Dear All,

My 1995 XJR 5-speed manual recently went through a series of mechanical upgrades. After a few weeks of trouble-shooting and refinement it has become my daily driver. However, today it suddenly stalled a few times before coming to a stop before the traffic light (for manual cars, it is common to disengage the gear by depressing the clutch and letting the car slowly roll forward by momentum before braking for a full stop). The sudden stalling was sort of scary as there were cars from behind who might be unwary of a stalling car in front, especially at the traffic light. Fortunately, I restarted the engine quickly without problem, and, when noticing a stall while the car was still in motion, I depressed and released the clutch to get the car back in gear thereby recovering the engine (as in the case of a push-start which only works on manual car). This trick helped me drive her home but she stalled again 20 meters before the final destination. Hooked her up with the Autologic scanner but found no codes.

Before this episode, the engine was difficult to restart when hot, even after a short drive. The situation improves a great deal after recalibrating the O2 sensor and engine idle speed by the Autologic scanner, and using the car a bit more. If and when the symptom returns, cranking the starter a bit longer or trying again would work. Engine idles perfectly at 750 rpm. However, a day ago, I noticed that the engine hesitated a little when falling under 750 rpm and then went back up. Unfortunately, today, the hesitation lasted longer and it was unable to hold, then stalled.

Backtracking a little more, recent works done included the following:
(a) upgrading the lower supercharger pulley and replacing the AC belt and engine belt with shorter ones to avoid rubbing due to tighter clearance among the revolving parts;
(b) replacing three ignition coils and crankshaft sensor after detecting knocking on Bank 3 and random misfire;
(c) replacing the water pump, generator and harmonic balancer (this was part of the trouble shooting to kill a terrible high pitch squeak on engine start-up).

The car drives pretty well, but there is occasional misfire, only detectable with the windows down, but there are no codes.

Further backward was a long history of restoration from a bad no-start a few years ago due to long standing in the open - so the engine has new fuel pumps, fuel pump relays, fuel filter, ECU remapped by Andy Stodart, new fuel pressure regulator, fuel injectors, O2-sensors, all new coil packs manufactured in Japan, a good wash of the fuel tank and fuel rails, and stainless steel headers custom-made by Hayward & Scott in the UK. She also has new downpipes and floor pipes and tail boxes fitted. Simply put, there were no stones unturned.

Was wondering what might have caused the stalling? Fuel pressure, failed coils, ECU? Any thoughts?

 

Fuel pressure :

You can jumper the # 1 fuel pimp relay socket from 3 to 5 , the pump will run at all times so will drain the battery with the keys in your pocket

Jumper the # 2 fuel pump relay socket 3 to 5

The # 2 does not normally come on until 400 RPM and drops out at 3200

The fuel pressure should be 43 PSI , but hard to get a reading

Fuel pressure regulator , don't last forever

Keep the old coils ?

Fuel injector cleaner

Noticed the voltmeter drop on idle ? correlates to the alternator change

With the manual transmission you do not have a transmission connecter that can get oil into it

 

Could have a leak on the new exhaust manifold installation , causes over fueling at idle RPMs

 

My first suspect would be the IACV.

 

The 4 wire IAC valve ( stepper motor ) has 9 pin pair combinations to check with a meter

With a meter warm up the IAC motor as to make it fail

Some did find a IAC valve substitution

There should be a gasket under the valve mounting

The 5.5 mm bolts can snap off , loctited , so consider removing the throttle body to get heat from the inside

Vee's suggestion on giving the blades of the connector a slight twist to get better contact

Vee also had a IAC reset procedure

 

Here is an update. I took the car to a professional exhaust workshop to identify any possible air leak, and bingo, they found several leaks from the gaskets/seals between the exhaust manifolds and the downpipes, and another leak at one of the middle boxes. There was also some carbon build-up at the tail pipes, indicating that the engine has been running rich. After visiting the workshop, the car drove very well without a single stalling, but after a long drive, I still noticed a slight drop of engine idling speed below 750 rpm, but the ECU quickly intervened to push it back up to 750 rpm. So I would not rule out other factors causing the engine speed to fall below 750 momentarily. Will continue to monitor the engine performance over the next few days.

 

Here is another update. The next day after fixing the exhaust air leak, the engine stalled only once, but is a reminder that air leak might not be the primary culprit. The second day after a long drive and a short rest, the engine played up again - all previous symptoms re-emerged: engine refused to fire up during warm start a couple of times, and then fired up reluctantly and then died, and foot had to be on the accelerator to help maintain engine idle, but once the foot was off, it died. Cycled this a few times the engine struggled to idle around 750 rpm. With symptoms subsiding, took it out for a test drive and it died every time it came before standing still, i.e whenever it was not in gear (it is a 5-speed manual). Restarted quickly and then died. Gave it a big foot and it plunged back to zero. Took it home, scanned for codes and there were none. Then it started alright, initially with a shaky idle, and then became steady as if nothing happened. Took her out for a spin and then everything was fine.

I recalled that the first time such symptoms happened was the second trip after replacing the alternator, the water pump and the harmonic balancer. There were no codes and after re-calibrating the O2 sensors and the engine idle, the problem did not recur until two weeks later. The problem subsided after fixing the air leak but re-emerged only once the next day. It intensified the day after when not in gear, but it just came and went, not continual. My impression of such sporadic stalls is that it could be due to fuel deprivation, sudden drop in fuel pressure, or electrical interruptions. Would welcome any advice on trouble-shooting and fixes.

 

The # 1 fuel pimp enable after the starting sequence is the crankshaft position sensor , rarely if ever gives a crankshaft position sensor code P0335

Both fuel pumps relays control fuse ( is 1 ) is # 10 in the right side heelboard fuse box

This fuse # 10 requires that the relay in the corner of the fuse box to close and can be intermittent underperforming

Your fuel pump relay is point 7 double hash circle




This relay can be swapped with the one in the left engine bay fuse box ( this relay in reality only controls the horn )

" and foot had to be on the accelerator to help maintain engine idle, but once the foot was off, it died. "

Points away from fuel not being present

Do you see voltage drop on the instrument cluster on deceleration ? ( this points to voltage regulator response inside the new alternator )

The # 1 fuel pump relay can be periodically underperforming but not fully failing ( burnt power contacts making the fuel pump underperform )

See also the Papa Indy 61 connector subject of a TSB for corrosion



It is the black square under the conduit just like the white one

 

I have the NA AJ16, not the supercharged one you have.

I had a devil of a time resolving what was a dip in idle every 32 seconds. When the car was loaded up, you know AC, headlights, radio, etc, it would sometimes stall out. The problem ended up being a leak at the intake manifold. Two shops (one being a Jag specialist) could not find that leak. It was only after taking it to third shop that they were able to find the leak.

If that sounds similar, then perhaps that’s the problem?

If your car is stalling while driving, that’s a different story. I had a problem with a failing EGR valve that would randomly stall me out, while driving. I eventually was awarded with a code. Eventually. Replaced it and never had that problem again.

 

uncommanded egr because of a bad position sensor will cause the car to run awful at idle

bad iac stepper will do the same thing

bad tracks on a tps is also a possibility

 

Many thanks. I would check the intake manifolds. How was your leak fixed? Need you throw any new parts to it, as most parts are no longer available. As for the EGR, mine is a Hong Kong dealer’s car - a couple of years ago I bought a new one for preventive maintenance but could not see one on my car.

 

I just recently changed the CPS with three of the ignition coils, but it did not help. Would also consider the iac stepper and the tps next.

 

you can unplug the iac as a bandaid, aftermarket ones would give up in like 6 months. low startup idle but once warmed up you’re good to go

 

my intake manifold gasket was replaced and problem was solved.

you probably don’t have an EGR. I believe it’s a USA thing.

IACV and CPS are cheap parts that are easy to replace by anyone. I’ve used cheap aftermarket parts in both occasions with long lasting success on my 96 XJS with the AJ16.

(IACV uses tiny bolts which will snap if removed with force. Best to make sure the bolts are HOT before attempting to unscrew them, to break the Loctite bond)

The TPS is an expensive part. Simple to replace on the NA engines. Proceed with financial caution here.

 

Before replacing the TPS , with the engine not running but key at run position ................

The middle wire ( Green / Yellow color ) of the TPS at the TPS connector and connected should read 0 60 volts DC at the idle stop as you manually twist the throttle butterfly to the closed stop

This Green / Yellow wire comes up and over the fuel rail

You van also do this test from the ECU connector with key off and looking for resistance

On mine the TPS connector lock silver bar was missing to hold the connector on firmly

This 0.60 is a very precise value so digital meter

As you very very very slowly open the throttle you should see a very smooth increase in voltage toward but no to 5

No spikes or jumps on your meter

 

Thanks pals for the generous and helpful input. Will get hold of the parts first. A the XJR is less friendly when it comes to engine bay work, and very few people in Hong Kong have the luxury of their own garage and workshop tools, I can't do it DIY and will have to entrust the assignment to my mechanic.

 

I disagree with Parker regarding the 0.60v. While it is true, that the ECU is programmed to read 0.60v from the TPS as the base idle setting, the ECU is designed to learn and accept slight deviations from this value as the car ages and gunk accumulates.

This is the reason which makes the TPS Reset feature is so valuable. When throttle bodies are cleaned, when TPS sensors are replaced, when ECUs are swapped out, and other mysterious events, the car often returns with high idle issues. The TPS reset will teach the ECU to reset whatever value it is expecting to what it is seeing now.

0.60v is only the known value when the car and engine was new. Since then, if any mechanic "reset the TPS", that 0.60v value has been replaced. Furthermore, if over time the car got used to seeing 0.62v as the base idle because of age and gunk, then the 0.60v value has also been replaced.

Does that make sense?

 

Given how much you have already spent, and the considerable difficulty involved in working on them in the supercharged car, it would be tempting to take the inlet manifold off, enabling a new gasket together with new IACV and TPS to be fitted. Worth ticking these off as semi maintenance items anyway.
Just before embarking on that plan, have you checked your alternator / battery? Various mission critical components are very sensitive to voltage level. If your voltage drops as you come to rest, that could be a relatively simple explanation.

 

The battery is very strong and healthy and never disappoints during start-up; the alternator was only replaced new in an attempt to iron out its bearing being the suspect of the noise on start-up (traced to the harmonic balancer which was also replaced with one rebuilt by Dale in the US). Parker suspected that the voltage regulator inside the new alternator could be another suspect. I am keeping all old parts so will let the mechanic knock out all possibilities once the car is in his workshop. The car is now grounded until all parts are ready.

 

If you are replacing that intake manifold gasket, make sure to replace the ******* hose while you are there. Super cheap, and super easy while you're in there....