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Old 07-13-2008, 01:38 AM   #1
mrsladew
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Default 95 SC2 misfire

Hello,

I have a 95 SC2 that I recently purchased as a commuter. I recently replaced the rings/valve seals and reading this forum proved to be invaluable...

However I have an issue that I can not seem to figure out. My engine misfires on 3 of the 4 cylinders at all speeds. What I mean by misfire is that when I idle /drive around with a timing light hooked up, there is an intermittent missed spark on these cylinders at all engine speeds. I have tried Delco copper plugs, an have since replaced them with NGK copper. Resistance on the coil packs, ignition module, and wires check out good. I cleaned the coil pack towers as well as the ignition module grounds. I am not sure what else might cause this, and do not want to get into the expense of guessing at what parts to replace until I find the right one... has anyone here successfully resolved a similar issue?

Thanks!

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Old 07-13-2008, 01:52 AM   #2
Sky King
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1999 SC2
1995 SL2
Default Re: 95 SC2 misfire

The first thing that comes to mind is the firing order and plug wires. The Saturn engine utilizes a function called "Waste Spark". If you noticed, you only have two coils. Each coil fires two cylinders. The engine fires on the power stroke and the exhaust stroke. This could explain why your timing light shows the firing at times other than the normal power stroke.

I'll try to find a thread that shows which wires goes on what coil post.

I got this from a post from member Redkees@msn.com
Quote:
Originally Posted by REDKEES@MSN.COM
Hopefully this will help:Originally Posted by Luke
Reading the spark plug wells, from left to right, as:

[1]> > > [2]> > > [3] > > > [4]

The respective plugs wire should sit on top of the coils as:

[4]> > > [1]> > > [2] > > > [3]

With the above in mind, the top of the left most coil, should go to plug well [4].

The second from the left coil [2], should go to spark plug well [1]
The third from the left coil [3], should go to spark plug well [2]
the fourth from the left coil [4], should go to spark plug well [3].

...
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Last edited by Sky King; 07-13-2008 at 02:00 AM..

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Old 07-13-2008, 06:40 AM   #3
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Default Re: 95 SC2 misfire

1-The #1 priority for you is to look in the How-to library's first two posts about the infamous original engine coolant temperature sensor (ECTS) failures that usually runs the engine rich all the time. Fouled plugs, poor mileage, high idling, misfiring, flooding starts, erratic engine running, EGR valve problems, poor transmission shifting, etc., all due to the original sensor failing in the S-series cars. At the least, remove the two-wire sensor (with a cold engine to minimize coolant leakage) and see if its the resin tipped original; replace it immediately with any brass one from any auto store. Its cheap and not wasted money.

2-Search for the 'paper clip' method of retrieving trouble codes from the car then refer to the How-to library on page 5 titled OBD I Powertrain Codes to read what they mean. More info from differentracing.com.

3-Since you don't know the condition of the plug wires that may be contributing to misfiring, simply spray a water mist on the wires in the dark; any breakdown of the insulation would show as spark jumping off the worn out plug wires. Replace as necessary.

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Old 07-13-2008, 11:43 PM   #4
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Default Re: 95 SC2 misfire

Quote:
Originally Posted by Sky King View Post
The first thing that comes to mind is the firing order and plug wires. The Saturn engine utilizes a function called "Waste Spark". If you noticed, you only have two coils. Each coil fires two cylinders. The engine fires on the power stroke and the exhaust stroke. This could explain why your timing light shows the firing at times other than the normal power stroke.

I'll try to find a thread that shows which wires goes on what coil post.

I got this from a post from member Redkees@msn.com
Thanks for your reply. The firing order is correct per the engine bay sticker as well as per your post. I do see the waste spark on the timing light but I still have the intermittent miss.

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Old 07-13-2008, 11:54 PM   #5
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Default Re: 95 SC2 misfire

Quote:
Originally Posted by fdryer View Post
1-The #1 priority for you is to look in the How-to library's first two posts about the infamous original engine coolant temperature sensor (ECTS) failures that usually runs the engine rich all the time. Fouled plugs, poor mileage, high idling, misfiring, flooding starts, erratic engine running, EGR valve problems, poor transmission shifting, etc., all due to the original sensor failing in the S-series cars. At the least, remove the two-wire sensor (with a cold engine to minimize coolant leakage) and see if its the resin tipped original; replace it immediately with any brass one from any auto store. Its cheap and not wasted money.

2-Search for the 'paper clip' method of retrieving trouble codes from the car then refer to the How-to library on page 5 titled OBD I Powertrain Codes to read what they mean. More info from differentracing.com.

3-Since you don't know the condition of the plug wires that may be contributing to misfiring, simply spray a water mist on the wires in the dark; any breakdown of the insulation would show as spark jumping off the worn out plug wires. Replace as necessary.
1- Although I have not yet replaced the ECTS (It's on the to-do list and my nearest dealer is far away), my assumption is that it might cause a misfire due to an overly rich condition, not due to a lack of spark. I do not see how it would cause the ECM to call for cutting off the spark to any cylinder- or is there more to it than that? While we are on the topic is a NAPA sensor sufficient or do I need an OEM? I have a NAPA and Autozone just down the road...

2-There are no trouble codes logged.

3-I have sprayed the wires with a saltwater solution at night and did not see any errant sparks.

Thank you for your help!

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Old 07-14-2008, 12:10 AM   #6
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Default Re: 95 SC2 misfire

The Autozone sensor will most likely be adequate, it will cost less than NAPA anyway. As long as its brass and you read the directions all should be well.

You have verified that the insulation of the wires is OK.

Plugs are OK.

What about the routing of the wires? Is #4 running next to #1 from the coil pack to the head? Are the loom clips present? This can make a difference. You are zeroing in on either a bad coil pack or bad ignition control module. Look at he lamination stack on the coil. Is is rusty and are some of the laminations separated by the rust?

Last edited by OldNuc; 07-14-2008 at 12:17 AM..

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Old 07-14-2008, 12:16 AM   #7
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Default Re: 95 SC2 misfire

How can you differentiate between ignition cut-off or fouled plugs misfiring in a rich/flooded condition unless you removed the plugs to examine them?

Any auto store stocking the brass coolant sensor will do except for the die-hards insisting on genuine OEM parts. If you read through the numerous threads about this sensor, you'll be hard pressed to find any post relating any SES code to failure of the coolant sensor. There are many things in life that won't be spelled out in black and white, the reason for these forums to spread the word from collective experiences of many others before you with the same problems. Spraying the wires with water at least eliminates cross-firing problems, another area that may not be indicated as a code but seen visually.

...
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Old 07-16-2008, 11:41 PM   #8
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Default Re: 95 SC2 misfire

Quote:
Originally Posted by fdryer View Post
How can you differentiate between ignition cut-off or fouled plugs misfiring in a rich/flooded condition unless you removed the plugs to examine them?


Any auto store stocking the brass coolant sensor will do except for the die-hards insisting on genuine OEM parts. If you read through the numerous threads about this sensor, you'll be hard pressed to find any post relating any SES code to failure of the coolant sensor. There are many things in life that won't be spelled out in black and white, the reason for these forums to spread the word from collective experiences of many others before you with the same problems. Spraying the wires with water at least eliminates cross-firing problems, another area that may not be indicated as a code but seen visually.
I did pull my plugs and they look brand new. I had this problem immediately after replacing the plugs as well.
I will replace the sensor regardless of my personal feelings on this being the cause- Maybe it will help with my issue, if not it appears that I will likely prevent numerous other problems down the road...

Again thank you all for your input!

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Old 07-16-2008, 11:50 PM   #9
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Default Re: 95 SC2 misfire

Quote:
Originally Posted by OldNuc View Post

What about the routing of the wires? Is #4 running next to #1 from the coil pack to the head? Are the loom clips present? This can make a difference. You are zeroing in on either a bad coil pack or bad ignition control module. Look at he lamination stack on the coil. Is is rusty and are some of the laminations separated by the rust?
The coil laminations are beginning to separate due to rust, but "appear" to still be adequate enough to do the job. That is kind of where I want to draw the line- how many questionable parts will I have to replace in a $500 beater in order to maybe fix this problem?

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Old 07-17-2008, 09:00 AM   #10
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Default Re: 95 SC2 misfire

Using a timing light to check for misses on these cars yields freaky results because of the waste spark system. If you do a search on it, you'll find other posts where people were mislead using timing lights for this. If that's what you're using to determine you are getting misfires, you would do better to just post your symptoms.

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Old 07-22-2008, 09:52 PM   #11
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Default Re: 95 SC2 misfire

Quote:
Originally Posted by BarnOwl View Post
Using a timing light to check for misses on these cars yields freaky results because of the waste spark system. If you do a search on it, you'll find other posts where people were mislead using timing lights for this. If that's what you're using to determine you are getting misfires, you would do better to just post your symptoms.
My main symptoms are 30 mpg (and I am hearing 35 is the norm???) and a barely noticeable surge at speed. The timing light seemed to confirm a miss but maybe that is misleading...

I have replaced the rings, PCV, valve seals, plugs, and just replaced the ECTS. One thing I have noticed is that I rarely get over 1/4 of the way up the temp gauge. I will be messing with the coolant concentration this evening to see if I can eliminate that issue and tackle the thermostat next.

I know 30 mpg is not too bad, but I was hoping for a bit more.

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Old 07-22-2008, 10:24 PM   #12
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Default Re: 95 SC2 misfire

Quote:
Originally Posted by mrsladew View Post
One thing I have noticed is that I rarely get over 1/4 of the way up the temp gauge.

Replace the thermostat. Make sure that the connector for the ECT does not have any corrosion in the terminals.

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Old 07-23-2008, 12:59 AM   #13
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Default Re: 95 SC2 misfire

Coolant mixture has almost no effect on engine running temperature. It primarily affects freezing and boiling points, and of course, protection of the aluminum block and head. As said above, the thermostat has the most effect on engine temperature; replace it before experimenting with anything.

At what temperature does the cooling fan come on?

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Old 07-23-2008, 07:00 AM   #14
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Default Re: 95 SC2 misfire

Actually 30 MPG mixed is about right with a DOHC which is what you have.

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