87 Corvette. No start situation and it seems to be the fuel pump since I can't hear it when the key is turned. No apparent pressure at the schrader valve. I've checked that voltage is getting to the connection at the pump and pulled the fuel pump. Can I check the pump with it out of the tank? Should I check the resistance in the pump itself? What, btw, is the proper resistance for a fuel pump?

Another thing. The car has sat for a while and when I pulled the assembly out of the tank, the lower section of the assembly frame and the filter and the pump were pretty covered in rusty metallic(?) grains and the tray in which the pump sits has quite the accumulation of this material. Fortunately, it's heavier than the gas so it appears to have all settled in the tray. Any tips to clean it out without draining the tank. Which I will do if needed, of course.

By way of background (or probably not) the car has been sitting for a while. About a couple of months ago, I thought I had a water pump leak so I got a new one and started to pull things out to replace it when I came across a fairly large leak in a heater hose. So I replaced the hose and put everything back in. Up to then, the car started perfectly but now (then) it just cranked without firing. Now, I'm not a pro but I think I'm a decent shade tree mechanic and don''t see how what I did contributed. Does anyone see a connection? Just coincidence?

 

corvette central has a nice stainless sending unit plus pump. ....you can remove the old pump and apply 6v from a battery to see if it runs...sounds like it took a crap...you could try swapping relays. my 85 has one right next to the fuel relay that is the same....but again, it sounds like the pump...A fuel gauge and FSM would be really helpful....

 

I would also check the sending unit for corrosion if it has any, it might be shortening out the pump.
The sending unit shouldn't have any corrosion on it.

That's what happened to mine, the sending unit shorted out not letting power to the pump!

 

Just to be clear. When you put a DVOM on the terminals going into the pump, you get nothing and even when you turn the key FOR THE FIRST TIME in say 10 minutes, you get voltage?

Why take the long road? Sure you can have say a toy like
vacuum the bottom but I'd rather just siphon out most of the gas and use it in the lawnmower and use said toy to suck out whatever is left and toss it. Your call.

 

To answer your questions - YES - you can run the fuel pump while it's out of the tank - try to do so for only a VERY brief period of time (like a fraction of a second). And YES - you can check the pump with a meter - you should see somewhere on the order of a few ohms pos to neg terminals.

One other thing to check - you said you have power to the connection at the pump - did you check that with a meter ??? Go back and test it with a good old fashioned test light. Why you ask - because a modern digital multimeter has tremendously high input impedance - meaning it draws virtually no current - so a high resistance connection somewhere in the wiring essentially conducts perfectly fine for the micro amps the meter draws. But when you actually try to draw a little current - the high resistance connection shows up as a problem... Believe me - more than a few pros have been fooled by this one...

As for the crud in the tank - I'd suggest draining the tank - you can siphon most of the fuel out pretty easily.... Once the majority of gas is out - you can try to clean up the tank a little bit (it's easier to do while you have the fuel pump out) - basically with a rag tied to the end of a stick kind of thing - and with a hour or so of work and a lot of rags you can get a fair bit cleaned up - but it's not going to be perfect. Plan on changing out the fuel filter every few of tanks of gas for a little while. You might want to cut the filters open that you pull out to see how much crud they're catching - that will help you determine the next change interval...

 

Why? Tom400CFI proved to everyone that it ran for over 45 minutes without the fuel coolant that was supposed to be the reason or old wives tale that you need to have a quarter tank. I'd run for a few minutes to see if it moves smoothly.

 

You're probably right - many fuel pumps can probably be run for quite a while without the gas "lubricating" the pump. But I've also seen some fuel pumps that don't like that kind of treatment (a friend hurt one of the old Holley "Blue" electric pumps supposedly by running it for several minute while trying to get the last bit of gas out of a tank). Holley used to sell replacement pump parts for those pumps... Multiple decades ago - I hurt one of those "Facet" pumps (the ones with the big transistor cover mounted on the square sheet metal cover by dead ending it for several minutes....

In this case the purpose of the test was to diagnose the pump - if it doesn't run when power is applied - the problem has been located. If it does run - the next thing to determine is if it actually pumps. These cars are getting old - this might not be an OEM pump, and may have different materials in the pump - I guess I'm just risk adverse - why take the chance if it's not necessary ???

 

I guess I was hoping make sure that there was no undue vibration or shaking that was muffled by the tank since we have it out already and I never believed that if the pump runs dry it will break. If it was out, I'd also replace the pulsator since I am already there. Might be why I always budget way more for any project Because I often do "while I am here stuff.

 

As for cleaning a dirty fuel tank I have a method I have used successfully for many years.

My 1988 Coupe sat for a couple years and I did not want to use the fuel. I used a siphon hose to get 98% of it out. Then I used my hand and with paper towels I was able to get the rest of the fuel out.
Once the fuel is out of the tank I filled it with some water. I swirled around the water while using a shop vac to remove the water from the tank. This got out almost all the junk that was on the bottom of the tank and when the water was drained out and the tank was dry I would wash out the sections I could reach with paper towels. When done the sump for the fuel pump was perfectly clean and ready for pump and sending unit replacement.

At one point my car would not pressurize the fuel lines either. Like your situation I heard no pump running when I turned on the ignition. On my car there were a couple of issues preventing it from running.

First: Where the oil pressure sending unit is located are a couple wires connected. For the engine to have fuel pressure you need to have oil pressure. On my car one of the wires pulled out of the connector as it was not crimped correctly. I fixed the wire and then I had continuity all the way to the fuel pump wires at the sending unit. At that point applying power would activate the pump.

Second: The ground wires going to my fuel tank was disconnected/broken. I re-attached a new ground wire and the pump came to life. This also woke up my non-working radio antenna.

If you have a way to energize the fuel pump try applying power to the sending units wire directly. I would do this starting at the pump and working your way to the engine compartment. I use a gadget called a "Power Probe 4" and this allows me to apply either battery voltage or ground at the tip. There are three wires coming up from my sending unit. The little purple one is the fuel gauge sending unit wire, do not apply power to this wire. The other wires are ground and power for the fuel pump.

Behind the battery on my car is a little post with several wires on it. One is a positive wire from the battery and it is supposed to supply voltage for several critical Fusible Links. If you see any corrosion on this clean it and grease it. This is where a lot of the interior gets its power from. After cleaning this terminal I had closer to full battery voltage at the accessories. This is very important as it can wreak havoc in your car. I had between 9-10 volts at the accessories prior to cleaning this post behind the battery in front of the drivers door on the 1988.

One more thing, measure your voltages at the battery and then measure the voltages at each individual fuse. Each fuse should have full battery voltage at either side (IF the fuse is "good"). On my Coupe the fuses had become corroded so much that they were NOT conducting the power through them. They all "looked Good" but not one of them would allow power through it. The fuse connectors were made of aluminum and had a layer of corrosion built up. I cleaned the fuse plugs with a old Points File and then installed new fuses. This was the biggest problem my car had, from here the little stuff was easy.

Like people suggested earlier, check your fuel pressure, your regulator and then start tracing Vacuum lines. The vacuum system on most of these cars need some updating with new hoses. When I bought my 1988 it had two broken vacuum hoses, one at the EGR Solenoid (near the thermostat housing) and the other was near the cruise control unit.

Good Luck and I wish you the best in solving your Corvettes problem!

 

I thought that was the backup circuit? IIRC, I got my car to start with 0 psi since I disconnected the sensor to test that theory.

 

First of all, deep apologies for posting and then disappearing. Not cool. The Corvette is not my daily drive (well, not exclusively) and I was suddenly confronted with an airbag issue in my 2013 Sonata. Major learning curve (not to mention acquiring a sensor with SRS function).
Anyway, thanks to all of you for the responses as I return to this issue. It does seem to be the pump as 6 volts direct result in nothing. But I will also go over these other suggestions to be sure.
As for cleaning the tank, yes, I will siphon the gas out and vacuum the crud. And change the filter.
Again, thanks to all for the responses.

 

Why 6 volts and not 12?

 

I said that....usually there's a big 6v battery somewhere in my garage....those square things in the flashlight. it will only turn it on half speed but will tell you if it works or not....

 

You have tried it with a fuel pump before, right? Good to know. I have always hooked it up to 12V battery from the car just to be sure.

 

i've done it with several...don't want to admit how many times i've had that crap out to test.....

 

Again, good to know. I either use a 12V car battery or if it is lower amp, my battery charger which has 4 ports, 2 of which might be used in the winter.

 

Throw 12 volts at it and see if it runs.. horseshit from internet gurus on it will burn up. Just like the garbage disposal in your house. Sealed bearings. You can run it to test with out fear.

BigPoop

 

Tom400CFI has run an old one for over 45 minutes without fuel so....

Keeping batteries off the concrete floor is my 2nd favorite old wives tail