Help. Chasing a hesitation issue

[Matt Conner]

Don’t know if this is the right place for this but... 95 k1500 5.7 5 speed. So, I’m chasing this hesitation/ falling flat on its face. Anyways, I’m about 4th gear 45-50mph or so, taching about 1700-2000 rpm the truck will just fall flat on its face, no missing or stalling just bogs down super hard, and when I’m running up about 2300-2700 rpm in second or third it hesitates and misses Untill I push in the clutch and blip the throttle. I’ll let back out on the clutch and it’ll go back to Normal no issue after. It does this on light acceleration. If I do a heavy acceleration it will not do it. I checked for vacuum leaks, inspected plugs and plug wires to make sure the wires haven’t been burnt by the headers(these are brand new plug wires) , pullled the distributior cap and inspected the cap and rotor, both were fine, I should note the pickup coil is kinda rusty. Cleaned the air filter and added some sea foam to the tank to see if that would help any. I’ll take any advice I can get, thanks.

 

[PlayingWithTBI]

Do you have any way of data logging? You should be able to trap what's different when it happens. See what you O2 sensor is doing, maybe wild spikes in timing, TPS, CTS, IAC, etc.

Could be your EGR is wigging out. When you are cruising, it'll open up until your TPS shows somewhere around >60% throttle. Maybe when you blip the throttle, your PCM will close the EGR and then, after a certain amount of time (in the program), it'll open the valve back up again.

 

[Bigboom997]

I had a similar issue with my auto k2500 hesitating. Take off your spark plug wires and test them with a multimeter. I had a bad wire and since I changed it everything works good now. And don't lose the order of your spark plug wires. I took one off at a time so I wouldn't lose track of what order they're in.

https://www.gmt400.com/threads/engine-jumping.50179/page-3#post-1114889

 

[Matt Conner]

Do you have any way of data logging? You should be able to trap what's different when it happens. See what you O2 sensor is doing, maybe wild spikes in timing, TPS, CTS, IAC, etc.

Could be your EGR is wigging out. When you are cruising, it'll open up until your TPS shows somewhere around >60% throttle. Maybe when you blip the throttle, your PCM will close the EGR and then, after a certain amount of time (in the program), it'll open the valve back up again.

I wish I had a way of data logging, my Solus pro had an obd1 connected but it got lost somewhere. Could it hurt that I have no cats? The o2 is installed but there are no cats on the truck. It has a true dualed exhaust system, along with headers


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[Matt Conner]

I had a similar issue with my auto k2500 hesitating. Take off your spark plug wires and test them with a multimeter. I had a bad wire and since I changed it everything works good now. And don't lose the order of your spark plug wires. I took one off at a time so I wouldn't lose track of what order they're in.

https://www.gmt400.com/threads/engine-jumping.50179/page-3#post-1114889

I have brand new plug wires installed since I broke a few of the old ones installing my headers


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[smdk2500]

I have brand new plug wires installed

Not saying that it is the problem but new doesn't always mean good. Ive had several new parts bad or out of spec out of the box.

 

[Matt Conner]

Not saying that it is the problem but new doesn't always mean good. Ive had several new parts bad or out of spec out of the box.

Yeah I’ve been there too, when I had my ‘90 I put 3 new distributors on before I got a good one

 

[PlayingWithTBI]

The o2 is installed but there are no cats on the truck.

The TBI system only uses one O2 sensor upstream of the cat, it doesn't care what's going on behind it, LOL. Now, an exhaust leak upstream from it can/will cause issues introducing more oxygen making it think it's running too lean. You can try plugging off the vacuum line to the EGR valve and see if it runs better, although it'll throw a code 32 but, it's a quick and dirty test. If it doesn't throw a code, you have other issues.

 

[Matt Conner]

The TBI system only uses one O2 sensor upstream of the cat, it doesn't care what's going on behind it, LOL. Now, an exhaust leak upstream from it can/will cause issues introducing more oxygen making it think it's running too lean. You can try plugging off the vacuum line to the EGR valve and see if it runs better, although it'll throw a code 32 but, it's a quick and dirty test. If it doesn't throw a code, you have other issues.

I do have a small exhaust leak at the head where one of the gaskets didn’t seal well, could that play into the hesitation?


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[PlayingWithTBI]

I do have a small exhaust leak at the head where one of the gaskets didn’t seal well, could that play into the hesitation?

That's a possibility...