Keep losing cylinder #2, what's going on?

bigpoppa822

Registered User
A week or so ago I was driving my car to work and what I thought was my coil pack gave out on me. It was the OEM coil pack and 20 years old so I had no problem replacing it. I ran codes and got a 46, "cylinder 2 circuit failure". I replaced the coil pack and went for a test run and the car was alright for 10 minutes then dropped cylinder 2 again. I thought maybe a plug was bad, so I bought plugs. The plug I had in it was fine (AP2544? I believe in the car for about 10k miles) but I replaced it anyway. The car still ran on 5 cylinders so I changed the wire. Nobody has SC wires in stock so I ended up buying ones for a DIS Ranger and swapping the bad wire. This may be where I went wrong, someone let me know. The car ran fine for this week, but just dropped the same cylinder on me again (code 46). Except this time with a new coil pack, plug, and wire. Car has a newer motor (10k miles), cam and crank sensors were replaced with the motor.

Can anyone tell me what's going on?
 
The main issue here is that it can be pretty odd to get a single cylinder problem since each cylinder is paired with another due to the ignition system. There are only 3 coils, so anytime a spark issue happens on one cylinder and not 2 cylinders it is usually a bad wire or plug.

Since it is neither for you since you are sure you have good parts there, then the only other single cylinder thing I can think of would be a bad fuel injector or a problem with the harness at the fuel injector for cylinder #5.
 
Mike, why the #5 cylinder? Also how would a bad injector cause me to lose spark in one cylinder (the code is "bad ignition circuit cylinder 2")? When it goes out I can smell fuel, not sure if this is the rest of the injectors compensating or the cylinder with no spark dumping raw fuel out the exhaust.
 
Mike, why the #5 cylinder? Also how would a bad injector cause me to lose spark in one cylinder (the code is "bad ignition circuit cylinder 2")? When it goes out I can smell fuel, not sure if this is the rest of the injectors compensating or the cylinder with no spark dumping raw fuel out the exhaust.

if the injector is faulty and perhaps flowing at full rate it will flood the cylinder causing the plug to foul. just a possibility.
 
that code is set by some feedback the DIS module looks for. It fires the spark, then it looks for a electrical behavior in the kick back of the circuit. That it is saying only cylinder #5 indicates that something happens that causes the information it expects to not occur.

Typically that would be a bad plug, or a bad wire. But it could be related to an improper combustion event as well. It could also be an issue in the DIS module which is responsible for doing the interpretation of the data.
 
So I ran the car again today to see what was going on. I am getting a code for fuel pump circuit open to the battery which it clearly isn't as the car does run. I'm still getting 41 and 91 for left and right bank lean. I decided to unplug the MAF and run the car, and it idled alright and the lean codes dissapeared. Does this mean my MAF electronics could be bad?

Also this code 46 (which is coil pack 2 circuit failure not cylinder 2, d'oh on my part) has become intermittent. Sometimes the car runs on 6 cylinders, sometimes on 5. I have replaced the wire for cylinder 6.

I'm pretty stumped here, I'm trying to find some pinpoint tests but am not having any luck. I know I can throw parts at it until I'm blue in the face but I'd rather hunt down the issue.
 
I should have looked up 46 before. This means either the coil pack is bad, or the dis is bad or the wires between the two. Here is one section of the pinpoint tests for that code.

Continuous Memory Codes 45, 46, or 48: CHECK CONTINUITY OF COIL CIRCUITS FROM DIS TO COIL PACK

Service Codes 45, 46, 48 indicate a fault has been detected by the processor in one of the three coils contained in the ignition coil pack.
Note: Codes 45, 46 and 48 refer to faults detected in the circuits related to coils 3, 1, or 2 respectively. Coil 1 provides voltage for cylinder 3 and 4 spark plugs. Coil 2 provides voltage for cylinder 2 and 6 spark plugs. Coil 3 provides voltage for cylinder one and five spark plugs. The IDM pulse train contains a corresponding pulse for each operating coil. In the event that a coil fails, the corresponding pulse will be absent from the IDM pulse train.

Possible causes:
  • Open in coil circuit from DIS module to coil pack.
  • Shorts to coil circuit GND or PWR in DIS module.

  • Key off, wait 10 seconds.
  • Disconnect Dis Module
  • DVOM on 200 ohm scale.
For Service Code 45:
Measure resitance between pin 8 at the DIS module and coil 1 at the ignition coil pack.
For Service Code 46:
Measure resitance between pin 11 at the DIS module and coil 2 at the ignition coil pack.
For Service Code 48:
Measure resitance between pin 9 at the DIS module and coil 3 at the ignition coil pack.

Is each resistance less than 5 ohms?

No : Service the Open

Yes:
CHECK COIL PACK CIRCUIT FOR SHORTS TO GROUND AND POWER
  • Key off
  • DIS Module disconnect pins 7-12
  • Disconnect coil pack
  • DVOM on 200,000 ohm scale
  • Measure resistance between pin 7 and pins 8, 9 and 11 at the DIS module connector.
  • Measure resistance between pin 1 and pins 8, 9 and 11 at the DIs module connector
.
Is each resistance greater than 10,000 ohms?

No: Service short circut

Yes: Trouble shoot the DIS module.
 
Awesome, thank you very much Mike! That's exactly what I was searching for. I'll try the pinpoint test tomorrow. Coil pack is brand new I just bought it last week so I'm thinking it may be the DIS.
 
Replaced the DIS and that did nothing, so I just got done running the pinpoint test. No resistance between pin 7 and 8, 9, and 11 so I have a short somewhere. Going to pull out the wiring harness tomorrow.
 
I had an injector plug that caused the same issue. Cut it off & replaced with another and the problem never returned. Give it a try, what do you have to lose?
 
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