I'm still struggling with getting the V12 to start in a non-embarrassing fashion in cold weather. It is not unusual for me to have to crank it for up to 10 seconds (and at times longer) to get it to light off.

Reflecting on this makes me think about the basics of starting. My limited automotive knowledge (this is the only car I've ever really worked on) is keeping me from understanding the problem.

The basic are, I suppose, that for it to start it needs air, a spark, and some fuel.

Air...I have no reason to think it's not getting that. If I put my foot down even a little, the butterflies should open enough to eliminate that as a problem.

Spark...I have that since it does, eventually, start. What would keep me from having spark (or possibly not enough spark in all cylinders) for 5 to 10 seconds ?

Fuel. Not sure how to test this. I hear the fuel pump run. I don't have any fuel leaks that I can detect with they eye or nose. Is there some mechanism whereby fuel could be draining out of the fuel rail after a prolonged period of sitting....and thus I'm just injecting air for the first several seconds of each start cycle? Would a bad injector allow fuel to drip into the cylinder and somehow let air into the rail?

FWIW, when it's "warm", it still takes longer to crank than I think it should, maybe 3-4 seconds.

Once I get it started, I have to baby the throttle for about 30 seconds or so, then it idles fine. On the road it runs great.

In my non-automotive mechanic mind, the only thing that really changes from start to 30 seconds after start is that the cylinders have gotten significantly warmer, as have the tips of the injectors. Maybe the injectors are doing a better job at vaporizing fuel after 30 seconds of running?

The starter. Maybe it's not turning the engine quickly enough? It "sounds" fine, but as I said I don't have enough experience to know, and there are no V12's around that I can listen to and compare.

FYI during the last year I rebuilt the dizzy, replaced the plugs, plug wires, ignition wiring to the amp. Battery is new, and I routinely trickle charge it every night.

Thoughts?

Thanks,

John
1987 XJ-S V12
63,000 miles

 

Cold start should always be "feet off" of pedal. The air from the .002" throttle gap should be enough. Are your throttle bodies clean, the linkages adjusted, and the throttle gaps correctly set? Worth doing on general principle even if it does nothing to solve the problem.

Contrary to most fuel injected cars, a slightly depressed throttle pedal is specifically suggested for warm starts. It's right in the owner's manual. I've never found that doing so changes anything, to be honest. Others will chime in.






In this case you'd probably be looking for a "weak spark" condition rather than a [temporary] "no spark" condition.

If you hadn't already replaced the wires I'd tell you to look for corrosion at the coil wire ends.

A weak coil comes to mind as a possibility....along with the usual mention of loose/dirty/corroded wiring connections








Fuel drain-back is possible, as is a drippy injector(s). Both would cause a bleeding off of fuel pressure. The latter would obviously cause over-fueling the corresponding cylinder(s).

If the fuel is draining back then the '2 second prime' feature of the ECU should recharge the fuel rail. Try turning the key 'on', wait for the pump to stop, then repeat a couple more times. This should positively recharge the fuel rail. If starting behavior improves then you're on the right track.

It should be added, though, that the fuel pump operates while the starter is cranking. It really shouldn't take more than 2-4 seconds to recharge the rail....so if you're having to crank the engine for 10 seconds the idea of a drained fuel rail seems less likely.

As for possible drippy injectors, are you sensing an over-fuel condition? Chuffing after start-up? Black smoke? Rich smell to the exhaust?

You can remove the fuel rail and visually inspect for drippy injectors ...or check with a fuel pressure gauge, charging the rail then pinching off the supply and return hoses...and watching for a pressure drop.






That isn't all *that* bad.




On both hot and cold starts?

Are you not getting a high idle speed with a cold engine?

During this 30 seconds is the engine very rough? Or is is just a matter of it conking out if you don't baby the throttle?





Well, partially clogged injectors can cause starting problems. Good general principle idea to remove them for professional cleaning. I'm not sure if I'd go there quite yet, though, in an effort to make the engine start more easily.




Possible, yes. Hard to judge. The standard issue V12 starter has a unique sound which makes it a bit hard to judge how fast the engine is cranking. I eliminate other possibilities first.



Have you checked the coolant temp sensor? It plays a key role in cold starting and, if skewed, can also influence warm starts. If you don't/can't check it, replacement is only $20 or so......not hateful as guesses go.

Others will chime in with more.

In many instances these "takes lots of cranking to start" problems are the result of a subtle fault (or a stack-up of subtle faults) rather than a big fault that jumps right out at you. Diagnosis is more along the lines of methodically checking and testing multiple systems to simply eliminate possibilites.

Cheers
DD

 

One more thing....

With the key 'on' give the throttle one pump. This will actually pulse the injectors and give a solid shot of fuel to the cylinders.

A cold engine will like the extra fuel. A warm engine might not.

Try it and report back if anything changes

Cheers
DD

 

Hi Doug, and thanks for the comprehensive response.

I've done the throttle linkage adjustment per the engine performance guide. Whether I did it right may be in question :-)

All the connections to the coil in the engine compartment have been cleaned. I'll have to admit that I have never even looked at the coil in front of the radiator. I need to do that.

I'm not really seeing anything that would indicate a rich start/run condition. When it's cold, it will die if I don't play with the throttle to keep it going for the first 30 seconds or so. I don't recall having to do that quite so much in warmer weather.

I've actually tried the prime-key off-prime again thing. I didn't hurt, but it didn't seem to help either.

I did go and take a resistance measurement of the water temp sensor. At 35 degrees F the engine guide says it should be around 5.7K, mine was at 3.5k. So, I soldered a 1K and a 4.7K resistor in series, unplugged the temp sensor and substituted the resistors. It started so quickly it was shocking, no kidding. I don't think it cranked for 2 seconds! Now...I still had to baby it for the first 30 seconds or so, but still that was a huge improvement.

Having spewed forth all that optimism, the real test will be in the morning when its sat all night (I did run it a bit this afternoon, and it always seems to start easier anytime it's been run in the last 6 hours or so). I'll report back.

I did let it come up to operating temp, and then measured the water temp at 190 degrees F (using an independent sensor) and the resistance of the OEM sensor at 260 ohms...about where the performance guide says it should be.

Keeping my fingers crossed...

John
1987 XJ-S V12
63,000 miles

 

Doug has covered it all, as usual.

One of mine was/is a mongrel when cold also.

The single "pump" of the gas pedal with the ign ON (before going to START) fires all 12 injectors ONCE (as Doug mentioned), and that is the ONLY way that sucker would start without the "wind up" feeling. I went through it toooooo many times, and nothing altered, so I resided to the single pump when cold, and that was 6 years ago.

The feathering of the throttle is not normal, so I suspect the AAV is hissy. Once lit up, they should settle at "about" 1200pm, and drop slowly as the engine warms up.

I got heaps of "word" docos on these issues if you want them, more stuff still in the brain also, just PM your email address. They are too big to attach here, as I have tried in the past.

Spark plug gap is critical on the HE.

You have done HEAPS on this car from the threads I have followed, and this will be simple (as Doug also said), and you will sort it.

 

Well...all "testing" has been suspended due to the 13" of snow on the ground and the -12 below zero F temps and high winds. This should be by us in a couple days.

I did get a chance to try substituting the resistors for the water temp sensor yesterday...

Good news: it lit of in less than a second

Bad news: it wouldn't stay lit off. No amount of messing with the throttle would keep it going.

I pulled the resistors out and plugged it back into the water temp sensor, and got it to start and run with the usual difficulty.

Of more concern was the smoke...and not from the exhaust. While I was cranking it (bonnet fully open) , I saw a whiff of smoke rise from somewhere in the vicinity of the left rear of the engine, in the general area of the master cylinder. In reading Palm's book, I remember someone running into this because the block wasn't grounded to the body, and the motor was grounding itself through the throttle cable. I took the preventative measure of installing another grounding strap from the block to the body, using clean connections and anti-seize compound to get ahead of that problem. After the engine started the smoke went away. I then metered the block, body and cable, and never say anything more that .5 ohm resistance.

So....not sure what that is about. Maybe I need to put a ground strap on both sides.

All right, I'll post again when the experiments resume :-)

Thanks,

John
1987 XJ-S V12
63,000 miles