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#1 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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.
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#2 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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
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#3 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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.
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#4 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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Re: tbi low fuel pressure
anybody got any thoughts or ideas?? or info??
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#5 |
Registered User
Join Date: Sep 2003
Location: The Netherlands
Posts: 994
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Re: tbi low fuel pressure
check the oil pressure switch next to the distributor.
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#6 |
Registered User
Join Date: Oct 2003
Location: OC CA
Posts: 1,374
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Re: tbi low fuel pressure
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
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"The Beast" 1975 Chevrolet C20 longbed 350/700R4! with 3inch body lift Dual Flowmasters Super 40's! TBI retrofit completed (2007-07-29) ![]() New 383CID (+030) 08-304-8 9.5:1CR x36,005 (2012-12-17) |
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#7 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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.
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#8 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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 |
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#9 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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?
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#10 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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?
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#11 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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
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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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#12 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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
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#13 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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
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#14 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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. |
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#15 | |
Registered User
Join Date: Oct 2003
Location: OC CA
Posts: 1,374
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Re: tbi low fuel pressure
Quote:
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
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"The Beast" 1975 Chevrolet C20 longbed 350/700R4! with 3inch body lift Dual Flowmasters Super 40's! TBI retrofit completed (2007-07-29) ![]() New 383CID (+030) 08-304-8 9.5:1CR x36,005 (2012-12-17) |
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#16 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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?
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#17 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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
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#18 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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 |
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#19 | |
Registered User
Join Date: Oct 2003
Location: OC CA
Posts: 1,374
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Re: tbi low fuel pressure
Quote:
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
__________________
"The Beast" 1975 Chevrolet C20 longbed 350/700R4! with 3inch body lift Dual Flowmasters Super 40's! TBI retrofit completed (2007-07-29) ![]() New 383CID (+030) 08-304-8 9.5:1CR x36,005 (2012-12-17) |
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#20 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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. |
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#21 |
Registered User
Join Date: Jan 2007
Location: Lexington, TN
Posts: 1,427
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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.
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#22 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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.
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#23 |
Registered User
Join Date: Feb 2009
Location: washington the state
Posts: 730
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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 |
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#24 |
Registered User
Join Date: Jun 2009
Location: marshall, texas
Posts: 16
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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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#25 |
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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