Bizaare misfiring - coil issues?

[bstone]

Got into the car this afternoon after making a stop for some lunch. Check engine light began to flash and then was steady after about a minute. I immediately scanned it, having my Actron sitting on the passenger side seat. It said Cylinder 2 & 4 misfire. The only way they would both suddenly begin to misfire is the coil pack going back. I am on my third coil pack so I knew I needed to find out what was making the coil pack to bad.

Got to the shop and asked the smartest mechanic there what he thought. We looked through the circuit diagrams of the engine and he showed me two main grounds for the engine. Said they might be corroded and need cleaning. Where they are, that is a good question. After several minutes of looking I indeed found two grounds on either side of the motor- one under the throttle body and under on the passenger side of the intake manifold. I removed each, sprayed them down with Liquid Wrench and put them back in. I then cleared the codes and let the car run for 10 minutes. No codes and the engine acted as smooth. I then removed the wires from the coil one at a time, and each produced a very rough engine.

Then drive home, 12 miles. No check engine lights, no roughness, good gas mileage (30mpg +/- 2).

So- are the two grounds the ones I saw on the diagram? Moreover, any ideas?

The ECU has already been replaced and the wires/plugs are NGK.

[johnceggleston]

Originally Posted by bstone

It said Cylinder 2 & 4 misfire. The only way they would both suddenly begin to misfire is the coil pack going back. I am on my third coil pack so

not the coil. the coil splits the cylinders front and rear, not side to side. i can't imagine 3 bad coils in a row, the odds of that are very, very low, i would think.

have you checked the igniter?

i don't know about the grounds.

[SuBrat84]

I wish i knew.. mine does it too.. except it's 1&3. So far I have been able to determine the ambient air temperature matters (100+F makes it worse.) And electrical load matters.. Headlights, AC, Stereo on makes it worse. Grounds? Alternator? So far I've replace my plugs and wires, fuel filter, pcv valve (cleaned all the hoses) and adjusted the knock sensor.. each time I did one of those things it 'got better' for a couple of days and then came back....
(Does your fuel gauge work?)
Maybe she's just not feeling loved.. and wants to be touched more often?

[Fairtax4me]

Originally Posted by johnceggleston

not the coil. the coil splits the cylinders front and rear, not side to side. i can't imagine 3 bad coils in a row, the odds of that are very, very low, i would think.

have you checked the igniter?

i don't know about the grounds.

Well you can't rule it out completely. It might be producing a weak spark which isn't able to jump the plug gap under compression*. Which could be due to low input voltage.
But I don't think the ground points for the wiring harness on the engine would affect that. I'd be more suspect of the ground cable from the engine to battery/frame. But you would likely also have starting issues if that were the case. (slow or no cranking)

It might also be poor connections or high resistance in the spark plug wires.

* From what I understand about wasted spark systems, it is very important that spark plug gap is even across all plugs, and is set close to the lower end of the gap specified by the manufacturer. That will make it easiest for the spark to jump the gap and induce combustion.

[nipper]

Coils split the power 1-2 and 3-4 as the engine is 2 4 on one side and 1 3 on the other side. firing order is 1 3 2 4. Yes bad grounds can do this. Technically thier may be another ground on the transmission. I cant tell how many grounds there are. You may have one coil weaker then the other so that may be why one coil is affected first or weaker wires.

[Allpar Mod]

Have you checked the charging voltage? Sounds weird, I know, but I posted about this a couple of weeks ago. Weak charging voltage will effect the performance of these cars. The altertnator is only an 85 amp model which means that it is only putting out maybe 20 amps or so at idle.

I'd look at the charging system as a whole..battery, terminals, cable connections and alternator output under various loads. This sounds like it may at least part of the problem with the post mentioning how the performance is effected by turning on electrical items like the radio, etc.

Since I installed a voltimeter in a pillar pod, I can see exactly how the charging system reacts to load and driving conditions since I replaced the alternator and reconditioned the battery. It doesn't take much to pull down the charging voltage of these very limited alternators.

[bstone]

Originally Posted by Allpar Mod

Have you checked the charging voltage? Sounds weird, I know, but I posted about this a couple of weeks ago. Weak charging voltage will effect the performance of these cars. The altertnator is only an 85 amp model which means that it is only putting out maybe 20 amps or so at idle.

I'd look at the charging system as a whole..battery, terminals, cable connections and alternator output under various loads. This sounds like it may at least part of the problem with the post mentioning how the performance is effected by turning on electrical items like the radio, etc.

Since I installed a voltimeter in a pillar pod, I can see exactly how the charging system reacts to load and driving conditions since I replaced the alternator and reconditioned the battery. It doesn't take much to pull down the charging voltage of these very limited alternators.

We have a charge tester at the garage. I'll try it tomorrow and see what I see under different loads. What voltages should I be seeing? I usually think 13V is around normal.

[nipper]

No need for a tester. Just trun EVERYTHING on and raise the RPM to 1800-2000 and check the voltage. SHould be 13-13.5

[bstone]

Originally Posted by nipper

No need for a tester. Just trun EVERYTHING on and raise the RPM to 1800-2000 and check the voltage. SHould be 13-13.5

Gotchya. I'll turn it all on (lights, window wipers, etc) and check. I have an Optima Red Top battery (very new) in there, so I'll assume it's a bad alternator if I don't have at least 13V.

[Fuzpile]

One bank,code. Sounds like one is correct for the timing sensor and the other is out.