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Hello All,
What's the best way to tell if my known good coil is sending spark?
I have a no start issue, and have narrowed it down to electric.
Checked plugs for spark, not getting any.
Cap, rotor, plugs and wires are all new. Used coil to start other Volvo, so it works!
It is getting fuel.
1993 240 wagon 225k
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"It is getting fuel."
if you're really sure about that (verified pumps run when cranking and wet plugs from un-ignited fuel), there is just ONE known suspect:
• The ignition Ignition Amplifier, aka "Power Stage".
Here's my reasoning:
1) Fuel operation requires timing pulses from the Ignition CU...
2) The Ignition CU requires timing pulses from the Crank Position Sensor...
So FI operation means that the CPS, ICU, and Fuel ECU are all working OK.
When the ICU sends timing pulses to the FI ECU, it ALSO uses those timing pulses to control the Power Stage (or "thinks" it does). The Power Stage is what "triggers" the coil to produce the spark—similar to the "points" in the old days.
But there is no built-in test* or feedback from the Power Stage, except for the wet plugs clue when it fails — are the plugs wet after cranking?
* If the PS is working, a Test Light on coil terminal #1 should flash when engine is cranking.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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I'm sure you said all this when I was troubleshooting my 91 last month (it was the CPS) but I hadn't put it together.
If no spark:
a) wet plugs point to bad power stage but flashing test light on coil terminal 1 = a working Power Stage
b) Dry plugs points to CPS.
Good rule to remember
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The plugs are wet after cranking.
Which terminal on the coil is #1?
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The terminals are numbered in the top of the coil. You may have to wipe it clean.
There should be 1 or 2 red-white wires on #1, Blue wire(s) on #15 (voltage input).
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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I have light pulses from #1 terminal. I checked for spark again, and I now have spark on all plugs(yesterday I had none-must be those gremlins).
The (new)plugs are wet and fouled.
I left the lower and upper timing belt covers off to verify timing marks, all three spot-on. The rotor points to #1 when it should.
You guys on this great site have talked me through a blower motor, radiator and alternator replacement, timing belt, seals and water pump change, and many various relays and sensors changes. I'm confident this not-so-old girl will be back on the streets soon. She just won't start!
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Any chance the plugs are too fouled to fire now? I see that you have good spark and fouled plugs.
Any chance the CPS is failing and you sometimes get no spark?
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With both spark, fuel, and apparently correct timing, I wonder if the Cam drive sprocket has sheared its pin — resulting in loss of valve timing & compression?
Check by setting up for #1 TD Compression Stroke and verify that #1 and #2 valves are closed - look thru the oil fill hole, #1 cam should be pointed slightly up and inboard, with #2 pointed horizontally outboard.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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At what I think is #1 TD, the cam lobe #1 is horizontal and pointing out-towards the tire. The #2 lobe is slightly down and pointing in-towards the engine.
I can look through the #1 spark plug hole and see the piston move up/down while I manually crank. As I slowly line up the crank with its mark, the #1 piston reaches its apex. As I pass the crank mark, the piston begins its downwards movement. It's at that point when I notice the cam lobe positions, right?
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"At what I think is #1 TD, the cam lobe #1 is horizontal and pointing out-towards the tire. The #2 lobe is slightly down and pointing in-towards the engine."
That's definitely wrong for #1 TDC Compression. I just rechecked on my 940, and would revise my cam positions slightly to...
>>look thru the oil fill hole, #1 cam should be pointed inboard and up about 45°, with #2 pointed horizontally outboard.<<
Even if you had mistakenly timed the belt at #1 TDC Exhaust (the pulley notch would line up the same) I don't think the cams would be as you describe.
I think you need to get the pulley off and verify the TRUE #1 TDC Crank position, as shown in the bottom 3 pictures at THIS SITE .
I believe you said your HB/Pulley is new, but that notch only a secondary reference, and I'm not sold on MTC products. You need to make sure those 3 sprockets are in sync—starting right at the crank sprocket.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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OK. Here is where I am at. It's confusing.
I don't have the pulley on or the TB covers.
I lined up all three timing marks, the cam lobes were in the position I stated before=#1 horizontal pointing out/#2 slightly down pointing in. I rotated the crank 1 full revolution to timing mark align(the cam and inter sprocket marks are opposite of their respective timing marks) and the cam lobes are now in the position you stated=#1 slightly up and in/#2 horizontal pointing out.
With each full revolution of the crank I see the top of #1 piston through spark hole, which happens twice for 1 full revolution of the cam sprocket.
Should the cam lobes be in the position you stated when all three timing marks are lined up?
Am I making any sense? Because I just re-read my post and I'm staring crossed-eyed.
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This isn't a fix for the no start, but may explain why your cam lobe description seemed to baffle me. If you looked straight down into the oil fill hole and called that cam #1 and the next one back #2, that would explain your description below:
"I lined up all three timing marks, the cam lobes were in the position I stated before=#1 horizontal pointing out/#2 slightly down pointing in."
That's exactly the positions for #2 and #3 cam lobes, with the cam sprocket at the 0° degree mark. I just checked it on my spare camshaft.
To see the #1 cam lobe, you have to look forward from the oil hole.
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Well, let's break it down...
1) "I lined up all three timing marks, the cam lobes were in the position I stated before=#1 horizontal pointing out/#2 slightly down pointing in."
• The cams are wrong, assuming the crank sprocket was lined up like the pictures I linked you to. That's what defines #1 TDC on the compression stroke, when both valves should be closed, and both cam lobes should be nowhere near pushing a valve down, like you say #2 is.
If the cam sprocket mark was lined up (and correctly keyed to the shaft), I see no way the cam lobes could be as you say they are.
2) "I rotated the crank 1 full revolution to timing mark align(the cam and inter sprocket marks are opposite of their respective timing marks) and the cam lobes are now in the position you stated=#1 slightly up and in/#2 horizontal pointing out."
• Again, that sounds like the cam sprocket must have slipped on its shaft. With the cams in that (0° TDC) position, the 0° cam mark should be lined up — not "opposite" it's reference mark.
[And the #1 cam should be more like a 45° up angle—I took a closer look today on my car.]
3) "With each full revolution of the crank I see the top of #1 piston through spark hole, which happens twice for 1 full revolution of the cam sprocket."
• By my reckoning, the piston should be at TDC for the 3rd time (comp-exh-comp) when the cam comes around to the #1 position again. (360° of cam rotation = 720° of crank rotation.) But lets pass on that for now.
4) "Should the cam lobes be in the position you stated when all three timing marks are lined up?"
• Yes—and they should be like that again after two complete crank revolutions. [One complete cam and distributor rotation.]
My best guess is that somehow the cam sprocket "key" (roll pin?) has sheared. You may have the Crank and Int in sync, but with a Camshaft that's gone astray.
Look in the 700/900 FAQ for info on removing the Cam Sprocket. I think you can do it without pulling the Cam Cover by putting something thru one of the sprocket holes as a counterhold for wrenching the bolt.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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I took off the TB and cam sprocket, the key is there and in good shape.
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"I took off the TB and cam sprocket, the key is there and in good shape."
Then I have no explanation for the cam lobes being as you said, with everything
lined up:
"I lined up all three timing marks, the cam lobes were in the position I stated before=#1 horizontal pointing out/#2 slightly down pointing in."
In fact, I don't see how those two cams can ever be like that. Looking at an "M" camshaft on the bench, those two lobe tips are at least 90° apart. Meaning with #1 "horizontal pointing out", #2 is pointing almost straight down, holding the intake valve about full open — not what you'd want with the #1 piston at TDC on the compression stroke.
Playing with the shaft on the bench, the only time I see the #1 cam lobe at all near horizontal is about 1/2 way after #4 TDC, on the way to #2 TDC.
I'd guess it's back to Square One time.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Please don't shoot me, I'm only a humble cook.
After your last post, I took off the valve cover to take a picture. I discovered that all along I have been looking at the #2 and #3 lobes through the oil cap. Oy Vay!
The #1 and #2 point the correct way as you said.
Can I start a new thread and try to get this girl started?
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I guess a new thread would be in order, if your sure now about the timing.
The problem is that with fuel, spark, and correct timing there's
nothing left to suspect.
It appears that something is not as it appears.
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Hi bruce
i read a simular situation where there was so much gas washing down the cylinder walls there was not enough compression to start the car, or something like that and a little oil in the plug holes cured the problem?
what da ya think
good luck
mike
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You were right!
Any other ideas for the no-start problem?
I still think it is electrical.
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If spark is intermittent look at the wire on the crank position sensor. The insulation frays causing a short. Dan
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I checked that, it's good. That was replaced last year.
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Couple of things to double check.
Firing order. 1342. It's not that difficult to mix them up when you wire up the cap. Swapping two wires will cause a no start. So will going the wrong way around the cap.
Continuous spark on all wires. I use a timing light to test this. Start with the coil wire, crank for a good fifteen-twenty seconds. Then move through the wire set, from one to four. If you're getting strong consistent pulses from the coil wire, but none or spotty results from the plug wires, check the cap and rotor for proper seating. If spotty or non-existent from the coil wire, (and you've already done a coil swap out, right?), try swapping out the power stage from your other Volvo, and test both ways, PS #1 in the running car, and PS# 2 in the non running car.
Run the on board diagnostics - the drill is in the 700 FAQs.
Fuel test. Spray some starter fluid into a vacuum port on the throttle body. If the engine fires briefly, you have a fuel delivery problem. Wet plugs don't necessarily mean that you're getting the proper amount of fuel. A certain volume of fuel in the combustion chamber is necessary to develop the compression required for the fuel air mixture to reach the temps necessary for ignition. A weak fuel pump (or pumps) can provide enough fuel to get the plugs wet, but not enough to fire. I had a similar problem with a 740 a couple of years ago, good spark, fuel at the rail, wet plugs and no fire. Turned out to be both fuel pumps.
Air restrictions. Less likely to cause a no start, but worth checking that there are no serious blockages between the airbox and the throttle body.
Too much air. Check the injector seals for a tight fit. Look for traces of wet around the seals.
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Both valves on #1 cylinder are closed when the engine is at TDC of the compression stroke. Look through the oil filler cap opening to confirm this, then make sure all the timing marks are correct. Dan
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"Both valves on #1 cylinder are closed when the engine is at TDC of the compression stroke. Look through the oil filler cap opening to confirm this..."
How do I get the engine to TDC of the compression stroke? What does that mean?
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You set it by first lining the crankshaft so it is at the timing mark, #1 cylinder will be on top. (Bruce posted a link to the pictures)
The intermediate shaft is set to it's mark or the rotor pointing to the tic mark on the distributor.
The camshaft makes two revolutions to the crankshafts one revolution as you noted so you need to use the correct position.
In order for the engine to run you need the cam shaft set on the timing mark when both valves are closed for #1 cylinder (compression stroke). If it is set one revolution off (exhaust stroke) the engine will not run. Dan
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Can I check that both #1 cylinder valves are closed(compression stroke) by looking at the camshaft lobes?
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Yes both #1 cylinder cam lobes will be up or off the cam followers meaning both valves are closed. Dan
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Check continuity in the CPS or just replace it.
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