3.1 Ignition Control Issues

[Geologist]

After doing all of this to my 92 Grand Prix I am stumped and need help.

 

Symptoms:

After removing/replacing the negative battery terminal the car drives great till it reaches operating temp, then cuts out randomly during cruise, acceleration and deceleration (complete engine shut off, not just one cylinder) and will die as you begin to stop the car. The furthest it has ever gone is 60 miles or so before it just dies completely (crank – no start). At this point we checked it for spark and no spark at any of the coil packs. We tested the pink wire feeding the IC circuit and it has 12V (but oddly it has 0.14V less than the rest of the car at all times).

 

Already Replaced with NAPA Echlin brand:

ICM (3 different ones), Crank Position Sensor, O2 Sensor, Fuel Pump Relay. I also fixed all broken vacuum lines and several half-broken wires and cleaned up the grounds.

 

History:

1992 Pontiac Grand Prix SE 3.1 4T60 trans, at around 169k miles the car just started to cut out randomly during cruise, acceleration and deceleration (complete engine shut off, not just one cylinder) and die as you begin to stop the car (sometimes it will drive perfectly for miles in between these little fits). At this point I repaired a few vacuum lines and put in an O2 Sensor. Ran better for a couple of days then cut-out and died completely (crank– no start) with code 42 (IC Circuit). At this point there is no spark. Replaced the ICM and the same thing happened: 2 days and dead with code 42. Replaced the Crank Position Sensor and same thing (this time no code 42). Put in my OLD ICM - fired right up, 2 days later dead again. Bought ANOTHER new ICM and it almost didn’t even make it home (8 miles), cutting out (AFTER it warmed up) almost the whole way like someone were just turning the engine off-and-on repeatedly.

The car has good exhaust flow so I don’t believe the CATS are plugged, it also runs very strong.

I use this car mostly to run to town (~20 miles) to take my son to school and pick him up. It has left me stranded twice now (luckily never with my son there) so I need to figure out where this ghost in my system lies.

 

Does anyone have any ideas why it loses spark after warm-up on all 3 coil packs at the same time?

Edited February 10, 2013 by Geologist

[Schurkey]

Connect a REAL scan tool, look at sensor data.

 

First Guess: Not an ignition control module problem.

 

Second Guess: Loss of crank signal, the computer doesn't know that the engine is running. Could be crank sensor, could be wiring.

[Geologist]

Thanks for your reply.

 

Connect a REAL scan tool, look at sensor data.

 

First Guess: Not an ignition control module problem.

 

Second Guess: Loss of crank signal, the computer doesn't know that the engine is running. Could be crank sensor, could be wiring.

 

If I could afford a Tech2 I would be using one. Given the limited budget of a 40 yr old student who is also a father, that may not be for some time.

 

I also suspected the new CKP sensor so I tested it several times. As a result I do know that the Crank Position Sensor is putting out 0.7V AC (at the ICM end of the wiring) during the crank - no start episodes (specs are between 0.3 and 1.7V AC I believe).

[Turbocharged400sbc]

crank sensor likely, ive replaced hundreds over the years

its not enough to look at the ac voltage you need to scope it on a DSO (digital storage oscilloscope) to see the degraded waveform and how the trigger point disappears when hot and at low rpm's

 

be very carefull when taking it out as oil coking/carbon buildup will make it difficult for the sensor to slide through the hole, you will be doing craploads of twisting and pulling a tiny bit then pushing it back in.

i used to pull the drainplug and bend it into an arc to spray the inside of the motor near/above the crank sensor with brake cleaner then PB blaster after every couple cycles. the outside i just hit with pb and compressed air

 

if the top snaps off youll need to drill the end and screw in a woodscrew to give you something to grab onto

[Geologist]

Thanks for the info Turbocharged.

 

So do you really believe a brand new Echlin CKP with less than 2 hours on it failed to the point that it won't produce a clean enough waveform to trigger the ICM?

 

Also this does not explain crank-no start for 5 days, replace ICM and it fires right up. Literally tried to start it, no spark, put my OLD ICM in and it started up and ran perfect for over an hour. On this ocassion it gave almost no warning that it was gonna croak, maybe a few minutes.

Edited February 11, 2013 by Geologist

[Garrett Powered]

its the IAC motor. needs cleaned, and if not, replaced, and if not, tuned. I had to tune all 3 of my cars.

[Crazy K]

wait... how about the ECM? or another phantom issue?

 

next time the car will crank but not start, do the paperclip test and see if the check engine light cycles through it's codes. (assuming the bulb works)

 

http://chevroletforum.com/forum/general-tech-10/obd-i-codes-37494/

[Garrett Powered]

I want to know the car's voltage at the second it dies. a datalog would be all you need. a $40 cable and a laptop.

[Geologist]

Problem solved, kudos to Schurkey.

 

The problem was the CPK wiring that runs under the engine. It was twisted (not sure if that is factory) and something had leaked into the loom and melted the coating on the wires causing them to short together. If you pulled the wire from the ICM it would back the tension off of the twist, opening the short, so testing it made it appear to be OK.

 

After having been parked for several months (bought a different car) I decided to replace the ICM yet again with new coil packs. It ran for ~2 minutes then died. I noticed that it would fire briefly again only after pulling the CPK wire and plugging it back in, which is what inspired me to remove the wiring. I felt like a complete moron when I pulled the wires from the loom and saw the melted coating (the ONLY wires under the hood I had not completely removed from the loom).

 

Replaced the wires and have put ~1000 miles on it, runs strong and never misses a beat! Thanks again to Schurkey.

[Schurkey]

[Elvis Voice] Thankyew. Thankyew verra much. [/Elvis Voice]