Weird hesitation issue

[deerseed]

I recently purchased a 91 V10 Blazer, 5.7l, 700r4 with 175k miles on the odo. It ran okay for a while, but then started to have a weird bogging/stumble/lagging issue. It will putt around town on partial throttle all day. However, the truck would not accelerate up hills or on the highway at speeds greater than 40 mph. 1st, 2nd, and 3rd gear acceleration are fine, but the truck will not maintain speed up hills with normal application of throttle. I have to give the truck enough throttle to have the trans downshift to start accelerating again.

I have a vacuum gage on the truck. I have a rock solid 20in at idle, 17in with AC on, part throttle response between 15in to 3in depending on amount of throttle. On the hills or at highway speed, the gage will drop low and stay there as I apply throttle. The engine is seeing the vacuum drop but has no response.

Stuff I’ve done/ checked: New plugs, cap, rotor, wires, TPS, ESC, new 02 sensor, new cat, new fuel filter, new injectors, rebuilt TBI, checked for vacuum leaks, compression test, fuel pressure test, spark test, reset timing, no engine codes

Stuff to do: CTS, Unhooking the EGR...Beat my head against the wall

I have no idea where to go from here.

 

[Georgeb]

What is your fuel pressure reading? Can you read fuel pressure when the issue is occurring? Where is the timing set?

 

[deerseed]

Timing is set at 0* with the computer control disconnected. Fuel pressure was reading 11psi when I checked it in the driveway, but I do not have a way to check it while the issue is occurring.

Something else I realize I forgot, it started stuttering (like running over a washboard road) up a hill at ~45-50 mph, the other day , but hasn't done it since.

 

[Jrgunn5150]

Timing is set at 0* with the computer control disconnected. Fuel pressure was reading 11psi when I checked it in the driveway, but I do not have a way to check it while the issue is occurring.

Something else I realize I forgot, it started stuttering (like running over a washboard road) up a hill at ~45-50 mph, the other day , but hasn't done it since.

I've taped gauges to windshields or cowls before to monitor while driving.

 

[Georgeb]

9-12 PSI is good but it may be dropping under load. Try to find a way to monitor it while driving it. It is possible to plug a new filter pretty quickly if there is junk in the tank. It is also possible the pickup sock on the pump in the tank is plugged up. There is a short piece of hose from the pump to the sender in the tank that fails allowing fuel pressure to leak out back into the tank. First and foremost verify you are getting proper pressure when the issue occurs.

 

[Camar068]

Might want to inspect the trans cable to make sure it's held to the bracket by the throttle body.. After that run through the cable adjustment.

 

[deerseed]

First, thank you for the help and replies. I've got to figure out how to Navy rig a fuel gage so I can see it. I also don't want to drop the tank right now, a combination of nearly full and an extra set of hands arriving in a couple weeks. I'm a throw a new pump in at that time anyway. They're cheap.

I tried the EGR disconnection since it was on my to do list anyway. No change, but it won't even throw a code at me... huh?

Turns out the truck wants to surge at idle now. Only a couple hundred rpm with a 2in vac drop. I swear I've triple checked this beast for vac leaks. Maybe spark?

I'll try the TV cable adjust tomorrow if my health lets me.

 

[Cuba]

TV cable will only affect driveability & shifting... nothing at idle.

The fuel gauge can be done but maybe a PITA due to needing to be inline on a TBI (carb too, come to think of it...I'm too used to newer vehicles with schrader valves).

Here's a pic of my setup... but on yours, I'd add another fitting with barbed end in place where I have the gauge so that you can add hose to extend it. This way you can tuck the hose under the windshield wiper with the gauge at the end to keep an eye on it while driving.

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The pressure line is 3/8" & most gauges are 1/8" NPT. Make sure you get one that only reads to 15psi, so it's more accurate for your setup.
This is the one I got. I've ordered 3 so far without issue.
https://www.amazon.com/gp/aw/d/B007VRAFBE/ref=yo_ii_img?ie=UTF8&psc=1

With this inline adapter or similar
https://www.amazon.com/gp/aw/d/B007VR8ZBQ/ref=yo_ii_img?ie=UTF8&psc=1

Obviously if you want to extend it though, you'll need the 2 extra fittings and hose.

 

[deerseed]

New update. After driving my wife's 5 speed Subaru, it got me thinking on a different path. I found that I am fighting two different problems. I disconnected the TCC plug and Eureka! It turns out that my torque converter was locking up way too early and would not unlock with any expediency. The bogging was similar to having the car in the wrong gear for the speed/rpm.

Now to deal with the surging issue (only when warm)...

 

[rt66paul]

Be sure to replace that little piece of hose if you do go into the tank.

 

[Camatruder]

About the stuttering, running over a wasboard, that's exactly what i'm experiencing with my '91.
http://www.gmsquarebody.com/threads/heavy-vibration-when-accellerating-slowly.19322/
In 4th gear teh TCC is always on as long as you don't touch the brake and engine temp is above 149°F.
My idle is good though.