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Old 10-19-2011, 09:45 PM   #1
dorisSL
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Default where to start (stumbling)

so, Doris is having a bad month.
battery died, got a new one.
radiator died, got a new one.
now a new problem.
I believe the proper term is stumbling, and it nearly feels like bucking.
happens only in gear and only with more than ~10% throttle. gets worse with more throttle till about 50% then seems to go away.
no odd noises.
in neutral it doesn't make any funny noises/excess vibration all through rpm range and pedal travel.

i *think* it's a spark issue, mostly because the exhaust smells rich, but i really don't know.

where sould i start?

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-19-2011, 10:18 PM   #2
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1997 SC2
Wrench Re: where to start (stumbling)

Well....

FWIW, I'd start by checking the fuel pressure. It is fairly critical (too much and it floods in open loop, too little and it won't atomize right and will run lean). Make sure that the pressure regulator reference line to the intake manifold is attached and in good shape (attached to the TB on your car I think, it is on mine anyway). Check to see if the goofy plastic lines from the clip on top of the TB might be cracked.

Check the usual suspects- ECTS, IAT, etc. You could also check the EGR to see if it is stuck or plugged.

Then I'd check the ignition pack, plugs and wires. Since it smells rich, have you replaced the O2 sensor lately? The resistance of all four wires should be in the same range and you could try reducing the plug gaps. Try maybe 0.032"-0.035" or so as a test.

Try running the engine in a dark place. Look for spark overs on the coils or wires. Replace or repair anything that arcs.

Oh, and check the MAP sensor and the passage into the manifold for being clogged. It happens. If clogged the MAP sensor will give incorrect readings and can cause all sorts of troubles. If you have (or can borrow) a sensor tester and hand vacuum pump, be sure to test it.

I'll look in my FSM, but because it is for a 1997/98 I am not sure how much good it will do. If I find something else I'll post it.

Our son just had a similar type of issue with his car, but it has a MAF sensor, which turned out to be the issue. Of course these cars don't. Point being that it could be a fuel delivery issue too.

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Old 10-19-2011, 10:33 PM   #3
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Default Re: where to start (stumbling)

oh, i forgot to mention, it feels pretty rythmic when it happens. very regular pulse to it.

going to go out and check for codes and sparks, and maybe run the EGR test now.

i have not tested or replaced the O2 sensor, so it could be getting lazy, as OldNuc says.

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-19-2011, 11:11 PM   #4
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Default Re: where to start (stumbling)

sorry for rapidposting, but here's some more info.

checked for codes, no codes.
checked for sparks, no signs, but it wasn't 100% dark.



when this first started, it was only noticeable in low gears and only from about 2k-2500 RPM.

i did notice today on my drive home from work that i was blowing smoke pretty bad for about a block. stopped smoking when i was at a stoplight and didn't start again. I couldn't tell if it was white or blue. car wasn't warmed up at the time so i think it could've been condensation, but i don't know for sure.

when i was checking for sparks i went around to the exhaust to see if it seemed to be smoking or anything and it did not. it did seem like it was skipping a beat or something, though. a little more putter-y than normal.

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-19-2011, 11:12 PM   #5
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1997 SC2
Wrench Re: where to start (stumbling)

Rythmic?

Well, according to the FSM it could be described as a surge or chuggle from your description.

The things they say to check (in order of precedence) are- EGR operation, generator output voltage, vacuum lines (for kinks, disconnections and breaks), fuel filter and pressure, spark plugs (cracks, wear, contamination, deposits and gapping), ignition system in general, and fuel quality.

As for ignition, the things it says to check are- plug gap (0.040" per FSM, but you should try running it smaller as a diagnostic), tower-to-tower coil resistance of 8-15k ohms, wire resistance must be less than 12k ohms, and of course no flash overs, wire cracks, carbon tracks and so forth.

Since it happens at partial throttle under load, it could be too low an octane or comtaminated fuel.

Yes, I know that these cars are supposed to run on 87 octane regular, but you could have gotten a bad tank full (or your fuel filter is full of crud from the bottom of the filling station's tanks, or water, or ?????).

It happens all the time. Try putting some Techron injector cleaner in the tank and when it gets down to about half a tank, fill it with premium. See if it changes the symptoms.

If the knock sensor is being tripped, the engine timing will be retarded, then it will try to advance again until it is tripped, retards it again, and so forth, a rythmic event .

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Old 10-19-2011, 11:31 PM   #6
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1998 SC2
Default Re: where to start (stumbling)

Check the plug wire routing. If the wires are as old as the battery get new ones and then replace the plugs. Periodic misfire is an ignition issue usually and if one plug/wire dies it takes out 2 cylinders.

As you look on the engine/coils your left to right

Engine
1 2 3 4

4 1 2 3
Coil Towers

Connect the matching numbers with a plug wire and #1 and #4 must run parallel to each other and be in wire clips.

Fuel pressure is not a bad idea or if it is a 97 or older a nice new fuel filter from WIX or NAPA.

As you have a 95 a dirty ground on the ICM will also cause this problem or a bad battery ground or a semi shot CKP (CPS)

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Old 10-20-2011, 01:19 AM   #7
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Default Re: where to start (stumbling)

Quote:
Originally Posted by OldNuc View Post
Check the plug wire routing. If the wires are as old as the battery get new ones and then replace the plugs. Periodic misfire is an ignition issue usually and if one plug/wire dies it takes out 2 cylinders.

As you look on the engine/coils your left to right

Engine
1 2 3 4

4 1 2 3
Coil Towers

Connect the matching numbers with a plug wire and #1 and #4 must run parallel to each other and be in wire clips.

Fuel pressure is not a bad idea or if it is a 97 or older a nice new fuel filter from WIX or NAPA.

As you have a 95 a dirty ground on the ICM will also cause this problem or a bad battery ground or a semi shot CKP (CPS)
the wires are older than the battery, but only because i replaced it last week :P
thy'er less than a year old, i think less than 6 months.
is there a test for the CPS?
i cleaned all the grounds on the ICM and such when i did my clutch last winter, but i will again now since it's a free test anyway.


"Connect the matching numbers with a plug wire and #1 and #4 must run parallel to each other and be in wire clips." never seen this info before. i believe mine are, but what's this all about? is it just because of impedence/inductance?

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-20-2011, 07:52 AM   #8
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1998 SC2
Default Re: where to start (stumbling)

Quote:
Originally Posted by dorisSL
"Connect the matching numbers with a plug wire and #1 and #4 must run parallel to each other and be in wire clips." never seen this info before. i believe mine are, but what's this all about? is it just because of impedence/inductance?

It is how the system knows when the cylinders are supposed to fire. It is the cam position sensor. The only way to check the CKP is with a scope. Just replace it and the ICM will not function correctly if the system voltage is low so check the battery terminal voltage with the car running. The running voltage should be over 14.2vDC and preferably 14.5->14.7vDC.

Still sounds like wires, plugs, and/or ignition module or fuel pressure/delivery

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Old 10-20-2011, 10:32 AM   #9
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1997 SC2
Post Re: where to start (stumbling)

Quote:
"Connect the matching numbers with a plug wire and #1 and #4 must run parallel to each other and be in wire clips." never seen this info before. i believe mine are, but what's this all about? is it just because of impedence/inductance?
Pretty much. It has partially to do with the way the wires radiate EMI and also act as antennas. Believe it or not, wire routing matters even on engines that use traditional coils and distributors. They can cause misfires or cross-fires if routed incorrectly, though usually only on high(er) performance applications (think drag racers).

Running wires of the same circuit closely and parallel to one another tends to cancel out magnetic fields because the current is obviously running in opposite directions in the wires. Due to the method that Saturn chose to use to sense "camshaft position", this matters.

As OldNuc said, the waveforms on the wires is how the ignition module figures out which cylinder is being fired at the moment. The cylinder that is on the compression stroke requires a higher voltage to arc over the plug gap (more "insulation" present is in the gap), so there is a net imbalance in the waveforms on the wires that can be sensed. Clever scheme, but all in all I'd have preferred it if they had just mounted a real cam sensor and been done with it.

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Old 10-20-2011, 08:42 PM   #10
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Default Re: where to start (stumbling)

Blocked off the egr ports with quarters, didn't help at all.
Checked the plug wires, 1 and 4 were not routed parallel. They are now, and the stumbling seems better but far from gone.
Picked up some techron concentrate, I'll toss that in and fill up with premium tomorrow

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Old 10-20-2011, 09:47 PM   #11
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Default Re: where to start (stumbling)

Try new NGK BKR5ESA-11 plugs and consider a nice new set of wires. No point in digging into the coils and ICM until you actually know it is not wires and plugs.

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Old 10-20-2011, 10:31 PM   #12
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2001 L-Series 3.0L Wagon
Default Re: where to start (stumbling)

And now for the dumb question, have you tried an injector cleaner? I had the part-throttle bucking thing some years ago, and Ernie at Saturn of Norwood (man, I miss Saturn of Norwood!) just used some techron injector cleaner and the problem went away.

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Old 10-21-2011, 08:10 AM   #13
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Default Re: where to start (stumbling)

Techron is on the passenger sea waiting for a fill-up.
picking up plugs and wires after work, hopefully the weather will cooperate.

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Old 10-21-2011, 08:33 PM   #14
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Default Re: where to start (stumbling)

changed the plugs just now.
here are the removed plugs, and i think we can safely assume which cylinder is giving me issues (1-2-3-4 left to right)


now, what is the issue? they all smell like umburnt fuel, #4 had black/gray deposits and they are pretty hard. haven't taken it for a spin yet to see how she drives, but i'm about to.

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-21-2011, 08:55 PM   #15
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Default Re: where to start (stumbling)

#4 is carbon fouled. Lack of focus precludes any intelligent statement about the other 3 though.

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Old 10-21-2011, 08:57 PM   #16
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Default Re: where to start (stumbling)

Quote:
Originally Posted by OldNuc View Post
#4 is carbon fouled. Lack of focus precludes any intelligent statement about the other 3 though.
phone camera hates me. the other 3 look like every other set i've ever pulled out.

so, where to start on why #4 is fouled?

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-21-2011, 09:09 PM   #17
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Default Re: where to start (stumbling)

quick drive around the block and it is 100% smoother. no stumbling at all.
there was a fairly soft sound, somewhere between a tap and the pitter-patter of an exhaust leak pn sudden trottle changes. popped the hood, sounded like it was coming from the area around the EGR and TB. i do still have the quarters installed on the EGR, could it be a side-effect from that or something else (i intend to pul those quarters as soon as the engine cools down enough that i won't burn my hands.)

...
1995 SL, born 12/23/94, manual, WAI 190,500, "Doris"
(I'm Ben, the car is Doris)

you can't mulch at those speeds man, that's too fast

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Old 10-21-2011, 09:44 PM   #18
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Default Re: where to start (stumbling)

Hard to tell but find it and remove it if it is a leak. The #4 cylinder runs hotter than the others and that may have been the initiating event. Run the car for 2-3 thousand miles and pull the plugs for a look see. Could have been a bad wire also.

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