Hi There
Please suggest possible causes of 3.6 xj40 hard start
-car cranks normally but wont start unless i floor accelerator which clears flooded motor and than starts almost ok
-sometimes starts normally for no aparent reason mostly from cold
-ECU will show: instant fuel #99l/100km from time to time during the drive
-no errors on ECU display
-once started runs fine
- seems to be engine temperature related, longer the drive more certain it will go to #99l/100km and cause starting problems
The condition of flooring accelerator during crank pionts to CTS problem which i have changed but didnt help, the sensor connector wasnt very fresh and was replaced with push on clips instead, now only stripping the harness is left but i prefer ask for your wisdom before undertaking this mission
Would other sensor cause similar issue on this car? anything like MAF or TPS? This engine have no CAT or EGR, only sensors are CTS, TPS, CPS and MAF
Kind regards

 

I was going to suggest the CTS, but as you already replaced that (and it made no difference) I think if it were my car I would have a look at the fuel pressure regulator - do a search of the forum on the regulator for a test procedure - there is a problem with the diaphragm leaking and injecting raw fuel into the intake, so your super rich fueling and hard hot start would be accounted for if the FPR was at fault ..

good luck

Larry

 

Hi xjack,

I wouldn't be too worried about the onboard computer reporting unusual fuel consumption except that it indicates the ECM believes these unusual conditions exist. I've carefully tested the fuel economy on our '93 by the traditional method (fill up, drive a known distance, fill up again and calculate the miles per gallon used), and the onboard computer was always wrong, often by more than 2 mpg.

On the early XJ40s there was a known issue with fuel vaporizing at the fuel pump inlet, causing a kind of vapor lock. Jaguar's solution was to install a second fuel pump.

Intermittent fuel pump issues such as a failing pump or problem with the fuel pump power supply could also be possible.

It seems possible the ECM is not receiving correct signals from the CTS due to the harness modification, which could lead to the ECM applying cold-start fuel enrichment at all times.

Another possibility is that the charcoal canister purge valve is stuck open and fuel vapors from the canister are being inhaled into the intake at times when they shouldn't be.

Regarding the fuel pressure regulator issue Larry mentioned, you can pull the vacuum hose off of the FPR and check for wet fuel at the hose fitting which indicates failure of the diaphragm and raw unmetered fuel being inhaled into the intake.

Symptoms like yours often have multiple contributors. If it were me, I would replace the fuel filter and check to ensure the air filter is clean.

I would also clean the battery terminals and posts and the battery ground connection to the body, as well as the large jump start post in the engine bay and all the ground points in the engine bay, including the two on the intake manifold and the one on the bulkhead/firewall behind the cylinder head, and also the engine ground strap. I have photos on some of these topics, including the purge valve, ground points and battery power connections. See the link in my signature.

Cheers,

Don

 

Hi
I had a look into FPR as Larry sugested but it is dry and no signs of leak, i believe failing FPR would not affect ECU readings as fuel economy is calculated from injector pulse not the gas flow, so gas lost before injector would go unaccounted.
I agree with you Don that ECU shouws approximate numbers but in this case numbers are waay to high pointing for failure somwhere in the system. plus gas tank got empty pretty quickly this time and exhaust gases smell a bit raw petrol.
Air filter still looks right, i have fuel filter replaced last week, yesterday soldered new CTS in place as socket was damaged, car started at first crank in the morning, run great till operating temperature reached and some minutes more and than: bang #99l/100km again, paked it, and tried to start - no start without flooring gas pedal
I start to believe something electrical is shorting when hot or a ground connection issue. Does anybody know typical voltage at CTS terminals?
I got check engine 6 time ago, could TPS be at fault here?
Bad grounds definitly are part of problem here, gauges like engine temperature or fuel level go few bars up anytime headlight is turned on, i gonna go with Don advice and clean them if found.
The last thought - i hope it is not part of planned obsolescence, car reached his 400k km birthday and as urban legends go, strange things happen after this mark.
Thanks and regards

 

Hi Again
Some more testing and i can tell that #99l/100km onboard computer is not related to hard start, after some driving vcm stops to see car velocity and is unable to count fuel use, it affects trip computer only while main gauges are fine but if i switch to mpg/mph it shows 0mph
Any idea where did it fail?
I gonna replace FPR and see if it cures hard start issue, it is only thing that makes any sense to me, FPR and CTS harness
Regards

 

Another component to suspect is the fuel check valve. The check valve helps keep the fuel pump primed and works with the FPR to maintain pressure in the fuel rail.

If I recall correctly, on the 3.6L cars the check valve is in the fuel line just before the fuel filter. I don't know if new check valves are still available from Jaguar, but you can add an additional check valve anywhere convenient in the fuel line between the tank and the fuel rail. Click on the photo below for a photo album showing how I added an inexpensive check valve to our '93:

Welcome to Jag-lovers - Members Photo Viewing Page


Cheers,

Don