Do I have a failing coil pack or something else?


Well-Known Member
Drove my car to work last Monday & Tuesday after sitting for about a month. The car ran great especially withe the upper 50's and low 60's. On the way home Tuesday a couple miles from my house the car bucked/hesitated a couple times, almost seemed like the trans was acting up. I got it home and it started doing it a lot on my street plus I heard a lot of racket under the hood. Pulled in my drive way and shut it off, opened the hood and found my belt had peeled off one or two of the ribs and was whipping the broken piece around. Once i cut off the bad loose and listened to the motor and trans all was quiet. I picked up a new belt Friday and installed it yesterday...started the car and all seemed good. This morning I took the car out to a Sunday morning Cruise hangout that is about 28 miles away. About half way there at around 55 mph it starts bucking again almost like it is slipping in and out of gear and then I hear a bunch of racket again. I pull over and pop the brand new belt peeled off a rib or two again. I cut off the loose piece, turned around and headed back home. It ran OK for a couple miles then started bucking again but this time if backfired through the exhaust a few times. I pulled over and shut it off for about 15 minutes then started it back up and headed home. It ran fine the rest of the way home...~20 miles or so? So what is going on to cause my belt to shred? The backfire makes me think the ignition cut out possibly by the coil pack failing or the battery is shorting out and going bad? But what would lock up and cause the belt to shread...or can the bucking of the engine misfiring and cutting out cause the belt to jerk and break? The belt before this one was about 5 or 6 years old with maybe 8-10K miles, the alternator and battery are both fairly new. Voltage is a steady 13-14 volts and the alternator is nice and quiet. I had a MAF go bad years ago and the car just cut in and out but never backfired...replaced MAF with LT1 and Translator. Any ideas?

Hi Scott,

I had a issue close to yours. Car back fired out the exhaust, jerked, .. It ended up being the locator tab on the cam sensor was sheered off. This happens when you rev your engine past stock shift points... Wears..

Take a really good look at the locator tab, it's small.

I bet the balancer bolt is loose causing the balancer to move forward and sheer the belt. When that happens you lose your crank signal.

That sucker needs to be tq'd down to like 200 ft lbs.
I'll check both...I have some other replies on the other boards that have mentioned the balancer and crank sensor ( I have never had the balancer off though). Also the AC compressor was mentioned as well...I did have the defroster on when the bucking started and shortly after it started I heard the belt slapping around before I could get off the highway. Doesn't the compressor come on with the defroster and if so if it is seizing up I'm guessing that could eat up the belt pretty fast but what would cause the bucking? Could the lose strip of belt interfere with the crank sensor while it is whipping around and cause it to get out of sync and backfire...only backfired 2 times. When I headed back home I turned off the defroster (didn't need it anymore) in case it was the compressor seizing up and the car ran perfect all the way home...almost 20 mile. I even got into to it a few short bursts once I was near enough to my house and again ran perfect. I suppose another thing to check would be the idler pulley but I would think it would be noisy if the bearing was failing?
Sounds like you are on to the issue with the compressor, yes it engages when the defroster is on, even if the selector is on for hot air, it runs as part of the drying of the air process. If it is seizing that would explain why the belt keeps breaking and I supposed it would cause the engine to buck fairly good since just the compressor turning on and off normally cause a significant load, think about how the engine would react when that pulley stops turning... I have never had a compressor seize but I image it would put a lot more load all at once on the motor causing it to sputter.
Try running it some more with the ac and defroster off to see if the issue arises again before looking further.
You asked about the compressor. I've never had a compressor lock up and free up again.
When my 93's went, it was locked solid from no oil in the system.
I'd check the pulley bearing. When the compressor is not running, it spins a bearing in the pulley.
It wears out over time or can rust away.
It might cause the noise and misalignment of the belt.
When they go, the clutch starts rubbing together without being engaged and makes metal shavings.
It also makes noise which goes away if you turn on the AC because the clutch engages and takes up the slack.
Check that out.
The other thing I've heard of is the rubber in the crank balancer goes bad causes misalignment down there.
I'll check both...I have some other replies on the other boards that have mentioned the balancer and crank sensor ( I have never had the balancer off though). ?

So your racing on the factory plastic timing chain gear then? o_O
Razor said:
So your racing on the factory plastic timing chain gear then? o_O

Shush!!! Lol...sure am but the car only has 50k miles on it though that probably doesn't matter with it being 23 years old ;-)
Its the 23 years old thingy.. :eek:

Change front cover seal.. and do rear main since pan has to come off/dropped.

Remember its an interference motor.. so if the chain gear comes apart... piston will hit valves.

If the compressor is bad.. the compressor is bad. If the AC doesn't work then don't turn it on.
Definitely change timing chain, that was something I did on the driveway with car on two jack stands. If I can do it any one can. Also you don't need the tensioner with a double roller chain.
jarredsoon said:
Definitely change timing chain, that was something I did on the driveway with car on two jack stands. If I can do it any one can. Also you don't need the tensioner with a double roller chain.

Where did you get your parts from?
From a local speed shop I can't recall what brand but they do buicks all the time and it was double roller.
Sorry I'm not much help, try TA performance or weber racing I finally had a chance tho check my car out yesterday. Just idling in my driveway the car was running excellent...very smooth then I turned on the defroster and immediately the compressor started cycling on and off. Every time it did the engine would baug way down and almost sputter then come back to normal with each cycle. I unplugged the compressor and let it run for 15 minutes or so and everything seemed fine...I didn't get a chance to drive the car though. I decided to drive it to work this morning and after about 20 minutes (20+ miles of driving) it started to surge/buck again some with a small issues with the belt this time however it was not nearly as bad as it was before when the compressor was plugged in. All my pulleys look good, balancer looks wobble that I can see. Obviously something is failing and causing the motor to stumble ocassionaly backfire after it is running for a while. Last week when the surge was bad it literally felt like the car was shifting in and out of gear and was almost violent at times...again wasn't nearly as bad this morning but still there. How do I know if the crank sensor or cam sensor is bad or going bad...any way to test them?​
Update to yesterdays post...
On my ride home from work the car started stumbling much sooner (only a couple miles or so). Now it appears to be cutting out and then coming back on...very similar to when my original MAF went bad. A few times after it cut out and came back on it did backfire through the exhaust. I also noticed every time it cut out my tach lost signal. The further I went the worse it got at times causing me to drive on the shoulder with flashers on...still occasionally taking off and running somewhat normal again. About 1 mile from my house the CEL came on briefly and it was so bad and cutting out that it eventually stalled. I waited a few minutes and it started right back up and I drove it the rest of the way home. The problem is definitely seems worse under a idle it seems perfectly fine. While running in my driveway I tapped on the MAF and didn't notice any stumble...the MAF is relatively new (LT1 and Translator from Full Throttle a few years ago). I had an ignition module go bad on one of my other cars a few years ago and it acted similar. Not sure why but my Scanmaster did not record any malfunction codes?
Here are a couple videos of the ignition cutting out, backfiring and the tach loosing RPM signal on my way home last night just before it finally stalled out. I have the Scanmaster set on RPM in one of the videos.

Have you looked at the ecm recently? Any corrosion on the connections, or possibly something with the chip?
Update...I'm keeping my fingers crossed! I swapped out my coil-pack and ignition module with Doug's good ones and that seemed to do the trick. I need to to drive it more to make sure it's not time or heat related. I'm pretty sure at this point it was the ignition module failing as it heated up. I pulled the damaged belt off and while on the ramps checked the crank sensor, balancer and all the pulleys. Crank sensor was oil soaked from my leaky front main so I cleaned it off real good with brakekleen. I also checked the balancer with a pry bar and Paulie suggested for any movement or damage and possible thrust bearing wear while the belt was off and it was solid with not a bit of movement. So I think I can rule out the crank sensor going in and out of sync do to a bad balancer or movement from a worn thrust bearing. Thanks Doug for the I need to order a new one!
I'm still not sure what caused the belt to shred off a a couple ribs though unless that was related to my AC compressor seizing or acting up? I plugged it back in and it definitely cycles constantly and causes the motor stumble when it does...unplugged for now. I did a half a$$ R134 conversion last Summer that didn't really work all to well and probably damaged the compressor from some posts I have read. Will probably rebuild the AC system next Spring and hopefully solve that problem.