downshift it starts to do a slight lunge or lurch

1995 FORD RANGER
200,000 MILES • 4.0L • V6 • 2WD • AUTOMATIC
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EWC177
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  • 144 POSTS
Driving at about 50 MPH, and release the accelerator, when it gets near 45 MPH, it starts to do a slight lunge or lurch. after it drops to around 42-40 MPH, it smooths out and runs good until it drops to the mid 30s, then it does it again for a few times and clears the rest of the way up. was going to change the fluid, filter, and modulator to see if it stops this, but wanted another opinion..
Jul 22, 2021 at 6:01 AM
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JACOBANDNICKOLAS
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  • 110,240 POSTS
Hi,

It does sound like it's happening when the transmission is downshifting. By chance, have you checked for diagnostic trouble codes? This has an OBD1 system and doesn't require a scan tool to get them.

Take a look through this link. It explains how it's done.

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Now, when you check the fluid in the transmission, is it clean and full?

As far as the vacuum modulator (vacuum diaphragm), remove the vacuum hose and see if there is evidence of ATF being drawn into the vacuum hose. Also, if you take a look below, I provided the directions for testing it.

Let me know what you find or if you have other questions.

Take care,

Joe

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Jul 22, 2021 at 1:19 PM
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EWC177
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It is an obd2, manufactured later in 1995, so it had the upgrade. codes that I'm getting right now are for o2 sensors, replaced all 4 last month,but apparently they were internet crap. got some Bosch premium on order..fluid looks normal, level okay, haven't pulled vacuum. looking at all options before complete rebuild.
Jul 22, 2021 at 7:17 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

The vacuum modulator is a good suspect, so your thought to check it are a good idea. Follow the directions above to see if it holds a vacuum. Also, inspect the hose to see if there is evidence of ATF in it. Keep in mind, there could be a leak before the vacuum modulator on the transmission causing problems as well, so make sure to check for leaks.

IF you have a chance, let me know what you find or if you have other questions. I'm interested in knowing what you find as a cause.

Take care and let me know if there is anything I can do to help.

Joe
Jul 23, 2021 at 11:30 AM
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