2007 xc70 no power to coil No. 4 - 5 cyl turbo

raquette · Post by **raquette** » 16 Jan 2022, 13:29

engine running rough. codes multiple misfire 3-4-5.

check timing marks - good

found spark plug 4 black.

Replaced spark plus with iridium denso

when unclicking coil 4, engine roughness stays the same, all other coil disconnects engine roughness worsens

swapped coils around any no coil fires on cylinder when repeating above coil disconnect.

chased coil 4 wires through the rubber grommet entering the engine top, found a spot in the wires to coil 4 where tape around wire was melted, thought problem was discovered.

at that spot, separated wires, tugged on wires and verified wires were connected, still coil 4 is not firing.

I'm at a loss, what is the next step to diagnose?

Post by **jonesg** » 17 Jan 2022, 08:57

I would remove the melted tape.
Then go to the computer and clean the terminals but I'd suspect the melted tape has more to it.

raquette · Post by **raquette** » 17 Jan 2022, 11:19

ok thanks- I checked the melted tape and the 3 wires are in tact. was convinced that was the problem.

The green white wire to cylinder 4 has 12v with a test light after the engine runs and shut off, like the other cylinders, so that is working.

black wire is ground, in tact, so I/m thinking the brown wire may be the culprit, how to check that?

I'll check out the computer, Is it near the washer fluid reservoir, Is there special tool needed?

Post by **abscate** » 17 Jan 2022, 11:33

The coils get constant 12 Volts from the power relay and are fired by grounds triggered at the ECU.

raquette · Post by **raquette** » 17 Jan 2022, 12:19

ok thanks, power relay must be green/white wire that has 12wv until shortly after engine is

I look at the ECU connectors next...

raquette · Post by **raquette** » 17 Jan 2022, 17:40

removed the ECU, all pins and connectors look good. reinstalled and same condition, seems no. 4 has no trigger pulse.

not sure what to do now??

Post by **abscate** » 18 Jan 2022, 07:41

Check continuity of ground wire from coil connector to pin on ECU

This is after confirming

Known good coil on 4
12v present on coil connector
Good spark plug
Ground plug to engine with clamp
No spark at plug on cranking observed (approximate 1 hz or so)

raquette · Post by **raquette** » 19 Jan 2022, 20:45

ok thanks, will look at those steps next.

not sure how to locate cyl 4 coil ground connection to which pin at the ECU, I downloaded the wiring diagram but not sure about the pin location.

have 12 v at the green/white wire.

Post by **abscate** » 20 Jan 2022, 04:59

I’m driving by Syracuse today to see five rivers today. I can throw some diagnostics in the car

Give me a text at the

Albany area code

The number of the beast , 666, plus 3

And the last four are 15 and 84

Let’s see the bots try do dig up that phone number.

Post by **vtl** » 20 Jan 2022, 06:34

Run the compression test, just in case.