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Tbi fuel pressure?

ConwayMuddy

ConwayMuddy

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Jerkwater wi
91 gmc turdburban, 5.7 tbi, wont start. Pressure tested with a gauge that goes on the filter exit, not between the line and tbi unit. Key on, needle didnt move, cranking same thing. Bled air out of line, got fuel going into a can, key on or cranking needle didnt move. Jumped power to the fuel pump relay, can hear pump running, needle doesnt move, but I can bleed fuel from the line off the gauge. This is the second or third new filter and fuel comes out clear. Tried starting with power jumped to the relay, still nothing on the gauge and still doesnt want to fire. I seem to remember tbi should be about 16psi.

Pump functional but tired?
Filter plugged?
Sock on pickup fucked?

Filter is easy, pump or sock issue both will get replaced.


Edit, tried all of the above testing with the gauge plumbed inline before the filter and still zero pressure on the gauge.
 
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Iirc you need to put the gauge on the return line at the tb.

There is a company out of tx that rebuild and modifies tbi and they sell adjustable regs and gauge port adapters.
 
total newb said:
Iirc you need to put the gauge on the return line at the tb.

There is a company out of tx that rebuild and modifies tbi and they sell adjustable regs and gauge port adapters.
Click to expand...
I went with what the instructions for the tester said to do. The last time I tested a TBI system, it connected the inlet and return lines bypassing the tbi all together
 
Checked the haynes manual, said to test between the inlet line and tbi. ain't no way the fitting is going in there without bending the line. I did jump power to the relay and will get fuel out of the line at the t.b. just dont know at what pressure.
 
Just for fun, I used a noid light on the injector plugs, both pulse. I'm still thinking the pump isnt putting out enough pressure or the possibility the injectors are plugged up.
 
I THINK around 5-7psi EDIT: GOOGLE SAYS 9-13 bb are higher around the 13psi that you said.

I would put (and have before) the gauge after the fuel filter under the truck.
 
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I thought it was 12-15 psi. Is your filter not down on the frame rail? Ive pulled the filter and put the fitting in line in its place to test for pressure on tbi trucks. Id imagine its the same.
 
Oh! Check the o ring on the fitting and end of guage line. Some of those kits are junk. I had one that was a swivel unit... Same thing would bleed fuel off, but couldnt get a reading. Noticed o ring was bad. I found a fuel pressure unit off amazon, took a schrader valve thingy from my original kit and frankensteined it together. Its the same length of the filter housing, so the filter has to be removed. But it works!
 
www.summitracing.com

OTC Tools 518487 OTC Fuel Pressure Tester Adapters | Summit Racing

Free Shipping - OTC Fuel Pressure Tester Adapters with qualifying orders of $109. Shop Fuel Injection Test Adapter Fittings at Summit Racing.
www.summitracing.com www.summitracing.com

Thats what i have, K.I.S.S.

You can see links on summit for the actron swivel unit that goes on up near line inlet at tbi. If its like mine...it was junk after one use from the oring
 
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Snoop dogg said:
www.summitracing.com

OTC Tools 518487 OTC Fuel Pressure Tester Adapters | Summit Racing

Free Shipping - OTC Fuel Pressure Tester Adapters with qualifying orders of $109. Shop Fuel Injection Test Adapter Fittings at Summit Racing.
www.summitracing.com www.summitracing.com

Thats what i have, K.I.S.S.

You can see links on summit for the actron swivel unit that goes on up near line inlet at tbi. If its like mine...it was junk after one use from the oring
Click to expand...
Yes the swivel fitting in the link is what was in the kit. I didnt notice any damage, didnt look like the kit had ever been used to be honest. I dont remember what brand it was, but it came from oreilly. Filter is on the frame rail.
 
TreeClimber said:
squirt some ether down that throttle body and see if it runs.
Click to expand...
Cosby spray will get it to fire over. Pouring some gas in will get it to run briefly as well, about long enough to get around the door and have it die before you can see if any fuel is coming from the injectors
 
ConwayMuddy said:
Yes the swivel fitting in the link is what was in the kit. I didnt notice any damage, didnt look like the kit had ever been used to be honest. I dont remember what brand it was, but it came from oreilly. Filter is on the frame rail.
Click to expand...
Kit was brand new for me as well : (. I think i got one use /reading out of it before reg 87 octane damaged the o ring. Just sayin this exact thing happened to me, could be coincidence but i think its your swivel fitting.
 
In trying to check things off the list, I know the fuel pump relay is connected to an oil pressure switch. If I jump power to the fuel pump relay, would that negate any issues with oil pressure switch?
 
Rebuilt the tbi today, did not replace injectors. Primed the system, no leaks. Tried starting, no go. If I give it some cosby spray it will fire up and die. If I start it like a pulling tractor it will stay running as long as I fog it with either.
I did notice while fogging it, I am getting fuel from the injectors, basically drops and dribbles.
 
Replace the fuel pressure tool!!!

Ok...just having fun with ya. Was the driven on the regular? Those injectors can get sticky but we have a few tbi trucks left in the fleet that barely get driven, and they still fire up. When they dont...its usually the cap and rotor corroded (not your case), or the fuel pump.

But ya know what would really pin down your issue, and doesnt cost that much....a good fuel pressure test kit:lmao:
 
Snoop dogg said:
Replace the fuel pressure tool!!!

Ok...just having fun with ya. Was the driven on the regular? Those injectors can get sticky but we have a few tbi trucks left in the fleet that barely get driven, and they still fire up. When they dont...its usually the cap and rotor corroded (not your case), or the fuel pump.

But ya know what would really pin down your issue, and doesnt cost that much....a good fuel pressure test kit:lmao:
Click to expand...
Truck only really gets driven from September to maybe December, fired up occasionally outside of that. Started having issues last October. Would start and die, or run for a while and die, then struggle to restart. Replaced the ignition control module which seemed to work right up until it wouldnt start at all. It's on the list of shit to check again if I can find a socket to get the cap off.

I only went through the tbi because I know the injector screens can get gummed up. Truck sat for a few years before i got it, bunch of old gas, hence the reason for going through a filter or 2 a year. I've only ran ethanol free premium in it.

Dont worry, i picked up a new pump today as well :flipoff2:
 
maybe the little section of rubber hose between the pump and the sending unit's steel lines got all blowed up

would cause flow but no pressure

give the FP gauge a blowjob with the air hose to see if the needle moves
 
[486] said:
maybe the little section of rubber hose between the pump and the sending unit's steel lines got all blowed up

would cause flow but no pressure

give the FP gauge a blowjob with the air hose to see if the needle moves
Click to expand...
tester got returned already. Guess I can check and see if napa has one to borrow. Or just buy one... with a random plug and wire I get spark. Checked for codes jumping the pins on the obd plug, nothing flashed. Cleaned grounds, 2 years ago the door button for the dome light caused a no start, unplugged and taped the wire and was good until last year. I did notice with the key on, the alternator buzzes similarly to a fuel pump running.
 
Checked advanced, they dont loan pressure testers. Napa has the same kit as oreilly, but it was already out, so I couldn't get it to compare. Neither had a kit for sale that would work for me.

Tested the injectors with a 9 volt battery, both go clicky clicky.

Checked the coolant temp sensor with the multimeter. According to the book, its showing resistance for somewhere north of 90 degrees, coolant was reading about 76 degrees according to my kitchen thermometer.
 
ConwayMuddy said:
Checked the coolant temp sensor with the multimeter. According to the book, its showing resistance for somewhere north of 90 degrees, coolant was reading about 76 degrees according to my kitchen thermometer.
Click to expand...
hey neat
swap that shit out
 
[486] said:
hey neat
swap that shit out
Click to expand...
This is one I pulled from another motor to replace the bad one that was in the truck. Guess I may have to try a new one. Hasnt caused the check engine light to come on, or register a code. Then again, doesnt run either
 
how far north of 90... well you didn't say 100 or 200 so...
I suppose that's fairly close and really should run nonetheless
 
Rechecked the coolant temp sensor, was reading closer to 70 and coolant temp was around 90. Swapped in a new one, still no start. Started dropping the tank to do the fuel pump. Found whatever vent hose that runs to the engine compartment was pinched between the tank and a crossmember, looks like it's been that way forever. Need everything to dry up so I can disconnect the lines and drag the tank out.
 
This way or other way?
20210829_161625.jpg


Edit, only fits this way :homer:
 
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[486] said:
maybe the little section of rubber hose between the pump and the sending unit's steel lines got all blowed up
Click to expand...
I think you got it right with this one. Hose had a hole and a metric assload of cracks in it. Was ridiculously soft as well. Need to finish installing the tank tomorrow hopefully.
20210829_151513.jpg
 
shitty
I always replace that shit with the hard plastic, either scavenged from old black framerail fuel lines, or with the milky white polypropylene stuff they sell at every hardware store
don't need to clamp it if its short like that, the press fit over the barbs and the bracket holding the pump in place is enough

fun fact, you leave that sit in the sun a few weeks and it'll go rock hard
drop it in fuel for a day and it'll be spongey again
learned that trick after spending a day heating and stretching an old dried filler neck hose into place, then the next time I looked at it after having filled the tank, the fuel vapor had softened it to where it was easily workable
 
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