4l80e downshift with no reason
Re: 4l80e downshift with no reason
Also, can I change my tach input signal from the ISS to an msd 6al output. I know there is a special circuit to do this for the megasquirt board but i'm not sure of the gpio board. thanks,
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Bernard Fife
- Posts: 1696
- Joined: Fri Apr 04, 2008 1:28 pm
Re: 4l80e downshift with no reason
RICH454MC,
Yeah, tach and ISS are similar, but definitely not the same.
For the MSD box, the GPIO board uses the 'easyVR' circuit described here: http://www.megamanual.com/ms2/msd6a.htm It can handle a large range of signal voltages and wave forms. If this was mine, I would probably scope the signal first just to see what it looks like. If it's anything near normal (it very likely is, since it has to drive a normal tachometer's input) then I would hook it up and see how it works.
Lance.
Yeah, tach and ISS are similar, but definitely not the same.
For the MSD box, the GPIO board uses the 'easyVR' circuit described here: http://www.megamanual.com/ms2/msd6a.htm It can handle a large range of signal voltages and wave forms. If this was mine, I would probably scope the signal first just to see what it looks like. If it's anything near normal (it very likely is, since it has to drive a normal tachometer's input) then I would hook it up and see how it works.
Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw
Re: 4l80e downshift with no reason
Ok. I will have a look at that. I mangaged to finally load that new program you sent into the gpio. I've been driving it for 2 days now and the weird downshifting problem seems to be fixed. Thanks.
Re: 4l80e downshift with no reason
Hello,
I just thought about your post when looking at my logs.
If you use the input shaft instead of RPM, in fact the IS is located after the overdrive, so in 1st, 2nd and 3rd gear, the IS and RPM are equal (is we consider no slip in differential) but in 4th gear, the engine RPM is lower then the IS RPM: Engine speed = 0,75xIS
Guillaume
I just thought about your post when looking at my logs.
If you use the input shaft instead of RPM, in fact the IS is located after the overdrive, so in 1st, 2nd and 3rd gear, the IS and RPM are equal (is we consider no slip in differential) but in 4th gear, the engine RPM is lower then the IS RPM: Engine speed = 0,75xIS
Guillaume
Re: 4l80e downshift with no reason
gui67, I believe that statement is incorrect. From what I know, the ISS reads the input shaft which is thechnically the output of the torque converter. If there was no slip in the converter, the reading would be identical to the tach signal. I believe GM used this sensor along with th VSS to determine if the transmission is slipping.
Re: 4l80e downshift with no reason
Hello RICH454MC.
the ISS uses the teeth from the forward clutch housing, not directly on the input shaft.
This housing has the same speed as the input shaft in all gears exept in overdrive where its speed is higher. It is clearly writen in the hydramatic technicians guide.
Look at your logs: you will see no ISS RPM change when the trans is shifting from 3rd to 4th, while the engine RPM drops.
the ISS uses the teeth from the forward clutch housing, not directly on the input shaft.
This housing has the same speed as the input shaft in all gears exept in overdrive where its speed is higher. It is clearly writen in the hydramatic technicians guide.
Look at your logs: you will see no ISS RPM change when the trans is shifting from 3rd to 4th, while the engine RPM drops.