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Engine running rough

Tiny
TASMERE
  • MEMBER
  • 1995 BUICK LESABRE
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
Was driving and hit a hard bump on the shoulder and all the sudden the engine is running rough, feels like it's missing. Check plugs and wires. Still running rough. After talking over the issues, rough/missing on acceleration, with a couple fairly knowledgeable guys as well as a brief scent of the catalytic converter (rotten eggs) smell, we cut the converter off to test it. That's not the issue. Kind of stuck at this point and now considering coil pack, Egr valve, or throttle position sensor. What could I have broken, upset, or shaken loose in a hard bump that would be causing the rough running? Also, when I just lightly feather the accelerator, the engine revs high and low. Check engine light is not on.
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Thursday, September 19th, 2019 AT 3:25 AM

13 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

The converter turned red from too much fuel.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

I would start by checking for a spark to each cylinder to be sure there is spark there.

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Beyond that, check the compression on each cylinder.

https://www.2carpros.com/articles/how-to-test-engine-compression

Check all the wire connections at the module to be sure they are tight and secure.

Roy
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Thursday, September 19th, 2019 AT 4:30 AM
Tiny
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Thank you so much for answering quickly. I will try this today and see what kind of luck I have.
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Thursday, September 19th, 2019 AT 9:27 AM
Tiny
ASEMASTER6371
  • MECHANIC
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You are welcome.

Keep us updated.

Roy
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Thursday, September 19th, 2019 AT 9:33 AM
Tiny
TASMERE
  • MEMBER
  • 7 POSTS
Hi Roy

We're still here working on this and having trouble just diagnosing the actual problem. No check engine light but we did finally get a read out on a P0300. So we've been focused on the issues on a global misfire. Which frankly, is a lot.

It's definitely not the converter. We took the hard head version of that and removed it and then replaced it. It's definitely not the MAS, got a new one. Got new plugs and wires. Swapped out coil packs. Sprayed around and replaced any vacuum lines. Took the vacuum line off the fuel reg to be sure no fuel was coming into the vacuum.

Ran two bottles of seafoam through it. Replaced fuel filter.

We're kind of confused about how this could be such a serious and difficult issue to diagnose with no check engine light.

Of course we're not made of money and realize we could still replace the throttle position sensor but one of the things that throws us off on some of the symptoms of a couple issues that are left is the fact that the car isn't isn't cutting off, still running, and shows no sign of improvement or deterioration.

Feel like the revving issue is significant since it only started after the big bump.

Thanks ahead of time for any advice or suggestions.
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Friday, October 11th, 2019 AT 12:46 PM
Tiny
ASEMASTER6371
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Okay, the next thing I would do is check the fuel pressure. The most common cause for the 300 code is low fuel pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

You can rent a tester at a parts store for this test.

Roy
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Friday, October 11th, 2019 AT 12:57 PM
Tiny
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On that. Thank you. I'll definitely be back and won't leave this thread hanging once I actually fix the issue!
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Friday, October 11th, 2019 AT 1:08 PM
Tiny
ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
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Friday, October 11th, 2019 AT 1:15 PM
Tiny
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Is there any type of diagnostic tool that is something besides the basic handheld device that you can have checked at your local auto parts store? Considering we have no check engine light and a 1995 model vehicle? I keep seeing something mentioned on help articles that doesn't sound like a basic diagnostic option.
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Friday, October 11th, 2019 AT 3:26 PM
Tiny
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A scan tool for OBD1 is the other option. Plan on spending $500.00 to $1,000.00 for a tool like this.

Roy
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Friday, October 11th, 2019 AT 3:34 PM
Tiny
TASMERE
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Okay. It looks like this was one of the coil packs. Finally got it put on a mechanic's machine and it indicated which pack it was. That means that the coil packs we used to test were probably not working.

Also, we found this out as we were about to pay a mechanic to replace the intake manifold gaskets. We assumed that was the issue since many mechanics and help articles and videos said that this was a common problem on the 3.8 GM and an even worse one on the 3.4.
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Thursday, October 24th, 2019 AT 10:47 AM
Tiny
ASEMASTER6371
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Good deal. The 3 4 is very common for the intake manifold gaskets.

Roy
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Thursday, October 24th, 2019 AT 11:53 AM
Tiny
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  • 7 POSTS
Thank you so much for your help. You were quick to reply and gave excellent help with links and that helped a lot with the anxiety over fixing this car.
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Thursday, October 24th, 2019 AT 12:07 PM

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