Engine miss, no miss codes

[S10Fan]

Started the truck to move it and suddenly the darn thing runs like a top. No miss, drives great. I've run up 50-60 miles this week with no issues at all. SMH!!

[S10Fan]

Yet another update.................

The truck began bucking and jumping again last week. Starts and idles fine, no fuel smell, but, the fuel pressure is down to 48-50 lbs and drops like a rock at shut down. The fuel pump has less than 500 miles on it, and as was the case before, no codes. I'd gladly buy a new spider/regulator assembly from Rock Auto, Delphi, if I thought for sure it would fix this thing.

[speedygonzales]

What you have to do is eliminate the pump or the FPR or the injectors, to figure out which one needs changing.

If you block off or partially block the return, the pressure should come up. If it does, that indicates the pump is up to task. If it does NOT that indicates it is shot.

I've also seen the tubing in the sending unit cause an issue but that still puts the problem back at the tank.

Now let's get back to the part of the test that shows the pressure comes up when you block the return. If the pressure comes up, then you have a problem with the injector unit. Most likely the FPR. In the Vortec's, the brilliant engineers came up with the idea of putting the entire regulator UNDER the upper plenum. There by not requiring a hose to the vacuum port. It's just wide open to the inside of the intake. So if the diaphragm gets a hole in it, it dumps the fuel right into the intake.

If this is the case, you should check the smell of the oil on the dipstick because it can get contaminated with fuel and get diluted.

[S10Fan]

Originally Posted by speedygonzales

What you have to do is eliminate the pump or the FPR or the injectors, to figure out which one needs changing.

If you block off or partially block the return, the pressure should come up. If it does, that indicates the pump is up to task. If it does NOT that indicates it is shot.

I've also seen the tubing in the sending unit cause an issue but that still puts the problem back at the tank.

Now let's get back to the part of the test that shows the pressure comes up when you block the return. If the pressure comes up, then you have a problem with the injector unit. Most likely the FPR. In the Vortec's, the brilliant engineers came up with the idea of putting the entire regulator UNDER the upper plenum. There by not requiring a hose to the vacuum port. It's just wide open to the inside of the intake. So if the diaphragm gets a hole in it, it dumps the fuel right into the intake.

If this is the case, you should check the smell of the oil on the dipstick because it can get contaminated with fuel and get diluted.

Thanks, I'll check it out this evening.

[S10Fan]

Spent a few minutes with the truck last night.............

Key on, 60 lbs.
Running, 50ish, jumps towards 60 when pressing the pedal.
Key off, now the pressure holds for quite a while.

Planning to round up a longer hose for the gauge this weekend so I can drive around the neighborhood and see what happens.

Clamped the return line at the tank area, the gauge would flutter up and down, just a pound or two.

[1mrtimk]

How is the antifreeze level?
My 99 5.7 ran good until under a load at 55 to 70 mph. The truck would loose power and shudder until I would pull over and let it idle until it evened out.
I was losing a small amount of antifreeze so I did a leak down test on all cylinders. Number 5 and 6 both ended up having small cracks in the heads.
I put on a rebuilt set of heads and all is well.
Good luck!

[S10Fan]

Originally Posted by 1mrtimk

How is the antifreeze level?
My 99 5.7 ran good until under a load at 55 to 70 mph. The truck would loose power and shudder until I would pull over and let it idle until it evened out.
I was losing a small amount of antifreeze so I did a leak down test on all cylinders. Number 5 and 6 both ended up having small cracks in the heads.
I put on a rebuilt set of heads and all is well.
Good luck!

I haven't performed a compression check, but I'm not losing any fluids and the plugs look good, all the same.

[S10Fan]

Yet another update............

Planned on spending the morning checking the truck from tank to throttle body. Fired up the truck last night to move it into a better position to work on, it stumbled and cut off three times in 30 feet.

Pulled the pump (man I like the access hole I cut last time!), the sock, hose, clamps, wiring all looked good. Prior to pulling the pump I disconnected the harness plug that bolts to the cross member just forward of the fuel tank. The bolt holding the plug is very rusty and the ground wire held by the bolt was literally connected by 2 maybe 3 strands of wire to an aftermarket crimp connector. I added (soldered) a foot of wire to the ground wire along with a soldered ring connector. The factory bolt was replaced by a 1/4-20 bolt, star washers, and a nut after grinding a clean spot on the cross member.

I put everything back together and fired it up, runs like a top, drove a few miles with zero issues.

I'm not sure it's "fixed" but I have to believe that poor ground wire wasn't helping things.

[S10Fan]

Nearly two years later all seems to be well.

[speedygonzales]

Thanks so much for sharing and updating us. Who would ever thought there was such an important ground point there of all places.

Now that we are smarter for this information, we can check to be sure we won't be having the same problem.

[Tom]

FYI 50psi while running was the give away, thats way too low. Glad you found the reason for it.

[speedygonzales]

Originally Posted by Tom

FYI 50psi while running was the give away, thats way too low. Glad you found the reason for it.

Where did you see him say he had 50 PSI running?

[Big Daddy Bear]

A few posts and a couple years back:

Originally Posted by S10Fan

Spent a few minutes with the truck last night.............

Key on, 60 lbs.
Running, 50ish, jumps towards 60 when pressing the pedal.
Key off, now the pressure holds for quite a while.

Planning to round up a longer hose for the gauge this weekend so I can drive around the neighborhood and see what happens.

Clamped the return line at the tank area, the gauge would flutter up and down, just a pound or two.