50% drop in mpg linked to not releasing gear while stopping - JeepForum.com

 
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post #1 of 12 Old 06-30-2011, 08:39 PM Thread Starter
joburocks
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50% drop in mpg linked to not releasing gear while stopping

I have an intermittent issue.

My mpg cuts in half after about 1/2 of driving, sometimes only after 2 minutes. Another connected symptom is that when coming to a stop the car won't shift out of gear and sputters and tuggs until I stop fully and the car rocks back (then buttery smooth).

What controls both these things? Computer? They only happen together.

I thought the hole in my manifold was causing a poor mileage issue until I noticed I was getting 15-24 depending on hills. In an instant it will drop for the rest of the ride to 8-12. Same amount of push on gas pedal, same hillls.

Overall average for last 1k miles is 10.2 mpg. Ouch!

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post #2 of 12 Old 06-30-2011, 09:09 PM
ratmonkey
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Torque converter isn't releasing. Lots of things can cause that.
Do a torque converter stall speed test and report your findings. Search for the procedure, I've posted it quite a bit.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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post #3 of 12 Old 07-01-2011, 09:02 AM Thread Starter
joburocks
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It's intermittent so results will vary depending on what state the car is in.

What controls torque converter that is electrical? Is there a computer that also might be linked to fuel mixture?
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post #4 of 12 Old 07-01-2011, 09:38 AM
ratmonkey
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everything is computer controlled.
there's a lock up solenoid, its normally closed operation. when fluid is vented by the noid the converter locks up. if changing the solenoid pack(the od solenoid and tcc solenoid are on one pack and it's kinda expensive) doesn't fix things the converter is fried.
a converter stall test will give you a good indication of health on the converter.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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post #5 of 12 Old 07-01-2011, 10:16 AM Thread Starter
joburocks
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I'll do it next time I leave the house. Here are my thoughts on it...

If my torque converter was responsible for a sudden drop of 20mpg to 10mpg on the highway, wouldn't I feel it slip, jerk or the rpms would raise? When the drop comes, nothing happens in the drivetrain. How would Torque Converter issues affect MPG without me feeling it?

Example: I leave the house, drive through town, everything is buttery smooth. I hop on the highway, 10min down the highway my mpg drops by 50%, other than that nothing has changed. I hop off the highway 10min later and when I slow to a stop the car won't shift out. If the gas mileage is poor the car always has TC issues.

And thanks for the help rat
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post #6 of 12 Old 07-01-2011, 10:26 AM
ratmonkey
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ah, that's better detail.

drive around a bit with your upstream o2 sensor unplugged and see what happens.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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post #7 of 12 Old 07-01-2011, 10:36 AM Thread Starter
joburocks
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Ok I will put this thread on hold for a few days while waiting for my exhaust manifold to get here. Start with that, drive a bit and see what I get, then unhook the upstream o2 sensor depending on results. Then post findings.

Will also do a TC stall test when it's running well.
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post #8 of 12 Old 07-09-2011, 03:42 PM Thread Starter
joburocks
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TC stall test was 1750rpm in Drive and Reverse assuming I did it correctly. That is when things are running correctly. If I get the intermittent issue again as I suspect I will, I will post another stall test with the car running poorly.

Installed the manifold today and we shall see how it affects the mpg in the next few days. I will post with more info.


unrelated issue..
Noticed this connector had no home... any idea where it goes?
It is part of a bundle of which the thickest of the 3 goes into the brake booster. The skinny one drops in behind the master cylinder and connects to an unseen place, and this one is the medium size one that goes?..
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post #9 of 12 Old 07-09-2011, 04:08 PM
Candymancan
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Could be the plug to the washer fluid tank sensor. Also looks like the hose attached to the pcv valve on the valve cover is missing, that plug on the side of the airbox shouldnt be open like that

2013 6.2 V8 Camaro SS 30k
98 5.9 V8 ZJ 180k
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post #10 of 12 Old 07-09-2011, 07:03 PM Thread Starter
joburocks
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took the pcv hose off for the picture
the washer fluid tank sensor has one in it, I think that may be the one that wraps around the back of the masters cylinder.
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post #11 of 12 Old 07-09-2011, 07:15 PM
airwolf9090
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Washer tank has one or two hooked to it? idk about yours but mine has two one for the pump that pumps the fluid for the front and one for the pump for the back window....

1996 Jeep ZJ Orvis
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post #12 of 12 Old 07-10-2011, 12:12 AM Thread Starter
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