I have a small issue with my Jeep Liberty CRD that happens sporadically when the jeep is stopped with the brakes applied, the transmission in drive and the A/C is on.

The engine surges upward and downward 1 or 2 increments on the tachometer quickly and continuously.

If the shifter is moved to the park position or to the neutral position while the A/C is on, the engine runs normal.

If the A/C is turned off while the shifter is in drive, the engine runs normal.

The issue only happens while the jeep is warm, the shifter is in drive, the A/C is on and it has been running for 5 minutes or more.

Can anyone help decifer what is happening here?

As always, I appreciate the help.

Racer

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2006 Liberty Limited CRD, Deep Beryl Green, Yeti tune, Arp studs, new cams, rockers, lifters, TB. "Green Monster"
2005 Liberty Sport CRD, Deep Beryl Green, GDE Hot Tune, ARP studs. "Rocket"
1982 Fiat 124 Spider Convertible. "Fiona"

The wifes will do the same thing. What about when the clutch on the AC comp. comes on? will it do it then or just at random?

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06 Cummins 2wd- industrial injection sliver bullet 66,pdi manifold,smarty(tnt tune),Dr. Performance predator w/ race tune,Fass 150/200,Goerend full billet trans,Pusher intake manifold,snow meth,boost fooler,cal tracs, Stage 2 AFE, about 9 isspros, II dual feed lines, wicked injection pump, mag hytec's, studs,spings and cam.

2005 CRD

It will only happen when the transmission has been engaged into drive and running hot for some time and the A/C is on, not sure when the A/C clutch engages, I thought that the A/C clutch would always be engaged when the A/C switch is on.

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2006 Liberty Limited CRD, Deep Beryl Green, Yeti tune, Arp studs, new cams, rockers, lifters, TB. "Green Monster"
2005 Liberty Sport CRD, Deep Beryl Green, GDE Hot Tune, ARP studs. "Rocket"
1982 Fiat 124 Spider Convertible. "Fiona"

A pressure switch causes the AC compressor clutch to cycle on and off under normal operation. The load of the compressor clutching in and out can be noticeable at idle.

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Matt B.

05 Limited CRD. Bought it new. 112k on the clock now.

GDE Eco-tune, rear differential drain plug (drilled and tapped the pumpkin), transmission pan drain plug, Fumoto oil valve, fuel filler neck restriction removed, front hitch, Hayden fan clutch, Sears P1 battery since 08, Mobil 1 5w40, 5 volt glow plugs, DIY timing belt at 109k

The ECM controls the idle speed, if you have a tune, talk to your Tune Guru. Choices are made when parameters are selected and altered to achieve the desired results but for ever action there is an opposite reaction. So the idle speed when the AC cycles may be a trade off to having better fuel economy. Again ask your Tune Guru, it may or may not be the case, but there may be something else that can be tweaked.

One other thing to check would be the amp draw on your electric fan & AC clutch by measuring the draw going into the Power Distribution Center, this would be a long shot but can be a possible cause contributing to the problem. Post what you find and another member could check theirs as a base line.

I am still running a stock tune (upgrade coming later) and I don't notice any RPM changes, only a little louder diesel clatter when the AC kicks on or shifting into or out of gear. My fuel cooler also has made my idle speed less sensitive to minor load changes than before I installed it a couple years ago. Hot fuel is thinner and has slightly less BTU/unit than cool fuel, this may be why the idle speed is more stable with my fuel cooler.

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2006 Pearl Green CRD
Magnaflow 2 1/2" Cat Back
KJ Extra Leg Room Brackets, Carter Lift Pump, V6 Airbox, ORM
Fuel cooler, Oil Separator, Progard 7
Gauges EGT Boost Trans Temp Oil Pres, Michelin LXT AT2 245 70 R16
7,000# Draw Tight hitch, PML EX Deep Trans Pan
Centrifuge, SunCoast, Transgo, RAM TCM, InMotion Stage 2
Wife's 99 TDI VW Beetle

When the vehicle surges up and down, like I explained in my post above, it sounds like it is starving for air or fuel.

This does not happen when the transmission is in park or neutral and the A/C is on.

It only happens when it is in drive with the A/C on.

You think that the Hot tune may be the cause of this issue?

I will be speaking to GDE on Monday.

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2006 Liberty Limited CRD, Deep Beryl Green, Yeti tune, Arp studs, new cams, rockers, lifters, TB. "Green Monster"
2005 Liberty Sport CRD, Deep Beryl Green, GDE Hot Tune, ARP studs. "Rocket"
1982 Fiat 124 Spider Convertible. "Fiona"

x2

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06 Cummins 2wd- industrial injection sliver bullet 66,pdi manifold,smarty(tnt tune),Dr. Performance predator w/ race tune,Fass 150/200,Goerend full billet trans,Pusher intake manifold,snow meth,boost fooler,cal tracs, Stage 2 AFE, about 9 isspros, II dual feed lines, wicked injection pump, mag hytec's, studs,spings and cam.

2005 CRD

I dont have have a tune yet and mine does it........

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06 Cummins 2wd- industrial injection sliver bullet 66,pdi manifold,smarty(tnt tune),Dr. Performance predator w/ race tune,Fass 150/200,Goerend full billet trans,Pusher intake manifold,snow meth,boost fooler,cal tracs, Stage 2 AFE, about 9 isspros, II dual feed lines, wicked injection pump, mag hytec's, studs,spings and cam.

2005 CRD

x3 and I've seen this on multiple vehicles tuned or not tuned.

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2005 Stone White KJ Limited CRD 4x4
Off-Road Pkg
Trac-Lok
Emu 790s/948s
Skyjacker H7088s rear/Bilsteins front
15x7 Black Rock Lobos/31x10.50 Firestones
GDE HOT Tune + TCM Tune
Euro TC
CB radio
Thrush Turbo muffler
AEM DryFlow filter

"The load of the compressor clutching in and out can be noticeable at idle"

The up and down surge while at idle, causes the SUV to rock back and forth and lurch forward with stored energy if I let my foot off the brake pedal.

This can't be normal.

Should the pressure switch be replaced?

Or what else could it be?

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2006 Liberty Limited CRD, Deep Beryl Green, Yeti tune, Arp studs, new cams, rockers, lifters, TB. "Green Monster"
2005 Liberty Sport CRD, Deep Beryl Green, GDE Hot Tune, ARP studs. "Rocket"
1982 Fiat 124 Spider Convertible. "Fiona"

To be honest i dont know what to replace or if you even need to replace anything. You need to find a friend/member on here that does a bunch of automotive AC work. I have had several AC classes and im certified in Automotive AC service but its just a run of the mill thing.....My daily driver corrola(get out of the way!!!! hahaha) does the same darn thing when the AC was on. shortly after the comp died. Not to scare you, crap happens i guess. I will call a friend and post back. can someone elts help????

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06 Cummins 2wd- industrial injection sliver bullet 66,pdi manifold,smarty(tnt tune),Dr. Performance predator w/ race tune,Fass 150/200,Goerend full billet trans,Pusher intake manifold,snow meth,boost fooler,cal tracs, Stage 2 AFE, about 9 isspros, II dual feed lines, wicked injection pump, mag hytec's, studs,spings and cam.

2005 CRD

Just got off the phone. Friends says when the AC comp clutch comes on, a signal is sent back to ECU/ECM that says bump the RPMs up a little to compensate for the load the AC puts on the engine.

Anyone care to say other wise?

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06 Cummins 2wd- industrial injection sliver bullet 66,pdi manifold,smarty(tnt tune),Dr. Performance predator w/ race tune,Fass 150/200,Goerend full billet trans,Pusher intake manifold,snow meth,boost fooler,cal tracs, Stage 2 AFE, about 9 isspros, II dual feed lines, wicked injection pump, mag hytec's, studs,spings and cam.

2005 CRD

My tach stays the same, but the engine clatters a bit louder when the AC compressor cuts on.
Anyone else with a fuel cooler notice this?

Before anyone gets the itch to change the pressure switch, hook up the gauges and check the pressures. A clogged orifice tube can cause high pressure resulting in higher compressor loads, but you can't tell with out the gauges.

All my AC headaches were caused by the top harness plug near the TCM that the clip popped loose on. Squeeze that plug together for grins and giggles. If you are lucky, it may be a miss communication signal going through the plug, solved by a squeeze.

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2006 Pearl Green CRD
Magnaflow 2 1/2" Cat Back
KJ Extra Leg Room Brackets, Carter Lift Pump, V6 Airbox, ORM
Fuel cooler, Oil Separator, Progard 7
Gauges EGT Boost Trans Temp Oil Pres, Michelin LXT AT2 245 70 R16
7,000# Draw Tight hitch, PML EX Deep Trans Pan
Centrifuge, SunCoast, Transgo, RAM TCM, InMotion Stage 2
Wife's 99 TDI VW Beetle

Warp.

I agree 100 percent but I suspect you have somthing wrong with the AC, fan or charging system and it's not taxing the engine enough when the engine power is increased to compensate for the added load. It's supposed to keep the idel the same when the AC is cycling
Both my 96 Passat and 99.5 jetta TDI's had that feature programmed into the ECM but the idel speed never sped up it just stayed the same. That's how it's supposed to work My crd with both the eco tune and stock tune the idel remaines the same when the AC cycles on and off. But my AC is working fine and is ice cold I do hear more clatter when the AC is on but again the tac remains the same

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Atlantic Blue 06 CRD Limited (his)
Joined by a 2000 XJ Classic (hers)

So your say'n that the ecu would not, or should not put out higher rpms? i dont know.

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06 Cummins 2wd- industrial injection sliver bullet 66,pdi manifold,smarty(tnt tune),Dr. Performance predator w/ race tune,Fass 150/200,Goerend full billet trans,Pusher intake manifold,snow meth,boost fooler,cal tracs, Stage 2 AFE, about 9 isspros, II dual feed lines, wicked injection pump, mag hytec's, studs,spings and cam.

2005 CRD

Just enough to keep the idel the same. I don't think it's "smart" enough to maintain a certain speed, just a boost to compensate for a certain power load. So for whatever reason you don't have the "predetermined load" then you end up with the surging your talking about

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Atlantic Blue 06 CRD Limited (his)
Joined by a 2000 XJ Classic (hers)

Sounds like a dilemma.

How do I locate the source of the problem?

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2006 Liberty Limited CRD, Deep Beryl Green, Yeti tune, Arp studs, new cams, rockers, lifters, TB. "Green Monster"
2005 Liberty Sport CRD, Deep Beryl Green, GDE Hot Tune, ARP studs. "Rocket"
1982 Fiat 124 Spider Convertible. "Fiona"

Idle should stay the same AC on or off with the ECM working to keep it the same.
If the Compressor load is too much, the engine RPM will drop. If the tune has changed the idle RPM stabilization to gain something else like fuel economy, the idle RPM will vary. Best plan is to hook up the gauges and check the pressure, squeeze the top harness plug near the TCM just to make sure (loose plugs lie like a Chicago Politician), and ask the Tune Guru if having the RPM fluctuation is normal for the tune.
Older cars had a kick up solenoid to try to make up for the AC induced RPM drop, you would need to adjust it to make the idle speed the same. Our CRDs is a closed loop system that should hold the Idle RPM the same.

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2006 Pearl Green CRD
Magnaflow 2 1/2" Cat Back
KJ Extra Leg Room Brackets, Carter Lift Pump, V6 Airbox, ORM
Fuel cooler, Oil Separator, Progard 7
Gauges EGT Boost Trans Temp Oil Pres, Michelin LXT AT2 245 70 R16
7,000# Draw Tight hitch, PML EX Deep Trans Pan
Centrifuge, SunCoast, Transgo, RAM TCM, InMotion Stage 2
Wife's 99 TDI VW Beetle

My alternator and charging system is working fine, but the battery is the original optima and may need to be replaced.

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2006 Liberty Limited CRD, Deep Beryl Green, Yeti tune, Arp studs, new cams, rockers, lifters, TB. "Green Monster"
2005 Liberty Sport CRD, Deep Beryl Green, GDE Hot Tune, ARP studs. "Rocket"
1982 Fiat 124 Spider Convertible. "Fiona"

Exactly what RPM does it surge up to? 900? 1000? 1200!!!

A little bit of RPM surge, when the A/C compressor clicks on, is normal, but should also be
un-noticable.

While idling in park with AC off, RPM should be ~800. If you put it in drive RPM should go down.
HOWEVER, the ECU is programed to keep RPM at ~800 and will add a little fuel to bump RPM
back up to 800 rpm. The ECU is always ready to anticipate this action and will add a prescribed
dose of fuel immediately when you put it in drive. Thus, this action should go un-noticed.

Same thing happens when the A/C compressor clicks on or when you turn the steering wheel.
The ECU senses the A/C click on or pressure in the P/S lines and adds a prescribed dose of
fuel to keep the RPM from dropping. Again, this action should go un-noticed.

If RPM is noticably rising under any of these conditions either the load (transmission engagment,
A/C system, power steering, etc) has changed or the ECU programming has changed.

Dave

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U.S. Army Retired