Hesitation completey at a loss

[Jksconny]

So I just signed up for this site after researching it for the last couple years. I have a 91 k2500 bone stock tbi other than ultimate tbi bench top mod, 3” free flow cat and muffler. The problem is hesitation under light load with throttle held in same spot then it catches up and takes off again, and so on. No codes and I have literally replaced every sensor and and engine Managmemt items with “nos” parts. Brand new “nos” ignition with pertronix flame thrower coil and D.U.I plug wires with stock delco plugs. I have 160 psi in all cylinders 20 hg vacum at idle fuel pressure solid at 14psi and does not change when hesitation occurs. Brand new rebuilt 700r4 with corvette servos and beefed up a little. I just bought another truck with the exact same motor that runs excellent so I had somthing to compare with.swapped tbi from that truck to mine, still same hesitation issue. I have looked and searched and searched again to figure this one out. Bought the factory service manual for it as well. I am not very computer literate and that is why I haven’t done any data logging with tuner pro or win aldl, I do have the brick though to make sure sensors are within spec. I look forward to any help and direction, i am BEYOND frustrated.

 

[Drunkcanuk]

Welcome from Alberta Canada.
Sorry to hear about the issue with your truck, they can be super frustrating to diagnose for sure.
A few things to throw at ya.
Have you checked the transmission fluid level? Cold and hot. Maybe it's low and is building up pressure then "catching up".
Has the TV cable been readjusted at all? They can be very finikey and lead to drivability problems like you describe.
When was the fuel filter changed last?
How about the fuel pump itself? Ask because the pump because the little rubber line in there can get eaten up by the ethanol.
How about the battery condition? Connections and grounds....ALL the grounds.
I'm sure others will be by to chime in.

 

[SAATR]

So I just signed up for this site after researching it for the last couple years. I have a 91 k2500 bone stock tbi other than ultimate tbi bench top mod, 3” free flow cat and muffler. The problem is hesitation under light load with throttle held in same spot then it catches up and takes off again, and so on. No codes and I have literally replaced every sensor and and engine Managmemt items with “nos” parts. Brand new “nos” ignition with pertronix flame thrower coil and D.U.I plug wires with stock delco plugs. I have 160 psi in all cylinders 20 hg vacum at idle fuel pressure solid at 14psi and does not change when hesitation occurs. Brand new rebuilt 700r4 with corvette servos and beefed up a little. I just bought another truck with the exact same motor that runs excellent so I had somthing to compare with.swapped tbi from that truck to mine, still same hesitation issue. I have looked and searched and searched again to figure this one out. Bought the factory service manual for it as well. I am not very computer literate and that is why I haven’t done any data logging with tuner pro or win aldl, I do have the brick though to make sure sensors are within spec. I look forward to any help and direction, i am BEYOND frustrated.

Lots of possibilities. Potentially an EGR valve issue. If I remember correctly, the vacuum port to the EGR valve is supposed to have a very specific, very small orifice to help open it gradually. If yours doesn't have it, it may cause strange tip in or part throttle issues. I am by no means 100 percent certain, so let's see if we can conjure the right man for the job...

@L31MaxExpress

 

[Jksconny]

Lots of possibilities. Potentially an EGR valve issue. If I remember correctly, the vacuum port to the EGR valve is supposed to have a very specific, very small orifice to help open it gradually. If yours doesn't have it, it may cause strange tip in or part throttle issues. I am by no means 100 percent certain, so let's see if we can conjure the right man for the job...

@L31MaxExpress

That was the last ‘nos’ part I replaced, like a fool the first one I had was a port egr, so it has the new old stock negative one on it now. It works with vacum gauge dosent stick and reacts well.And to be more thorough I have replaced all the grounds and cleaned them as well. Also swapped ecm from the good running truck, still no dice. I even flipped over the new old stock map sensor and pulled vac from the intake as well as tb, found that in the old fast track trouble shooter users manual, thought I was on to something there but nope. One thing I kno is once I figure out how to navigate this site I do have lots of helpful info to share.

 

[Jksconny]

That was the last ‘nos’ part I replaced, like a fool the first one I had was a port egr, so it has the new old stock negative one on it now. It works with vacum gauge dosent stick and reacts well.And to be more thorough I have replaced all the grounds and cleaned them as well. Also swapped ecm from the good running truck, still no dice. I even flipped over the new old stock map sensor and pulled vac from the intake as well as tb, found that in the old fast track trouble shooter users manual, thought I was on to something there but nope. One thing I kno is once I figure out how to navigate this site I do have lots of helpful info to share.

Oh I also forgot to mention I did put the flex-a-light truck and suv electric fan setup on it instead of clutch fan. Also engine is timed at 0 spec. There’s so much I have done and gone threw over and over again and again.

 

[Keeper]

Is this a 350 or a 454?

 

[SAATR]

See if any of this is helpful:

Thread 'BIZARRE end to the hunting/stumbling idle issue on my ‘95.' https://www.gmt400.com/threads/bizarre-end-to-the-hunting-stumbling-idle-issue-on-my-‘95.62133/

 

[Jksconny]

Welcome from Alberta Canada.
Sorry to hear about the issue with your truck, they can be super frustrating to diagnose for sure.
A few things to throw at ya.
Have you checked the transmission fluid level? Cold and hot. Maybe it's low and is building up pressure then "catching up".
Has the TV cable been readjusted at all? They can be very finikey and lead to drivability problems like you describe.
When was the fuel filter changed last?
How about the fuel pump itself? Ask because the pump because the little rubber line in there can get eaten up by the ethanol.
How about the battery condition? Connections and grounds....ALL the grounds.
I'm sure others will be by to chime in.

Tv cable set perfect, the guy that built the tranny prefers to take them in and out himself instead of deliverd for such reasons like tv cable and such. Fuel filter just replaced last week no change. Fuel pump is a 1996 vortec 155 lph and put in 2 years ago along with new tank, also my injectors have been cleaned and checked by a professional. All the grounds have been cleaned the ones from engine to cab have been beefed up. I have not checked transmission fluid, I never seen it loose any or slip is main reason. I will check tomorrow and report back. Now that you mentioned it it does act like a tranny that’s low. But also feels strong. I can override the hesitation by putting the hammer down shell snap out and come clean. Also when you hold foot steady when it’s hesitating I’m waiting for it just to fall right down on her face but when she gets a hair from stalling out completely she’ll buck up and hit Like 8 day clock…. Then fall again. Beyond so far beyond frustration. Worse part about it is there suppose to be a simple platform.

 

[Jksconny]

Is this a 350 or a 454?

350, so clean you can eat off it.

 

[Drunkcanuk]

Tv cable set perfect, the guy that built the tranny prefers to take them in and out himself instead of deliverd for such reasons like tv cable and such. Fuel filter just replaced last week no change. Fuel pump is a 1996 vortec 155 lph and put in 2 years ago along with new tank, also my injectors have been cleaned and checked by a professional. All the grounds have been cleaned the ones from engine to cab have been beefed up. I have not checked transmission fluid, I never seen it loose any or slip is main reason. I will check tomorrow and report back. Now that you mentioned it it does act like a tranny that’s low. But also feels strong. I can override the hesitation by putting the hammer down shell snap out and come clean. Also when you hold foot steady when it’s hesitating I’m waiting for it just to fall right down on her face but when she gets a hair from stalling out completely she’ll buck up and hit Like 8 day clock…. Then fall again. Beyond so far beyond frustration. Worse part about it is there suppose to be a simple platform.

I ain't no mechanical surgeon, but to me, this sounds like a fuel delivery issue.
Maybe take the fuel lines off the back of the throttle body, take the fuel filter off and disconnect the return line to the tank and shoot some compressed air through the lines. Could be some sort of blockage somewhere in the system.
How does the spray pattern from the injectors look? At idle and revving it up.
Oh....does it only do this when driving, or even in park/neutral?