1987 Chevy Truck Issues (TBI)

[sg5492]

I have a 1987 Chevy 4x4 Pickup 305 TBI (all stock).  I had it running the other day to warm it up and it ran for about 10 mins and just died.  I can make it run with starting fluid, so I'm thinking it has something to do with fuel delivery.  I was wondering how much fuel pressure there should be on the TBI unit and where is the port to check it?  Is there anything else I should be looking for?  This is the first time this truck has given me any issues.  It does have dual fuel tanks but I'm only using the drivers side because the passenger side leaks.  Also, when I turn the key on I can hear the pump running in the drivers side tank for about 3-5 seconds so I think the regulator is working.
I'd appreciate any help and guidance I've done everything I know to do.

Thanks!!

[Irish_Alley]

ok heres how the fuel system works on the tbi, engine gets primed for 3 seconds when ecm is first powered on. then once you turn the engine over and build 3 psi of oil the oil pressure switch will then trip the fuel pump relay and turn the fuel pump on as long as 3 psi of is sustained. then the distributor tells the injectors when to fire. does it try to start without starting fluid? do you have a noid tester for the injectors?

[bd]

Did you check the fuses?

Irish, the ECM is the primary control for the fuel pump, via the firewall mounted relay.  The ECM energizes the relay for ~3 seconds (KOEO) as you stated.  It also energizes the relay during crank and while the engine is running.  The OPS is a redundant failsafe control in case the relay fails.  If the relay fails, prolonged cranking is required to build sufficient oil pressure (~3 PSI) to close the OPS contacts, which then powers the fuel pump directly bypassing the relay.

[Captain Swampy]

There is a red wire sticking out of the relay for testing. If you apply power to it the pump will run.

[Captain Swampy]

There is no test port for fuel pressure. You have to check it at the fuel pump or back of the throttle body. 9-12 PSI I think. If you need a pump get a EP 381 instead of the EP 386.

[Irish_Alley]

Did you check the fuses?

Irish, the ECM is the primary control for the fuel pump, via the firewall mounted relay.  The ECM energizes the relay for ~3 seconds (KOEO) as you stated.  It also energizes the relay during crank and while the engine is running.  The OPS is a redundant failsafe control in case the relay fails.  If the relay fails, prolonged cranking is required to build sufficient oil pressure (~3 PSI) to close the OPS contacts, which then powers the fuel pump directly bypassing the relay.

knew there was something i was forgetting but couldnt think of it. the way i said is how my 91 crew is wired up. and we been over how it is before like you stated lol but heres the schematic for more confusion to what bd was talking about.

There is no test port for fuel pressure. You have to check it at the fuel pump or back of the throttle body. 9-12 PSI I think. If you need a pump get a EP 381 instead of the EP 386.

this is correct also and the part about the red wire

[hatzie]

There is a red wire sticking out of the relay for testing. If you apply power to it the pump will run.

Some, but not all, ALDL jacks have a fuel pump "test terminal" in position G.  If you apply power to this terminal the fuel pump should run.  The jack terminals are 12124313 Female Metripack 280s. Use 12092346 Male Metripack 280 terminals to plug into the ALDL jack without damaging the jack terminals. 
BTW if the PO chewed up your original Metripack 280 ALDL jack... GM 12020043 is available from Mouser Electronics.


The relay is energized by the ECM during cranking to offload the, much higher, fuel pump motor startup current from the Oil pump switch contacts to an easily replaceable relay. 
The relay is energized by the ECM only when cranking.  The oil pressure switch carries the fairly low pump motor run current after startup till shutdown.  It's done this way as a safety measure.  When oil pressure drops in a rollover or other accident the fuel pump stops immediately.  This is far more reliable than the inertia switches used by Ford, Chrysler, Honda, etc.

[Irish_Alley]

so the relay is only used to take the initial high amp load off the OPS and to prime the system?
so the way i have my set up is the fuel pump only turns on while cranking via OPS and the OPS keeps it on after the engine is running. so i dont need the fuel pump relay?

[bd]

That's contrary to what GM taught us, but is an easily testable hypothesis.  Unplug the OPS and see if the engine starts and continues to run.

[Irish_Alley]

havnt unplugged mine yet but not sure if the test is testable with the cummins having its own fuel pump (VE pump) it should pull past the fuel pump in the tank. when i initially start my truck up im only pushing 9 psi of fuel with (10-12 volts). then if i rev the engine to excite the alternator i push 14-15 psi (14 volts) if the engines not running im at 0 psi

[Captain Swampy]

I have a 1987 Chevy 4x4 Pickup 305 TBI (all stock).  I had it running the other day to warm it up and it ran for about 10 mins and just died.  I can make it run with starting fluid, so I'm thinking it has something to do with fuel delivery.  I was wondering how much fuel pressure there should be on the TBI unit and where is the port to check it?  Is there anything else I should be looking for?  This is the first time this truck has given me any issues.  It does have dual fuel tanks but I'm only using the drivers side because the passenger side leaks.  Also, when I turn the key on I can hear the pump running in the drivers side tank for about 3-5 seconds so I think the regulator is working.

I'd appreciate any help and guidance I've done everything I know to do.

Thanks!!

The pressure regulator is on the throttle body, you would have to check fuel pressure to tell if it's working. It may have a broken spring.

[hatzie]

That's contrary to what GM taught us, but is an easily testable hypothesis.  Unplug the OPS and see if the engine starts and continues to run.

The 1991 Fuel and Emissions Manual states on PDF pages 84 & 86 that:
-The ECM/PCM powers the fuel pump relay for 2 seconds when the ignition is first switched on. 
-The ECM/PCM also powers the Fuel Pump Relay when the key is in the crank position. 
-The Fuel Module on the 7.4L & 8500GVW or larger 5.7L and all G series Vans overrides the ECM/PCM to run the fuel pump for 20 seconds immediately after switching the  key on and leaving the engine off.  It also overrides the ECM for 20 seconds after engine shutdown to prevent vapor lock.
-The oil pressure switch powers the fuel pump directly when oil pressure is above 8PSI.

Some TBI ECM/PCMs keep the relay energized as long as there are pulses from the ignition module and for an additional 2 seconds after ignition activity ceases.  I am positive that not all ECM/PCMs do this.  Whether this is a malfunction or modified programming is anyone's guess.

[bd]

Whether this is a malfunction or modified programming is anyone's guess.

I doubt whether all the techies at GM even know or agree on how everything works.  lol

[sg5492]

Thanks for all the replies, there was a lot of information I didn't know.  I have checked all the fuses and they test good. It kinda acts like it wants to start without the starting fluid. I'm going to pull the fuel line and see if I have any fuel to the injectors.  One thing I want to check before I try it...on the fuel pump relays I think I have 2 one for each tank if I'm looking at it from the front of the truck the one on the right should be for the driver's side...correct??  Also, all I have to do it pull the red wire and put power to it and the pump should run continuously? What is a noid tester?  All I have is a multi-meter.

If all that checks out ok I'll be back for more answers on taking injectors apart!

[Irish_Alley]

only one relay should be on the passengers side firewall. the red wire might be tucked into the wire loom. and noid tester is kind of like a led that plugs into the fuel injector pigtail. it will light up if the injector is getting signal to fire
you can also apply 9v to the injector and it should fire