Help with Codes

[quern]

Hello All:

My father came into town with his "new to him" 96 Eldorado. He has been trying to diagnose a rough idle that smooths out when on the gas. He thought it might be in the computer because 1,3,5 & 7 have good spark but 2, 4, 6 & 8 seem to have bad spark. I asked him if he had tried using forums but he isn't much into them yet. So today I helped him pull the codes and this is what we obtained:

Code Status
P0300 - Engine Misfire Detected Current
P1370 - IC 4X Reference Circuit Too Many Pulses History
P1377 - IC Cam Pulse To 4X Reference Pulse History
P1566 - Engine RPM Too High - Cruise Control Disabled History
P1579 - P/N to D/R at High Throttle Angle - Power Reduction Mode Active History

Does anyone have any suggestions as to what the "fix" could be?

Thanks in advance!

[Ranger]

1,3,5 & 7 have good spark but 2, 4, 6 & 8 seem to have bad spark.

This makes me think ICM or maybe 2 bad coils if the bad cylinders are on the same 2 coils.

P1370 - IC 4X Reference Circuit Too Many Pulses History
P1377 - IC Cam Pulse To 4X Reference Pulse History

This makes me think cam position sensor. Maybe someone else will have some thoughts to narrow it down.

[submariner409]

The 1566 and 1579 look like someone did a N to D high RPM shift - a no-no.

As the codes other than P0300 are History, forget them for the time being. Just log the date and the codes and whether they are C or H. Don't clear anything. Because the ICM feeds both cylinder banks, it appears that the trouble might be a CMP (CaMshaft Position sensor) fault - connector or sensor itself.

Are you comfortable with removing the coils and ICM from the top of the rear cam cover ?? Your problems also may be as simple as old spark plugs and wires, coupled with intermittent coil ground connections. You'll notice that plugs 2,4,6,8 come off the same relative coil towers. It's possible that the plug wires are reversed on the coils - see the last sentence to find out how that's possible.

The car uses AC Delco #41-950 Platinum plugs and an AC Delco wire set. www.rockauto.com or call Luke in Parts at Lindsay Cadillac over there >>>>> tomorrow morning.

Use the wiring diagrams faithfully to check coil-plug wiring - click on the diagram to enlarge it. The order is critical - Google "waste spark ignition to find out why.

[chubbyranger]

How did you determine that the even numbered plugs have weak spark? One of my favorite culprits for a rough idle that smooths out is a vacuum leak - check over the fittings and connectors while verifying the plug wiring per Sub's instructions above. There aren't that many hoses/fittings on N* and you just have to pull the beauty cover so it can be done quickly.