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So to start here’s what I’ve done to try to fix it. Checked all grounds and connections, new batteries, new timbo apps. I don’t have any fuel pressure gauges so I don’t know if it’s a fuel thing. I am looking to get some today if I can. So the problem is once I get to about 43 it starts surging. It will stop as soon as I go back to 40 or under. The problem seemed to appear after I replaced my whole A/C system. And only when the Ac is on. But will keep happening even after the AC is turned back off. But if I never turn it on in the mornings, it doesn’t seem to do it. Although I never get too far about 15min before turning it on because of the heat here. It seems like when it started it was only at about 43-48 that it would do it and over or under it was fine. But now it’s anyspeed over 43. I would give it decent throttle to passed the bad zone and jump straight to 50 and it never had problems, now it does it even when it downshifts to accelerate harder. Any help would be appreciated. Almost forgot, I used code reader and found no codes. (There was one for apps signal low but went away after Timbo apps)

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Posted (edited)

First thing I would do would be put a fuel pressure gauge in. Check it at idle and under a load. I believe around 14psi the check valve opens. That keeps the electronics on the pump cool and keeps the pump well lubricated. The VP can run with low or no fuel pressure. It’s just hard on it and it won’t last long. 

Edited by Threadzy

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I just found out that it does not surge at all if overdrive is off. I can go 45, 50, even 55 with overdrive off and no surging. 

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I would definitely check the fuel pressure on the lift pump. Idling and under a load, throttle smashed! 

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Posted (edited)

Colt

 

It sounds like you are locking/unlocking the TC.  The indicated speed you mention is exactly where it will happen.  This is usually an AC noise issue or a grounding issue. 

 

Edit: I re-read your post and the last sentence may throw that idea out the window, but odd it happens or started happening in that speed range.

 

I just got my first automatic 2nd gen.  I am noticing this at certain times too, and will be hunting for the cause.

 

GL

Hag

Edited by Haggar

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20 hours ago, ColoradoColt said:

It seems like when it started it was only at about 43-48 that it would do it and over or under it was fine. But now it’s anyspeed over 43. I would give it decent throttle to passed the bad zone and jump straight to 50 and it never had problems, now it does it even when it downshifts to accelerate harder.

 

53 minutes ago, Haggar said:

I re-read your post and the last sentence may throw that idea out the window, but odd it happens or started happening in that speed range.

Yup your right... It is a AC noise issue...

 

 

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Posted (edited)

I tried to find the article, but didn't find it quickly.

 

Have a good DVM.  Set to AC.  put one probe on positive battery terminal and the other on the negative.  You will see AC volts.  This AC will change with how hard the alternator is charging and engine speed. So if you see bad numbers before you do anything, there is no reason to keep proving the problem.

 

I couldn't find the exact numbers, but you are looking for

found it  it is in transmission section, not electrical.  I think it should be cross posted.....

 

HTH

 

Hag

Edited by Haggar
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Posted (edited)

I had this problem some years back and was able to resolve it for a couple years by moving the ground wire away from the alternator. The problem returned after doing a band adjustment on the transmission not too long ago. I am still planing to do the W-T ground mod just been slacking on it. Simply moving the ground wire away from the alternator might help and confirm that you have the alternator interference

IMG_1148.JPG

Edited by Irie808
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Check the ac voltage at the B+ alternator terminal; it's the big terminal on the alternator.  I've seen lower voltage readings when testing at the driver's side battery.

 

To test if ac voltage is causing the problem remove the alternator fuse and take it for a short drive.  If the transmission problem clears up then you know it's an ac voltage problem.

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I have always tested mine on the alternator charge wire to a battery ground. I have also checked on the bat + to the bat - with similar results.

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