new to me jimmy under went alot of maintenance work. i replaced a rusted out tank and transferred whatever aftermarket fuel pump.(not stamped anywere) it read empty after install and moved a hair when i threw 2 gallons in it

i take it to the gas station and throw ten gallons in it and now the needle is all over the place. im a electrician by trade and start taking ohm readings. im at 160 ohms on the sender.

i read through these threads and appears we should be a 0-90 ohm setup.

it get interesting however when i get specs on some new aftermarket direct replacements that advertise a 30-240 ohm sender.

im in the process of taking the tank out now to further investigate it but my ? is.... do we know for sure that all 97 models are 0-90?

ok. fuel sender is out. it is 40-240 ohms. 40 empty 240 full. is this correct for this model? 1997 4x4 jimmy . 4door slt. 4.3


update: with different information out there i tried some things out. if indeed my fuel sender should be 0-90 ohms i figured if i lock my 0-250 ohm sender at 90 id get a full reading. so i taped the sender at 90 and did an out of the tank plug in and i get just over a 1/4 tank. im starting to believe my 97 is a 40-250 ohm and NOT 0-90. maybee an end of the model year run? i still get a bouncing and jittery needle(although not as bad as 3/4 of a tank mark)

ive traced out the ground wire in the engine compartment and inspected all plugs and did multiple ohm readings from plug end to plug end. the wire reads good.

im kinda stuck now. its either the buffer module or the guage cluster?

anyone know where the guage cluster ground runs to?

 

What you need is a shop manual. Not a Haynes or Chilton, but the one GM uses. You can get them on ebay reasonably cheap. That'll give you the actual specs.

Fuel senders and in-tank fuel pumps: I really believe it's best to stick with AC Delco parts on these. Almost the same price as the aftermarket ones on Amazon anyway...

 

after some more googling im thinking someone put a 1998 or newer pump in. im seeing listings for 98 up pumps with 40-250 ohm senders and 1997 pumps with 0-90 ohm ones.

any one out there got a 1997 that they have read the sender ohms on with a working guage? thanks

 

I have one out of a pickup, not sure if that's the same.
I would like to point out that the 97's have a fuel level buffer module (only year I think)
That module is located under the glove box wrapped up in foam and velcro.

Let me know if you want me to take a reading off my pump?

 

You are correct zdog. The older trucks, including your '97, work off of a 0-90 ohm sending unit while the 98+ trucks are 40-250 ohm.

 

thanks. if you could take a reading that be great. i do have the buffer module pulled down also. i believe that its also bad.

tank is out. if i pull the buffer mod the guage goes full. if i ground the guage lead guage goes empty as it should. purple wire to sender plug has been verified and reads clean(no shorts to ground).

as soon as i plug the buffer mod back in guage goes empty with the sender still unplugged. this leads me to believe the buffer module has an internal short.

i still need to verify what my range of sender ohms should be. the truck is new to me so i can not verify its history and dont want to reinstall tank if my sender is wrong. i may have a double problem between buffer and sender. thanks for all any any info


we must of posted at the same time. can you tell me more about the fuel buffer module? does the module go to empty with no input or does it sound like my buffer is shot also?

i got an idea for another little test. im locking my sender at 88 ohms and plugging it in out of tank. to see what the guage reads. im also going to play around with upsizing some grounds to chasis and tracing back sender and fuel pressure ground.(they factory splice together in loom)

 

All that the buffer does is even out the sloshing of the fuel in the tank. Without the buffer, the gauge would wiggle all over the place.

And please use the edit feature to include more information in your post rather than posting consecutively.

 

sry. edit feature crashes on me when i go to save.

 

That's a problem with your computer that needs to be fixed so that you can comply with the rules of the forum. Maybe post up about it in the Help & Suggestions section to get help with that issue, but try to get everything together and post once then wait for a response rather then send in minute by minute updates.

 

just some observed data.

1997 jimmy 4.3 4 door.

fuel sender is 40 -250 ohms.

fuel buffer module part number #12135193 sends a 5 volt reference signal out accross the sender resistor and reads whats returned.

it outputs to the pcm and to the dash guage a modified voltage. again appears to be between 1-5 volts.

since mine doesnt trip on i can only speculate the pcm uses that input voltage to trip the check guage light when fuel is low

it appears guage needle erratic swing is being caused by voltage spikes from the buffer module according to my recording meter that i left on for 2 hours, key on. i had two meters running. one on the sender(ohms never budged) and one on buffer output. (jumped around)

the only part of the puzzle im really missing is the buffer modules internal circuitry schematic. my fuel guage stays on E even with the sender unplugged but pegs F when buffer is removed. all im getting at is im not sure if unplugging the sender on a 1997 is an accurate test for the guage.

in the next week or so i will be attempting to create a bypass circuit to elimate the buffer module from over the counter radio shack parts. it may not "buffer" the gas quage needle but at least it will be a working non ticking guage.

i also need to hook up my meters again on the sender input and buffer out put to find out excactly how they relate to each other

i also may play with adding a small capacitor to the 5 volt reference signal and or ignition feed.

when i get this resolved i will post the conclusion and if a jury rigged fix is succsessful

now to take a day off