2005 XC70 Intermittent start... Gathering ideas.

[vtl]

So once in a while my car does not catch up first time I turn the key. That happens 3 or 4 times a year, usually around spring/fall time when the temperature is slightly above freezing point. Never happens when the engine is hot, only after prolonged parking. No power loss or other suspicions once the engine is started: idles well, pulls hard, sounds nice, etc.

Few days ago it had a hard start, then it finally started, and the engine sounded like it misfired for 3 seconds. I attached VIDA and it showed no codes stored.

Today the car sit for 4-5 hours in freezing rain and rejected to start. I did 3 attempts: first one was fully dead, the other one it tried to ignite but died, third one, with some throttle applied, it caught up and revved high.

I also notice that the starter acts with hesitation (turns slower) than the TYC replacement in wife's V70. The battery is fine, it is an oversized 2 years old AGM type battery with lots of amps, 95% long highway trips (70 miles a day), so the battery is charged. Cluster lights don't even really dim when the starter works. Also the car was doing that with old battery too, and with this AGM when it was new, so the battery is out of suspect.

The car got stage 0 when I bought it 2 years ago, fuel filter, plugs are in a good condition. Fuel pressure gauge shows that the fuel pump develops pressure instantaneously and keeps it steady at all times. Exhaust smells good.

I hardly recall that old plug in cylinder 3 was darker than the rest, like it was missing sparks, but the electrode looked good.

I don't see any engine problems otherwise, no codes are stored, so that's a bit of mystery to me. Ideas?

[draser]

I'd check starter cables and battery cables first, also battery voltage w/engine off, on and during crank. I'd get a parameter scan as well and post here. There are several ways to check cables, easier is to hook up a voltmeter on low scale between starter cable ends and crank and read voltage drop on meter. You'll need 2 jumpers with crocodile clips, Radio Shack should have them.

[vtl]

Battery terminals are good, thanks to battery placement in trunk, and also I keep them clean. Voltage is like 13.8 V on battery and 14.3 with running engine.

Good point on starter's contact, I'll clean them.

I pulled out coils and plugs, two plugs were not tightened well and there were signs of exhaust gases making their way through plug holes.

All 5 coils have small cracks like that:



Resistance between 1 and 4 pins are:

1 - 8.57M
2 - 8.64M
3 - 7.70M
4 - 8.58M
5 - 8.79M

So, yes, coil 3 is somewhat out of spec. Don't know how bad is that, but new Beck&Arnley coil measures 11.92M. I'll try to replace OE coil in 3 cylinder by B&A.

Also I measured coil's (low voltage half of) response to 10Hz and 100Hz modulation:

10 Hz, coils 1 through 5:











Coils 1 and 3 closer:





100 Hz, coil 1 and 3:





Coil 3 deviates, but nothing criminal, IMO.

New B&A coil is more energetic (10Hz):

[vtl]

Other thing I noticed is badly tightened ignition coil bolt in cylinder 1. Almost ignored that fact, but now, looking at the scheme, I see that this contact provides ground for high-voltage part of coil. This alone could explain why the car resisted to start yesterday. Though it does not explain why it generally hesitates to start from time to time, because usually those connectors are tight.

While here, I poured some Seafoam engine treatment into plug holes. Cylinders 1, 4 and 5 became dry just in minutes, I had to pour more. In 2 hours, after coils test in my attic lab, plus lunch, these cylinders were again dry, I used Mityvac pump to remove residue only on cylinders 2 and 3. Guessing the engine has compression problems too, because piston rings are stuck. Car used 800 ml of extra oil in 6800 miles between oil changes, and at the time of change oil dipstick was 3/4 from max, so that would translate to 1200 ml * 0.75 = 900 ml. 1700 ml in 6800 miles, 250 ml per thousand miles - that's too much in my opinion. I'll perform the real overnight Seafoam treatment closer to next oil change to release piston rings.

[draser]

Question on the modulated signal test: do you actually apply a 10hz signal to primary and read response in secondary or high voltage side? And did they pass the test? What tester is this?

[vtl]

No, I don't have a high-voltage probe, so I can't safely measure real response on high-voltage side w/o damaging my equipment. I fed ~2.8V 10 HZ square wave to one side of low-voltage coil and looked at response on the other side.

All coils are in a working condition, though coil 3 is a bit different. From what I can tell, it generates smaller spark on the plug, I actually see that the plug 3 has different, darker color than the rest.

This is not a spark plugs tester, just a digital oscilloscope. Scope is Rigol DS2072A and signal generator is built in another handheld scope DSO203, if you're curious.

[vtl]

As for the harder starter work, this most likely can be explained by a smaller intake manifold on turbo engine and way longer pipes from air filter to intake. On natural aspiration engine in wife's V70 there's like 10" of thick rubber hose between ETM and MAF, no wonder it requires much less power to crank up engine, which is essentially an air pump.

[abscate]

250 ml per thousand miles - that's too much in my opinion.

1 liter in 4000 miles is perfectly normal oil usage/seepage/burn/levitation

Loose spark plugs and loose coils...make sure you clean those ground points shiny.

Cracks on the coils aren't meaningful unless there are arcing signs.

[vtl]

1 liter in 4000 miles is perfectly normal oil usage/seepage/burn/levitation

Well, the other P2 does not burn that much oil. It used one mark on dipstick in 5800 miles -> ~55 ml/1k mi. Though it is NA engine and runs on 5w40. It was eating 5w30 oil, and the tappets were loud, so I bumped oil viscosity with a good result.

I'm willing to move both to "thin" 10w40 (thin for 40 grade) in summer: temperature rarely drops below 0F in Boston, while 90F for weeks is not uncommon.

Loose spark plugs and loose coils...make sure you clean those ground points shiny.

Coils have coated contact surface, I just need to buy a smaller torque wrench and tighten up to the spec Also will be useful for work on my mountain bike, my hand has a bad low torque precision.