1986 S10 Blazer. About year ago, water temp would go to 250, then slowly to 190. Both sensors changed, same result. All freeze plugs changed. Computer showed temp holding 190. Took dash out, tested independently. Dash ok. Reinstalled dash.added external temp gauge. Gas gauge acting erratic. Installed new Delphi pump with sender. gauge was reasonably. Now it goes from full to empty in about 90 miles. Removing ground or or attaching ground to purple sender wire both cause gauge to go to empty. Don’t want to drop tank again. Pump is working fine. Problem is gas gauge is not working. Suggestions as to what to do next?
Maybe the fuel gauge float attached to the fuel pump is binding.It picks up sediments at the bottom of the tank over time.
Maybe the instrument cluster has failed.
I agree that sounds like an instrument cluster issue; probably the least DIY part of a vehicle!
I’ve gotten really good help from https://www.instrumentclusterstore.com/Chevrolet_instrument_clusters.htm in the past. Give them a call, they’ll help you get it sorted out.
Parts I ordered were for 1986 model. The guy at the shop where I took it finally checked p/n on the cluster and it showed 1987 instead of 1986. Since car was purchased in June 1986, end of model year and dash for 1987 was installed. Swapped parts for 1987. Gauge appears to work, nut not the most accurate
The fuel pump was new. Everything I read said gauge problems were in fuel pump or sending unit. I replaced it with a new Delphi, pump and sending unit included together. After I swapped parts in dash for 1987, which is what p/n corresponded to, started working, but still not most accurate.
Parts I replaced were for 1986. Shop checked p/n on dash and found it was actually 1987. Since car was purchased June 1986, assumed 1987
Dash was installed due to end of year. Parts were exchanged for 1987.
Gauge is sort of working, but not the most accurate
Gauge just keeps getting worse. Which type would be better replacement, mechanical or electric?Delphi said replace fuel filter when installing new pump. Supposed to be in fuel rail coming up from back near frame. Neither myself or shop could find it. When I got home started looking again. Finally found it behind power steer pump. Unable to free nut on filter. Looks like if I put enough pressure, metal line will bend. Shop could not free it either. Any ideas? Behind pump is a real pain
The fuel filter you speak of(2.8L throttle body injection?) can be removed with the proper crow foot on a 12" extension turning the nut while holding the filter with an open end wrench. Once all the proper pieces are in place disconnecting the filter is not difficult.
Define “getting worse”? and are you positive it is a gauge issue, and not just a really poor fuel mileage issue? Or fuel sender issue (even if pump/sender is fairly new?)
I’ve ever only owned Chevy’s and they aren’t known for being the most accurate fuel gauges. Fist half a tank (according to the gauge,) takes forever, then the second half (again, according to the gauge,) drops like a ton of bricks shot out of the bazooka of a freefalling skydiver. (terminal velocity aside…)
Make sure you verify where the issue really is before throwing any more parts at it.
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When it gets to empty, is it dropping at a normal rate and then suddenly it drops to empty? If that is the case, the sender has a dead spot in it caused by contamination of the wire wound resistor or a bend in the resistor so that the pickup doesn’t always make contact. In either case, the sender has to come back out and the resistor wires cleaned or the wiper bent to make better contact or the resistor bent and made straight.
Some of these gas tanks require that you disconnect the sending unit from the fuel pump before installing because you will damage the sending unit trying to get both through the hole at the same time. You have to insert the pump about half way first, then insert the sending unit and finally screw the sending unit to the pump before finish inserting the rest of the way.
That sounds like a couple of Toyotas we’ve owned over the years 
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I’ve had a couple of GM trucks with fuel gauge (and later fuel pump) issues.
Personally, I just learned to live with filling up the tank by mileage. I think it I figured out every 150-200 miles equaled the tank being about half empty. Never failed me.
It takes a little more effort… but if it were me, I wouldn’t keep throwing more money and parts at a 34 year old truck that otherwise seems to run well.
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Pardon my ignorance, but I don’t know what a flat crow is. After read your reply, I got to thinking about when I replaced the pump. Since the dash checked out, I should have checked to make sure the float was not bent providing full movement. The shop dropped the tank after a strong odor of gas was present. They said seal on top of tank was leaking. So that was twice the float assembly was removed. Another response said keep up with miles and fill up at 150-200 miles. Probably will do that, but still bugs me that something wasn’t right about me replacing the pump. My wife says I’m a glutton a for punishment. Thank you for your Response
After reading your reply, I got to thinking about when I installed pump.before buttoning everything back, I should have made sure float had full range of motion and gauge responded correctly. About a week later I was beginning.to notice gasoline odor so I took it back to shop since I was about fed up with it.they said there was a leak on top where the cap screwed into tank so they removed pump and reset cap. That gave 2 opportunities for float arm to be bent. Since new Delphi pump came with new sending unit wouldn’t that eliminate cleaning around sending unit? Another reply said just go with mileage 150-200 miles for fillip so I think that’s what I I’m going to do. Thank you for your response
First 25 or so.it drops about like what I think it should. From there on, it drops pretty significantly. Right now, it’s showing about 95 miles and only 1/4 left.another response said fillup by miles, 150-200 so I think that’s what I’m going to do. Thank you for your response
A 1986 S10 has a miles to empty reading ? If so you should have an idea of what your MPG is so fill up and if it takes close to the amount of fuel you think it should then just refill when the read out says 200 miles to empty .
These are crow foot wrenches
There is no room to turn an open end wrench on your fuel filter line’s attachment nut… You must hold the filter with an open end wrench and attach the proper crow foot to a 12" extension so that it can be turned from above.
Thanks again for your reply. Advance auto said they might have a set to rent. Harbor Freight catalog shows they have them. At $50-80, don’t want to buy something I might use just once. Trying to get lawn mower back together. Blazer is still drivable and not primary vehicle
I tried the method of dividing number of gals to fill into number of miles driven.Best I have gotten is 54 miles and 12.2 gals added. If this was
Daily driver we would be parting company. Odometer is off a little, 235 vs 205 tires. Found crow foot wrench at Harbor Freight