Hard to start AJ16 4.0l

Item 8 says “start the engine”. When I turned the key the starter motor engaged and the engine cranked and cranked and cranked as per usual; cranking got faster as it tried to fire but didn’t catch - ran up to about 700 rpm like this but the starter motor inertia was the only thing keeping it turning so when the key was released and the starter motor stopped helping the engine turn over it stalled. Are you absolutely sure that the procedure you describe is correct for the AJ16 throttle body IACV? I think it is different to the AJ6.

If the IACV was preventing it from starting surely it wouldn’t idle correctly either? But it does.

Took it down to my local independent in the week - he cleared accumulated codes and starting again from no codes and tried to start it. Same problem with v long cranking - but no codes thrown. Therefore, the problem can’t be related to a sensor which is monitored by the diagnostic system and I assume the IACV stepper motor is monitored.

Frankie

Problem found and cured - turned out to be the camshaft position sensor (as distinct from the crankshaft position sensor). Apparently the EMS needs both inputs to start, but once running can perform quite happily with the crankshaft sensor input only.

Now have a misfire, but I expect that is because I have disturbed a number of connections/inputs trying to locate the problem. Having just given the car a blast up the road the misfire is becoming less as the systems settle down again. One more “Italian tune - up” and I hope to be back to normal!

Frankie

My optimism has proved unfounded - the misfire persists. the symptoms are:- random misfire on load; several cylinders affected, not one; problem comes and goes during a trip; dashboard warning lights for washer reservoir, seat belt, handbrake, illuminate from time to time when driving apparently in conjunction with misfire; dashboard battery indicator (voltage) needle jerks in conjunction with misfire on idle.

I suspect electrics but battery and its voltage are good and I have checked/remade as many ground connections as I can see.

Anyone any ideas?

Frankie

I hope you have the ability to read data from your OBD2 port.

What are the long term fuel trims showing? (LTFT)

Left field, alternator going south?

Yeah, the voltmeter jerking around must be a symptom of something important. That’s just not supposed to happen. Considering how easy it is, I think I’d have the alternator tested.

Checked with a multi-meter this morning:-

Engine off, no accessories - 12.46v (across battery connections)
Engine at idle, no accessories - 12.2v when misfiring (across battery connections)

Filed paint off the battery earth strap to body connection to improve connectivity (looks to have been like that from new) and reassembled and took readings again:-

Engine off - 12.72v
Engine at idle - 14.53v (engine no longer misfiring)

Took for a run. Misfire seems to have gone but dashboard lights still come on and off and seatbelt warning still chimes occasionally.

Tried “loading” the system by switching on accessories whilst stationary and at idle. Turned on heated rear window; after 5 seconds or so engine spluttered and HRW circuit dropped out and dash warning lights blinked again.

Unsure whether an intermittently faulty alternator or poor electrical connection in the car wiring.

Frankie

Ran a couple more checks this afternoon. Misfire back as bad as ever.

12.65v between alternator “B” cable end and battery -ve
12.65v between alternator +ve “D” connector and battery -ve
0.13v drop between battery +ve and alternator “B” terminal with engine running and accessories “on”. However, the HRW relay kept dropping out and would not hold the circuit “closed” as before.

I read from this that the charging circuit is OK and that it is a faulty alternator causing the problems.

Would appreciate any further comments.

Frankie

Veekay - LTFT showing 0.00% for both

STFT showing 2.3% - 8.6%.

I’m afraid you’ll need to tell me whether those are acceptable results.

Frankie

The LTFT at 0…that’s exactly where you want to be. Rules out vacuum leaks, fuel pressure, even oxygen sensors…unless you haven’t driven it enough for it to register. I’m assuming the STFT flip flop all the time, that number should not be static.

Is there any chance at all the oxygen sensor plugs could have gotten mixed up somehow? You have two sets, one pair of upstream sensors and one pair of downstream. Could the A-Bank possibly have gotten plugged into the B-Bank by accident? I don’t think there’s enough slack on the wires to mix up upstream and downstream, but would it be worth your time to check this out. Basically you have to unplug both A and B-Banks and plug them into the other plug. Make sense?

Let me chew on this for awhile. ECU and the wiring itself are the only bones of contention for me right now…

The thing that has me scratching my head is that your misfire is intermittent and under load. Those other dashboard lights are also strange…as if…as if it was losing power somehow…but not enough to drop the engine, just the electronics within the car.

I’ve had misfires before. I had a ton of rain water get stuck in the plug wells. The engine ran like crap, and I got the blinking check engine light, multiple misfire codes, but not all of the other associated lights as well. That’s the part that’s troubling. I think those lights all tend to go on when the car actually stalls out? But you’re not stalling out.

I’ve never had an alternator tested, but perhaps you go to your local Napa or Advance Auto and have them check it for free?

1 Like

Yes - the Short term trim figures rise and fall within the range I gave above. I have replaced a few oxygen sensors on that car now and have always done one at a time so as not to mix up the plugs - alert to the need to keep them plugged into the correct sockets. You refer to upstream and downstream but on my AJ16 6 cyl engine there are only 2 sensors - one in each downpipe - European spec is different to the USA spec in 1996 I think. The code reader also gives the real time O2 sensor voltages and these readouts seem reasonable.

Misfire has been getting worse - now on idle - not only on load. I’ve never heard of a bad alternator causing this sort of misfire before - but then I’m only a home enthusiast, not a professional (which is why I bring issues I can’t resolve myself to the experts on this site!)

The alternator has done 77,000 miles so I’ve had my moneysworth; I can get a replacement at a reasonable figure so am thinking I might just do it and see if it solves the problem.

Frankie

Pins on the ECU are straight and clean?

You said that the crankshaft position sensor was swapped out. Can you swap it out again? Is there any difference?

Could it possibly have not been installed correctly? Could the bracket be damaged? Out of alignment? Not plugged in all the way?

What kind of spark plugs are you using?

Does anything change if you wiggle the wires that connect to the coils?

On AJ16 engines, hard to start is usually the |CPS starting to fail or
a bad connector. Misfiring under load can be fuel filter blocked or
failure of coil on plug (worth buying the best for this part). I think
you’ve tried these but worth checking again.

Jim XJSC 3.6 Manual

Brighton UK

Update. Fitted new alternator today - no difference. Starts “on the button” but within a minute starts to misfire on tick-over; the same warning lights on the dashboard come on and off (washer fluid level, handbrake and brake warning light) and the seat belt warning chimes. Seemingly at random the engine recovers and idles smoothly - the lights extinguish and the chimes are silent. Then problem repeats. Haven’t even bothered to try it on the road today.

CKPS swapped several times and it HAS been installed correctly; bracket fine and connector properly pushed home; Champion plugs haven’t been changed for the last couple of thousand miles so can’t see it could be them. Trying to think of a fault that could cause engine misfire and warning light illumination at same time. The fault is intermittent so I favour electrical over mechanical.

The only things I’ve changed recently are fitted a new fuel pump (can’t see it would be that) and a replacement (salvaged) Camshaft PS (to cure the long cranking issue). I don’t think that would cause the misfire but just to be sure I’ll put the old one back in and see what happens. And yes, I did make sure it was replaced at TDC with all marks aligning.

Frankie

Oh yes - the other light that comes on with the misfire is the seat belt warning light (same circuit as the chime I suppose).

Well, I took off cleaned and re-fitted the engine earth straps this afternoon and unplugged/replugged the cam PS whilst the engine was running - no difference.

I still think it’s a bad connection somewhere - finding it is the challenge.

I am beginning to fall out of love with this car!

Frankie

Does the 4.0 have that load thingy connected to the alternator?

I know the 94 xjs aj6 doesn’t and I would bet the later aj16 doesn’t either.

Turn on the interior lights. Report on whether they appear steady or flickering when the engine is acting up.

The symptoms could be explained by a fault in the ignition switch/circuit I suppose - the electrics behave as if the ignition connection flicks on and off in rapid succession. I will look out the wiring diagrams later and see if I can check the possibility out.

Another possibility is that I have disturbed something during recent work:- fuel pump replacement (tank out and wiring harness/relays etc in boot moved); wet and dry compression tests (much turning of starter motor with fuel relay removed); plug coils bench tested for resistance; fuel injectors back probed for resistance; screen wash bottle and fluid pipework flushed - but I am clutching at straws now.

Not aware of a “load thingy”!

Will try the interior light check and report back.

Frankie