Crank but not start

Tiny
JIMSMITH2354
  • MEMBER
  • 2003 PONTIAC GRAND AM
  • 3.4L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 158,000 MILES
No codes, no security light. Replaced fuel pump, pressure regulator, injectors, crank and cam sensors, fuses, relays. Original ECM and reprogrammed ECM act the same. ECM grounds are good. Replaced gas and checked pressure and flow. Plugs and injectors working. Compression is good.
Do you
have the same problem?
Yes
No
Monday, June 26th, 2017 AT 1:41 PM

11 Replies

Tiny
STEVE W.
  • EXPERT
You need to test it and see if you are actually getting the signals from the crank and cam sensors. It is possible that there is a broken wire or shorted bias voltage to them. Do you have a scan tool that can read live data? If so look at the engine rpm and timing numbers while cranking. If one or both are missing you have a signal problem.
Then you will need to test for the bias voltage and grounds at the sensors.
Was this
answer
helpful?
Yes
No
Monday, June 26th, 2017 AT 2:02 PM
Tiny
JIMSMITH2354
  • MEMBER
I was able to see the throttle position, about 200 rpm at crank, and the O2 sensors bouncing around, and the timing going 0 to 10 degrees during crank. Still no codes. If I use starting fluid it will hit a few times. Is there something that would keep the fuel injectors from working?
Was this
answer
helpful?
Yes
No
Monday, June 26th, 2017 AT 6:25 PM
Tiny
STEVE W.
  • EXPERT
The security systems immobilizer can kill them. Do you hear the pump prime? Perhaps jump the pump to make it stay on and see if it runs, if it does go through the relay socket and be sure it has good contacts. Then try a hard reset. Remove the battery cables, hold them together for about thirty seconds, reconnect and see if it starts.
Was this
answer
helpful?
Yes
No
Tuesday, June 27th, 2017 AT 7:44 AM
Tiny
JIMSMITH2354
  • MEMBER
The pump comes on and the pressure stays up. I do not know if the immobilizer is the same as the security light, but when the security light is on, the starter does not work. I have had the battery off for days at a time with the same result, but will try the hard reset tonight. I am leaning toward a new body control module as it is the only part that I have not swapped out or replaced.
Was this
answer
helpful?
Yes
No
Tuesday, June 27th, 2017 AT 8:33 AM
Tiny
STEVE W.
  • EXPERT
The immobilizer is part of the security system. It can activate without turning on the security light if the BCM gets scrambled data. It will shut off injector pulse.

Injectors are activated when the ECM gets the signals from the crank and cam signals telling it that the engine is cranking. Once started it uses those signals to alter timing and injector pulse. Does a noid light show you have injector pulse when cranking?
Was this
answer
helpful?
Yes
No
Tuesday, June 27th, 2017 AT 1:31 PM
Tiny
JIMSMITH2354
  • MEMBER
Yes, I checked all the injector drivers and all six seemed to be working. Only while cranking of course because the intake was off. I just did the hard reset and it did fire a few times on the first try, then nothing for any other cranks. It also does this if I leave the battery off overnight. Is this looking like a bad BCM?
Was this
answer
helpful?
Yes
No
Tuesday, June 27th, 2017 AT 6:40 PM
Tiny
STEVE W.
  • EXPERT
It's possible, I'm leaning more to either a bad signal feed into it but without seeing it myself it's a pain to track. Especially when it tries to start then dies. The immobilizer shouldn't let that happen.

Check the Engine Coolant Temp. Sensor. I've seen those fail and cause strange problems.
Was this
answer
helpful?
Yes
No
Wednesday, June 28th, 2017 AT 8:39 AM
Tiny
JIMSMITH2354
  • MEMBER
I replaced the engine temp sensor when I had the intake apart. Which signal (missing) should I be looking for?
Was this
answer
helpful?
Yes
No
Wednesday, June 28th, 2017 AT 11:03 AM
Tiny
STEVE W.
  • EXPERT
I would look at the crankshaft and cam signals, TPS and what the ignition module is showing for speed data. Have you tested the ignition control module? It sends the "run" signal over the data bus, if that signal doesn't show the injectors won't fire.
Was this
answer
helpful?
Yes
No
Wednesday, June 28th, 2017 AT 6:13 PM
Tiny
JIMSMITH2354
  • MEMBER
I replaced the ignition module. The throttle position signal looks good and the crank speed shows up as about 200 rpm. Each hard reset will let it fire a few times.
Was this
answer
helpful?
Yes
No
Wednesday, June 28th, 2017 AT 8:37 PM
Tiny
STEVE W.
  • EXPERT
OK, it almost has to be a comm error, a signal is not getting to the ECM to turn on the injectors once the engine starts turning over. About the only thing left. What do you have for a scan tool? The Tech2 win would allow you to watch both communication bus systems and you could watch the actual activation cascade during start-up.
That would at least show you where the failure happens and which module is shutting it down.
Was this
answer
helpful?
Yes
No
Thursday, June 29th, 2017 AT 4:23 PM

Please login or register to post a reply.

Recommended Guides