boost issues or transmission problem?
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boost issues or transmission problem?
I have a 2001 f 350 7.3 diesel r 400 tranny 320000 miles. . Im having transmission issues. It makes a slight whine/ grinding noise only in first And reverse. And it surges. Sometimes its fine though to. Check engine light came on. Only codes i get are #4 glow plug out and a low boost pressure. Checked boost before fixin Running fine at the normal about 20 psi. ive read a bad or dirty map or iat sensor can cause transmission issues along with the low boost error code. But in my experience and some reading it sounds like a stall converter. Any advice???
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,732
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From: SE Florida
I don't understand what you mean about a stall converter. Every torque converter ever built is a stall converter. They all have a stall speed.
Low boost will cause transmission problems. The first rule of fixing ANY transmission problem is to fix any engine problems first. This often fixes the transmission, too.
Low boost will cause transmission problems. The first rule of fixing ANY transmission problem is to fix any engine problems first. This often fixes the transmission, too.
Hotshot
Joined: Jan 2011
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From: Puget Sound
Whuh? Are we talking boost from the turbocharger on the engine? I spent a lot of time under the hood and never saw any connection between air in/out and the transmission. I acknowledge low boost makes heat, and transmissions probably have a distaste for a lot of heat up front - but I'm confused on the direct correlation.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,732
Likes: 2,661
From: SE Florida
The direct correlation is that the shift schedule and pressure schedule is programmed for a certain output of the engine. If the engine isn't making the power it should be making you will press the go pedal further than normal. The shift and pressure schedules now see that you're further into the pedal, so the upshifts will be delayed and at too high of a pressure.
There is no direct mechanical connection between the air in and out and the transmission, but there is a programming connection.
There is no direct mechanical connection between the air in and out and the transmission, but there is a programming connection.
Postmaster
Joined: Dec 2010
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From: Gary,Indiana
I don't understand what you mean about a stall converter. Every torque converter ever built is a stall converter. They all have a stall speed.
Low boost will cause transmission problems. The first rule of fixing ANY transmission problem is to fix any engine problems first. This often fixes the transmission, too.
Low boost will cause transmission problems. The first rule of fixing ANY transmission problem is to fix any engine problems first. This often fixes the transmission, too.
Mind you have no codes but I might have a slight up pipe leak because I can only get 22psi boast.
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Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,732
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From: SE Florida
It uses almost all of it's sensors at one time or another to schedule WHEN to shift, and how much pressure to use for each shift.
The WHEN to shift is mainly pedal position and vehicle speed. This can be modified by temperatures (engine and trans,) vehicle acceleration rate, rate of change of the pedal, etc.
The pressure used is determined both from hard coding and an engine torque calculation that is made from injector pulse width and mass air flow. It can be modified by conditions, too, but I didn't work a lot with this calculation. That was someone else's responsibility. I just used the output of the calculation.
EBP is probably in there. It might not be a direct input to the torque calculation because the effect of the EBP is going to reduce the mass airflow through the engine, so if the EBP is restricting flow it's accounted for there.
An exhaust leak before the turbo can cause harsh shifts at higher boost levels. If the boost isn't what it should be the engine isn't making the torque that is expected. The torque calculation will correct for it, but it has limited authority. The hard coded porting of the pressure is going to be too high and that will cause harsh shifts.
The WHEN to shift is mainly pedal position and vehicle speed. This can be modified by temperatures (engine and trans,) vehicle acceleration rate, rate of change of the pedal, etc.
The pressure used is determined both from hard coding and an engine torque calculation that is made from injector pulse width and mass air flow. It can be modified by conditions, too, but I didn't work a lot with this calculation. That was someone else's responsibility. I just used the output of the calculation.
EBP is probably in there. It might not be a direct input to the torque calculation because the effect of the EBP is going to reduce the mass airflow through the engine, so if the EBP is restricting flow it's accounted for there.
An exhaust leak before the turbo can cause harsh shifts at higher boost levels. If the boost isn't what it should be the engine isn't making the torque that is expected. The torque calculation will correct for it, but it has limited authority. The hard coded porting of the pressure is going to be too high and that will cause harsh shifts.
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Hotshot
Joined: Jan 2011
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From: Puget Sound
The shift calculation has been the cause of great speculation and consternation. I look at the data and felt my own truck with a faulty EBP (everything else 100%), and something is going on there.
Postmaster
Joined: Dec 2010
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From: Gary,Indiana
Thank you Mark for sharing your knowledge on the subject. You answer has been very helpful to me. Because in my case I was thinking or hoping it was due to boost levels being alittle lower than it should be per EBP. Also I think it could be the TPS is giving the wrong input. But thank you for confirming and helping me get a better idea of what effects shift strategy.
But it doesn't seem to be as clear cut as I hoped but it does back up the fact that the engine & sensors need to be 100% for the trans to work correctly.
But it doesn't seem to be as clear cut as I hoped but it does back up the fact that the engine & sensors need to be 100% for the trans to work correctly.
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