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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: sg5492 on March 11, 2016, 08:01:37 pm
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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!!
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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?
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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.
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There is a red wire sticking out of the relay for testing. If you apply power to it the pump will run.
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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.
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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.
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27609;image)
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
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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 (http://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkey12020043) is available from Mouser Electronics.
(http://johnnynightstick.s3.amazonaws.com/IMAGES/ALDL_plug.jpg)
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.
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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?
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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.
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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
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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.
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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.
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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
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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!
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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
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OK... This is what I have. I see a red wire that's hanging out on the one on the left. So the one on the left is for testing power to the fuel pump, what is the box on the right for? Just curious.
(http://i103.photobucket.com/albums/m143/sg5492/fuel_zps0cbkaqtg.jpg) (http://s103.photobucket.com/user/sg5492/media/fuel_zps0cbkaqtg.jpg.html)
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OK... This is what I have. I see a red wire that's hanging out on the one on the left. So the one on the left is for testing power to the fuel pump, what is the box on the right for? Just curious.
(http://i103.photobucket.com/albums/m143/sg5492/fuel_zps0cbkaqtg.jpg) (http://s103.photobucket.com/user/sg5492/media/fuel_zps0cbkaqtg.jpg.html)
One is the FPR the other is the fuel module for vaporlock that I mentioned in my last post.
If you feed 12v to the red wire the selected fuel pump should run. This assumes the tank switch on the dash is ok.
My Droid from orbit
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on my 91 v3500 i have the one on the left(with the red wire) and nothing on the right. theres a spot for it just nothing there.
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A noid light plugs in place of a fuel injector. While cranking the engine it needs to flash. If it doesn't come on or stays on continuously there is a problem. No flashie= No workie ;D
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Well you said you hear the pump in the tank once the key is on...so it may be something simpler. Like fuel filter, return line clogged or the actual tank selector switch failing.
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So how come it appears that not all trucks have that second relay? I have an 87 with factory TBI and fully functioning dual tanks and I only have the one relay on the left? My truck runs fine regardless of which tank is selected, although I tend not to use the driver's side tank since it leaks when it's full.
I've noticed it seems like the early TBI systems were a finicky beast. If they're not tuned just right and in tip top shape, they tend to not run right. My truck seems to run rich and has an intermittent stalling issue when the engine is cold and also backfires through the exhaust when cold for example. I've thrown all kinds of parts at it with little change. It's better than it used to be but not completely right. Tired of throwing parts and money at it.
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So how come it appears that not all trucks have that second relay? I have an 87 with factory TBI and fully functioning dual tanks and I only have the one relay on the left? My truck runs fine regardless of which tank is selected, although I tend not to use the driver's side tank since it leaks when it's full.
I've noticed it seems like the early TBI systems were a finicky beast. If they're not tuned just right and in tip top shape, they tend to not run right. My truck seems to run rich and has an intermittent stalling issue when the engine is cold and also backfires through the exhaust when cold for example. I've thrown all kinds of parts at it with little change. It's better than it used to be but not completely right. Tired of throwing parts and money at it.
The hot fuel handling module is only on certain engine and GVW combinations.
Download the drivability and emissions manual for your rig.
They aren't that finicky or complex. They don't respond well to shotgun repairs. You'll spend a bunch throwing parts at it and probably wont fix it.
Plug in with a cheap $100 laptop and a DIY ALDL cable running free software... TUNERPRO or WINALDL and watch sensor behaviour when she misbehaves.
A Fuel pressure gauge and a decent $50 DMM like the Extech 330 are your friend too.
Don't assume new parts are good or meet spec... most are made in China now.
Sent from my SM-P605V using Tapatalk
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The hot fuel handling module is only on certain engine and GVW combinations.
Download the drivability and emissions manual for your rig.
They aren't that finicky or complex. They don't respond well to shotgun repairs. You'll spend a bunch throwing parts at it and probably wont fix it.
Plug in with a cheap $100 laptop and a DIY ALDL cable running free software... TUNERPRO or WINALDL and watch sensor behaviour when she misbehaves.
A Fuel pressure gauge and a decent $50 DMM like the Extech 330 are your friend too.
Don't assume new parts are good or meet spec... most are made in China now.
Sent from my SM-P605V using Tapatalk
I second these motions...espe ially the last one it has bitten me a few times!! Never say ' it's a new part so that can't be it'. That's the first place to look!
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So how come it appears that not all trucks have that second relay? I have an 87 with factory TBI and fully functioning dual tanks and I only have the one relay on the left? My truck runs fine regardless of which tank is selected, although I tend not to use the driver's side tank since it leaks when it's full.
I've noticed it seems like the early TBI systems were a finicky beast. If they're not tuned just right and in tip top shape, they tend to not run right. My truck seems to run rich and has an intermittent stalling issue when the engine is cold and also backfires through the exhaust when cold for example. I've thrown all kinds of parts at it with little change. It's better than it used to be but not completely right. Tired of throwing parts and money at it.
There is a ton of information at tbichips.com. Also check for a vacuum leak at the throttle shaft. Brooke's was worn and it made the truck run like crap.
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So how come it appears that not all trucks have that second relay? I have an 87 with factory TBI and fully functioning dual tanks and I only have the one relay on the left? My truck runs fine regardless of which tank is selected, although I tend not to use the driver's side tank since it leaks when it's full.
I've noticed it seems like the early TBI systems were a finicky beast. If they're not tuned just right and in tip top shape, they tend to not run right. My truck seems to run rich and has an intermittent stalling issue when the engine is cold and also backfires through the exhaust when cold for example. I've thrown all kinds of parts at it with little change. It's better than it used to be but not completely right. Tired of throwing parts and money at it.
There is a ton of information at tbichips.com. Also check for a vacuum leak at the throttle shaft. Brooke's was worn and it made the truck run like crap.
Thanks Captain! I know you've mentioned that site before, just haven't checked it out yet. I rebuilt the entire throttle body like a year and a half ago or so and replaced the base gasket. The problems I described were there from day one, but were diminished after that. All other major tune up parts have been replaced new in that time as well. I don't drive the truck much, I've owned it for three years and have only put about 7500 miles on it! Would some of these symptoms be emissions related? I still suspect fuel as well since the truck stumbles on start up once it's started warming up. It cranks and fires just fine with a cold engine. There's also no codes being thrown. The service engine light operates on start up as it should.