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Old 10-26-2019, 09:26 PM   #1
Hermit89
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Default Weak Spark

Hello, everyone. I've scoured this forum all day and found several instances of this issue before, but no real solution. I have a '98 SL2 5-speed with approximately 180,000 miles on it. I've owned the car for about 5 years now and have always maintained it well, as did the previous owner. I replaced the TPS a few months ago, but the rest of the electronics look factory.

My wife was driving it yesterday when it started to run rather rough. The SES light flashed several times, but she managed to limp the car back home. The car has very weak spark on the #3 and #4 cylinders. This seems odd because #1 and #2 are strong and each shares a coil with #3 and #4. I first pulled the old wires and found the coil terminals heavily corroded. I cleaned them with a steel brush and they look new again. This didn't result in any change.

I then pulled the plugs from the coils and the spark looks very strong alternating across all 4 coil terminals when the engine is cranked. I replaced the wires, plugs (NGK), and made sure I had the correct 4-1-2-3 wire order on the coils. The issue still persists.

If I swap the wires around, the problem remains on the same cylinders, so the wires aren't the issue. While the car is running, I can pull the wires from the #1 and #2 cylinder and see a very strong spark jumping to the valve cover bolt. #3 and #4 won't jump unless the wires is placed very close to the bolt.

Do you suppose it's most likely the ICM? The coils don't seem likely as it's the #3 and #4 cylinders, and not #1 and #4 or #2 and #3.

The check engine light went off after I unplugged the battery to clean the coils, and hasn't come back on. I may buy a cheap OBDII scanner tomorrow.

Thanks.

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Old 10-26-2019, 11:15 PM   #2
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Default Re: Weak Spark

I've had to replace coils in both my Saturns. My '98 had a P0303. I didn't get the code on the '99, back in 2012, but bad misfire and flashing SES light. Per OldNuc the ICM is the one component that will drop a single cylinder. Coils are relatively cheap and are known to go bad with age. Here was my '98 experience.
http://www.saturnfans.com/forums/sho...&postcount=213

My new NGK coils are awesome.

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Old 10-27-2019, 10:03 PM   #3
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Default Re: Weak Spark

Quote:
Originally Posted by Waiex191 View Post
I've had to replace coils in both my Saturns. My '98 had a P0303. I didn't get the code on the '99, back in 2012, but bad misfire and flashing SES light. Per OldNuc the ICM is the one component that will drop a single cylinder. Coils are relatively cheap and are known to go bad with age. Here was my '98 experience.
p=2302722&postcount=213[/url]

My new NGK coils are awesome.
Thanks. I pulled the coils and ICM today to clean them; everything was pretty dirty and corroded. The ICM connector was still sealed and as clean as a whistle, though. I'm going to install everything tomorrow and try again.

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Old 10-28-2019, 11:13 AM   #4
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Default Re: Weak Spark

Quote:
Originally Posted by Hermit89 View Post

The check engine light went off after I unplugged the battery to clean the coils, and hasn't come back on. I may buy a cheap OBDII scanner tomorrow.

Thanks.

I highly recommend having a scanner on hand. I use an OBD dongle plus a phone app. I got the BAFX brand, it's about $22 and seems more reliable than the $10 cheapies. You can also get codes read for free at a FLAPS.

...
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Old 10-28-2019, 02:04 PM   #5
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Default Re: Weak Spark

+1. My Bluetooth scanner is awesome, and cheaper than Harbor Freight.
https://www.amazon.com/gp/aw/d/B005N...b_b_asin_title

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Old 10-28-2019, 02:49 PM   #6
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Default Re: Weak Spark

I agree with many here with a relatively inexpensive Bluetooth adapter and OBD II third party app like Torque Pro. I was gifted an expensive reader and was impressed until the wrench light turned on. Nope, it can't read wrench (abs, airbag, ecm, bcm, tcm and a few more) codes ('B', 'C' and 'U' codes). Reluctantly, I'm 'interviewing' a better scantool that costs less the half what my original reader went for but it does almost what GMs Tech II scantool does, including program remotes and test sensors. Far too many things to describe but I'm impressed as it pulled history codes for my xmission and all past errors. Unfortunately and like many scantools, this one's specific to GM. Not usable on Ford or any other brand. The overwhelming list of things this can do is amazing and I haven't gone thru the entire menu. This GM compatible scantool covers many models but I'm more interested in it helping me uncover Saturn error codes that aren't emissions related. One easy test I performed without blowing up something was the lamp test, enabling all instrument panel lights to turn on and stay on then manually switching this test off. Strictly third party scantool but seems very much worth the price for entry level scantools. It even has the setup to tie into GMs TISWEB for online GM support as long as I'm paying for access.......

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Old 10-28-2019, 06:54 PM   #7
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Default Re: Weak Spark

I swapped the coil packs around today and #3 cylinder is still misfiring. I guess it's time to do a compression test. I really hope it isn't a burnt valve.

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Old 10-28-2019, 08:17 PM   #8
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Default Re: Weak Spark

It's either burned valve or ignition control module (ICM).

I had a serious P0301 error on my L300 3.0L V6 engine. It went away then came back permanently. Only a few things to make one cylinder misfire; valve damage, dead spark plug, lost compression or ignition coil pack. 104k miles. The V6 engine uses two coil packs. One for cylinders 1, 3, and 5. The other for cylinders 2, 4, and 6. The 135 coil pack was replaced. The engine was always smooth especially at idle. This P0301 made the engine run very rough at idle and thru the rpm band. Worried about sending unburned gases into the catalytic converter to destroy it as excess fuel burns the converter out, I didn't drive it until checking everything. Spark for cylinder #1 seemed ok and a faulty compression gauge borrowed from a well known auto store failed. My guess was coil pack. New one a week later and the car purrs as it always did.

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Old 10-28-2019, 08:30 PM   #9
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Default Re: Weak Spark

Quote:
Originally Posted by fdryer View Post
It's either burned valve or ignition control module (ICM).

I had a serious P0301 error on my L300 3.0L V6 engine. It went away then came back permanently. Only a few things to make one cylinder misfire; valve damage, dead spark plug, lost compression or ignition coil pack. 104k miles. The V6 engine uses two coil packs. One for cylinders 1, 3, and 5. The other for cylinders 2, 4, and 6. The 135 coil pack was replaced. The engine was always smooth especially at idle. This P0301 made the engine run very rough at idle and thru the rpm band. Worried about sending unburned gases into the catalytic converter to destroy it as excess fuel burns the converter out, I didn't drive it until checking everything. Spark for cylinder #1 seemed ok and a faulty compression gauge borrowed from a well known auto store failed. My guess was coil pack. New one a week later and the car purrs as it always did.
Burned valve confirmed. Cylinder #1 175, cylinder #2 170, cylinder #3 0, cylinder #4 170.

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Old 10-28-2019, 09:15 PM   #10
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Default Re: Weak Spark

I'm wondering if it would be worth it to rebuild the head, or just find a good used engine? I've rebuilt cylinder heads on Hondas before and installed and lapped new valves, so I have the experience. The engine has 180,000 miles on it, but it seems to be pretty healthy aside from the obvious.

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Old 10-28-2019, 10:37 PM   #11
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Default Re: Weak Spark

It is a gamble.

I did just what you are contemplating many years/miles ago on a '95 DOHC. I replaced just the one valve, ground all, and put it back together using just a "valve grind" gasket set. The valve was under $10, but the gaskets (head and stem seals, mainly) ran over $100. I figured about $200 total. A used engine is going to be an "unknown", it may lose a valve (or something else) very quickly. You can probably get one with a warranty, but rarely does that include the labor to R&R or the incidentals required.

When I did mine, I re-used the head screws, but I am very experienced in judging how a fastener is yielding.

Again, it is a gamble. I was looking to try keeping my old grocery-getter on the road as cheap as possible, and it worked for me.

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Old 10-29-2019, 12:19 AM   #12
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Default Re: Weak Spark

I'd vote go for it. Biggest pain is getting the timing cover on with no leaks. From my experience I'd drop the oil pan when sealing the timing cover, and then seal the oil pan back on. People have been able to seal the timing cover without dropping the pan but I failed.

...
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Old 10-29-2019, 03:06 PM   #13
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Default Re: Weak Spark

I did not drop the pan, but do be sure to remove the screws that fasten the pan to the timing cover!

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Old 10-29-2019, 03:22 PM   #14
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Default Re: Weak Spark

Quote:
Originally Posted by billr View Post
It is a gamble.

I did just what you are contemplating many years/miles ago on a '95 DOHC. I replaced just the one valve, ground all, and put it back together using just a "valve grind" gasket set. The valve was under $10, but the gaskets (head and stem seals, mainly) ran over $100. I figured about $200 total. A used engine is going to be an "unknown", it may lose a valve (or something else) very quickly. You can probably get one with a warranty, but rarely does that include the labor to R&R or the incidentals required.

When I did mine, I re-used the head screws, but I am very experienced in judging how a fastener is yielding.

Again, it is a gamble. I was looking to try keeping my old grocery-getter on the road as cheap as possible, and it worked for me.
I'm going for it. I don't have much to lose except the cost of the parts and my own labor. Would you recommend that I only replace the burned #3 cylinder exhaust valves, or replace all the exhaust valves while I have the cylinder head off? I'll definitely use new head bolts.

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Old 10-29-2019, 03:27 PM   #15
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Default Re: Weak Spark

I'd do all of them.

You could have a couple more that could benefit
from a bit of attention.

Post pics!!!

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Old 11-01-2019, 12:43 AM   #16
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Default Re: Weak Spark

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Originally Posted by Pitcher View Post
I'd do all of them.

You could have a couple more that could benefit
from a bit of attention.

Post pics!!!
I'll definitely snap a few pics. I'll probably start on the disassembly tomorrow.

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