1994 Chevy 1500 5.7 TBI Running Issues

[Madcrafter52]

Update
Finally got a chance to do some work on the truck. New plugs, wires, cap, rotor and coil are installed. seems like maybe it runs a little smoother but not too much of a difference, oh well at least i can cross it off the list. I got a fuel pressure tester and adapter and my fuel pressure is low, hardly even registered on the gauge with the key on and when running was probably about 8psi. I can also hear the fuel pump whining quite loudly. So I have a new fuel pump assembly on the way. I sure hope its the answer.

 

[H2814D]

I had the problem you are describing in my 1994 Full Size Blazer with the same 5.7 TBI 350. The fuel pump in the fuel tank had a deteriorating rubber hose between the pump and the fuel supply line. It was part of the pump assembly inside the fuel tank. It was worse when the fuel level was low, because the pump would (I assume because I wasn't in the tank to watch it) allow fuel to spray out of the rubber hose instead of delivering the full fuel pressure to the TBI, similar to what you have discovered with a fuel pressure test. When the fuel level was above the rubber hose, it didn't do it as bad, because of the pressure of the fuel level on the hose. Replacing the fuel pump assembly inside the fuel tank solved the problem, but I could have gotten away with just replacing the rubber hose connection, because the fuel pump was still working fine. Let us know what happens.

 

[Madcrafter52]

Haven't updated in awhile but man alive this truck has been fighting me every step of the way. Dropped the fuel tank and man was it a mess. Nasty grease all over everything, the fuel pump wasn't even locked in properly and everything was rusted despite all the grease. Snapped the strap bolt that goes into the frame. Twisted off one of the fuel lines on the assembly. But finally got the tank out. Pulled out the old rusty assembly and go to put the new one in. Low and behold it doesn't fit due to a manufacturing defect (Sure love 2023 QC.) So due to the shape of everything I ended up getting a whole new tank and fuel pump assembly. Went to take off the strap that was around the old tank to transfer to the new one and that bolt snapped off. Man I sure love rust. So now I have a new tank, fuel pump assembly, mounting hardware, and am waiting on new straps. I sure hope this is all worth it in the end.

 

[Komet]

Yeah I dunno what it is about the airflow down there but my pump was buried in grease too.

Broken parts are just weakness leaving your truck. A nice tight clean fuel system is the core of a successful running machine, you're on the right track. Sometimes that track is just 3x longer than you wanted it to be.

 

[Schurkey]

Yeah I dunno what it is about the airflow down there but my pump was buried in grease too.

Some guys deliberately fill the fuel pump lock-ring area with grease, to prevent water build-up causing rust. The grease doesn't accumulate from vehicle use.

Broken parts are just weakness leaving your truck.

Clever.

 

[dave s]

When I dropped my tank on the 94 that same grease/paste type stuff filled the entire lock ring area. Everything under it was like brand new. They should have covered the whole frame in that stuff for people in the rust belt! Lol!

 

[Madcrafter52]

Finally got everything put back together and it seems to be running better. Still have a couple things to do before the road test but so far so good. I was poking around under the truck trying to find the source of my trans leak and noticed a few things.

First and most important is that the O2 sensor was just completely unplugged, so I obviously plugged that back in.

Then I remembered that the torque converter cover is missing. Anyone know where to find one? I need the six bolt obviously, thinking of just trying the local junkyard.

I was also looking for the trans ID code and there just seemed to be nothing. Its supposed to be on the passenger side above the pan right?

Lastly the trans leak seems to be coming from the dipstick area, is that a common spot? Any suggestions?

Hopefully next post is a victory post. Guess we will just have to wait and see.

 

[Schurkey]

First and most important is that the O2 sensor was just completely unplugged, so I obviously plugged that back in.

How old is it? Maybe there was a reason it was unplugged.

Then I remembered that the torque converter cover is missing. Anyone know where to find one? I need the six bolt obviously, thinking of just trying the local junkyard.

4WD? Aluminum casting, with bosses for the bolts that hold the two strut rods coming from the motor mounts?

I was also looking for the trans ID code and there just seemed to be nothing. Its supposed to be on the passenger side above the pan right?

The way I remember it, it's on the side of the pan rail, small stampings. Need to clean the aluminum before you'll see it.

Lastly the trans leak seems to be coming from the dipstick area, is that a common spot? Any suggestions?

It was common on dipstick tubes with a rolled groove for the o-ring seal. The tube would crack at the rolled groove.

Later dipstick tubes use a "Top Hat" seal that did away with the rolled groove. Much more reliable. I don't know when they switched from an O-ring seal to the Top Hat seal.

Is the dipstick tube secured to one of the bellhousing bolts? If it's just flopping around, no seal will keep the fluid in.

 

[Madcrafter52]

Update: It drives! Sorta...

Had to get a replacement dipstick tube because the one in the truck was completely wrong. After that and the new seal were installed I filled it up with fluid and took it for a drive, thankfully the transmission seems to shift fine after being run low on fluid for so long.

The idle is smooth and it rev's smoothly but has an extreme lack of power, even at like 80% throttle it struggles to continue accelerating. However there is no more hesitation or misfiring so it seems like we are going in the right direction.

Just an list of everything done so far: Plugs, Wires, Cap, Rotor, Coil, Fuel Pump, Fuel Tank, and Fuel Filter.

This feels like an AFR issue to me but correct me if I'm wrong. I found that the PCV was a major vacuum leak so I disconnected and capped it off, that seemed to help. I'm leaning towards an o2 sensor as it seems worse once it goes into closed loop, and it was unplugged when I found it. I've also heard that a bad ICM can cause lack of power? The truck has an aftermarket exhaust with no cat so its not an exhaust restriction. There is still a loud sucking sound from the TBI while accelerating but apparently that's normal with an open element (K&N) air filter?

Does anyone have a link to a diagnostic cable? I might just give in and buy one.

 

[Madcrafter52]

4WD? Aluminum casting, with bosses for the bolts that hold the two strut rods coming from the motor mounts?

Yes the 4wd Aluminum casting one.

The way I remember it, it's on the side of the pan rail, small stampings. Need to clean the aluminum before you'll see it.

I found the stampings. Nothing interesting, just a truck 4L60E.