Hi,
My 1995 XJ6 runs well except I have to have my foot touching the gas pedal on startup. Otherwise it stalls 70% of the time. Hot or Cold.

If I just put a tiny bit of pressure on gas pedal it always starts immdiately and always runs perfect.

Idle is perfect otherwise (around 800, can't remember). But on startup it drops down to 300-400 for a second and stalls most of the time.

This happens with multiple ECUs (I've swapped to check). Something is dropping the RPMs way low only on the first second after cranking.

Any suggestions? Maybe related to the Idle Air Control Valve, Idle Speed Control Valve, Fuel pressure regulator or some sort of purge valve on startup? Or maybe ECU needs Throttle reprogram? Or I guess a simple vacuum leak somewhere. Wondering what is most likely place to start.
Thanks.

(maybe similar problem in this thread : https://www.jaguarforums.com/forum/x...p-rpms-176691/ ) "STARTING UP RPMs"

 

Still having this issue... runs great, but needs a gentle touch on accelerator on startup to avoid low-RPM dip and stall (75% of time, I'm guessing, it would stall without extra gas-pedal touch).

 

Bad crank position sensor and ignition coils are common causes of this behavior. What kinds of coils do you have on it right now (original? aftermarket? recently replaced?)? I'd check the coils first if this doesn't get worse when the engine warms up.

 

Crank Position Sensor seems OK (RPM meter seems right. And I thought car wouldn't run without the sensor).
Coils are probably all original from 1995. I'm curious as to why they'd cause the engine to drop RPM just for first 3 seconds (then it pops back up, if it doesn't stall)... Thanks!

 

A failing CPS can be intermittent, getting worse when hot; on second thought that's probably not the cause of your problem if it's a problem when cold. My random stalling problem went away when I replaced all six coils with the correct OEM-spec ones; I still get an occasional dip in RPMs, maybe down to a vacuum leak. Have you replaced your fuel filter recently? I had an X308 that would occasionally stall when idling, and that went away with a new fuel filter.

 

My guess is your Throttle Body is gummed up. As a first step I would inspect and clean it.

There should be a small gap at the butterfly but if this is gummed up then the engine is starved of air at start up until the IACV comes in to play and adjusts the air flow. Your slight opening of the throttle is compensating for the lack of natural gap on the butterfly. Just my theory.

 

That makes sense. So you recommend just taking a toothbrush to the butterfly without removing throttle body?

 

Suggest putting finger on fuel pump relay and feel the thump , 5 second on then off priming of the fuel rail with key to on ( not start ) position . As the ECU sees rotation ( after start ) you should feel the relay thump again to power the pump for the duration of your drive .So you are feeling for 3 thumps the 3rd being the one of interest . You may have fuel starvation as it only has the prime charge to work with . Try this test cycle 5 - 10 times for if this is the issue it my be intermittent . It's the 2nd one from the far right in the trunk . You can swap the relay with the accessory relay in case the fuel pump relay has bad power circuit contacts not fully spinning up the pump to give you enough fuel pumping volume to sustain the engine beyond the initial fuel charge . 4th relay from the far right .

With the Hall Effect sensor in theory you should see a pulse with an old school needle analog meter with the voltage setting . With the slow rotation of the starter you may see the 6 different durations of the 6 different window gap dimensions that identify exactly which # cylinder it is looking at . Since the AJ16 will run just fine without this Camshaft sensor as XJR Engineer pointed out only in the initial spark timing and then the Crankshaft sensor takes over . I personally would not concern myself with the Camshaft sensor for your issue as you define it is after this point in the start to run sequence .

If you are close to an O'Reily auto part store they have a free coil tester that all stores do not have and the staff is not trained on how to use ( the on switch is on the back ) not rocket science .
INNOVA's 4400 Coil Tester with adapter # 34 gives pass / fail test for whatever it is worth . I'm tempted to design my own tester that will give a voltage value that that can be used to determain the degradation from 100 % new . Some coils took 3 trys before they would pass so gives me no confidence in it being a valid test ( other then the on car variables of considerations which is not simulated on the bench ) .


Thanks , Parker

 

You can obviously do a better job of cleaning the Throttle Body with it on the bench and it's not that difficult to remove on the NA cars.

But if time and/or enthusiasm is limited you can do a decent job in situ. Take care not to contaminate the TPS which is at the bottom of the Throttle Body.

 

Madijag,

have you found the problem to our issue?

 

No, I just tap the gas a bit on startup and all is OK. I've yet to clean the throttle...
John

 

LadyP,
if the fuel pump relay is bad, shouldn't I have tons of other problems? can the car run well with a bad fuel pump relay? thanks!
>> You can swap the relay with the accessory relay in case the fuel pump relay has bad power circuit contacts not fully spinning up the pump to give you enough fuel pumping volume to sustain the engine beyond the initial fuel charge

 

john,

Can you give an update please? Having same issue here. Always have to give it some gas when I crank it.

 

I've yet to try some of the suggested things...soon, when I have time...lots to check.
1) clean throttle
2) check all coils
3) look for vacuum leak
4) idle air control valve
5) EGR purge valve
6) fuel pressure regulator

 

My fuel pump control circuit was intermittent . If it only stall as you put it in gear from what I have read the on the transmission connector will kill the engine , A current problem solver was able to fix his shift stalling problem by keeping the switch in the sport mode . Hasn't checked the connector yet . The pulse duration time of the injectors are at the lowest during idle and if you have a couple of slow responding injectors issues would show up in this area of operation . Plugs are critical on this engine ( Jaguar TSB recommends Champion RC12YC on one and another is to gap out to 0.040 from the previous 0.035 to reduce the current on the coils ) . You can regap back to the 0.035 to compensate for weak coils . One person used a new fangled E3.48 plug to resolve his stalling . Price is not bad. Any thing on a binding IAC valve , maybe a code . The parts stores will read the OBD2 codes for free . As you have the throttle body off this is the time to remove the IACvale for the mounting bolts are buried aterwise . Look at it's installation first before removing TB and you'll see why

 

Hi, the stalling is not related to putting it in gear. It stalls on its own only when first starting. Runs fine after 2 seconds of revving.

But yes, adding "clean fuel injector" to list and "check fuel pump control circuit/relay"!

 

You might be getting that first 3-5 second prime then off but not the 3rd click to constant on as the engine eats the primer fuel charge . The crankshaft sensor gives the ECU the engine rotation signal to turn the pump back on again . The sensor can show on the gauge but fail to show at the ECU

 

Lady Penelope, I thought the ECU would shut down if it didn't get a crankshaft reading?
I did change the camshaft sensor last year, so I think both are OK.
thanks.

 

Yes on the crankshaft sensor if it is a complete failure , but as it degrades somewhere below 100 % the ECU will not see it . See if you can return it as a swap out like I did with mine as I was troubleshooting mine . Some people suggest keeping a spare in the trunk out on the road . Camshaft sensor is only used in the initial start first rotation before it's finer cylinder location function is taken over by the crankshaft sensor . The camshaft sensor sees each 1 - 6 cylinder but the crankshaft sees only 1 or 4 and has to " learn " which pulse is truly 1 . Crankshaft turns at twice the rotational velocity relative to the cam . The engine will start without the camshaft but will take a few more engine rotations . You may be doing fine on the camshaft but the ECU can't transfer over to the crankshaft . If you wan't to really clean a lazy injector you have to remove them and pulse some MEK trough them . Your coils at this age should have dropped below 100 %

Thanks , Parker

 

UPDATE:
When the weather is very cold (at around 10 degrees F, or -12 C) the car won't start. Car sits outside and temps going even colder at night. It seems like it wants to start, but after 2 seconds it dies. Always. I can try pressing gas and get it rev up for 1 second then it dies. When weather is a bit warmer car runs great.
Installed new spark plugs, coils, fresh battery and cleaned throttle. Also swapped Crankshaft sensor. Camshaft sensor would be a 50/50 thing (and I replaced a year ago) . Fuel definitely getting to cylinders. One thing I noticed is a gurgling sound from mufflers(silencers) when running. No engine codes.

I'm going to try a different computer with latest EPROM.

Other possibilities:
Leaky Injector flooding engine over time
Fuel Pump Solenoid intermitent flaky
Fuel Pressure Regulater intermitent flaky
stuck EGR valve
Frozen exhaust pipe?

Anything else to check? Thanks for your help.
BTW: Stall without pedal pumping on startup still occurs in warmer weather. But in very cold weather pumping gas doesn't keep engine going.