Change to a different trans
Lead Driver
Joined: Jan 2003
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From: Ohio
So, it sounds like the VSS has enough to do with computing of line pressure, blah, blah, blah, that it could, in a way, cause the problems you are having?
With what I read, you have electronic issues that need resolved before throwing the towel in on the E4od. I hope you can work through it.
With what I read, you have electronic issues that need resolved before throwing the towel in on the E4od. I hope you can work through it.
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Posting Guru
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So, it sounds like the VSS has enough to do with computing of line pressure, blah, blah, blah, that it could, in a way, cause the problems you are having?
With what I read, you have electronic issues that need resolved before throwing the towel in on the E4od. I hope you can work through it.
With what I read, you have electronic issues that need resolved before throwing the towel in on the E4od. I hope you can work through it.
Lead Driver
Joined: Jul 2007
Posts: 7,868
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From: Rhode Island
Load is not calculated from VSS. Load is a function of calculated engine air flow, engine displacement and engine RPM.
TV Pressure as Mark mentioned is primarily calculated from TPS, Engine Torque (which is derived from load) and transmission temp. There are a few other things that can influence TV Pressure too, like whether or not you have O/D canceled and what particular gear you're in.
There is only one situation where the TV pressure can really be influenced by speed, and that is during a manual downshift while coasting. Like if you're coasting down a big hill and hit the Cancel O/D button or manually shift into 2nd or 1st. It will add some line pressure as vehicle speed is higher to aid clutch engagement.
But it's not a big deal, since with no VSS signal, the computer will use a default "safe" TV pressure.
TV Pressure as Mark mentioned is primarily calculated from TPS, Engine Torque (which is derived from load) and transmission temp. There are a few other things that can influence TV Pressure too, like whether or not you have O/D canceled and what particular gear you're in.
There is only one situation where the TV pressure can really be influenced by speed, and that is during a manual downshift while coasting. Like if you're coasting down a big hill and hit the Cancel O/D button or manually shift into 2nd or 1st. It will add some line pressure as vehicle speed is higher to aid clutch engagement.
But it's not a big deal, since with no VSS signal, the computer will use a default "safe" TV pressure.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,739
Likes: 2,669
From: SE Florida
Not true. Neither VSS nor TPS is an input to the load calculation.
VSS has almost nothing to do with computer line pressure. See this post:
Good post!
Load is not calculated from VSS. Load is a function of calculated engine air flow, engine displacement and engine RPM.
TV Pressure as Mark mentioned is primarily calculated from TPS, Engine Torque (which is derived from load) and transmission temp. There are a few other things that can influence TV Pressure too, like whether or not you have O/D canceled and what particular gear you're in.
There is only one situation where the TV pressure can really be influenced by speed, and that is during a manual downshift while coasting. Like if you're coasting down a big hill and hit the Cancel O/D button or manually shift into 2nd or 1st. It will add some line pressure as vehicle speed is higher to aid clutch engagement.
But it's not a big deal, since with no VSS signal, the computer will use a default "safe" TV pressure.
TV Pressure as Mark mentioned is primarily calculated from TPS, Engine Torque (which is derived from load) and transmission temp. There are a few other things that can influence TV Pressure too, like whether or not you have O/D canceled and what particular gear you're in.
There is only one situation where the TV pressure can really be influenced by speed, and that is during a manual downshift while coasting. Like if you're coasting down a big hill and hit the Cancel O/D button or manually shift into 2nd or 1st. It will add some line pressure as vehicle speed is higher to aid clutch engagement.
But it's not a big deal, since with no VSS signal, the computer will use a default "safe" TV pressure.
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Posting Guru
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When I said VSS and TPS are used to calculate load, I was thinking in terms of the transmission controller. There are no inputs for it to calculate torque or load through air flow, but infers load from VSS and TPS.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,739
Likes: 2,669
From: SE Florida
Well you're wrong. It does not use VSS or TPS for the load determination. It gets that information from air flow. I used to do this for a living, I worked with this calculation every day. There is no separate transmission controller. There is one controller, called the PCM (Powertrain Control Module.) It controls both the engine and transmission.
Logistics Pro
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From: Chillicothe
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Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
Mark, read this post:
He states he is using an aftermarket controller. Thus the major confusion.
I am using a U4P0 ECU, it doesn't control the trans at all in my application. The trans controller reads the RPM, TPS, and VSS to control the solenoid pack. Its the older Baumannator TCS - http://www.becontrols.com/downloads/bectcsinstall.pdf
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Posting Guru
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I was able to determine the speed signal was not intermittent but I could reproduce some behavior of it working and then not. And while watching it, the behavior reeked of being a computer of some sort.
I replaced the ECU and that didn't fix the issue, I then removed the PSOM and found my problem, these three items are fried:
I replaced the ECU and that didn't fix the issue, I then removed the PSOM and found my problem, these three items are fried:
Lead Driver
Joined: Jul 2007
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From: Rhode Island
Those items are not "fried". The issue is that the capacitor right next to them, leaked its guts out and corroded the PCB.
I suspect cleaning those 3 surface mount components, then replacing that big capacitor at the bottom of the image will probably resolve your issue.
I suspect cleaning those 3 surface mount components, then replacing that big capacitor at the bottom of the image will probably resolve your issue.
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I put in my spare PSOM and went for a long drive. Speed is reporting fine and the trans seems to be fine as well. This replacement PSOM is a little wobbly on the speed but not bad, but I am going to look into fixing the original and maybe the replacement, if needed.
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Posting Guru
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Those items are not "fried". The issue is that the capacitor right next to them, leaked its guts out and corroded the PCB.
I suspect cleaning those 3 surface mount components, then replacing that big capacitor at the bottom of the image will probably resolve your issue.
I suspect cleaning those 3 surface mount components, then replacing that big capacitor at the bottom of the image will probably resolve your issue.
In my research for PSOM repair I found prices starting at $180 and up. It could be that one or two of these caps (or the Varistor) need to be replaced to fix a PSOM and the $180+ seems to be excessive.
Found two videos that help explain:
this one is of the repair itself but doesn't list the parts -
this video lists the parts in comments -
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