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boltonranger2
Dodge Dakota
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9/16/2009
11:59:46
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 Subject: 3.9 flat spot / bogging problem
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Message:
2002 quad cab 3.9 / auto 42re / 4wd / AC - 103K miles
The problem:
Truck bogs from approx. 1800 - 2300 rpm.
Feels like a vacuum leak.
What I've done (thank you modders):
tps @.726v - (verified consistent rising voltage as throttle opens also)
cleaned IAT sensor
crank sensor mod
180 degree t-stat
3923 autolites @ .40 in
new cap / rotor / non - oem wires
new tranny fluid and filter.
(Oh yes upstream O2 sensor last year.)
Truck was boggy before these mods - they mask it now; but it's there. I found a vacuum leak one time and the truck was night and day different when I fixed the split hose.
I can't find a leak but I can feel "something" going on. Frustrating.
If I have the truck idling and goose the throttle it will "chuff" for a moment like it's getting too much air and can't react quick enough then it will catch and quit stumbling; this is very noticeable warm or cold.
I have looked down the throttle body but seen no puddling of oil; maybe there is a sheen of oil and some carbon there; but no puddles.
I checked with a vacuum gage and found pressure in the crankcase; not vacuum.
I DID notice that the pressure did not seem to go above 1 pound of pressure.
That made me wonder if there could be a mild leak that won't allow the pressure to build beyond a small amount of pressure.??
Can you help me - I really want this to go away.
I realize it's a v-6 but it used to pull quicker and harder - now I have to wait for higher rpms
-br
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hey
Dodge Dakota
JOIN HERE
9/16/2009
12:30:07
|  RE: 3.9 flat spot / bogging problem
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Message:
Have you checked the fuel pressure?
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boltonranger2
Dodge Dakota
JOIN HERE
9/16/2009
13:08:13
| RE: 3.9 flat spot / bogging problem
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Message:
No - I honestly hadn't thought of that.
I'll look tonite provided no rain :)
Do you know what the spec pressure should be?
-br
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Bob Lincoln
Dodge Dakota
JOIN HERE
9/17/2009
08:26:42
| RE: 3.9 flat spot / bogging problem
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Message:
Never do mods on a vehicle that is not performing properly already - it complicates the diagnosis.
"I checked with a vacuum gage and found pressure in the crankcase; not vacuum." Which would indicate that your PCV system is not operating. So check that.
"3923 autolites @ .40 in" That for sure would be a problem - almost a half inch spark plug gap. LOL. I think you mean "0.040 inches".
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boltonranger2
Dodge Dakota
JOIN HERE
9/17/2009
09:19:05
| RE: 3.9 flat spot / bogging problem
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Message:
Thanks for the reply Bob.
Yes .040 on the plugs.
The pressure in the CC is when everything is blocked off - The normal check for belly pan gasket leak.
The unusual thing or at least the noteworthy thing is that pressure doesn't continue to climb past about 1 psi.
The problem exists mods or no. Just more tolerable with mods.
Any other thoughts?
-br
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withheld
Dodge Dakota
JOIN HERE
9/17/2009
10:36:56
| RE: 3.9 flat spot / bogging problem
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Message:
Hi Bob
I agree that the PCV may be faulty or not working.
But
"flat spot / bogging problem"
highly unlikely the PCV.
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Bob Lincoln
Dodge Dakota
JOIN HERE
9/18/2009
08:27:43
| RE: 3.9 flat spot / bogging problem
IP: Logged
Message:
Yes, but a vacuum leak could affect the PCV operation, and can also cause bogging. He already found and fixed one leak.
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J and J Auto
GenII
9/24/2009
02:58:05
| RE: 3.9 flat spot / bogging problem
IP: Logged
Message:
dodgeram.org
here you will find a methoid of how to check for
a pletium leak
another thing it could be is a glitch in the
TPS
fuel pressure while cranking around 45psi
they will still run down to 30psi but mileage
and power will suffer higher is better I run
an aftermarket pump at 50 55psi
Larry
J&J Auto
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