Transmission stutter/jerk hard shift on 1st after driving a while

Jeremy Martin

Member
Oct 26, 2017
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1999 Mustang GT with 2001 Romeo motor and TR3650 transmission

I am going to try my best to explain what im talking about here and hope someone has some ideas.

When i first start up my car it shifts smooth as butter into first and then into second. Dont have any issues. Its as if the idle is just perfect and things slip right where it needs to go. As the motor heats up though, and i drive it a lot, it starts to get more jerky when shifting into 1st and second. Eventually i find at a light, when its been driven a bit and its good and hot, that getting the car going in 1st is more of a challenge. As i let out of the clutch i notice i have to rev it up higher in hopes of taking off without it stuttering. A few days ago I let out of the clutch and tried to just ease into 1st and the car was jerking and bucking...i pressed in the clutch again for it to gather itself and it knocked it off when i tried again but i was rolling already from the previous attempt. i could have swore it was wheel hop but i dont have that kind of a beast. I was simply trying to ease into 1st gear from a light. Taking off from 2nd seems to help a bit more when this is going on. Im not sure if its a heat thing or some kind of sensor though. I noticed the other day, after it was bucking and I pulled in to get gas, the car was fine for a bit after i started it back up. Im not sure if its the gas, some sensor that the computer is reading, or just random luck that it worked fine.

Things I have done or noticed:

I have changed out the transmission fluid already trying to fix this and used Motorcraft Mercon V in it.

Replaced the spark plugs with Motorcraft Platinum plugs

I was thinking bad gas or perhaps theres some kind of water in the tank that was getting picked up by the fuel pump. So yesterday i filled up the tank and put some royal purple max octane in there in hopes of drying up anything and cleaning out the injectors. The jury is still out on that. Perhaps im on the right path and would need more treatments with a few fill ups.

When this was bucking and jerking like it was at the light i had less than a quarter tank of fuel left. The time before that it happened like that i believe it was that low as well but I cant swear to it.

The car is lightly modded. Nothing major really at all.
75mm intake
CAI
No EGR
New O2 sensors with rear MIL eliminators (although the codes are still showing for the rears but i didnt change them out or add the MIL eliminators until the codes showed up)
A 93 Octane Bama tune (was doing this though with my predator tuner as well)
Long tubes
3:73 gear
Underdrive pulley kit (for the love of God if any of you have the stock crank/water pump/alternator pulleys and dont want them send them my way. I want to replace them with the stock ones)

Nothing really major done to the car other than above.

Known issues with the car though:

Suspected valve stem seal leak on passenger head. If i let it idle for long periods of time blue smoke will eventually come out the back when i rev it up until it clears out. Doesnt do it when driving or sitting at lights (unless the light is like 10 mins long and i have been driving it for a while).

Battery light comes on almost all the time. Its 100% due to that under drive pulley kit that I didnt put on that I really want to replace with stock.




Any ideas what it could be? Was thinking i will check the MAF to make sure its clean and check that filter to make sure its clean too.
 
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wmburns

SN Certified Technician
Aug 14, 2009
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Houston Texas
For bucking/jerking the first thing to rule out is excessive EGR flow. But since you don't have EGR that wouldn't seem to apply.

Frequently buck/jerk is timing and/or ignition related. What's one thing that can "cause" ignition problems? How about unstable or low system voltage? IMO it's not a good idea to ignore the battery light.

What's another thing that can "cause" timing problems? How about an unstable CKP sensor signal? What's one possible cause for an unstable CKP sensor signal? How about a crank damper problem such as:
  • broken crank damper
  • incorrectly torqued crank damper bolt
  • cheap under drive crank damper pulleys.
 
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Jeremy Martin

Member
Oct 26, 2017
29
4
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Ty for the reply. Im not ignoring the battery light. I would really like to replace the underdrive pulley kit with the stock pulleys. Do you think that could be causing it? I know today when i was driving around i was just over 12v while driving and the battery light was on. I have seen some good deals on the pulleys but they have been a bit far away. People online are proud of their pulleys and want close to 100 bucks for them. I wish i could just find one in a junk yard near me but all they seem to have are V6 Mustangs.

I dont think its a timing problem though. The car runs just fine until it starts getting hot. When it gets hot thats when things dont act they way they should be. Also i had the timing chain cover off a month ago and the chains were very tight and the guides were new. You think its still a possible timing problem with it?


This car seems to run just fine at first every day. Just seems to be once it starts getting hot and has been driven a while that it starts in on its BS.
 

Jeremy Martin

Member
Oct 26, 2017
29
4
13
41
Would a possibility be the COPs failing when hot? I mean it drives fine and doesnt idle any more rough than when it is first started up. When it acted up at the light it was on a flat spot where i was just trying to take off. A time before that it was on an incline and I looked like a damn fool trying to get going until i just essentially revved up the car and popped the clutch to get going.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,849
505
204
Houston Texas
Would a possibility be the COPs failing when hot?
Do you have any kind of ODB2 device? IF so you could rule your theory in or out simply by looking at the ODB2 mode 6 misfire data. Make note of the number of misfires before a test drive and then compare the cylinder by cylinder misfires after the test drive.

Here's some information on an affordable and very powerful Windows based ODB2 scanner.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

Note, to access ODB2 mode 6 data does not require a scanner. A basic function ODB2 reader will do this. However some budget ODB2 devices do a better job than others at displaying the data. Some budget devices will display the data in raw form leaving you to figure out which bucket is the misfire data.