This just seemed to happen one day while driving. No SES, but there was a stored code for the 24x CkPS signal error at ignition coil. This car is a 95 with the OBD1. I had replaced that sensor a couple of years ago, and thought maybe it went bad so I went ahead and changed it out again with the original Delco, that i knew was good. Made no difference in the running. All 3 coils are new on the car, as well as plugs and wires. I have fuel and spark. FPR is ok, and fuel pressure is good. I tested the ICM with a light and meter, and voltage is fine and switching was ok. I even moved the coils around and swapped them out with a couple of good spares, with no difference in the running. Can an ICM be weak??
I verified voltage to the 24x CKPS as well as the CPS, but didn't test them. The car would still run without the 24x or the CPS connected, and no codes. There was NO difference in the running with these sensors disconnected. But when I disconnected the MAP, the car new right away and cut out, and got the SES. I sometimes get a slight backfire and pop from the intake when starting as well. All vacuum lines are good even for the age of the car. PCV ok.
I'm stumped..

 

Anyone know why the car will run with the CKSP and CPS disconnected? As mentioned there is no difference in the running with these sensors disconnected. ?? Thanks

 

The chugging is probably the result of the engine misfiring. The engine will run without the Cam sensor, but it won't fire right until it reaches higher RPM. Once the engine is started it may run with the Crank sensor disconnected. The ICM needs an initial input from the Crank sensor in order to know when to fire, but once the engine is running the PCM remembers the crank position and will fire the plugs accordingly. The Cam sensor allows the PCM to fire the injectors sequentially, if it is disconnected the PCM will default to batch fire, alternately firing one bank at the time.

 

Thanks. This is the 24x CKPS, and the car will start and run without it or the cam sensor connected. I know the ICM must see a signal from the 3x crank sensor to start, so I know it's ok. I guess I'm wondering if the ICM isn't sending a signal from the 24x, or the cam sensor to the PCM since they both signal through the ICM. Is it possible to test at the ICM for signal? I know I can probe each connector and turn the motor and test for signal that way. But the 24x connector is a pita to get to and usually have to hold the lead in place, making it impossible to turn the motor at the same time lol.
Wanted to add as well that this chugging reminds me of older carburated cars that had fuel/timing issues. Don't know if that helps or not.

 

May want to swap out the ICM with a known good one, if nothing else the ICM connectors can get corroded and cause strange problems. Besides providing the PCM with injector firing signal, the Cam sensor clocking is used by the PCM to stabilize ignition timing below something around 3000 RPM. SO if the Cam signal is bad, it could result in poor idle. I am assuming you already have checked spark plugs, ignition wires, & fuel pressure.

 

Yes wires are relatively new as well as plugs. Plugs are Delco, and I rechecked them all. No arcing with the wires. Fuel pressure was good and held, so I assume there isn't an open injector. FPR seemed fine too. When the car was scanned, it showed injector pulseing. Assuming that meant all 6 ha. I've checked all of the ICM connectors and wires and tested for voltage and switching is there. Just went and pulled each plug wire one at a time (from coil) and drove the car each time, and it definately ran worse each time I killed a cylinder.
It chugs from cold start through op temperature (open and closed loop) with no difference. I'll have to test the cam and crank sensors. 24x is a pita from the ground lol. Appreciate the replies Pete.

 

Can the cam sensor be tested for signal while the engine is running? Or just with key on and turning the motor? Also, when I tested for spark, none of the coils for the corresponding cylinders made a nice blue spark and none made that noticeable snap arcing sound. I used a known good plug and plug wire ground to battery for the spark test. Each coil for each cylinder resulted in a wide and orange spark that made no sound at all. In fact I had to look real good at most to even see the spark. Only one was blue, and still was wide and not very noticeable. It was sunny out, but I made sure I was holding the plug out of sunlight. I've read other places that others have had the same results with the 3.4 when doing the spark test, so I kinda thought it may be normal? Thought I would mention those results as well.