Jeeps Canada - Jeep Forums - Re: 04 Wrangler Spark Knocking

Roughly 12/22/03 17:26, Wrangler x's monkeys randomly typed:

>
> Here is a follow up to the story above for those of you wondering what happened
> here. I appreciate the few responses I got.
>
> I went to a different Jeep dealership, and they said it sounded like perhaps my
> transmission was the problem. The resident transmission expert hopped into my
> Jeep with me and rode around town with me for 30 minutes listening to the
> engine. Nice guy - very smart - he seemed to know his ----.
>
> I approached a hill with overdrive engaged (it engages by default), and we began
> to ascend. The transmission shifted from 3rd to 4th, and then RPM's dropped to
> around 1200. The engine starting the pinging/spark knocking noise, and I said,
> "THERE IT IS!"
>
> This is a summary of what he said.
>
> 1. That's not spark knock. That's "lugging." Your engine is working to pull the
> hill. Spark knock on a jeep sounds like a the engine suddenly became a huge
> diesel engine. You wouldn't have to listen for it. It will be loud.

"Lugging" is another cause of preignition, predetonation, also
known as pinging. A short mild burst of it won't hurt anything,
old time hotrodders have been known to adjust timing by cranking
it forward until this burst of pinging happens upon mild lugging.

Short bursts of pinging under lugging tend to be harmless. If
it KEEPS pinging under lugging, the engine is mistimed or
misprogrammed or has a hot spot in it. And the transmission
shift points are poorly matched to the engine.

Sustained lugging probably won't hurt a 4.0. On the other hand,
the reason oldtimer Porsche drivers always run around in a low
gear is that the old roller crank Carrera engines would tolerate
no more than a few milliseconds of lugging before they crunched
a crank bearing or two.
>
> 2. 2004 Wranglers with automatics have a new feature this year: 4 speed
> transmissions. 2003 and earlier were all three speeds. The 2004 is a four speed.
>
> 3. The ratio between gears 3 and 4 is not so great.
>
> 4. Overdrive is the use of that 4th gear.
>
> 5. When you are flying down the highway at 70mph, your engine doesn't lug
> because you are at high RPM's in overdrive.

Unless you put your foot in it, or try to climb too steep a hill
and your transmission doesn't downshift properly to eliminate
the lugging condition.
>
> 6. When you are driving around town, you should disable overdrive as soon as you
> start your car. Unfortunately, overdrive enables automatically on every power
> recycle (turning it off and back on), so you have to push the button on the dash
> every time you start your car. Only enable overdrive on the freeway with no
> traffic for long distance trips.

This is just plain silly or BS. But given number 8, will refrain from
suggesting
the mechanic doesn't know shift from Shinola.

The transmission should simply downshift when the load on the
drivetrain is high enough to lug the engine. If this means coming
out of overdrive, it should do so. First it should unlock the
torque convertor to allow a bit of slip, and if that doesn't
reduce the lug condition on the engine, it should downshift.

>
> 7. Replacing the transmission will not help, as all 2004 transmissions are four
> speeds, and all have the same problem. He says they have seen this a lot in
> Jeeps owned by perceptive drivers. Most are sorta dumb and never notice the
> problem. They just drive through it.

There are thousands of Jeep 4 speeds that don't lug at highway speeds.
I have a mild ping at 45-50 if I step on the gas very lightly, for the
first coupla seconds as the vehicle catches up with throttle position.
Only happens on sealevel grade regular. As soon as the vehicle
catches up with throttle position, it quits pinging, or if I push the
gas pedal only slightly harder, it downshifts.

Up hills it don't ping, it just downshifts.
>
> 8. He said that flashing the controller software would help if Jeep changes the
> settings at which the Jeep decides to upshift. Currently, it is set to upshift
> from 3 to 4 way too soon, making overdrive use around town a pain. There is no
> flash upgrade available at this time. He told me to keep checking because one
> was expected eventually - so many people had complained about lugging in 4th
> gear. Recall expected...

This is very likely true, and the fix. Perhaps an aftermarket
shop can switch the shift points.

There is kinda a fine line here, if the downshift is made too
sensitive, the transmission may "hunt" between 3 and 4 on
moderate hills. If not sensitive enough, the engine will lug
and may ping. If it is less than a coupla seconds, you may
find the ping less annoying than a hunting transmission...and
can simply move from regular up to midgrade to get rid of it.
>
> Otherwise, my Jeep is fine. We drove it around with OD set to off, and it works
> great without the lugging. I wasn't aware that it reset to on with each power
> recycle, so I thought it was compensating, when in reality the overdrive was
> re-engaging.

Probably also the lockup torque convertor isn't releasing. This
isn't as annoying as a transmission that can't make up its mind
between 3rd and 4th.
>
> So, two things Jeep needs to get straight on automatic Wranglers:
>
> * Overdrive should default to OFF, you should push a button to turn it on, and
> the setting should be persistent from one power cycle to another.

Doubt if they could get away with this, could cause a CAFE failure.
Far better to reprogram the transmission to match the vehicle's
weight and rear gearing.
>
> * The controller software needs to be updated so that the Jeep doesn't leave 3rd
> until reasonably high RPM's, to prevent lugging on hills around town.

The real fix.

--
Fan of the dumbest team in America.