Fuel Pressure Problems

[bigj-dog]

'97 C/K 1500 5.7L

My friend's truck turns over longer than normal before starting, hot or cold, has been doing this for awhile, now it's started to idle rough and loping, so he finally brought it to me to fix. First off, the intake leaks, and I was planning on removing and resealing it anyway, I figured when I got it off I'd see that the regulator was leaking gas. To my dismay, it wasn't. So, I rigged up a vacuum pump to the regulator and jumped the fuel pump to check fuel pressure. Here's the stats: 53 psi with pump running and everything hooked up as normal (I didn't try to turn it over as I had a bunch of stuff unhooked and lying everywhere), with no vacuum to the regulator it jumped to 62, and with the return line pinched off it went to 75. Lastly, as soon as the pump shuts off the pressure drops to zero. So, what I'm wondering is if the pump's check valve or whatever holds the pressure in the line being bad would cause the pump to only have 53 psi when everything is hooked up as it should be. I am planning on replacing the pump after I'm done with the intake job, but I'm wondering if I should replace the regulator too, even though it seems to work. I don't want to take it back apart 15 minutes after I put it together. Sorry the post is so long, but I wanted to add as much detail as possible. Also, fuel filter is new. Thanks for reading.

[randy78]

check fuel pressure

weak dying pump will cause difficulty in starting hot or cold

need high pressure in order to start

less than this to just run


i vote for fuel pump until it is ruled out

common issue here


hard starting is the first and most common symptom and trouble with a dying pump

[eeservicecenter]

When fuel line in pinched off, pressure should rise to 100psi with no problem.

[J-Ri]

Originally Posted by bigj-dog

...as soon as the pump shuts off the pressure drops to zero. So, what I'm wondering is if the pump's check valve or whatever holds the pressure in the line being bad would cause the pump to only have 53 psi when everything is hooked up as it should be.

I don't see how the check ball could cause reduced pressure with the engine off. It could possibly cause low pressure with a fuel demand, but probably not with no fuel being used. I would guess the regulator is bad (or your guage). It should keep the pressure in range until the fuel pump can't put out the required pressure. Since the pressure rises to 75 PSI with the return pinched off, the pump is ok. Since the pressure bleeds off, and the check ball is part of the pump, you need one anyway if your friend cares about the long crank. Check the fuel pressure again with the engine running to determine if the fuel pressure is droping with increased fuel demand.

[j cAT]

Originally Posted by bigj-dog

'97 C/K 1500 5.7L

My friend's truck turns over longer than normal before starting, hot or cold, has been doing this for awhile, now it's started to idle rough and loping, so he finally brought it to me to fix. First off, the intake leaks, and I was planning on removing and resealing it anyway, I figured when I got it off I'd see that the regulator was leaking gas. To my dismay, it wasn't. So, I rigged up a vacuum pump to the regulator and jumped the fuel pump to check fuel pressure. Here's the stats: 53 psi with pump running and everything hooked up as normal (I didn't try to turn it over as I had a bunch of stuff unhooked and lying everywhere), with no vacuum to the regulator it jumped to 62, and with the return line pinched off it went to 75. Lastly, as soon as the pump shuts off the pressure drops to zero. So, what I'm wondering is if the pump's check valve or whatever holds the pressure in the line being bad would cause the pump to only have 53 psi when everything is hooked up as it should be. I am planning on replacing the pump after I'm done with the intake job, but I'm wondering if I should replace the regulator too, even though it seems to work. I don't want to take it back apart 15 minutes after I put it together. Sorry the post is so long, but I wanted to add as much detail as possible. Also, fuel filter is new. Thanks for reading.

if at fuel pump shut down fuel pressure drops to zero i'm thinking fuel pump check valve, bad injector leaking, fuel line leak.....for starters......


as i'm sure you know after fuel pump shuts off for 5min , pressure should not drop more than 3psi.......

as this vehicle has many problems,,, this is going to be a PITA to get running properly......

[bigj-dog]

Finally got some time to work on the truck. Since the only code was a misfire in Cylinder 3, I decided to check compression before I started to reassemble the engine, 30lbs in number 3. Ended up taking the heads off and having a valve job done to fix the leaking exhaust valve. Put in a new regulator and bought a fuel pump too, hopefully have it back together soon, will post as soon as it runs again. What's anyone's opinion on the 'updated injector pod' that I've heard rumors about? Does it even exist?

[bigj-dog]

$1500 later, it's all back together and runs fine. New fuel pump ended the long start time, pressure is up to specs, valve job and tune up fixed lope, new intake gaskets and water pump and a frost plug solved the antifreeze leaks and an alternator cured the whine. Thanks for the advice, hopefully this truck won't come back to my shop, except for a little preventative maintenance.

[j cAT]

Originally Posted by bigj-dog

$1500 later, it's all back together and runs fine. New fuel pump ended the long start time, pressure is up to specs, valve job and tune up fixed lope, new intake gaskets and water pump and a frost plug solved the antifreeze leaks and an alternator cured the whine. Thanks for the advice, hopefully this truck won't come back to my shop, except for a little preventative maintenance.

thats a lot of work/expense for a vehicle that old.. ...

why do you think the one valve went bad ? intake leak ?

[bigj-dog]

The truck is in nice shape, and in Minnesota, if your truck is rust free, you should fix it, but yeah, it's a lot of money. I would guess that the valve problem was caused by a combination of the hard starting (which made it run like crap when it did finally start for a bit) and lack of maintenance. The truck in general just hadn't run real good for a while. Sure seems to work good now though. Hopefully it'll continue to.