I'm having trouble with starting the Jeep Liberty, 2004 2.8 CRD. It will crank, turn over then cut out straight away. OR, crank for ages and do nothing. OR start, idle very badly, the idle dips, then it cuts out.

Seems worse if it has been left for more than an hour or so. If I've just used it, it starts fine.

Mechanic diagnosed cam sensor, I've also spoke to a CRD parts specialist, and they say it could also be crank shaft sensor, or both, as that is what it usually is, despite the codes saying otherwise.

My question, I get that this would cause a starting issue, but would either of these affect the revs at idle? It goes up and down, eventually dipping too low and cutting out.

What are the codes that you're seeing?

Air in fuel (check for leaks) or vacuum leaks are possibilities, but knowing what the codes are would help.

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2005 KJ CRD Limited 4x4:
245/75R16 BFG TA KO2s
OME / Clevis 2.5" Lift
JBA Lifted A-Arms
IRO WJ Short Rear UCA/WWDiesel mount
Skid Row Skidplates
HDS Model 001 Thermostat (190°F)
Suncoast TC
Full Weeks Kit
Bosch 5V glow plugs
Hayden 2986 fan clutch / GM 11-blade fan
Samco / Sasquatch Intake Hoses
Carter in-tank pump
Provent 200
V6 Airbox

I don’t have a way of swing codes myself, but mechanic said something about low current to the cam sensor being the only code.

Yes

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GDE FT Ecotune, EHM, Weeks kit stage 1 & 2, Carter 4600 lift pump, Upgraded tranny, Fishing boat hauler!
New at 164K: head gasket, rockers, exhaust valves, ARP head studs, Injectors, 5v Bosch glow plugs, water pump, timing everything, serpentine everything,
New at 225k: new head, timing belt

without ability to read the codes you are significantly handicapped. Generally when the crank position sensor goes bad there are no codes and it is hard to start back after the engine warms up then when cools off some after sitting a while it may start back.. It may also be helpful to note whether or not when it cranks but won't start if the rpm needle on gauge moves to show the rpm or not. If the rpm needle doesn't move it may mean the crank or cam sensor isn't functioning. Actually, I am not sure if our CRDs show some rpm when they don't start or not. I just tried mine and just as I think I see some movement beginning it starts. I know for sure my F350 truck won't start if it doesn't show RPM on a functional gauge.

I didn't disconnect fuse to keep it from starting but may be able to try it tomorrow. Perhaps someone else will comment on this.

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05 Blu LIM, OME GDE Tbo, wk II 245/75/17, KC Lights, bull bar, 195K H TC
05 Blu Lim, Dayton, GDE HT, 255/75/18 , 210K , H TC
06 Bla Lim, GDE Eco, Destination AT 245/75/17, 151K, H TC
06 D Khaki Lim 126K wkII Eur TC
05 D khaki Lim 145k refurbishing
All CRDS: Fumoto, Lift , Fan Shroud mod, fuel head Gen II, SAMCOS,self TB, 2 Mic filt, Hayden

Your battery doesn't have to be completely bad (will still crank) for the engine to not start, or to run very poorly. I believe the threshold for the computer to trigger the injectors, is 11v. If the battery voltage drops below that when cranking, it probably won't start. Have your battery and alternator load tested as soon as you get a chance. On this side of the pond, most automotive parts stores will do this for free. Not sure about the Euroside.

Crankshaft position sensors are notorious for causing start/miss/die problems with no DTCs whatsoever. So without replacing it, it can be really obnoxious to identify.

TKB4 identified common symptoms.

When mine failed, (is a 2006), if it managed to get fully to operating temperature, it would run all day as long as it wasn't shut off. Once shut down long enough to cool 15-20 degrees F., it would not engage the starter to crank. I have a switch to manually operate the starter, and with that, it would crank, but not start, until the engine had cooled off for 45minutes or more. In that circumstance it would crank and start properly, but only run until almost fully warmed, then, usually, stumble and die, until it cooled down again.

I'm pointing this out, because these buggers don't always exhibit identical symptoms.
Sometimes they crank, sometimes they don't.
Sometimes they go wonky when full temp, sometimes very nearly, sometimes when cold, or just about anywhere in between. I'm not certain why this is, but there is a quite long thread describing scenarios with quite a bit of variation in specifics, but all fixed by replacing this item.

Mine, and many others showed no DTC at all. A few others yet got a DTC indicating the CKP (crankshaft position sensor)

I haven't had a CMP (camshaft position sensor) fail, so I am unfamiliar with their symptoms, on this vehicle.

All this said, I have to concur with others who have guided you towards an air-in-fuel issue, as that is far more common in stock vehicles that have no in-tank fuel pump.

Please let us know what fixes your little gem.

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'06 Lbrty Sprt CRD 150K

Sasquatch
DSS Turbo
CAT-elimntr
Weeks Stg1&2 EGRfix
PV-200
BLING
vent gauges

IDParts
head
cams
rockers
Timing set
ARP studs
eTn1 GX2123 5v GPs

YETI Custom Tune
Flowmaster 8325508
Carter P76611M
GM 12611872
Hayden 2986
GM 15976889
PATC Custom Billet
2010 Ram Hemi Trans
Sonnax 44957
Transgo kit
Cooper 51770

Well I tried to prime the pump in the fuel filter head last night. Pumped about 200 times and nothing, very little air, and no fuel bled out. Then it wouldn’t start at all, to the point of the battery being drained from trying. Got towed to the garage this morning, will have to see what they say.