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850 weak spark from coil

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.
1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

850 weak spark from coil

Postby cet » 15 Apr 2010, 02:06

Strange sequence of events upcomming 'cause you never know what the answer is.

Car had been running well, though some bad carbon out the exhaust after putting in a $27 o2 sensor that got it past inspection then threw a code in 2 days.

Break in nursing school,parked the car, come back 2 days later (and after the battery ran down thanks to the kids playing with the visor mirror) car cranked slow, no start. Charged battery, cranked faster, no start. Checked fuel pressure, none, checked relay, operating as it should. Power to the pump but no pump no pressure replaced pump, nice noisey pump, good pressure.

Start looking at spark, good at the plug furthest from distributer (i think its 5) weak to absent at all others, clean carbon off of rotor and cap contacts, shift test spark plug to the coil output.

original coil, weak spark
coil from Ford Ranger stronger but still orange/yellow not blue

I checked my original posting from when i first got the car, and saw that the red/blue amplifier output to the coil had been showing 5.5 volts AC, it is now 2.5- 3

Is this amplifier going bad or could the output of the sensors before it be throwing the whole thing low. My favorite Pittsburgh recycler dosnt have the coil amplifier in stock and i see that even the used price on that amplifier is ridiculous. It looks to be a 1000x amp (5.5 millivolt to 5.5 volt) is there some kind of aftermarket substitute?

Thanx
CET
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Re: 850 weak spark from coil

Postby whoa » 15 Apr 2010, 05:03

Hmmm. Have you pulled the codes?
1996 850 Turbo Wagon
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Re: 850 weak spark from coil

Postby cet » 15 Apr 2010, 09:51

dont have reader, its post 95, should try to borrow one
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Re: 850 weak spark from coil

Postby BEJinFbk » 15 Apr 2010, 23:10

Is the battery Fully charged? Like, overnight?
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Re: 850 weak spark from coil

Postby cet » 17 Apr 2010, 04:29

Battery fully charged,ran and got a 49.99 scan tool; no codes (it initially says there are 2 codes which cannot be identified or erased, went out and read and cleared the 0441 code from the Dodge caravan so the tool seems to work) I found this hard to believe so i disconnected the wires from the Mass Air Flow meter and idle air control to see if that would throw one but it didnt. something about the way it is cranking ( a little faster than normal) caused me to take the cover off the timing belt to see if the cams were lining up; looks fine. sounds like 1 cylinder out of the 5 is almost catching.Testing each plug with its wire individually similar news, strongest spark on the plug furthest from the distributer, weak on others. will head to junkyard for cap rotor and wires, should i grab the injector rail while I'm there?Dont have gauge but hitting the valve yieds about 3-4 cc's at what looks like normal pressure. I am running out of time, anybody have a guess.
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Re: 850 weak spark from coil

Postby whoa » 17 Apr 2010, 05:32

Yeah, you can't pull codes with a regular OBD reader. Here's a cheap way:

http://www.volvoforums.org.uk/showthread.php?p=585182
http://www.volvoforums.org.uk/showthread.php?t=46943

Here's a good thing to look at:

http://www.volvoclub.org.uk/tech/servic ... esting.pdf

Along with some of the other documents:

http://www.volvoclub.org.uk/volvo_works ... docs.shtml
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Re: 850 weak spark from coil

Postby cet » 17 Apr 2010, 19:44

Thank you for your help on this, i dont think i have been specific enough.This is a 96 non turbo 20 valve with 1 engine computer + an Asian for the tranny. the engine ECU is a GW2 (picked up a FD2 out of a similarly engined 96 at the junk yard dont know if its compatable) the engine numbers under the spark plug cover say it is a B6340 3.1 on the lower right 10001671 PO2
the plate over by the battery has this
854 T3 337520
YV1LS5543T3337520\

31
3650
189-23
EEXAAMS

i broght home everything i could think of which would cause a no start, crank, cam and mass airflow sensors. i have studied electronics so would have no fear of the LED set up if it is applicable to this engine. The cheapo OBD2 reader is nice, it could give freeze frames and all sorts of stuf on the dodge guess the volvo ecu isnt as talkative. thanks again, gotta figure out how to send you a badassed botle of beer when i get this runnin.
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Re: 850 weak spark from coil

Postby cet » 17 Apr 2010, 22:03

switched out mass air flow sensor 2X more detonations than before but still anemic. Tried LED no flashes. tryed OBD2 again same as before. it sees 2 codes on initial read but then cannot read them "the modual has no codes stored" and it can not clear them, guess i am stuck in that between the LED and the $10,000 Volvo scanner that was mentioned in the thread.Will search the data you linked and the schematics for anything else electronic that could be causing this. and will try to line up a fuel filter though i dont think that is it , will try changing out the crank and cam sensors first.
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Re: 850 weak spark from coil

Postby whoa » 17 Apr 2010, 23:07

No flashes at all? You should get 1-1-1 if all is okay. Plus you pulled the MAF, so that should throw a code.

Do check out that first article; it specifies voltages you should find at the coil and so on.
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Re: 850 weak spark from coil

Postby claymore850 » 18 Apr 2010, 04:17

Did you test the ground cable on the coil?? maybe its a little rust on it. check if there is no a cracked side on the coil, near the support brace.
A year ago i changed my coil, because it has a crack who leaves the spark go to ground.. I replace with a MSD 8207 at half price on the ebay..good luck
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Re: 850 weak spark from coil

Postby cet » 18 Apr 2010, 19:26

Following the link that was sent, the following results were found:

bosch ez 129k


1) spark test coil= spark there but still orange/ weak

2) coil terminal 15 red to ground for battery voltage=battery voltage

3) coil termuinal 1 blue crank starter look for .7-1.3 volts= 8.5 volts

4) check crank sensor resistance look for 200- 400 ohms= 295,000 ohms (both the sensors i have read this)
check cam sensor resistance look for 200-400 ohms= both sensors give a fleeting reading around 10 Megaohms before heading to infinity (and beyond)

5) check cam sensor harness voltages

2 to ground look for variation from 0-5 volt= variation 0-10.6 volt

3 to ground ingnition on look for 10 volt = battery voltage

1 to ground look for 0 ohms= 1.2 ohms

8) check power stage control signal, crank engine, from 4 to ground look for .7 to 1.3 volts= 163 millivolt

so we have blue terminal voltage high (not enough drop cause its not working hard

for the crank and cam coil resistasnces i wonder if the target voltages should be in K ohms, even so both the cam sensors i have are reading in the 10"s of M ohms even so the voltage on crank generated by the crank sensor is higher than expected or should this have been an AC reading? he sensor is being fed more voltage than expected at terminal 3 and the harness ground resistance is at 1.2 ohm instead of zero.

the article says if controll volts and ground are faulty check wiring, time to trace the harness, disconect clean and silicone grease all the ground points.

Thanks Claymore for jumping in to help as well, i wish it were high voltage phenominae, thats a lot more fun to chase.
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Re: 850 weak spark from coil

Postby whoa » 18 Apr 2010, 19:52

does the tachometer move when you crank the engine?
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Re: 850 weak spark from coil

Postby BEJinFbk » 18 Apr 2010, 20:10

It sounds like you're jumping around checking a lot of things. Focus on one thing at a time and eliminate it.
I'd start with verifying the coil. It works hard and you probably still have the original. Usually, they work or they don't,
but sometimes they die in really strange and often intermittant ways. Good news? EASY TO REPLACE! :lol:

Here are a couple of things that may help:
( Disclaimer: I'm getting all this info from OEM Volvo wiring diagrams. I haven't had any problems like this with my '98.)

The MAF should have No Bearing on spark strength. As far as I know, it's a fuel side sensor. It helps regulate the mixture.

This is a pretty basic ignition system. The spark signal from the ECU is timing only, not strength. On or Off.
It feeds a very basic transistor circuit that you're calling a spark amplifier. The "Amplifier" is just a high speed
switch that get's triggered by the yellow/white wire from the ECU to carry the switching load.
When it gets a trigger from the ECU, it shows the coil a ground. But as far as I know, it's just On or Off.

The coil is very basic, like any coil going back for decades. It has a primary, two wire input. It's two connections are:
12v ign switch hot ( Red wire AT the coil ) , ECU triggered ground ( Blue AT the coil) to fire a spark.
For the plugs, it has a secondary, High Voltage output, the Big wire and the Ground to Chassis.
Be sure to check that ground. Resistance from the block to the coil frame should be very low.
If you want to eliminate that as a suspect, you can run a jumper between them.

So - Is the coil OK ? Unhook the ground side ( Blue AT the coil) and check spark at the coil by simply
shorting the ground side and releasing it to fire a spark. If it's still weak? Get a new coil.

If that doesn't get it, keep moving backwards through the system.
Spark Amp, Timing Input sensors, Dirty connectors, etc.
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Re: 850 weak spark from coil

Postby whoa » 18 Apr 2010, 20:14

And no, they don't mean K ohms, but just ohms. My crank sensor read 347ohms or something like that when I checked it.

1.2 ohms is not far from zero; I doubt that's a problem.
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