tbi low fuel pressure - The 1947 - Present Chevrolet & GMC Truck Message Board Network

motroo · 06-10-2009, 07:52 PM

hello all, forum newbie here. looking for a thread about tbi fuel pressure problems. i seem to have low fuel pressure due to faulty wiring. need info on what wires go where. this is for 1989 (square body style) 1 ton chevy crew cab 4x4 with 5.7 tbi.
thanks

pig rig · 06-10-2009, 08:28 PM

I'd start with that $10 fuel filter and then if that dosnt fix it get a tbi rebuild kit and replace all the filters in it

motroo · 06-10-2009, 09:18 PM

thanks pig rig, but i've already been down that road. everything from the injectors down to the switching valve and all sensors have been checked/cleaned/replaced. i do infact have a low voltage problem. i have 12 volts going into my fuel pump relay and only 9 volts coming out. i have had 3 relays plugged in, so it's not the relay. i also found a hot wire down by my passenger side tank that was showing 9 volts as well. i don't think those pumps will put out on that low voltage. i just need a good wiring diagram, my chiltons and haynes manuals aren't showing what i actually have on my truck from what i can see.

motroo · 06-12-2009, 05:32 PM

anybody got any thoughts or ideas?? or info??

TwinTurbo · 06-12-2009, 06:09 PM

check the oil pressure switch next to the distributor.

rfmaster · 06-12-2009, 08:00 PM

Quote:

Originally Posted by motroo

anybody got any thoughts or ideas?? or info??

Check FP relay socket - it is not uncommon for them to go bad. See photo below:

Sockets may develop contact oxidation over years in service - increase relay contact resistance. Also check relay contact resistance. Oil pressure switch should be checked as it acts as relay backup system.

//RF

motroo · 06-12-2009, 09:31 PM

sounds like a good idea, as i have 12 volts going into the relay and only 9 coming out. it is the same on 3 different relays, so i will def. check that out.

motroo · 06-13-2009, 09:40 PM

ok, well no luck. the wiring on the truck doesn't match what i see in either one of my manuals. and the information i'm getting about what wire goes where doesn't match what i see on my truck. so here goes.
truck is 1989 chevy 1 ton 4x4 crew cab, this is still the older square body style. it has dual tanks and a switching valve which doubles?? my wiring, or at least is responsible for some of the splices down by the tanks. evrything worked fine one day and then just decided it didn't want to run anymore as i pulled out of the driveway. i did over heat the truck (twice) enough to blow a head gasket about a month before all this happened. which has led me to think maybe i have melted/burned a wire somewhere?? after replacing every single sensor and replacing the head gaskets, the problem remains exactly as it did before the repairs. now, since i have started looking at my wiring, i have managed to somehow get the truck to run quite a bit better on the right tank, and a bit worse on the left tank. i found some wires poorly spliced and repaired as best i could. i am so confused as to what wires actually power my fuel pumps, that i am wire blind. any information would be greatly appreciated, please keep in mind i have two tanks and two pumps.
thanks

pig rig · 06-13-2009, 09:59 PM

as I was reading your last post I was thinking your dash switch, because on the tbi engines that switch turns your pumps on and off but every one that I've had go bad it shut it down completly. but youve got yours to run right?

motroo · 06-13-2009, 10:15 PM

yes, mine will run. it seems i am supposed to have 12 volts every where, but i don't have 12 volts any where after the fuel pump relay, it's more like 9 volts. i tried to get at the switch inside but i couldn't find a way without tearing my dash apart. and right now i have bed moved, fuel lines unhooked, wires undone, and i'm starting to forget where this stuff all goes. so i'm not wanting to tear my dash apart but i'm glad you mentioned that because i had no clue that the switch did more than just switch. are you saying that the switch has power going to the pumps by way of the switching valve?

pig rig · 06-13-2009, 10:27 PM

the switch has power to it and it sends power to the pumps and to remove it reach up behind the dash and squeeze the top and bottom as you push it out of the dash and then unplug the wires (I hope that makes sents)
and I think the valve has power running to it also

motroo · 06-13-2009, 10:29 PM

i'll have to check it out again. i think it might just be an a/c duct in the way but i couldn't get to it earlier. thanks

pig rig · 06-13-2009, 10:38 PM

I have a haynes manual from 87 that the wire diagrames suck huge donky c0$( for our trucks but I also have one thats a 2008 edition thats a lot better its been revised a little bit for the tbi trucks

motroo · 06-14-2009, 02:37 PM

hey does anyone know if i'm supposed to have voltage on all four injector wires? i checked them today and had 11.88 volts on all four wires with key on engine off. i also ran direct ground wire from battery to left side fuel pump, made no difference, i ran a direct hot wire to left side fuel pump, made no difference.
will i be able to get the pumps out of the tanks without having to drop the tanks?? i have the bed moved but the acces is still a bit under the cab.

rfmaster · 06-14-2009, 03:08 PM

Quote:

Originally Posted by motroo

hey does anyone know if i'm supposed to have voltage on all four injector wires? i checked them today and had 11.88 volts on all four wires with key on engine off. i also ran direct ground wire from battery to left side fuel pump, made no difference, i ran a direct hot wire to left side fuel pump, made no difference.
will i be able to get the pumps out of the tanks without having to drop the tanks?? i have the bed moved but the acces is still a bit under the cab.

1) With engine off both sides of injector connector will read battery voltage (11.88Vdc in your instance). When engine is turning ECM is receiving distributor reference pulse (DRP) and pulls one of the two wires going to (each) injector to ground activating injector. Injector fires - fuel is sprayed.

2) In tank fuel pumps fail due to split rubber hose that connects pump outlet port to fuel assembly through (to outside). The hose slowly leaks - pump begins to spin faster since the back pressure is lower, eventually wearing itself out. One way to check for this condition is to look at current pulses on the Fuel pump circuit with oscilloscope and a current clamp probe. A typical OE pump turns at about 3000 RPM under load. With leaky hose this goes up to about 5000 RPM where it is does not last for long. In your case - due to age the pumps are probably are on their last legs.

//RF

motroo · 06-14-2009, 06:26 PM

ok, good news, left side tank had the split hose problem on the pump. went and bought new hose and decided i better find out if i can use regular fuel line hose or is there a specific hose rated to be submersible? next question is should i just replace the split hose or is there a way for me to test the pump to see if it is still worth keeping?

pig rig · 06-15-2009, 12:28 AM

if your already in to the tank and have the pump out I'd spend the money on pumps because it sucks to have a pump give up when you need it

pig rig · 06-15-2009, 12:29 AM

oh, yea! you can get the pump out when the bed is off or just moved back about a foot its tight but it can be done

rfmaster · 06-15-2009, 01:54 AM

Quote:

Originally Posted by motroo

ok, good news, left side tank had the split hose problem on the pump. went and bought new hose and decided i better find out if i can use regular fuel line hose or is there a specific hose rated to be submersible? next question is should i just replace the split hose or is there a way for me to test the pump to see if it is still worth keeping?

It is a false economy to replace that hose with anything other than SAE 30R10 fuel submersible rated hose. Over time gasoline additives will soften typical (commonly found in most auto parts stores) 30R7 or 30R9 hose and you will find yourself back in same situation. Since you have full access to FP in one tank - replace it with AC Delco Unit (EP386 or similar). It is very common for a pump to fail shortly after hose replacement. Do you want to do this job twice or three times over?

Just in case if you are wondering about Chinese made pumps sold by most auto part stores, in white boxes, these are purchased in bulk at about $13 @1000 unit quantity FOB, and depending on sourcing factory reliability is of some curiosity to me, as it varies from none (DOA) to acceptable.

Caveat emperor!

//RF

motroo · 06-15-2009, 07:04 PM

success!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
both pumps had a split hose! who would thought?
thank you pig rig
thank you rfmaster
i pray that the lord blesses you for the help you have given.
now, any thoughts about the best way to get some kind of wrench on my distributor hold down clamp bolt? i can't get anything on it cause of all the stuff in the way.

cjracing15 · 06-15-2009, 07:40 PM

They make a distributor wrench that has a 1/2 inch or a 9/16. They sell them at any parts store just ask for a distributor wrench and, if its any kind of parts store at all they should have it.

motroo · 06-15-2009, 09:36 PM

yes i have one of those. but with the metal fuel lines right there and the egr and some other metal coolant line, i can't even begin to get a distributor wrench to turn the nut, there just isn't any room. i think if i had a swivel socket and ground the socket down short, it would work.

pig rig · 06-16-2009, 01:02 AM

yea i remember have'n all the stuff in the way to get at the bolt I rerouted my fuel lines and moved my map sensor when I had my engine out just to make life easy on me

i pray that the lord blesses you for the help you have given.

well he was having fun at my expense to day because every thing I got a hold of went to hell

motroo · 06-16-2009, 09:40 PM

ok, tried to time the motor today, just by ear for now, and within 5 minutes it hit 220 degrees. i had to replace the head gaskets, and am pretty sure i set the valves properly, but i've never done it before, could the valves cause an overheating issue? could it be the timing off a bit? i don't have the fan shroud back on yet but it shouldn't get that hot that fast. any thoughts?
and what about a reset for the idle air control valve? i read that if they get disconnected, they need to be reset. what do ya'll think?

motroo · 06-16-2009, 09:41 PM

ok, tried to time the motor today, just by ear for now, and within 5 minutes it hit 220 degrees. i had to replace the head gaskets, and am pretty sure i set the valves properly, but i've never done it before, could the valves cause an overheating issue? could it be the timing off a bit? i don't have the fan shroud back on yet but it shouldn't get that hot that fast. any thoughts?
and what about a reset for the idle air control valve? i read that if they get disconnected, they need to be reset. what do ya'll think?

06-10-2009, 07:52 PM	#1
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	tbi low fuel pressure hello all, forum newbie here. looking for a thread about tbi fuel pressure problems. i seem to have low fuel pressure due to faulty wiring. need info on what wires go where. this is for 1989 (square body style) 1 ton chevy crew cab 4x4 with 5.7 tbi. thanks

06-10-2009, 08:28 PM	#2
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure I'd start with that $10 fuel filter and then if that dosnt fix it get a tbi rebuild kit and replace all the filters in it __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

06-10-2009, 09:18 PM	#3
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure thanks pig rig, but i've already been down that road. everything from the injectors down to the switching valve and all sensors have been checked/cleaned/replaced. i do infact have a low voltage problem. i have 12 volts going into my fuel pump relay and only 9 volts coming out. i have had 3 relays plugged in, so it's not the relay. i also found a hot wire down by my passenger side tank that was showing 9 volts as well. i don't think those pumps will put out on that low voltage. i just need a good wiring diagram, my chiltons and haynes manuals aren't showing what i actually have on my truck from what i can see.

06-12-2009, 05:32 PM	#4
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure anybody got any thoughts or ideas?? or info??

06-12-2009, 06:09 PM	#5
TwinTurbo Registered User Join Date: Sep 2003 Location: The Netherlands Posts: 994	Re: tbi low fuel pressure check the oil pressure switch next to the distributor.

06-12-2009, 09:31 PM	#7
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure sounds like a good idea, as i have 12 volts going into the relay and only 9 coming out. it is the same on 3 different relays, so i will def. check that out.

06-13-2009, 09:40 PM	#8
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure ok, well no luck. the wiring on the truck doesn't match what i see in either one of my manuals. and the information i'm getting about what wire goes where doesn't match what i see on my truck. so here goes. truck is 1989 chevy 1 ton 4x4 crew cab, this is still the older square body style. it has dual tanks and a switching valve which doubles?? my wiring, or at least is responsible for some of the splices down by the tanks. evrything worked fine one day and then just decided it didn't want to run anymore as i pulled out of the driveway. i did over heat the truck (twice) enough to blow a head gasket about a month before all this happened. which has led me to think maybe i have melted/burned a wire somewhere?? after replacing every single sensor and replacing the head gaskets, the problem remains exactly as it did before the repairs. now, since i have started looking at my wiring, i have managed to somehow get the truck to run quite a bit better on the right tank, and a bit worse on the left tank. i found some wires poorly spliced and repaired as best i could. i am so confused as to what wires actually power my fuel pumps, that i am wire blind. any information would be greatly appreciated, please keep in mind i have two tanks and two pumps. thanks

06-13-2009, 09:59 PM	#9
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure as I was reading your last post I was thinking your dash switch, because on the tbi engines that switch turns your pumps on and off but every one that I've had go bad it shut it down completly. but youve got yours to run right? __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

06-13-2009, 10:15 PM	#10
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure yes, mine will run. it seems i am supposed to have 12 volts every where, but i don't have 12 volts any where after the fuel pump relay, it's more like 9 volts. i tried to get at the switch inside but i couldn't find a way without tearing my dash apart. and right now i have bed moved, fuel lines unhooked, wires undone, and i'm starting to forget where this stuff all goes. so i'm not wanting to tear my dash apart but i'm glad you mentioned that because i had no clue that the switch did more than just switch. are you saying that the switch has power going to the pumps by way of the switching valve?

06-13-2009, 10:27 PM	#11
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure the switch has power to it and it sends power to the pumps and to remove it reach up behind the dash and squeeze the top and bottom as you push it out of the dash and then unplug the wires (I hope that makes sents) and I think the valve has power running to it also __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

06-13-2009, 10:29 PM	#12
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure i'll have to check it out again. i think it might just be an a/c duct in the way but i couldn't get to it earlier. thanks

06-13-2009, 10:38 PM	#13
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure I have a haynes manual from 87 that the wire diagrames suck huge donky c0$( for our trucks but I also have one thats a 2008 edition thats a lot better its been revised a little bit for the tbi trucks __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

06-14-2009, 02:37 PM	#14
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure hey does anyone know if i'm supposed to have voltage on all four injector wires? i checked them today and had 11.88 volts on all four wires with key on engine off. i also ran direct ground wire from battery to left side fuel pump, made no difference, i ran a direct hot wire to left side fuel pump, made no difference. will i be able to get the pumps out of the tanks without having to drop the tanks?? i have the bed moved but the acces is still a bit under the cab.

06-14-2009, 06:26 PM	#16
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure ok, good news, left side tank had the split hose problem on the pump. went and bought new hose and decided i better find out if i can use regular fuel line hose or is there a specific hose rated to be submersible? next question is should i just replace the split hose or is there a way for me to test the pump to see if it is still worth keeping?

06-15-2009, 12:28 AM	#17
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure if your already in to the tank and have the pump out I'd spend the money on pumps because it sucks to have a pump give up when you need it __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG



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06-15-2009, 12:29 AM	#18
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure oh, yea! you can get the pump out when the bed is off or just moved back about a foot its tight but it can be done __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

06-15-2009, 07:04 PM	#20
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure success!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! both pumps had a split hose! who would thought? thank you pig rig thank you rfmaster i pray that the lord blesses you for the help you have given. now, any thoughts about the best way to get some kind of wrench on my distributor hold down clamp bolt? i can't get anything on it cause of all the stuff in the way.

06-15-2009, 07:40 PM	#21
cjracing15 Registered User Join Date: Jan 2007 Location: Lexington, TN Posts: 1,427	Re: tbi low fuel pressure They make a distributor wrench that has a 1/2 inch or a 9/16. They sell them at any parts store just ask for a distributor wrench and, if its any kind of parts store at all they should have it. __________________ The fleet 94 Chevy 4x4 reg cab 2018 Traverse (wifes car) 1977 SWB stepside 1949 Chevy truck

06-15-2009, 09:36 PM	#22
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure yes i have one of those. but with the metal fuel lines right there and the egr and some other metal coolant line, i can't even begin to get a distributor wrench to turn the nut, there just isn't any room. i think if i had a swivel socket and ground the socket down short, it would work.

06-16-2009, 01:02 AM	#23
pig rig Registered User Join Date: Feb 2009 Location: washington the state Posts: 730	Re: tbi low fuel pressure yea i remember have'n all the stuff in the way to get at the bolt I rerouted my fuel lines and moved my map sensor when I had my engine out just to make life easy on me i pray that the lord blesses you for the help you have given. well he was having fun at my expense to day because every thing I got a hold of went to hell __________________ my sports car rolls on six wheels only because I'm to fat to get in and out of new corvette http://hubgarage.s3.amazonaws.com/ph...ped_detail.JPG

06-16-2009, 09:40 PM	#24
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure ok, tried to time the motor today, just by ear for now, and within 5 minutes it hit 220 degrees. i had to replace the head gaskets, and am pretty sure i set the valves properly, but i've never done it before, could the valves cause an overheating issue? could it be the timing off a bit? i don't have the fan shroud back on yet but it shouldn't get that hot that fast. any thoughts? and what about a reset for the idle air control valve? i read that if they get disconnected, they need to be reset. what do ya'll think?

06-16-2009, 09:41 PM	#25
motroo Registered User Join Date: Jun 2009 Location: marshall, texas Posts: 16	Re: tbi low fuel pressure ok, tried to time the motor today, just by ear for now, and within 5 minutes it hit 220 degrees. i had to replace the head gaskets, and am pretty sure i set the valves properly, but i've never done it before, could the valves cause an overheating issue? could it be the timing off a bit? i don't have the fan shroud back on yet but it shouldn't get that hot that fast. any thoughts? and what about a reset for the idle air control valve? i read that if they get disconnected, they need to be reset. what do ya'll think?

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