve, etc? Gotta find the fuel module first, alldata on mine doesn’t even show a fuel module under module location.

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Geoff Diagnostician
Hawaii
Geoff
 

“tank pressure sensor showing tank pressure off the chart” + “no fuel smell or change with fuel cap on or off” = FTP sensor is bad. (or a wiring problem, but you will figure that all out when you unplug it)

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Dee Technician
Tennessee
Dee
 

My GM service info shows UB3 option code for being for instrument cluster with oil, cool, temp, and tach gauges. I guess this would be different than a cluster with idiot lights. The GM info also shows the fuel module in the trunk…..behind the carpet panel….kind of near the left side hinge.

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Chris Owner/Technician
Alabama
Chris
 

Thank You big time Dee for the location picture. I hope I would have found it eventually.

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Chris Owner/Technician
Alabama
Chris Update
 

Here is a screen shot of the tank pressure…

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Phillip Educator
Ontario
Phillip
 

That pid my be displayed incorrectly by the scanner. With that much negative pressure you should have a code. I'd try a different scanner as well.

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Timothy Owner/Technician
Wisconsin
Timothy
 

As Geoff said: if the tank is being vented, cap off, and you've still got pressure on the scanner, it's time to get another sensor, or check the voltage PID or use a DVOM for diag. Normal on an older GM voltage at the FTP is 1.5V at zero pressure. I've never seen that PID ever read that high…

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Chris Owner/Technician
Alabama
Chris
 

Thanks Phillip and Timothy, I still have original Tech1A, it would not show the tank pressure (so I did try to verify that number), but the Autel was the only tool that gave me a tank pressure value. I will double check that number when I get it to my shop, I also have a G-Scan3. Will update this thread when I have the tank out and access to the wiring.

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Drew Mobile Technician
Pennsylvania
Drew
 

That vehicle does not utilize a ftp which is why the tech1a didn't display it. You will never see a legit scan data pid on an aftermarket scanner that is not on a factory scanner. Most aftetmarket scanners will not display N/A as you would hope, but instead display a default reading that could not happen such as what you have. 37,289 mm of mercury converts to 721psi which would never happen.

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Chris Owner/Technician
Alabama
Chris
 

Thanks but the tank does have a pressure sensor, at least according to FSM and GM parts illustration. With the replies here, I hope to not worry about it. Thanks for posting.

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Timothy Owner/Technician
Wisconsin
Timothy
 

If you check the wiring diagram on that vehicle, you'll see that Drew is correct: it does not have an FTP sensor. It has a vacuum switch that closes when the purge is turned on, to let the PCM know that the Evap system is purging. No true FTP sensor.

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Chris Owner/Technician
Alabama
Chris
 

Thanks

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