If the fuel gauge is way off, there’s definitely a chance there’s a problem with the pump ass’y ground connection. That would show up by probing the power connection at the pump ass’y. There should be no difference where the ground connection is probed, either at the pump itself, or the nearby chassis. It’s usually possible to hear the fuel pump running, you may need to device a stethoscope of some sort, listen to the end of a stick held against the fuel pump, use a length of discarded garden hose, etc. If you know for certain there’s a problem with the oil pressure/fuel pump switch, fix that first. The fuel pump has to be working for your truck to run properly. As mentioned above, that configuration is to protect the engine in the event the oil pressure gets too low. So first on the agenda, make sure your oil pressure is ok using a shop oil-pressure gauge.
So last week, I managed to replace the oil pressure/fuel pump switch. The space is very tight, even with the proper tool to replace the switch. When I removed the distributor cap, I noticed some oily residue and green rust, so I replaced it as well with a Delco brand. I also replaced the fuel pump relay. All this week, the truck starts easier and fast, but what I did not expect was how the truck now is driving uphills (that I always drive) much easier and in higher gear, and the engine seems way more smooth. Now that is a very pleasant surprise because my overall plan was to increase a few extra horsepower from the engine and make it more gas efficient. Id did an amp test of the pump from the fuel pump relay port, and I got 5.38 amps. Neither of my manuals, Chilton and Haynes) specifies an amp draw for the fuel pump, but the internet says that these pumps can run from 3 to 5 amps, so I was hoping I am right on target. Since my gas gauge is still way off, indicating way more gas than what I really have and never going down more than three quarters, that I would clean a new chassis spot, bolt a new ground wire, and add it to the existing fuel pump ground. The idea is to avoid dropping the gas tank. I was also thinking of replacing the gas tank cap and replacing my current paper air filter with a K&N Engine Air Filter, High Performance, Washable, Replacement Filter (just the filter, not the whole air distribution tubing since I think that would not increase anything).
What do you think? And thank you for your help!
The company I worked for tested the K & N air filter for efficiency.
When the testing was over I asked the technician who ran the test what they thought of the K & N filter.
Their response was, " If you want to keep birds and chipmunks out of your engine, that’s the filter to use."
Tester
That represents an electrical power 12 x 5.38 watts, a little over 60 watts. Seems within the expected range to run a fuel pump. I’m guessing replacing the oil pressure switch is what solved the no-starting problem, and replacing the distributor cap is what’s giving you the better driving performance. Suggest to go whole hog on this idea b/c it is working so well, and replace the spark plug wires, the distributor rotor, and the spark plugs as well. You’ll have a pristine ignition system.
It’s definitely worth a try to improve the fuel pump grounding point to try to make the gauge work better, but given what you say my guess is this will have little to no effect. Probably either going to have to live w/it or replace the sending unit, which probably means replacing the entire fuel pump ass’y. You might try measuring the sending unit resistance when the tank has a known amount of fuel and telling us what you get. Maybe you’ll get some useful idea.
Suggest to keep the air intake path to the engine stock. Changes in that area can sometimes result in a difficult to diagnose adverse effect on the fuel/air mixture.
I have never heard of a vehicle that shuts off the fuel pump if the oil pressure goes low. If this is the case it would have to include some time delay logic else the engine would never start, because oil pressure doesn’t always come up until the engine is started, and it can take over 60 seconds of cranking without starting before the oil pressure comes up, if ever. It can take a couple of seconds after starting for the oil pressure to come up too.
The problem seems to me like an ignition problem and a fuel problem. Did the low speed running after cranking problem only occurr when starting fluid was used?
In some vehicles the ignition module must be securely mounted to the chassis because that is its only ground path. If it is loose there will be no spark, and possibly damage to the unit as someone else said. There can also be weak spark which is much harder to diagnose, since the spark looks mostly fine.
Does this have a dead end fuel system or a loop system? If it is dead end it can get air trapped in it and need priming. There may be a small leak that is letting air in the system and the fuel is draining back in to the tank. A small amount of fuel remains right behind some of the injectors which allow for a few seconds of running. After that the rest is air and so it won’t run. Try following the proper service procedure for bleeding or priming the fuel system.
Additionally you may have or have haid low fuel pressure, which was causing the lean running code and the lack of power. Lean runnig is hard on the engine so avoid that. Without a knock sensor, lean running can cause knocking and blow valves in only a few thousand miles.
I know this sounds like a dumb question and maybe somebody has asked it. Have you verified that your vehicle does not have a battery drain? Sounds like when you replaced the battery it worked well for a few days and than had the issue again. This fits with a drain issue, the new battery works, than after a few days or so the drain empties the battery and you have the same issue again. Just my thoughts.
Someone needs to do a little research.
My Buicks had the extra fuel pump switch. It was a part of the oil pressure sender. You can look at the schematic in the factory manual. Where or how it is on a truck I don’t know. This was discussed prolly 30 years ago on a local radio car program. We also had the discussion here probably before the software changes. There was disagreement on how it worked and whether it would prevent a start or shut down an engine. I think it was very rare for it to fail but still something to check if power is not getting to the pump.
Now excess draw from a bad pump can ruin a relay which is why it is recommended to replace the relay and the pump harness when replacing the pump. As I have said in the past though, I have had my share of pump issues and would consider replacing the vehicle as well as a pump. At least in Gm.
So it is used on carburetors where there is enough fuel in the float bowl to get the engine started, and then the switch closes and turns on the fuel pump. I assume the fuel pump is also engaged when the starter is engaged regardless of oil pressure. If there was only a way to make such a simple thing work on a fuel injected engine.
You’re giving me more ideas for how cars were better in the past!
So when fuel injection became a thing they kept the oil pressure fuel pump switch but put it in parallel with a fuel pump relay. The ECU keeps the relay on all the time that the engine is running so it no longer offers low oil pressure protection. It does allow the engine to keep running if the relay fails, and to allow starting with a failed relay if the engine is cranked for a long enough time to build oil pressure.
Constantly adjusting valves, carburetors, wheel bearings, etc.
Not to mention older cars got worse fuel economy, didn’t handle as well, weren’t as nicely equipped, etc.
ah yes . . . the good old days! 
Carb? I don’t think the had electric fuel pumps with carbs. Carbs had the old eccentric operating off the engine. Can’t shut them off. Injection systems had electric pumps that can be shut off, but I’m getting a headache.
The Chevrolet Vegas had an electric fuel pump and carburetor. If the engine oil level was low enough for the oil pressure warning light to illuminate while driving on a clover-leaf highway ramp, the engine could stall after a few seconds. A design like that wouldn’t be allowed during the last 30 years, oil pressure or not, purposely stalling the engine and loss of power steering is a hazard.
It’s really an excuse to not protect the vehicle from severe damage with the excuse of blaming the driver. If it did stall due to low oil pressure it’s still the driver’s fault anyway for not checking the oil. Cars can stall for a number of reasons that are not preventable. Fuel pumps quit, timing belts break, fuses can blow, a vital sensor can fail, the ECU can crash, and an engine run out of oil will sieze up and stop running anyway. They could easily put the engine in a low RPM limp mode where the power steering would still work but most vehicles don’t implement that.
you can have a full crankcase and still have low engine oil pressure
Keeping the engine running and the power steering operational is protecting the vehicle and the people inside from a crash until the driver can stop in a safe place. You would rather protect a failing engine?
The number of vehicles I see with a ruptured engine oil cooler line outnumber the vehicles with oil consumption related failures. Either way, the engine can be replaced, engine shutdown in a turn is a serious hazard.
Absolutely! And going off the side of an exit ramp because an improperly trained driver doesn’t know how to steer without power steering is a good teachable moment anyway. How many lives in a 3rd world country could be saved from $5000 for an engine replacement? There was an incident that I know of were somebody backed down the driveway without starting the engine by accident, and the “brakes did not work”. Fortunately there wasn’t anything in the street at the end of the driveway. The driver in this case is not mechanically inclined, has insufficient driver training along with everyone else, seems to think that two fingers on the bottom of the steering wheel at 70 MPH is fine, and like most everyone else, has never read a vehicle owner’s manual. Last but not least, this driver has never been in an accident. It would actually benefit this driver to be in a minor accident for future caution and safety. If they won’t take advice seriously then physical pain may be what does it.
For crying out loud . What is wrong with you . You seem to think you know a lot more than you actually do . I said this before , find a Forum where someone might agree with your nonsense .