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Old 06-19-2017, 02:17 PM   #1
Joshtheclockman
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Default Rough Running rough start

So after replacing a ton of parts, i still have a problem. I was on my way home a few weeks ago and the car suddenly started to run like a lawn mower. My first thought was ignition coil, so I replaced them along with the module and the wires and the plugs. Put a timing light on it and all 4 cylinders appear to be firing, yet it doesn't run like it is. So i replaced the crank sensor and then shortly after the knock sensor. Egr has been replaced, ects has been replaced.

It just continues to run like crap. Does tend to smoke now that its missing, hasnt gone though any oil or coolant. Im at a loss. oh also the cat was replaced last year and the head has been rebuilt about 5 years ago...

No engine light


Clearly im missing something.

1994 saturn sl
254xxx miles
5 speed

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Old 06-19-2017, 02:31 PM   #2
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Default Re: Rough Running rough start

Might be time for a compression check, no?

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Old 06-19-2017, 03:01 PM   #3
Joshtheclockman
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Default Re: Rough Running rough start

Unfortunately I think you might be right. Ill be doing that in the morning... Although im really hoping that isnt what the issue is.

Last edited by Joshtheclockman; 06-19-2017 at 03:06 PM..

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Old 06-20-2017, 09:59 PM   #4
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Default Re: Rough Running rough start

So compression test comes back 1. 125 2.120 3. 0 and 4.0. Guess there lies the problem. So time to pull the head I guess.

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Old 06-21-2017, 07:04 AM   #5
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Default Re: Rough Running rough start

Those are horrid numbers.
You are sure they are correct?

I find it hard to believe that the car was running well up until WHAM, lost all compression on 2 cyl and incredible low numbers on the other 2 cyl!

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Old 06-21-2017, 08:08 AM   #6
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Default Re: Rough Running rough start

Something's wrong with the test method, the engine doesn't run on 2cyl. It'll run on 3, won't want to motivate but will run & go down the road.

Disable the injectors (or fuel pump), pull all 4 plugs, block throttle blade 100% open and start with a fully charged battery. Fully seat the compression tester in the spark plug hole, engage starter until the compression number stops increasing (healthy motor generally under 5 cycles, FSM procedure uses 10).

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Old 06-21-2017, 12:18 PM   #7
Saturn Night
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Default Re: Rough Running rough start

Quote:
Originally Posted by Joshtheclockman View Post
So after replacing a ton of parts, i still have a problem. I was on my way home a few weeks ago and the car suddenly started to run like a lawn mower. My first thought was ignition coil, so I replaced them along with the module and the wires and the plugs. Put a timing light on it and all 4 cylinders appear to be firing, yet it doesn't run like it is. So i replaced the crank sensor and then shortly after the knock sensor. Egr has been replaced, ects has been replaced.

It just continues to run like crap. Does tend to smoke now that its missing, hasnt gone though any oil or coolant. Im at a loss. oh also the cat was replaced last year and the head has been rebuilt about 5 years ago...

No engine light


Clearly im missing something.

1994 saturn sl
254xxx miles
5 speed
Check your ignition coils and the module.

Swapping the 1/4 coil, with the 2/3 coil can tell you if a coil is bad.
Modules can be sourced from a local yard, or brand new. Some parts stores/dealerships can test your module to make sure it hasn't bit the dust.

If there is no change in symptoms from the first two, try removing the O2 sensor and see if you have any change. the car will be very loud, but don't surprise yourself with thinking a cat won't clog within such a short time. a part, even when new, can fail at any given time.

A 4-cylinder will not run, or start, with 0psi on two of its cylinders. And 120psi is too low for combustion.

Once you have ruled out the ignition system, you will want to test your fuel pressure and injector resistance.

IF all of these tests show no change, run the compression test as you were already advised of.

Burnt valves can cause a misfire, similar to what you are describing for symptoms. However, the possibility of this is often rare and very minimal when compared to other areas of the engine that cause these symptoms.

I drove my 1992 Achieva with burnt valves, for a few days. I had good compression in 3 cylinders, and only 60psi in the number 4 cylinder.

My 1991 Grand Am had similar symptoms because of a bad CKP(which you have replaced and is uncommon to cause this issue on the Saturn 1.9L engine), but still had 150psi in all 4 cylinders.

Meaning, the compression test can tell you a relative ball park of what is wrong, but not always.

...
1991 Pontiac Grand Am @ 139k - More rust than paint & no leaks
1995 Saturn SC2 @ 179k - 17.2538 @ 77.91mph w/Stock TB
Mechanic: I can't fix stupid, but I can fix what stupid does.

Last edited by Saturn Night; 06-21-2017 at 12:28 PM.. Reason: Add Info

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Old 06-21-2017, 03:47 PM   #8
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Default Re: Rough Running rough start

^^ I believe the OP said he replaced the module in his first post. I presumed they meant the ICM / coils?

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Old 06-21-2017, 04:08 PM   #9
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Default Re: Rough Running rough start

Quote:
Originally Posted by Joshtheclockman View Post
So compression test comes back 1. 125 2.120 3. 0 and 4.0. Guess there lies the problem. So time to pull the head I guess.
Quote:
Originally Posted by toggenburg View Post
Those are horrid numbers.
You are sure they are correct?

I find it hard to believe that the car was running well up until WHAM, lost all compression on 2 cyl and incredible low numbers on the other 2 cyl!
Blown head gasket?

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Old 06-21-2017, 04:13 PM   #10
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Default Re: Rough Running rough start

I gotta disagree with some of the above...

A good compression reading isn't conclusive, as an exhaust valve that isn't opening can yield fine compression. But bad compression, like the two "zeros", always mean it is relatively a waste to consider anything else until that is resolved. It will never run well with those two dead cylinders, no matter how many other ignition or fuel parts are thrown at it.

Like others, I too am suspicious of the compression readings, so feel they have to be verified using a different gauge, trying the same gauge/method in a different engine, etc. There is little point in either condemning this engine or chasing other stuff until we have confidence in the compression readings

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Old 06-21-2017, 06:36 PM   #11
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Default Re: Rough Running rough start

I wonder how a compression gauge fails after recording two good readings. When I added the question mark to a blown head gasket, its my presumption of a possible head gasket blowing between cylinders 3 and 4. A question, not an answer so the OP can think on it or ignore it. Obviously, cylinder head removal may be the only way to verify head gasket damage. Once the cylinder head is removed, more things come into view - valves, pistons, scored cylinder walls, etc..

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Old 06-21-2017, 08:35 PM   #12
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Default Re: Rough Running rough start

Two good readings? Didn't the OP report a couple of 120s and a couple of 0s?

I have seen a compression gauge "fail" between good readings, all it takes is a small piece of crud caught in the gauge's check-valves to come up with bogus low readings.

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Old 06-21-2017, 08:58 PM   #13
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Default Re: Rough Running rough start

I think you're splitting hairs. Two compression readings of 125 and 120, followed with zero on the last two measurements. That's four readings. I understand your scepticism but facts are facts. You asked for compression numbers and have it. You can ask for another round but if it comes back the same what do you suggest?

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Old 06-21-2017, 10:13 PM   #14
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Default Re: Rough Running rough start

If we can confirm those low readings, then the engine is shot; it will need serious repairs. I just don't want the OP to charge in that direction and tear it apart, or junk the car, based on those first readings. I'm just asking for a "second opinion" on this engine's basic health.

My real point was that the OP shouldn't waste time or money on anything else (ignition, fuel, or other sensors/actuators) unless those poor compression readings can be disproved, if they can.

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Old 06-22-2017, 04:32 AM   #15
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Default Re: Rough Running rough start

Quote:
Originally Posted by fdryer View Post
I think you're splitting hairs. Two compression readings of 125 and 120, followed with zero on the last two measurements. That's four readings. I understand your scepticism but facts are facts. You asked for compression numbers and have it. You can ask for another round but if it comes back the same what do you suggest?
And with the readings the OP got, it is not possible for his engine to start or run(even poorly). Even an 8.2:1 compression engine will be over 120psi. Saturns run 9.5:1 compression on DOHC, and I think 9.0:1 on SOHC.

And with two cylinders, side-by-side, showing ZERO psi would clearly stall an engine with only 4 cylinders in it. The balance of the engine would be far too disrupted.

...
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1995 Saturn SC2 @ 179k - 17.2538 @ 77.91mph w/Stock TB
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Old 06-22-2017, 04:34 AM   #16
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Default Re: Rough Running rough start

Quote:
Originally Posted by fdryer View Post
Blown head gasket?
He stated he is not losing oil or coolant, in the OP. After rereading, it is leaning towards a burnt valve.

...
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