Ive got a '95 Saturn SL-2 with 1.9DOHC and an automatic transmission. Several weeks ago, the normally reliable Saturn started missing, and being a reasonably knowledgeable mechanic I did all of the standard tests. I checked my spark plug gaps and for improper firing (the No. 3 was wet), I checked my spark plug wires (visually and with my Ohm meter), I checked my coil packs for corrosion and resistance between the posts, I checked the wires going into the ignition module and the module itself. Everything pointed to the No. 3 cylinder firing very weakly, and to the ignition module being bad. Since it had been about 30k since changing the plugs, and 60k changing the wires I decided to replace everything(plugs, wires, coil packs, ignition module) just to be safe. The Saturn still has a very weak spark on the No. 3 cylinder and obviously still idles very rough. What else could cause this to happen? Would the next step be replacing the PCM?
How did you determine that the spark on #3 is weak? Could the spark be OK but the injector is leaking and causing the plug to be wet? Is the compression on #3 OK?
Yes, I would wonder about a stuck injector.
I’d run a compression test. This should be done every time a performance problem exists and the plugs are out so kill that bird right then and there.
A plug with a wet tip can also be a sign of lowered compression.
the way i found out that the no. 3 spark was weak, was by running the car with each spark plug wire removed in turn. as you guys know, running the car with a wire removed an in close proximity to the motor will, of course, spark. with plugs 1, 2, and 4 respectively, the amount of spark was as you would expect very solid and an almost constant flow between the end of the wire and the exhaust manifold. no. 3 was very weak and intermittent. also, there was no change in engine idle with this wire removed. in addition, i know that its not the “correct” thing to do, but to verify it was indeed the number 3, we swapped wires at the coil pack from the no.3 to the no.2 and then the no. 2 had the intermittent, weak spark. my reasoning behind the wet plug was that because there wasn’t enough (either constant or in power) spark to completely ignite the fuel.
the way i found out that the no. 3 spark was weak, was by running the car with each spark plug wire removed in turn. as you guys know, running the car with a wire removed an in close proximity to the motor will, of course, spark. with plugs 1, 2, and 4 respectively, the amount of spark was as you would expect very solid and an almost constant flow between the end of the wire and the exhaust manifold. no. 3 was very weak and intermittent. also, there was no change in engine idle with this wire removed. in addition, i know that its not the “correct” thing to do, but to verify it was indeed the number 3, we swapped wires at the coil pack from the no.3 to the no.2 and then the no. 2 had the intermittent, weak spark. my reasoning behind the wet plug was that because there wasn’t enough (either constant or in power) spark to completely ignite the fuel.
Do you have 2 coil packs or 4?
2, set up like this 4/1 2/3
Your problem is under the hood between the coil and spark plug. This car has a wasted spark ignition system. The two spark plugs associated with each coil pack fire together, with one spark plug firing on the power stroke, and the other firing on the exhaust stoke, wasting the spark. The coil packs are set up so that one terminal is a positive to the primary winding and the other terminal is a negative. For only one terminal to be causing the problem, it must be leaking spark somewhere before it gets to the spark plug. Otherwise, both plugs associated with that coil would be having problems if it were due to an ignition module or ECM.
A multimeter may not find the leak, since the ignition system jacks the primary voltage to 40,000 volts. The 9 volt charge the multimeter passes may not jump across the break.
Try this: get a spray bottle filled with water, run the engine, and lightly mist the water around the coil, spark plug wire and the booted plug if you can. Look for a spark to ground. Also, move the spark plug wires around to see if the trouble follows the plug wire. If it stays at the one terminal of the coil pack, that must be the problem. Maybe there is a problem with the coil pack you just purchased or maybe the flaw is in the mount somewhere.
A stuck injector would wash out the sparkplug but he doesnt have that problem as he stated he checked the spark external to the engine. If you have a wasted spark system like busted says then he is correct… I have bought brand new faulty plugs…try switching the plugs around and look at the spark quality…or just use a phillips screwdriver in the no3 wire and get it near ground while running. Check spark quality. Busted is right that if that coil pack fires both coils at the same time, you should have equal spark quality at both of those wires. It would have to be between the coil and the end of the wire somewhere like a bad wire…move a know working wire to the no3 location… This is all true IF it cannot fire the coils individually…I amnow suspecting that the car CAN fire them independently.
I am a little suspect about the wasted spark issue tho…if it is a wasted spark system then it HAS to be between the coil and end of wire.
I am suspecting that the system has a bit more complexity than we are giving it credit for…it may be able to differentiate a spark between all coils…if this is the case then the negative wire going from the ecu to coil may be corroded. Try disconnecting your battery and then locating your ECU connection…remove all of the harnesses at the ecu and reconnect them several times…you may get lucky and clean off the contacts going into/and out of the ecu…if it can differentiate between the coils then the only way it can do that is by having separate wires going into or rather out of the ecu for each coil…you may have a broken or shorting wire for the no3 coil pack. You can look up the ecu wire harness wire breakdown online somewhere…if you see 4 different wires for the coils in the diagram then you ned to find that no3 wire that fires that coil. If you can find 4 different wires for the coils then you can jumper a known working coil “firing” wire to the no3 only after you break the wire from the harness you dont want to feedback into the ecu… If you jumper a known coil wire to the no 3…you will prob immediatly notice the spark quality improve. The other way is to decode the wires at the coil packs. You would have to cut the no3 wire then ground it quickly i.e acting like the neg pulse you would normally get from the ecu. if you mimic this neg pulse you may find the spark at no3 is fine…that proves out the connection or wire for no3 coil pack…ALL ASSUMIG IT HAS THE CAPABILITY TO INDIVID FIRE THOSE PACKS…I SUSPECT IT DOES… Your prob lies there.
IN addition to seeing wires go bad for seemingly no reason YOu may also want to check your ground connections thoroughly…Saturns have grounding issues electrically all the time…I found this on a saturn forum…
“”""“Yes I did find a fix. In the engine compartment there is a fuse box. the pcm fuse is in there. the fuse was good but the underside had corrosion which kept the power from getting to the pcm. Take the bolts out of the fuse box and turn in upside down to examin it because you cant see it from the top. Since spark is controlled by the ignition module which has its own power suply I had spark but no injectors. The giveaway to my problem was that the check engine light didn’t come on when the key was first turned on for a bulb proveout. From what I gather from the people at saturn PCM’s hardly ever go bad but do incounter there fair share of power and ground problems. I did buy A hayes manual which had the diagram which helped greatly. Hope this helps. just remember if you have spark then your cps has to be good. and your ign module too. Fuel is controlled by the pcm or ecu. also make sure you have 12volts to the injectors with the key on the ecu controlls ground but not power to the injectors. Good luck”""""""