Initial Surging/Jerking on Cold Startup 2001 4.6 Expy

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Ulver

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So, it's been about a half year since I've had this vehicle, and much work and improvement has been made to my 01 Expy. The fuel trims are decent; around +5 to +7% LTFT on both banks. No codes.

However, there's this one issue that I still have.. My vehicle jerks on acceleration (from 0 mph) while the engine is cold. This happens only on take off. I'll press on the gas, and the RPM's will go up, but nothing will happen for a couple seconds, then suddenly I get this "jerk" forward. So the only time this happens is when the engine is cold, and when I first take off. This issue doesn't appear in any other instance. This doesn't happen at all once the engine is warmed up. What could this be?
 

1955moose

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Torque converter. The other possibilities are a bad front pump in your transmission. Any codes at all?. Do you have a trans shop or repair shop that's fair, and good with diagnosis? A friend of mine has a pumped up 67 El Camino, and had a similar situation, his turned out to be what is called a sprag gear go bad in his automatic. Let us know what they find.

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Ulver

Ulver

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No codes. I do have a reliable repair shop I could try.

I'll try running the Expy tomorrow with the manual mode and see if this still happens. If I remember correctly, if the problem happens in manual mode, it's most likely not a transmission problem, but if the problem does not happen in manual mode, it most likely is the transmission? Thanks for the feedback.
 
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Ulver

Ulver

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Okay, here's a follow-up. I changed my transmission fluid this weekend. And I mean all of it, including the fluid from the torque converter. I haven't had a problem ever since. So if anyone else has experienced this issue, be sure to drain all the fluid. Not just the fluid from the drain pan.
 
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