high load causing shift troubles
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Mountain Pass
Joined: Oct 2011
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high load causing shift troubles
I'm going to walk you through what I'm getting, cause I'm not sure whats up here. Its a 2000 with the 6.8L/4r100. First off, when I start up cold and drive off everything is fine, I can give just a little bit of throttle, it goes through the gears easily, shifts around 1800-2100. I drive 10-20 min, turn it off.
Jump back in it 15 minutes later and when I pull out I try and give it that same small amount of throttle and I'm accelerating noticeably slower, the rpms are going up to 2500, the 1-2 shift slams pretty hard, 2-3 seems to hang. If I give it more throttle the rpms shoot up but the speed slowly catches up.
I know it has some kind of tune on it, but I just got it a few weeks ago and its done it since I got it. Oh yea, its getting under 11mpg highway. That aint right even for this truck.
I'm wondering if the catylitic converter is getting hot and plugged up, or the torque converter starts slipping when it gets hot, but I dont even know if that possible. Or maybe its the tune? Calculated load is also at 50% ish at idle.
ANy ideas?
Jump back in it 15 minutes later and when I pull out I try and give it that same small amount of throttle and I'm accelerating noticeably slower, the rpms are going up to 2500, the 1-2 shift slams pretty hard, 2-3 seems to hang. If I give it more throttle the rpms shoot up but the speed slowly catches up.
I know it has some kind of tune on it, but I just got it a few weeks ago and its done it since I got it. Oh yea, its getting under 11mpg highway. That aint right even for this truck.
I'm wondering if the catylitic converter is getting hot and plugged up, or the torque converter starts slipping when it gets hot, but I dont even know if that possible. Or maybe its the tune? Calculated load is also at 50% ish at idle.
ANy ideas?
Posting Guru
Joined: Jan 2007
Posts: 2,364
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From: Gilbert Az.
You may have a minor problem, I can't remember who had it but it was similar to what you describe, I'm sure Mark will see this thread & give you a answer that is more reliable than mine but I would search the 7.3 forum I think that's where it was posted. Sorry I couldn't help 
Jim & fat Monty
Jim & fat Monty
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,696
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From: SE Florida
It might be the catalyst. The problem is the engine isn't making enough power. You have to press the pedal further which makes the shifts at a higher RPM. Pressures are set based on the expected power at that RPM. Since the power isn't that high the pressure is too high and the shift slams.
Figure out what's wrong with the engine (not my specialty) and the transmission will be fine.
Figure out what's wrong with the engine (not my specialty) and the transmission will be fine.
Thread Starter
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Mountain Pass
Joined: Oct 2011
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THanks guys, at least I know where to start troubleshooting. I found a link describing how to check my converter doing a vacuum test so i'll start there. If I have to i'll hollow out the converter to see if that helps.
I've never had an issue like this. Its like I'm driving in molasses after it warms up good.
I've never had an issue like this. Its like I'm driving in molasses after it warms up good.
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Mountain Pass
Joined: Oct 2011
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I had the same thought kicking around in my head. I notice there is no egr and some other small mods done to it though. If I go back to stock then I'll be dealing with a cel, but maybe it will throw codes again and help me fix it.
Lead Driver
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From: Corvallis, OR
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Mountain Pass
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I assume its deleted but I havent dug into it yet. I assume because the throttle body/upper intake has a plate bolted to it where it looks like an EGR would go.
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Thread Starter
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Mountain Pass
Joined: Oct 2011
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You were right on Mark. I hooked up my old snap on mt2500 and the calculated load at idle was 50% ish. I only have a generic cartridge so it won't show maf volt or tps volt, it shows g/s and throttle %. Do you all know what these values should be?
I also noticed it was in closed loop at start up, it was obdI, and I have no S2 o2 sensors.
I also noticed it was in closed loop at start up, it was obdI, and I have no S2 o2 sensors.
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Mountain Pass
Joined: Oct 2011
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Can anyone tell me what g/s and throttle % should be? Or what else I should be looking at?
I tried unplugging the MAF and that made all the shifts medium firm. At least I know its not the transmissions fault. When I unplugged the maf my O2's spiked .9+ and fuel trims pegged negative if that helps.
I tried unplugging the MAF and that made all the shifts medium firm. At least I know its not the transmissions fault. When I unplugged the maf my O2's spiked .9+ and fuel trims pegged negative if that helps.
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Mountain Pass
Joined: Oct 2011
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I only had a little time to work on it today, but here's what i did.
I probed the MAF voltage and got 1.1-1.2V at idle. When I goose it the voltage briskly jumps up to 2 or 3. The idle was also at 1000rpm.
I pulled the plug on the IAC and the battery. Plugged the battery back in and set the idle at 750/650 nuetral/drive. I ran out of time so I didn't play with the TPS, and I'm not sure what it should be set at anyways. I plugged the IAC back in and the rpms want to idle at 900.
I assumed I should start checking the TPS next.
I also sprayed around for vacuum leaks and nothing was found.
I probed the MAF voltage and got 1.1-1.2V at idle. When I goose it the voltage briskly jumps up to 2 or 3. The idle was also at 1000rpm.
I pulled the plug on the IAC and the battery. Plugged the battery back in and set the idle at 750/650 nuetral/drive. I ran out of time so I didn't play with the TPS, and I'm not sure what it should be set at anyways. I plugged the IAC back in and the rpms want to idle at 900.
I assumed I should start checking the TPS next.
I also sprayed around for vacuum leaks and nothing was found.
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Mountain Pass
Joined: Oct 2011
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I didnt have much time again today but I did hook up the scanner and check the TPS function. At idle I have 21.5% absolute throttle position. With KOEO I slowly ran the pedal to the floor and back and it smoothly transitioned up to 93% and then back down.
The idle stop screw is most the way in (butterflies opened).
I verified the engine speed is at 750 even though the tach says 900. That means I'll end up opening the throttle stop almost to the limit. But before I do that can any one tell me what the TPS should be set at at idle? percent or voltage is fine
The idle stop screw is most the way in (butterflies opened).
I verified the engine speed is at 750 even though the tach says 900. That means I'll end up opening the throttle stop almost to the limit. But before I do that can any one tell me what the TPS should be set at at idle? percent or voltage is fine