Fuel level for PCM
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Teching In
Joined: Sep 2020
Posts: 8
Likes: 1
Fuel level for PCM Hey guys having some trouble figuring out how I’m gonna send a fuel level signal to my pcm. I live in CA where this swap has to pass smog and fuel level is needed for the EVAP system to work properly. The problem is I have a 0-90 ohm fuel sender. Originally I was planing on just using a fuel link which converts my ohm readings to whatever I need them to be. The problem is they require a gauge to calibrate and I can’t find any 33-240 ohm gauges anywhere. They are all backwards. I planned to use the gauge as my reference for fuel level and then get rid of the gauge and run my signal to the ECM. If you know of any gauges let me know. The other option is to program the pcm to read the 0-90 sender but there is a problem with that as well. The smog ref requires I take the truck down to a dealership and get a factory tune. I have no experiencing with programming but I can only assume that will place me back where I am now. Any ideas?
On The Tree
Joined: Jan 2019
Posts: 103
Likes: 3
From: north-central Virginia
What vehicle is it? Is there any way you can fit two senders in the fuel tank? A 0-90 for your gauge, and a 33-240 for the ECM?
Edit: Another thought -- does the ECM need to see an accurate gauge? There's a chance it might work if you connected the ECM to a fixed resistor approximating a half-tank. The only reason I can see why the ECM needs to know the fuel level, is when it does it's leakdown tests. The ECM is monitoring fuel tank pressure or vacuum to determine if it's behaving as expected, depending on the position of the purge and vent valves. Of course, some of those leakdown tests might only be performed with a full tank, in which case, the "evap monitor not ready" message would continuously appear when viewed with a obd2 reader. Adding a resistor would a quick and simple thing to try first, assuming your truck can be driven around a bit for testing. You can buy a huge variety pack of resistors on Amazon for under $20.
Edit: Another thought -- does the ECM need to see an accurate gauge? There's a chance it might work if you connected the ECM to a fixed resistor approximating a half-tank. The only reason I can see why the ECM needs to know the fuel level, is when it does it's leakdown tests. The ECM is monitoring fuel tank pressure or vacuum to determine if it's behaving as expected, depending on the position of the purge and vent valves. Of course, some of those leakdown tests might only be performed with a full tank, in which case, the "evap monitor not ready" message would continuously appear when viewed with a obd2 reader. Adding a resistor would a quick and simple thing to try first, assuming your truck can be driven around a bit for testing. You can buy a huge variety pack of resistors on Amazon for under $20.
Last edited by kipps; Sep 27, 2020 at 04:42 AM.
Are you that California allows you to use the original fuel tank since the older tanks are not set up to recover the fuel vapors, using the same method as the newer ones. Also the evap tests depend on the tank to have a certain volume, since the test is a pressure change vs time test. Most tuning packages doesn't the ability to alter these values. Some tuning software does have the ability to alter the fuel gauge tables to allow the use of a 0 to 90 ohm fuel sending unit and activate the PWM fuel gauge output. So the fuel gauge part shouldn't be the largest issue you'll face. Tunercat, comes to mind, as a software that can make the gauge changes.
On The Tree
Joined: Jan 2019
Posts: 103
Likes: 3
From: north-central Virginia
I'm just now seeing that you have a 1986 k5 blazer(based on your user name). That tank has quite a bit of real-estate across the top face. I'd suggest looking for a universal-fit 240-33 sending unit. I'm putting a couple of links below to some example sending units. Either buy an adjustable one, or one that's pretty close to your tank depth.
Wire the 240-33 sending unit to the ECM as factory, and plumb up the necessary purge valve, vent valve, charcoal canister, and pressure sensor as factory. Wire your stock k5 sending unit to your dash.
The only thing that would not be stock for the engine would be the fuel tank capacity. It appears the LQ9 always came with a 26 gallon tank. If you use the 25 gallon Blazer tank, you'll be within spitting distance, and there's a very good chance the ECM won't even notice the tank size difference. If you're using the 31 gallon blazer tank, the ECM might notice that the pressure isn't behaving like it expects.
If you have the 31 gallon tank, buy an adjustable universal 240-33 sender that will fit both tank sizes. That way, if the 31 gallon tank throws fits, you can downgrade to the 25 gallon tank, and not have to re-purchase the sending unit.
https://www.ecklers.com/universal-fu...-388828-1.html
https://www.pegasusautoracing.com/pr...asp?RecID=9057
Wire the 240-33 sending unit to the ECM as factory, and plumb up the necessary purge valve, vent valve, charcoal canister, and pressure sensor as factory. Wire your stock k5 sending unit to your dash.
The only thing that would not be stock for the engine would be the fuel tank capacity. It appears the LQ9 always came with a 26 gallon tank. If you use the 25 gallon Blazer tank, you'll be within spitting distance, and there's a very good chance the ECM won't even notice the tank size difference. If you're using the 31 gallon blazer tank, the ECM might notice that the pressure isn't behaving like it expects.
If you have the 31 gallon tank, buy an adjustable universal 240-33 sender that will fit both tank sizes. That way, if the 31 gallon tank throws fits, you can downgrade to the 25 gallon tank, and not have to re-purchase the sending unit.
https://www.ecklers.com/universal-fu...-388828-1.html
https://www.pegasusautoracing.com/pr...asp?RecID=9057
