Volvo S70 Made from 1998 to 2000, this sporty model replaced the 850 sedan and instantly became a hit.

Weak spark 98 S70 GLT

  #1  
Old 04-04-2017, 11:04 AM
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Default Weak spark 98 S70 GLT

I can only find posts about no spark. My car has decent spark from the coil, but weak spark at the spark plug. That info sent me to the cam sensor. Unfortunately I've haven't been able to find too many definitive tests for the cam sensor. The biggest reason I question my test is, I have 12 volts on the signal wire. The test I saw said only five volts always on the signal wire with the key on. It it switches zero when I try to start it and then bounces between 5 and 9 volts. Please feel free to ask any questions pertinent to getting a diagnosis and thank you very much in advance for all your help.
 
  #2  
Old 04-04-2017, 12:05 PM
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Does the car not start?
 
  #3  
Old 04-04-2017, 04:30 PM
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Originally Posted by Johnny Gibson View Post
I can only find posts about no spark. My car has decent spark from the coil, but weak spark at the spark plug. That info sent me to the cam sensor. Unfortunately I've haven't been able to find too many definitive tests for the cam sensor. The biggest reason I question my test is, I have 12 volts on the signal wire. The test I saw said only five volts always on the signal wire with the key on. It it switches zero when I try to start it and then bounces between 5 and 9 volts. Please feel free to ask any questions pertinent to getting a diagnosis and thank you very much in advance for all your help.
If the cam position sensor is at fault - you will have no spark at all and a MIL code stored for it. If you have strong spark at the coil and weak at the plug - then it must be in cap, rotor, wires.
 
  #4  
Old 04-04-2017, 08:45 PM
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Originally Posted by Smith Volvo View Post
If the cam position sensor is at fault - you will have no spark at all and a MIL code stored for it. If you have strong spark at the coil and weak at the plug - then it must be in cap, rotor, wires.

I agree with this answer . The plug wires should have a certain amount resistance per/foot ,typically RF suppression wire is approximately 850 ohms per foot, any thing over 6000 ohms not good.
 
  #5  
Old 04-04-2017, 09:17 PM
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To answer your question about the coil, the voltage on the signal wire really changes between 12 volt and zero. When the engine is stationary you will always see 12 volts. The voltage you measure there with the engine cranking or running will depend entirely on the device you use to measure. That is, how fast can it follow what's going on. Reality is switching from zero to 12 really fast. It sounds perfectly normal to me.

Spark is pretty subjective, so I am not sure "weak spark" is really your problem.

As far as the cam sensor and crank sensor, you should forget that. The people talking to you have no idea what they are talking about. These are just sensors. If they quit working you won't have any spark. They are fine.
 

Last edited by firebirdparts; 04-04-2017 at 09:20 PM.
  #6  
Old 04-04-2017, 11:23 PM
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[QUOTE=tryingbe;445672]Does the car not start?[/QUOTE
Pardon that omission. No. It doesn't start. Thanks for the reply.
 
  #7  
Old 04-04-2017, 11:42 PM
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Originally Posted by firebirdparts View Post
To answer your question about the coil, the voltage on the signal wire really changes between 12 volt and zero. When the engine is stationary you will always see 12 volts. The voltage you measure there with the engine cranking or running will depend entirely on the device you use to measure. That is, how fast can it follow what's going on. Reality is switching from zero to 12 really fast. It sounds perfectly normal to me.

Spark is pretty subjective, so I am not sure "weak spark" is really your problem.

As far as the cam sensor and crank sensor, you should forget that. The people talking to you have no idea what they are talking about. These are just sensors. If they quit working you won't have any spark. They are fine.
When I said weak spark, I figured out I mean it's firing, just not enough to start the car. It sounds kinda bubbly out of the tailpipe. After further tests, it turns out the secondary winding in the coil is bad. When you said coil, did you mean cam sensor when you were talking about the signal voltage test? From what I understand from the repair manual , the voltage is supposed to constantly switch between 5 and 9 volts and hold a constant voltage of 5v. But, it's doing pretty much what you are saying it should do, and I do have spark.
 
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Old 04-04-2017, 11:43 PM
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Originally Posted by firebirdparts View Post
To answer your question about the coil, the voltage on the signal wire really changes between 12 volt and zero. When the engine is stationary you will always see 12 volts. The voltage you measure there with the engine cranking or running will depend entirely on the device you use to measure. That is, how fast can it follow what's going on. Reality is switching from zero to 12 really fast. It sounds perfectly normal to me.

Spark is pretty subjective, so I am not sure "weak spark" is really your problem.

As far as the cam sensor and crank sensor, you should forget that. The people talking to you have no idea what they are talking about. These are just sensors. If they quit working you won't have any spark. They are fine.
I appreciate the the help.
 
  #9  
Old 04-04-2017, 11:46 PM
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Originally Posted by tryingbe View Post
Does the car not start?
Pardon the omission. It doesn't start.
 
  #10  
Old 04-04-2017, 11:48 PM
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Originally Posted by tryingbe View Post
Does the car not start?
Good call out. See answer below. 👇Thanks.
 
  #11  
Old 04-04-2017, 11:53 PM
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Originally Posted by Johnny Gibson View Post
When I said weak spark, I figured out I mean it's firing, just not enough to start the car. It sounds kinda bubbly out of the tailpipe. After further tests, it turns out the secondary winding in the coil is bad. When you said coil, did you mean cam sensor when you were talking about the signal voltage test? From what I understand from the repair manual , the voltage is supposed to constantly switch between 5 and 9 volts and hold a constant voltage of 5v. But, it's doing pretty much what you are saying it should do, and I do have spark.
Please disregard what I said about the 5 and 9 volts. It says a constant 5v withe key on. I think I may be trying to stuff too much information into this small mind I've got. Lol
 
  #12  
Old 04-05-2017, 06:57 PM
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Originally Posted by tryingbe View Post
Does the car not start?
Again everybody thanks for all the replies. Did the tune-up Changed the coil with a no good one by the test and then repair manual. Still about the same the cam sensor does better on the voltage signal side but it's still bouncing all over the map from my 3-5-9 respectively. Per the repair manual, that's still not in spec. I didn't completely check the timing but I do know the cams are in line with each other at top dead center. Do you guys happen to have any other suggestions I can try? Thanks in advance.
 
  #13  
Old 04-05-2017, 08:38 PM
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Originally Posted by tryingbe View Post
Does the car not start?
known good coil. 👆I'll have to tighten up on my proofreading staff. Lol
 
  #14  
Old 04-05-2017, 08:39 PM
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Originally Posted by Johnny Gibson View Post
Again everybody thanks for all the replies. Did the tune-up Changed the coil with a no good one by the test and then repair manual. Still about the same the cam sensor does better on the voltage signal side but it's still bouncing all over the map from my 3-5-9 respectively. Per the repair manual, that's still not in spec. I didn't completely check the timing but I do know the cams are in line with each other at top dead center. Do you guys happen to have any other suggestions I can try? Thanks in advance.
known good coil. 👆I'll have to tighten up on my proofreading staff. Lol
 
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