fuel gauge...again

[jmagerl]

I have a 99 blazer with an erratic fuel gauge....lots of jumping around. I have checked the grounds and have replaced the sending unit ($ouch$) but the problem still remains. It's better but not like before. You can clearly see on the old sending unit that the wiper fingers are able to lift off of the ceramic substrate. I am assuming this is bad.

Question 1) I have a 96 service manual for a S10 pickup (no Blazer manual) that mentions a fuel gauge antislosh circuit but other than a mention in text, I see no indication of it in the schematics. Talking to the service guy, he mentions a buffer amp. Again no mention of it in the schematics. Where do I find this?

Question 2) If I compare gas gauge operation between the S10 pick up and the Blazer, I see that the Blazer gas guage goes to 0 when I turn off the ignition. THe S10 holds its position. Is this the way the Blazer gauge works? or is this an indication of a failure in the mystery buffer amp?

THis is the wife's car and she is unforgiving in anything to do with the fuel guage

[BlazerLT]

how erratic is it?

Does it happen more when the tank is around 1/4?

Does it happen when the tank is full?

Does it go from E to F and back all the time like the power was cut?

[jmagerl]

yes around 1/4 tank. Not so much when full. Before the sending unit was replaced, it did it no matter how full the tank was. THere is a 1/4 tank flucuation in the needle that is very rapid. IT is not a slow rise or slow fall like sloshing would be. THe wife is also complaining she can't fill the tank (maybe she is but the guage is wrong)

[BlazerLT]

Soundlike a like a ground is bad if the gauge needle is flicking.

[jmagerl]

Had a long talk with a Chevy service technician today. HE explained that it takes the vehicle computer several tank fulls of gas to recalibrate a new sensor and that I shouldn't be doing anything until then. HE also said that in the 99 model the sending unit goes to the VCM and the VCM controls the gas gauge. In the 96, the sending unit drives the guage directly.

He also said that you don't have to buy the whole fuel pump, pressure sensor, sending unit assembly for $480. You can buy just the sending unit and replace it seperately for $250.

In my case, I bought the whole assembly and guess what, the new assembly was bad also. So they refunded my $480 and when I went to replace just the sending unit, they explained that more often than not the fuel pump usually follows shortly on the heels of the sending unit and they recommend replacing the whole assembly. I wish they'd make up their mind.

Thanks for all the responses. I am waiting the few tank fulls of gas because even with the third sending unit, it still does funny things below a quarter tank. He couldn't explain why shifting into park caused the needle to be erratic when at rest.

[BlazerLT]

go to your VCM and make sure all the connections are firmly in place.

they tend to sometimes wiggle out a bit.