Saturn SL # 4 Cylinder Miss

[spitbits1500]

I have a 96 saturn SL, I have had it for about a month and it has been nothing but trouble for me. It has a cylinder miss on the number 4 cylinder at lower RPM's.

I have replaced the fuel filter, spark plugs, wires, coil pack (x1). Tried some fuel injector cleaner... As well as replaced the O2 sensor.

I am at a loss on what to do next. I hooked it up to a scanner and found it was the number 4 cyl. Replaced the coil pack for that cylinder, and it improved a little, but at the lower RPM's It still misses (intermittently).

The fan also will not turn on unless I run the A/C. I tested the relay with the scan tool and it turned on, I believe it is the sensor. I plan to replace that, as well as the self tensioner for the sirpentine belt which just also decided to sh*t the bed.

I got so much money into this car now I feel like I am forced to get it driving right again. Any help would be greatly appreciated.... Is there a chance that the coolant sensor is screwing up, possibly causing the missfire?!

Thanks,

-Ryan

[sierrap615]

the coolant temp sensor is a known problem with all 91-2001 S-Series.

http://www.saturnfans.com/forums/showthread.php?t=24003
http://www.saturnfans.com/forums/showthread.php?t=37884

i'm not going to say its impossible for the ECT to cause a missfire, but is about as likely as winning a billion dollar lottery.

did you gap the plugs to 0.040 or 0.060? the orignal spec for the 96 year was 0.060, however Saturn quickly found the larger gap was causing drivibilty problems and quickly returned to the 0.040 gap that was used in earlyer years.

also was there any rust or corrison on the coil hold down bolts or mounting area?

[spitbits1500]

I have the plugs gapped to .040 inches. There was not any corrosion on the hold down points of the coil packs or on the connections.

I figured someone would say it was highly unlikely for the cooling sensor to be affecting the driveability.

I'm trying to learn/understand the EI on the newer cars w/o caps/rotors... Is there a sensor that tells the computer to spark number 4 cylinder? If so could that be my problem, possibly a loose connection or a wearing sensor causing a miss?

-Ryan

[sierrap615]

most distribitorless ignition systems use the waste spark method, firing companion cylinders at the same time.1&4 - 2&3. as you surely noticed, the DIS system has two coils with two towers each, where as a conventional distributor uses one coil and one tower for all cylinders. on the conventionial system, energy travels from the coil to the distributor then to the spark plug and grounds itself in the cylinder head. in a DIS system the energy travels from the coil to the spark plug thru the head into the companton cylinder spark plug and back to the coil. so it fires every plug on both the compression and exhaust stroke. you are probilly saying - thats stupid, why would fire a plug that doesn't need to be fired? doesn't that waste spark energy? (like the name implies) well its cheap, its easy, it works better then a distributor(no moving parts) and doesn't waste that much energy. when a cylinder is on the compression stroke, say with a 10:1 compression ratio and 0.040 gap, the air/fuel molicules are so tightly packed the spark is basicly jumping a 0.400 in gap. on the exhaust stroke there is no compression, so the spark is still jumping a 0.040 gap. now compairing the two, the 0.040 in gap isn't that bad. also on a conventional system for a 4 cylinder engine the one coil has to fire 4 times in 720 degrees of crank rotation. sharing the load between two coils means each coil only has to fire 2 times in 720 degrees on the same engine. so the coils enjoy more off time and more charge time. the other, more expencive, more complex DIS system uses one coil for each cylinder(sometimes called a coil on plug system, the V6 VUEs has this system)

oops! almost forgot, the ignition module and PCM know when to fire the plugs based on a signal from the crankshaft position sensor, that reads a ring on the crankshaft, that can be seen somewhat on the right side of this picture http://www.saturnfans.com/photos/sho...p/photo/15616/
the toner ring has seven notchs, one every 60 degrees plus a double notch for TDC 1/4(at least for saturns, its different for all cars of course, some engines send a signal for ever 1 degree of crankshaft rotation) also most 1996 and later cars have a camshaft position sensor as well, its mainly used for fuel control, but sometimes can be uses as a backup for the crankshaft position sensor, its not on the 1.9L but why is a whole nother story....you don't have a P0340 or P0341 code too do you?

ok back to your engine, for the most part if there was no spark at all for cylinder 4 then there won't be a spark at cylinder one ether. i say for the most part because if 40,000 volts wants to fire, its going to fire, weather or not it has a ground path back to the coil. i would try to confirm this is a ignition problem. test compression and cylinder leak down if possible. buy one of those little "fake spark plug" adjustible tester, set it to 0.400 inches and see if you have spark across the RPM range(unplug that cylinder's fuel injectior or you will have problems). try swapping the two coil packs and see if the problem flows the coil. if you have a ohmmeter test the wires and coils(tower to tower)wires should be least then 12K ohms, coil 7K-10K ohms. also check the wires/coil towers for corrosion. if nothing else works you have the time and skill you may also want to swap the injectiors around. for the hell of it you may want to trying cleaning the combustion chamber(in my logic, cylinder 4 is most affected by carbon build-up) try this - http://www.saturnfans.com/forums/showthread.php?t=25237

[spitbits1500]

Thanks for the information, it is a great help to me with trying to understand how the system works....

I have installed the new tensioner, and the car is back on the road again. I had it hooked up to the computer again and in a 10 mile trip to my buddy's house the problem is still there.... On the way there and back the Missfire history counted 54 misses on cyl. 4 on the ride there, and 132 on the ride back...

Any Ideas on where I should go next?

Thanks,

-Ryan

[spitbits1500]

Another update... After a new coolant temp sensor, the fan still will not kick on, maybe I'm not waiting long enough... When should the fan activate (based on the temp gauge, at half way/ a little over mine still hasn't turned on and I can hear the coolant boiling).

Any Ideas on what the problem can be? Is there a separate sensor for the cooling fan switch?

Thanks for the help.

-Ryan

[sierrap615]

Originally Posted by spitbits1500

at half way/ a little over mine still hasn't turned on and I can hear the coolant boiling

if your coolant is boiling your cooling system may not be holding pressure, if that is true then its very unlikely your fan will kick on. the PCM turns on the fan when the ECT reads 220-222 F. without cooling system pressure, the temp won't go much above 212 F.(FYI if this is the case, even though the temp gauge only reads 1/2, you may be overheating, engine damage may accure) check your cooling system pressure before going any futher.

[spitbits1500]

Cooling fan was due to the system not holding pressure, the system was venting through the coolant cap res. The 'o' ring for the cap was bad allowing the pressure to escape.

After sealing the system the pressure was able to build and the fan tripped. Thanks for the good advice. Any Ideas on the miss though?

-Ryan

[spitbits1500]

I took it apart again today... Removed both coil packs and the backing plate completely off the block. There was quite a bit of corrosion between the backing plate and the block, I cleaned that up, used some dielectric grease and put back to the block.

I did notice on the backing plate what seems to be evidence of arching between the base of the coil packs to the metal portion of the backing plate on the outside side of the plate? Should this be reason for concern? Is this arching possibly the missfire I feel? Or is this just normal ware for the part?

BTW, I did test the compression of the cylinders, each cylander was 175 psi.

Thanks,

-Ryan

[sierrap615]

Originally Posted by spitbits1500

I did notice on the backing plate what seems to be evidence of arching between the base of the coil packs to the metal portion of the backing plate on the outside side of the plate? Should this be reason for concern? Is this arching possibly the missfire I feel? Or is this just normal ware for the part?

this is possibley your problem, swap your two coils around and see if the missfire moves. closely check the coil backside for a VERY tiny hole(i'm talking 1 mm max) arching should burn a hole thru the case. also check your old coil if you still have it. if the arching was from anywhere except the backside you might be able to pick it up with a standard 12V test light, waving it around the coil area.

[drew300]

Just curious, did you fix it?
I was going to suggest that maybe a new plug was bad.
I always save a "known good" set of plugs from a tune-up incase of new problems showing up after some work.

[TKTSCR]

what sierrap.... said about the coils fireing in the way they do is true. but your not alone. i also have the same problem. the only logical thing is what has been suggested. arching to ground from coil or module. i believe that there may be a leak at the coil instead of firing into the coil primary the energy is dumped to ground arching someplace. i have checked gm bullitens and found nothing that has come near what we are experienceing. i have found out that if you get a spray bottle with water and salt and spray fine mist in coil pack area you will see the flashing/arching. my conclusion is the module. if you have found anything new let the community read it. p.s. after spraying area and wires to determine any leaking rinse with just water or electrical cleaner so that no corrosion sets in.

[TKTSCR]

its not normal for this to happen. its odd when it does cause u cant explaine. not common thats all. im sure cleaning the area and backing plate made everything all better.