Mechanics

ERRATIC ENGINE OPERATION

Saturn Other

I have a 1997 Saturn SL2, 1.9L, twin cam, A/T, 135k Mi.
The problem(s) are as follows:
Hard starting, once started, very erratic idle, frequent stalling. When the vehicle is in motion it runs fine except when you have to stop. When you stop, you have to " Pop" it up in " Neutral" and feather the Gas pedal just to keep it running, but when doing so, the " Tach" will jump up to about 4-5 k when in neutral. Once the vehicle reaches " Operating Temp" if you have to shut it off for whatever reason, you have to put the Gas Pedal all the way to the floor in order to re-start the engine. Although, at " Cruising" speeds.(40-65 mph.) The vehicle runs perfectly. Yes, the " Check engine" light does intermittently come on.
I have hooked the vehicle up to my OBDII scanner and here were the results:
1) O2 sensor voltage above acc. Limits. (Bank #1 sensor#2).
2) IAT sensor faulty.(Intake air temp).
3) Coolant temp. Sensor above temp reading.
4) #3 cyl. Spark plug voltage not registering.

I then went ahead and did a cyl. Comp. Test and the results were:
#1cyl.- 135 lbs.
#2cyl.- 145 lbs.
#3cyl.- 005 lbs. (At 4 different tries)
#4cyl.- 150 lbs.

And here were the condition of the plugs:
#1-Oil Soaked (not carboned)
#2-Fine, normal " carmel" colored
#3-Carbon fouled, but Gasoline Soaked
#4-Fine, normal " carmel" colored
Note: the plugs and wires have LESS than 50 mi. On them. And are installed correctly.

But what gets me is why the spark is NOT registering in #3 cyl. The " Coil Pack" was swapped out with another " Working" one, with the same results.
Could the Computer have a bad " Leg" in one of the sectors? Or, is it simply a, " Blown head Gasket"? These problems are Driving me NUTZ trying to properly diagnose them. ANY help from another Technition would be GREATLY appreciated!
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Tonka_Dryden
February 16, 2006.




The erratic idle and hard starting you first allude to is a classic symptom of a cracked ECTS. The old style composite/plastic tip would crack and usaully ruin the connector. The updated all brass ECTS and new pigtail from Saturn is the answer.

What were the exact code numbers you pulled? The PCM compares the signal from the IAT to the ECTS. Usually is will cause a light to blink on the dash if the 2 are out of sinc.

I would assume that the fowled plug in #3 simply will not fire because it is fuel soaked. Do a leak down test to further troubleshoot the lack of compression.

Plugs 2 and 3 fire off the same coil at the same time. One is on compression while the other is on the exhaust stroke. This is typical of a DIS waste spark system. A bad plug, wire, or corrosion on the #3 coil terminal are the only other reason it would not fire and #2 does.

Not a pro tech but hope this helps.
Good luck and let us know what you find.
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Tiny
Peppermrj
Feb 16, 2006.
When last we spoke your instructions were to do a " Cylinder leak down test" which I have did. Believe it or not, there was not a Leak Down tester to be bought or rented here where I live. So I made one with the help of the " Net". Anyhow,
Here were the results.(From Left to Right) ( all were at TDC)
Cylinder#1- 195 LBS-No leakage anywhere.
Cylinder#2-198 LBS-No leakage anywhere
Cylinder#3-60-Lbs-Steady, but air comming up #4 spark plug hole, and Air comming out of tailpipe.
Cylinder #4-98 -Lbs-no leakage anywhere.
I performed the test 4 times over and the results were all the same. Right across the board.
I'm guessing bad exhaust valves for #3 cylinder. But there was NO coolant rise or bubbles in the resrevoir at all when the test was being done.
Could the Faulty exhaust valves make the engine operate that eratic. And what's up with only 60 lbs of comp. In cylinder #3 during the " Leak down Test". Cracked Rings.(Both WET and DRY tests come up the same.60 lbs.).I'm GOIN' NUTZ. Please help. In the event that there is a " Ring" problem. Any chance of " Pulling" that piston out from the bottom instead of the top?
Please enlighten. ASAP!
Thanx a million!
P.S. It's a 1.9 L, DOHC, A/T, 145K on eng. Saturn SL2

Tiny
Tonka_Dryden
Mar 15, 2006.
The erratic engine operation is due to both the bad sensor inputs (codes you previously posted especially the ECTS) and the problems on cylinder 3 and the head gasket.

A little info on the leak down test. First congrats on building you own. 8) The leak down test is done by adjusting air pressure via the regulator to put 100lbs pressure into the cylinder. Then whatever it leaks down to is the percentage of leakage (80lbs = 80%). The first link discusses the operation.

My interpretation of your results are that you have a bad seal on the exhaust valve of #3 cylinder. It could be stuck open by carbon. It could have a broken valve spring (bad, but not likely). It could be burnt or have a bad seat.
If you are getting air from #4 your headgasket is bad or the head is cracked. Neither are common.

The good news is that you can do a partial rebuild with the engine in the car. Once the head is pulled you can even put new rings and bearings on with out dropping the crank.

The other option is to get a used engine installed.

Good luck and let us know. : )

Tiny
Peppermrj
Mar 17, 2006.

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