Acceleration hesitation (1 Viewer)

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Here is a list of the order I diagnosed the problem in.

No CEL and had a studder when under load between 1300-2000 RPM's and when engine was warm:

-Did a drain and refill on the transmission (thought it was the transmission slipping)
-Visual inspection on all vacuum hoses
-Undid wiring harness near EGR and verified wires were good
-Rewrapped the harness near EGR and used a water proof harness tape that stretched and was waterproof
-Wrapped heat reflecting tape over the harness tape
-Zip tied harness away from EGR
-Verified ECM harness near the glove box was okay
-Verified the CEL was working
-Undid all vacuum hoses to charcoal canister (gas cap was hissing bad upon removal)
-Verified fuel pressure relay was working correctly
-Undid vacuum hose at the FPR to increase fuel pressure
-Cleaned MAF sensor with MAF cleaner
-Checked connections at o2 sensors
-Installed new PCV valve
-Unwrapped harness on the #6 fuel injector to verify injector wires were good and inspected the contacts (sometimes the heater hoses leak on that #6 injector)
-Unplugged TPS to see if it would change the problem
-Replaced air tube between air filter housing and throttle body after noticing a crack
-Undid random vacuum hoses to see if problem would change

Fixed with:

-Took off throttle body and cleaned royaly and noticed a severely clogged EGR port
-Cleaned EGR port
-Inspected and checked the ohm reading on all the plug wires per FSM
-Pulled spark plugs and noticed Autolite Double Platinum plugs that had large gaps, were not consistent in their gapping, and had some weird arching on the back of the curve
-Installed factory Denso Copper plugs gapped to .032
-Inspected the cap and rotor and notice that the contacts looked good, but when I tried to clean them up they were flaking metal
-Installed new cap and rotor (NAPA brand)
-Checked the ohm readings on the TPS and verified no dead spots and tested to FSM specs

Problem fixed! I hope this helps someone else with a intermittent mis and no CEL!
 
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I know this is an old thread but figured you guys would still be around with far more experience by now.

I have a 93 and only have hesitation (almost dies) when accelerating normally. Just acceleration though. In neutral it will rev up instantly. Power brake it and it has the same effect of hesitation. No codes, idles fine. Replaced Tps and adjusted accordingly, new distributor and timed accordingly, checked o2 sensors, used a propane torche and ether to check for vac leaks. New plugs, lots of sea foam through it. New tranny filter, fluid.
I will say that upon checking the o2 resistance they were at 6 ohms. I know the spec is somewhere around 12-15 but after purchasing a new bosch ($130) i checked it and it was 6 as well. Something to do with aftermarket ones? I did not end up changing them.

I know everyone has to put in their time trouble shooting these trucks, but i seem to have a slightly different problem seeing how it only happens on acceleration and the truck runs fine the rest of the time. And yes, i have searched this amazingly friendly and helpful website thoroughly. And thanks to you who post the FSM links.
 
I know this is an old thread but figured you guys would still be around with far more experience by now.

I have a 93 and only have hesitation (almost dies) when accelerating normally. Just acceleration though. In neutral it will rev up instantly. Power brake it and it has the same effect of hesitation. No codes, idles fine. Replaced Tps and adjusted accordingly, new distributor and timed accordingly, checked o2 sensors, used a propane torche and ether to check for vac leaks. New plugs, lots of sea foam through it. New tranny filter, fluid.
I will say that upon checking the o2 resistance they were at 6 ohms. I know the spec is somewhere around 12-15 but after purchasing a new bosch ($130) i checked it and it was 6 as well. Something to do with aftermarket ones? I did not end up changing them.

I know everyone has to put in their time trouble shooting these trucks, but i seem to have a slightly different problem seeing how it only happens on acceleration and the truck runs fine the rest of the time. And yes, i have searched this amazingly friendly and helpful website thoroughly. And thanks to you who post the FSM links.


Please try this test and report back. Power brake the engine and try to rev up the RPMs to recreate this scenario. If you're able to recreate it, then the issue is somewhere in the bundle of ECU harness that go right by the EGR area, near the firewall, on top of the valve cover. This is a common issue and doing a search will provide ample info with pics.
 
Thanks Alia, I tried what you instructed. If i mash the gas or step on it normally, i get the bog or hesitation. If i depress slowly it will slightly hesitate but then load up as expected. All the searches i came up with people had multiple symptoms along with the hesitation.
All i have is the slight moment on take off (hot or cold) where it falls on its face.
 
I wanted you to power brake, which is stepping on both pedals simultaneously to mimic a heavy load that causes the engine to move in one direction. It doesn't sound like that is the test you conducted.
 
Yes. Thats what i did. Are you wanting me to stand on it for a certain period of time?

ok, thanks for the update and clarification. I thought the vehicle was moving forward and I wanted to be stationery. Sounds like an abrupt throttle input is causing the engine to move under torque and causing your hesitation. This leads me to believe that ECU harness by EGR is in fact unhappy, which is common. This happened to me as well. A search will reveal more data with pics.
 
I thought I would post on my situation after gathering info from you all and reading through the FSM. It was none of those things.
I re-gapped my plugs and advanced the timing. 5 Plugs were capped about twice the distance they should be. I never thought I would make that much of a difference. Runs better than I imagined. Crisp throttle response and slightly more pep. Pretty sure if it had about 300 more HP it would do burn outs. Thank you all for your insight, I’m sure it will come in handy down the road.

I do have another question though. Does anyone know what the controller is to the left of the ecu behind the glove box? It has two plugs that aren’t plugged in...

D6EBD65C-F229-43D3-92FC-82A659F2CE4E.jpeg
 
That is the OEM radio amplifier. It was more than likely disconnected when an aftermarket stereo was installed. Leave it disconnected.
 
Hey congrats on resolving your issue!!!!
 

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