3.4 DOHC just stopped after running fine (Page 1/2) 355Fiero OCT 06, 12:13 AM All DOHC folks out there. I have had my 96 DOHC running a 91-93 ECU working great the past couple months. I have had it out on several occasions and it ran just great. I am not revving or doing anything crazy with it as it was a crate motor and I am being gentle whiel breaking in. I had the car out the other day and I was running fine in traffic with no issues at all and then the engine just dies with no warning at all. I was lucky enough to cruise into a parking lot and then tried starting with no luck. Thought about the fuel pump maybe or no fuel so put fuel in just to confirm there was enough. Turned the key and heard the pump prime so I am thinking not the pump. No luck so left for eth day as it died at work thankfully. Towed it home after work and started to diagnose tonight. Checked error codes with TunerPro and only error is a low water level error. Checked all the coolant and all is full. Confirmed water in the engine by loosening the vent screw on the outlet pipe. Rad and reservoir full. Fuel pump primes, fuel pressure is 40-50 when primed and I pulled a plug and found there is no spark. Checked fuses and no blown fuses in the panel. So a couple questions: 1. Would the low water level turn the spark off in the ECU? Similar to the oil pressure switch/sensor turning the fuel pump off. Really can't see that but want to clear everything. 2. What do I check on the coil packs? 2.1 Assume 12V to power pin on coil pack 2.2 Signals in. I saw on a youtube that you can check with cranking and seeing if the voltage cycles to the switching pin. Does that make sense on these coil packs? Anything else to help remove possibilities and drive to the fault? Thanks much for any help. Don 355Fiero OCT 06, 01:22 AM Update: Checked power to coils and no issues Checked continuity for all wires going from ECU to coil pack plate are good. It is starting to look like ECU issues...... Going to do some searching and see if i can figure out how to confirm outputs on the ECU to coil pack wires to see if my signals have stopped. Cheers Raydar OCT 06, 09:12 AM This may be useful. Maybe not. On GM ECMs, if the ECM doesn't see ignition pulses, it also will not pulse the injectors. During starting, the engine will run on base timing (from the ICM) until it reaches a certain RPM, then the ECM takes over. If it's not seeing pulses at all, it could be a problem with the ICM. I may be missing something. I'm sure if I am, someone will jump in and correct me. RichLo1 OCT 06, 11:59 AM Did you pop a timing belt? 355Fiero OCT 06, 01:58 PM Thanks Raydar; I will check this out tonight. Will do some research on how to check the ICM out. I am also doing searches on the ECU and how to see if the signals are getting to the coil packs as well. I wonder about the starting part of your post though as the car was running and I had been driving it for about 15 minutes when it just stopped with no warning. I can connect to the ECU and when cranking and watching Tunerpro, I see the codes cycling through and only water level low error 0014 remaining. I had not seen that error in any of my previous work with TunerPro so still wonder if that is connected somehow? RishLo1; Sure hope not as that would be bad........ In any cranking since, I do not hear any resistance in the engine at all so assuming so far that no timing belt slip which would cause interference. Adventure continues. Thanks much Don RichLo1 OCT 06, 08:30 PM They are non-interference engines so a timing belt doesnt cause any internal damage. I threw one on my old 3.4 TDC Fiero years ago while pulling onto an interstate at 5-6k RPM. No internal damage happened but it did everything you are explaining. That belt is under a lot of stress running 4 cams. Mike in Sydney OCT 06, 08:55 PM quote Originally posted by RichLo1: Did you pop a timing belt? That was my thoughts. Check for compression in the cylinders. If the valves aren't closing you'll likely have a couple or more cylinders without compression. I had a Volvo B21F in a 242GT that broke the timing belt. I had no compression in 2 cylinders because of the way the cam had stopped holding some valves open. Raydar OCT 10, 09:33 PM quote Originally posted by RichLo1: They are non-interference engines so a timing belt doesnt cause any internal damage. 96 and 97 got redesigned heads. The story is that they became interference engines at that point. Raydar OCT 10, 09:34 PM When you're cranking the engine, does the tach do anything? If it moves off of zero, that can eliminate a lot of stuff. msweldon OCT 19, 06:08 PM quote Originally posted by Raydar: 96 and 97 got redesigned heads. The story is that they became interference engines at that point. The 96 97 heads are still non interference, however the clearance is so low that when the belt does go, usually at higher rpms, there's enough rod stretch under the right conditions that the pistons and valves can knuckle bump.