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

 

When I had a 3.9, I had a similiar problem. Are you getting any codes?

I know you said you looked at the TB, but was there any build up there? Giving your TB a good cleaning could help quite a bit. Another obvious, but maybe over looked, is your air filter. Probably not the entire problem but if its pretty dirty it can't be helping.

 

Thanks for the reply bpark-
I Bought some electronic spray for the MAP sensor today.
I've had success cleaning them on other vehicles; but they had 2 thin wires that would carbon up and not read resistance properly. Is the 3.9 map this way or different?
Bore does not appear very dirty from looking through the top; but what could it hurt?
Oh; also no codes reported. I get pdone with the key trick.
Stock air filter could use a new element; a year old I think; have blown off recently with compressor.
-br

 

just spray the MAP and such and see what that does...my 3.9 will also choke out if i goose the throttle, so it's not just yours (I think it's a by-product of the smaller TB on our V6's and a delay in the computer). It's odd that it boggs from 18-2300...IIRC that's right in the prime torque range, and mine starts moving around 2500.

Here's my poor 12 second 0-70, I haven't put my V8 TB on yet (as bad as this sounds, I lost one of the butterflies..!)

[youtube]cbKeb16L18A[/youtube]

 

My 2003 quad with the V6 started doing the same thing last year. I know mine tents to do it when I'm stopped and start to take off, and it doesn't matter if it is warmed up and leaving a store or somewhere or if it is cold and just leaving my house in the morning. It doesn't always do it, just randomly. I also would love to get this fixed too. I'm going to keep a eye on this thread and hopefully with more and more other people having the same issue some one will find the answer and then everyone else will know what to do.

Also, just another thought, you don't think it has anything to do with the new ethanol gas. I think 99% of stations use at least 10% of ethanol in their gas. Has anyone checked their fuel filter? I haven't had time to check my.

 

I would check your cat converter and see if that is plugged up.

 

Yeah a clogged cat will do it too. You might want to think about getting a 5.2/5.9 TB anyway. The 3.9 is a dog to begin with, let a lone in a QC. You can get one pretty cheap and it will help the motor breathe.

 

Have you replaced the Cat and did that fix the problem?