99 Camry 4 cyl. intermittent coil not working.

Is this a dealer purchased coil? Did you perhaps check the Compression in #4 and other cylinders to compare results? These after market coils from parts stores can be the problem.

There are 2 coils. 2 ht leads per coil. We checked the spark output by disconnecting the ht leads one plug at a time and observing the spark jump from the end of the lead to the valve cover. The only one that did not produce a spark was number 4. The reason I don't believe the coil is at fault is because the problem started, then went away during which time I changed the plugs and wires, and then came back. When ever I had a coil go bad in the past it just failed altogether instead of it going on and off as an intermittent problem. I may be wrong in this but that has been my experience. I'm thinking that there is a signal wire that signals the coil to fire that maybe broken or the ignition controller itself might be the problem. Not knowing which one is the signal wire makes it difficult to check that. I suppose that I could switch the coils one for the other and see if that makes a difference. I do have a compression tester but since there is no spark to #4 it seems pretty obvious that is the problem. If you can tell me which one is the the signal wire maybe I can check that. Thanks, Bob

Ok...now I understand. This system fires 2 spark plugs/cylinders at the same time. You are correct. simply switching ignition coils is a good diagnostic procedure. If the problem follows the coil...you have a bad coil. If the problem remains with #4 you have a bad SP wire or as you suspect the ignition module or computer is bad. The "signal" wire you describe?? You need a wiring diagram Did you check to see if this condition set any codes? BTW. The best way to check coil output is with a spark tester available at any parts store. It looks like a spark plug with no center electrode and an alligator clip. It takes 25K volts to fire this tester...a very good way to load the coil for testing.

I have been reconsidering this interesting problem on this vehicle. If one coil is responsible for firing 2 cylinders, then what you must have is an OPEN in simple series circuit. Consider this. Firing #1 and #4 Plugs at the same time on a 4 cylinder engine. When #! is on the power stroke, #4 is on the exhaust stroke. When the engine rotates once, the situation reverses. #4 is on the power stroke and #1 is on the exhaust stroke. Electricity comes out of the coil, let's say to fire #1....it jumps the SP gap to the ground electrode, through the head to the ground electrode of #4, jumps that gap and goes back to the coil. This is called a "Waste Spark System" This is why we use a spark tester requiring 25k output from the coil to pass a coil test I believe the Ignition module/controller is built into these coils. The signal you refer to fires the coil which results in firing both SP. Therefore if #1 fires...this signal must be present. You might have a bad plug or wire. Switch the plug and wire to another cylinder is a good way to rule out the SP and wire. My experience? NEW PARTS ARE NOT ALWAYS GOOD PARTS. Good Luck

I must apologize to you all. I was relying on second hand information and had assumed that my friend's ex-husband had verified that the coil was producing spark by holding the ht lead to the valve cover. (He was the one that replaced the coil.) When I preformed this test myself last night on all 4 cylinders I found that all four cylinders ARE firing properly and I am now turning my attention to the compression test and to the fuel injector. The sheathing to the wiring going to injector #4 is somewhat torn up but I do not know yet whether the wiring itself have been compromised. Thanks for all your help and advise.

Ah-ha. Good job. We now have the CORRECT history on this issue. I like to use a NOID light and a stethoscope to check injector electrical and mechanical function. Good Luck