Fuel level ohm range

[86K5LQ9]

Wondering if its possible to adjust the fuel level workable ohm range in my 04 lq9 pcm. I have not yet bought a tuner and an answer to this will likely make the decision for me. I just recently swapped a lq9 out of an 04 Cadillac Escalade into an 86 k5 blazer with a 0-90 ohm sending unit. I need to somehow alter the ohm range being input to the pcm or program the ECM to a 0-90 ohm range. Is that possible? If so it would make things a hell of a lot easier for me. I live in the regulation state of California so this is required to pass our awful smog laws.

[blindsquirrel]

Download the VCM Suite demo software, it has a selection of sample tune files you can open and look through. But yes, there is a section for Fuel System that covers the gauge/sender config, tank volume, etc.

[kevin87turbot]

It is possible to rescale the range in the PCM.
Do they have to scan the PCM and scan for fuel level?
What gauges are you using?

[86K5LQ9]

No gauges at the moment, I will likely end up running a tablet for awhile until I get all the gauges figured out. I just need my pcm to have the correct fuel level for my evap system to work.

[Lotek]

In your car, the fuel level sensor goes straight on the instrument panel. In Escalade, it goes to the engine control module and then on the instrument panel. It is easier to leave an old sensor 0-95 Ohms just a pcm will not see the amount of gasoline, and you and the dashboard will see

[TheMechanic]

26.0 Gallon Tank (Short Bed Pickup and 4-Door Utility)

E
40-66 ohms
1.0 V
0-13%
0-11.9 L (0-3.1 gal)

1/4
83-110 ohms
1.25 V
30-35%
32.8 L (8.7 gal)

1/2
118-140 ohms
1.6 V
50-55%
51.3 L (13.5 gal)

3/4
150-190 ohms
2.2 V
72-78%
74.3 L (19.7 gal)

F
197-250 ohms
2.5 V
88-100%
92.8-98.4 L (24.5-25.9 gal)

Low Fuel Indicator On
62-72 ohms
1.1 V
11-17%
16.5 L (4.3 gal)

Low Fuel Indicator Off
74-83 ohms
1.2 V
14-25%
18.9 L (5 gal)

33.0 Gallon Tank (Suburban 1500 and 2500 Series)

E
40-58 ohms
0.9 V
0-13%
0-15.1 L (0-4 gal)

1/4
83-110 ohms
1.25 V
30-35%
41.6 L (11 gal)

1/2
118-148 ohms
1.9 V
50-55%
64.4 L (17 gal)

3/4
155-195 ohms
2.3 V
68-78%
84 L (22.2 gal)

F
199-250 ohms
2.5 V
88-100%
118.8-123.4 L (31.4-32.6 gal)

Low Fuel Indicator On
55-69 ohms
0.9 V
11-17%
14.3 L (3.80 gal)

Low Fuel Indicator Off
70-80 ohms
1.1 V
14-26%
19.3 L (5.1 gal)

34.0 Gallon Tank (Long Bed Pickup)

E
40-6 ohms
1.0 V
4-14%
4.5-15.7 L (1.2-4.1 gal)

1/4
80-11 ohms
1.5 V
30-36%
43.8 L (11.6 gal)

1/2
117-15 ohms
1.8 V
50-58%
70.4 L (18.6 gal)

3/4
155-195 ohms
2.1 V
70-80%
97.2 L (25.7 gal)

F
196-250 ohms
2.5 V
88-99%
123.6-126.9 L (32.6-33.5 gal)

Low Fuel Indicator On
61-72 ohms
1.1 V
11-14%
22.7 L (6 gal)

Low Fuel Indicator Off
76-83 ohms
1.2 V
13-25%
25.7 L (6.8 gal)

39.0 Gallon Tank (Suburban 2500 Series)

Important: The resistance values only reflect the specified fuel level when the signal circuits for both the primary and secondary fuel level senders are tied together.
The fuel remaining values are approximate.


E
12-29 ohms
1 V
2-14%
18.9 L (5 gal)

1/4
30-40 ohms
1.5 V
31-34%
45.4 L (12 gal)

1/2
43-64 ohms
1.8 V
50-58%
73.8 L (19.5 gal)

3/4
65-79 ohms
2.0 V
70-76%
98.4 L (26 gal)

F
95-125 ohms
2.4 V
87-100%
138.1-147.6 L (36.5-39 gal)

Low Fuel Indicator On
25-35 ohms
1.0 V
11-13%
28.3 L (7.5 gal)

Low Fuel Indicator Off
36-41 ohms
1.1 V
14-16%
30.2 L (8 gal)


straight from gmsi. hope it helps.
--------------------------------------------------------------------------------
Document ID# 675267
2002 Chevrolet Chevy C Silverado - 2WD


In 2004 GM switched from the OLD EMPTY-40ohm FULL-250ohm to the Opposite. EMPTY-250ohm FULL-40ohm.

[TheMechanic]

In your car, the fuel level sensor goes straight on the instrument panel. In Escalade, it goes to the engine control module and then on the instrument panel. It is easier to leave an old sensor 0-95 Ohms just a pcm will not see the amount of gasoline, and you and the dashboard will see

He needs the PCM to see an actual fuel level so it can run the EVAP diagnostic.

If you can't find a replacement aftermarket you could always run a resistor inline with the fuel level so it reads 1/2 tank so it can run the diagnostic and then flip to a full or empty resistance so the diagnostic will not run. It will likely fail if fuel level is to high or low.

[GmikeHall]

This is a little off the topic of this thread but it seems someone here may know. I did a cummins swap in a 2002 Suburban and when doing so removed the rear fuel tank. This has my fuel gauge not operating correctly being the rear sending unit is no longer in the system. Does the 2500 suburban use the PCM to drive the fuel gauge or do the fuel senders send the signal to the fuel gauge? Could I possibly alter my harness and run the fuel sender signal directly to the fuel gauge?

Thanks
Mike

[TheMechanic]

Fuel level sending units go directly to the ECM/PCM for EVAP system tests. It is then sent to other systems like the cluster. Depending on year make and model it is either a serial data or CAN communication.

Screenshot 2023-11-26 103806.png

[GmikeHall]

Well that sucks, Going to be more difficult to get the fuel gauge working than putting a cummins in this thing. hahaha

Thank you for that little diagram to help me see what is going on...

[GmikeHall]

I read above that the single tank vehicles send the fuel sender single directly to the fuel gauge or will it also go to the ECM/PCM? Could I possibly swap out the fuel gauge motor for one from a single tank vehicle such as a truck then do the wiring needed to get the signal to it? So little information on this subject....

[TheMechanic]

Big bucks but you might want to try one of these. I personally have never used one but have several customers who do and they all like them.
https://www.dakotadigital.com/index....=cat/cat69.htm

[GmikeHall]

I hate aftermarket gauges and want to make the factory cluster work. I have done many cummins swaps in fords and its so much easier to satisfy the cluster where this Suburban its darn near impossible.

[GmikeHall]

Looks like I could use the single sending unit and bridge it over to the secondary tank signal wiring and maybe satisfy the PCM enough to get some kind of fuel gauge reading. Of course the reading wont be correct through the range but should work to tell me when i am getting low on fuel.

[GmikeHall]

Well, i guess the most simple way would be to change the PCM to utilize only the primary fuel sender signal rather than both the primary and secondary signals. I am not all that versed with my HP tuner but maybe I can figure this out.

[TheMechanic]

Post your tune. To many variables to list.