87 chevy fuel problems

[missi]

OK bare with me, this is my first time.  I have an 1987 Chevy silverado 4X4 with a 350 TBI.  Fuel Gage has never worked, always on full.  Thought I was running out of gas but the other day it just wouldn't crank.  Adding fuel didn't help this time.  OK I have dropped the tank, replaced fuel pump and sending unit.  Still having problems.  It would crank but die when I would put it in gear.  Was gonna take it to the shop for help and got it to crank but when I added the fuel that was it. No fuel pump coming on at all.  Other people have worked on it also, heres a little about whats been done so I will be able to get some help.  I'm going crazy.  Took injectors off my 91 jimmy ,thats broke also, because at one time everything seem to work up to that point.  They looked the same.  OK, then still were having problems with the cranking or the staying cranked I'm not sure but for some reason they thought it to be faulty wiring.  So here they go and replace wire from top of yank to wherever it goes, they had forgot about the regulator.  Well the fuel pump ran even if the truck was not crank but on.  I knew that wasn't right.  So my brother figures out the regulator wasn't hooked up.  Well we get that going and still having problems with it staying cranked.  Then it needed gas for me to take it to be seen about but gas in it and boom no go.  Thats where I am at .  We are dropping the tank again to make sure everything is hooked up but we are confused about the junction block location and the fuel pump oil pressure switch.

[VileZambonie]

Once the oil pressure switch closes and the engine starts it's out of the picture. You could physically disconnect it and the truck would stay running. So if the truck starts and runs but then stalls when you try to take off it's not the oil pressure switch. Most importantly here if you think the problem is fuel related go to autozone and get a TBI fuel pressure gauge. The fuel pump relay has a bypass test lead you can jump 12 v to also to test to bypass the relay control and oil pressure input to the ecm.

[Fordeatinz71]

you might consider replacing your ignition module.  it controls injector pulse (the opening and closing of the injectors) and the ignition spark.  they aren't expensive and go out all the time.  it is under your distributor cap in the base of the distributor.  it has two plugs coming out of it and is a flat module with two plugs coming out of it.  also, are you POSITIVE it's losing fuel?  you need to see what element is getting cut out, fuel or spark.  you also may want to replace the relay for the fuel pump.  these can short out and become a really aggrevating problem, because they will continue to function sometimes and then just stop.  i would get someone with a multimeter to check all the factory wiring.  if that factory wiring is still good (man i hope ya'll didn't cut it out) then i'd strongly recommend continuing to use it.  just makes it easier for people who are working on it to troubleshoot the factory wiring that is already there and is shown in a factory wiring diagram.  plus you don't have to worry about it being wired up wrong.  once you find the fuel pump relay (i'm not exactly sure where it would be) you can look at a wiring diagram and find out what each pin does on the relay plug.  then you can get a jumper wire and hotwire the pump just to see if the truck will stay running that way (but DON'T leave it like that).  if the pump keeps working then most likely the relay is your problem...good luck and keep us posted!

[DnStClr]

It's kind of hard to follow your post. You removed the tbi from your 91 Jimmy- Did you swap tbi units between the 91 and 87?
Does your gauge stay inoperative when you switch from left to right tank?
The fuel pumps in the tanks will get power when you turn your ignition key to the on position. The truck does not have to be running.
The relay is located on the firewall in the engine bay.

[missi]

I'm sorry it is a little confusing.  I just the injectors and the fuel meter.  The fuel pump wire on the inside of the tank had a open circuit.  I fuel pump is suppose to cut off when you turn the key but don't crank it. right.  The fuel tank is going to have to be replaced.  When I first got the truck the tank was leaking, a friend put something in the tank to stop it.  Needless to say when I drop the tank whatever it was ,was floating in the gas.  The pump is working right know.  Thanks

[DnStClr]

I fuel pump is suppose to cut off when you turn the key but don't crank it. right. 

Not right. When you turn the key to the "on" position, the fuel sending unit inside the tank gets a signal and returns a signal (resistance compensated because of the amount of fuel) to your gauge.  Anyway, glad your sender is ok now. Tell your buddy not to add any more secret stuff to the tank. 

[VileZambonie]

This is how it works:

When the ignition is cycled to the run position the ecm energizes the fuel pump relay for 2 seconds. It will not do this again unless the ignition is switched off for at least 15 seconds. When the engine is cranked and oil pressure closes the sitch 12v goes to the ecm on the same circuit that energizes the fuel pump. Once the ecm senses 12v it continues to keep the relay energized until the ignition is switched off.

[monte85]

some trucks in 87 had a special fuel module that ran the pump for 20 seconds when you first turned the key on. its part of the pump relay circuit and part of the trouble shooting list for fuel problems in the gm service manual. the module is under the dash next to the steering column and has 3 wires going to it.

[Fordeatinz71]

err, all EFI trucks should have that...all '87-up TBIs.  it's part of the setup...

[VileZambonie]

err, all EFI trucks should have that...all '87-up TBIs.  it's part of the setup...

Nope, just 454's and some 350's came with the fuel control module. It was designed to help during hot soak restarts to avoid vapor lock when ambient temps are high.

[Fordeatinz71]

hmm, never knew that.  i just thought all TBI trucks had the system.  i knew what it did, i just thought it came on all trucks...

[missi]

Hey Ya"ll, Been Thanks for all the good advice.  Been out of pocket for a few days so I thought I would give an update on my poor old Chevy.  Well hopefully I am fixing to go put the tank back in, brand new.  It turns out that the sending unit wasn't good.  I guess I really don't need a gage.  Ill put it all back together and see what happens.  thanks again for all the advice. One person cant never learn to much, love the info.  missi

[Hank Hill]

I know nothing about fuel injection, sorry.
However about the gas gauge with dual tanks. On my truck when you switch from one tank to another you cant just flick the switch. You have to hold the switch down all the way for a few seconds in order for it to work. Example if I just flick the switch without holding it down for a few seconds the gas gauge will just show full tank regardless of how much fuel is in it.

[VileZambonie]

Sounds like a bad switch