'93 K3500, 454 TBI, poor drivability

[someotherguy]

I looked all over Amazon for a photo of that style TBI fuel pressure adapter, and couldn't find one. Too lazy to take a picture of the one I own.

For the record, that adapter is the style that goes between the fuel hose and the throttle body. It's not the kind that goes in place of the fuel filter. Much better, in my opinion, since it measures pressure AFTER the filter, so if the filter is plugged...it'll show up on the pressure gauge.

Some folks have complained about that style of adapter leaking. Must have had damaged O-rings inside.

It's been years since I tested pressure down at the filter area vs. behind the TBI, but if I recall correctly, that same fitting can be used before/after the filter, if you choose to do so. Seemed like that's where I had it on my '94 when it was intermittently crapping out, and I carried the gauge around with me in the door panel pocket for a week or two until I caught it. A little tough climbing under a dropped truck to hook the gauge up which is why after I replaced the pump, I moved the fitting to behind the TBI.

Richard

 

[Idaho83815]

It's been years since I tested pressure down at the filter area vs. behind the TBI, but if I recall correctly, that same fitting can be used before/after the filter, if you choose to do so. Seemed like that's where I had it on my '94 when it was intermittently crapping out, and I carried the gauge around with me in the door panel pocket for a week or two until I caught it. A little tough climbing under a dropped truck to hook the gauge up which is why after I replaced the pump, I moved the fitting to behind the TBI.

Richard

Thanks Richard. I checked it at the pump side of filter. Good Wix filter installed last week.
The kit is a loaner so I can’t leave it on, but it always runs the same lately… like crap at start and shudder at cruise.
It also leaked enough fuel that I would not leave it on, especially if at manifold with the hot exhaust manifolds.
I am going to check voltages and ground as suggested earlier. I may just lift the bed and if so replace the $60 pump and clean up wiring at same time while 3/4 of the work is done.

 

[Idaho83815]

Thanks Richard. I checked it at the pump side of filter. Good Wix filter installed last week.
The kit is a loaner so I can’t leave it on, but it always runs the same lately… like crap at start and shudder at cruise.
It also leaked enough fuel that I would not leave it on, especially if at manifold with the hot exhaust manifolds.
I am going to check voltages and ground as suggested earlier. I may just lift the bed and if so replace the $60 pump and clean up wiring at same time while 3/4 of the work is done.

Also will get to have it on a scanner a week from Friday

 

[Idaho83815]

Hello all,
I removed the bed today to get at the pump and wiring. The pump assembly has a lot of surface rust and looks original...wiring looks old etc. I want to go with a new pump assembly to get the new piping, strainer, wire harness etc... I also want to upgrade to the 96 vintage pump for added head room instead of being marginal in best of times with the stock tbi pump pressures. I will be getting a Delphi unit. Will the 1996 assembly fit in the 1993, just as the individual pump will fit? All wiring, piping etc?

 

[Idaho83815]

Verify fuel pump voltage on the supply wire, as close to the pump as practical. Check for voltage on the ground wire, as close to the pump as practical.

BOTH tests done with the pump RUNNING. Preferably with the engine running, and alternator charging.

Hey Schurkey, I have 13.6 volts at pump with engine running and battery a bit low in volts, and .003 volts on ground using a jumper wire (10AWG) between neg of battery and at ground of pump.
New pump assembly arrives today.

 

[Schurkey]

Those figures are exceptionally good.

 

[Idaho83815]

Those figures are exceptionally good.

Well the new pump went in. I opted for the 96 assembly. Only small difference was the vent tube location.
I cleaned up the pump ground as well as the one in The rear for the tail light harness.
Started right up, but is was still somewhat warm from my previous testing.
I will have to wait till morning for the cold start test.
I will also need to drop the bed back on and go for a drive to see if my shudder/grumble/pop at cruise is still there.
1 week from access to a scan tool and experienced user of said device.

 

[Idaho83815]

Well the fuel pump did not help the cold idle and she still has the shudder/burble/pop out the exhaust at steady cruise.
I also tested the TPS and it seems to test OK (0.59V with key on and it goes up in volts smoothly as I twist throttle)
Applied vacuum to EGR with hand pump and it holds a vacuum. Unsure about the egr control device mounted on the intake manifold.
I think I am done until Friday when I have an appointment to get it on a Scanner.

 

[Sabinoerc]

Well the fuel pump did not help the cold idle and she still has the shudder/burble/pop out the exhaust at steady cruise.
I also tested the TPS and it seems to test OK (0.59V with key on and it goes up in volts smoothly as I twist throttle)
Applied vacuum to EGR with hand pump and it holds a vacuum. Unsure about the egr control device mounted on the intake manifold.
I think I am done until Friday when I have an appointment to get it on a Scanner.

Thanks for update, bummer the new pump didn’t resolve the problem, but good to have that verified.

One thing to check when you get the scanner is whether the rough running goes away when going into closed loop. It might help narrow down the problem(s). Eg. If rough only in open loop it’s not likely anything to do with O2 feedback.

You can tell if it’s in open loop by shorting two pins on ALDL and watching cel flash. There was a thread on this a while back. I’ll see if I can find it.

That said, if you are close to getting the scanner I’d just wait for that info. There are people here who know this stuff inside out and once you have the scanner info someone can probably help point you in right direction.

Edit: this is the thread https://www.gmt400.com/threads/engine-idles-unevenly-and-almost-stalls-when-cold.65629/

@Road Trip and @Schurkey explain details on how the open loop/closed loop works which might be worth a read if your new to working on these engines.

 

[Idaho83815]

Thanks for update, bummer the new pump didn’t resolve the problem, but good to have that verified.

One thing to check when you get the scanner is whether the rough running goes away when going into closed loop. It might help narrow down the problem(s). Eg. If rough only in open loop it’s not likely anything to do with O2 feedback.

You can tell if it’s in open loop by shorting two pins on ALDL and watching cel flash. There was a thread on this a while back. I’ll see if I can find it.

That said, if you are close to getting the scanner I’d just wait for that info. There are people here who know this stuff inside out and once you have the scanner info someone can probably help point you in right direction.

Edit: this is the thread https://www.gmt400.com/threads/engine-idles-unevenly-and-almost-stalls-when-cold.65629/

@Road Trip and @Schurkey explain details on how the open loop/closed loop works which might be worth a read if your new to working on these engines.

Sabinoerc, Idles bad when cold, but it does smooth out after 1-2 minutes and idles pretty good. I am assuming after transitioning to closed loop once the O2 sensor heats up.
It still has the stumble burble pop at steady cruise. ???
Once warm it starts and idles fine but again the cruising issue is still there.
Friday is getting close so I found a good book, have some honey-do list to accomplish and will wait for the scan tool to point me in a direction.
Thanks.