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Author Topic: Bouncing tach and stumbling at ~4000 rpm  (Read 6327 times)

Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« on: January 21, 2012, 01:35:00 PM »
Folks

Today my 1991 NA started something strange, when the tach gets to 4000 rpm, it the tach bounces wildly, it will jump to 6000 then to 3700 then 5000, etc.  The car stumbles badly when this happens.  If I stay under 4000 it seems to run fine.  This happens in neutral as well as the other gears.

Any ideas???
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Gostlrs

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Bouncing tach and stumbling at ~4000 rpm
« Reply #1 on: January 21, 2012, 04:19:00 PM »
Check the

Dizzy
Plugs
Wires
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rcdraco

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Bouncing tach and stumbling at ~4000 rpm
« Reply #2 on: January 22, 2012, 10:35:00 AM »
Do a diagnostic on the distributor if you're familiar with it's workings.  Sounds like there's something wrong with the tach signal in there, or you could possibly have a problem with the VAF sensor's variable resistor giving a bad value for the fuel system.
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Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #3 on: January 22, 2012, 12:26:00 PM »
Could be with the VAF, it happend at high altitude, above 6500 ft.
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #4 on: January 22, 2012, 12:27:00 PM »
Started it this morning at 5280 ft and no issue.
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

rcdraco

  • Guest
Bouncing tach and stumbling at ~4000 rpm
« Reply #5 on: January 22, 2012, 12:33:00 PM »
You don't happen to be running an aftermarket air intake system, aka a cone filter.  If you went through high humidity it might cause some trouble.  Or even something as small as the small percentage of ethanol in the gas allowing a bit of moisture in the tank.  Intermittent faults blow big time.
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Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #6 on: January 22, 2012, 02:59:00 PM »
I don't have an aftermarket intake or cone filter.  Everything here has ethanol.  It even happened on a full tank.
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Rocketman

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Bouncing tach and stumbling at ~4000 rpm
« Reply #7 on: January 22, 2012, 03:11:00 PM »
I would check & clean the distributor ground on the thermostat housing. Sound like it could be an intermittent ground there
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1.8L Turbo All Wheel Drive Capri... the "GTXR2"


Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #8 on: January 23, 2012, 07:06:00 PM »
I will check that, it is being intermittent.
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #9 on: February 02, 2012, 05:24:00 PM »
Would you happen to have a pic of the ground?
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Rocketman

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Bouncing tach and stumbling at ~4000 rpm
« Reply #10 on: February 03, 2012, 04:10:00 AM »
I have to get a better picture, but this area here:

http://www.werbatfik.com/img/capriwork/capriwork67.jpg

It's the bracket that bolts using the t-stat cover bolt, and it has the tabs for the green O2 sensor connector to clip into it.

There's a mess of small black ground wires here held on by I believe a 10mm bolt, these are critical for the distributor to function correctly
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1.8L Turbo All Wheel Drive Capri... the "GTXR2"


azgtx

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Bouncing tach and stumbling at ~4000 rpm
« Reply #11 on: February 03, 2012, 12:19:00 PM »
Is your disty seal leaking at the head...check the dist connector for oil and sludge. That happened to me..worked for days chasing that one. The plug was all slopped up.
Clay
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Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #12 on: February 26, 2012, 02:42:00 PM »
Looks like the issue is that the electrical system cannot handles the stereo equipment.  I noticed that when it stammers, if I turn off the stereo, the problem stops immediately.  I have added 2 amps one 4-channel 600W and one 1-channel 600W running a 12" sub.

Do you think adding a second battery would help, or a stronger alternator.
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #13 on: February 26, 2012, 03:01:00 PM »
Obviously it is at high volume.  
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Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT

Snigalfriz

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    • 1991 NA Capri
Bouncing tach and stumbling at ~4000 rpm
« Reply #14 on: March 27, 2012, 10:52:00 PM »
Replaced the distributor and no more stumbling at all.
Logged
Why? I have more time than money, that's why I work on this car!

1991 Mercury Capri 5-sp
1992 Mercury Capri 5-sp swap
1999 Ford Contour SE 24v v6
2003 Lincoln LS
2007 Saturn Outlook XE AWD
2014 Chevy Cruze LT