Trouble Starting, Surging, Dying [Archive] - GrandAmGT.com Forum

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kornfox
12-20-2009, 03:48 PM
My 2001 Grand Am GT (3.4ltr 101k) randomly wouldn't start yesterday. It will turn over but not fire. At first, I assumed it was the Passlock system but the security light wasn't flashing. Tried the passlock fix where I waited 10 mins and all that fun stuff without result. Also scanned it with my obd2 scanner and nothing reported.

Next I assumed spark or fuel is my problem. I hear the fuel pump prime and I have fuel pressure in the rail. Checked all fuses and relays for ignition systems and fuel system, all is well. Today when I tried starting it and it was exactly the same. I attempted starting again feathering the gas and it fired up, ran at high idle for awhile then starting drastically surging. After 3 or 4 cycles of surges the tac dropped and the car died. Now, if I can get it started, this surging makes it impossible and completely unreliable to drive.

So I have fuel and spark but timing or something seems whacked? cam position sensor? mostly clogged fuel filter? any ideas?

Thanks in advance guys. It's like 10 degrees out and working on this thing is not going to be pleasant.

KhellendrosxS
12-20-2009, 04:17 PM
Vac leak.

When you open the throttle you let more AIR into the system, not more fuel. The addition of air leans out the rich fuel mixture being delivered by the injectors and allows the car to run. Surging like you describe is indicative of a major vacuum leak.

With an assistant I would have them hold the throttle enough to keep it running and spray starting fluid around the vac lines under the hood. When you spray it and you hear the idle smooth out you have found the area where a line is likely broken. Investigate all the lines in the area and see if anything is cracked, disconnected, worn out, etc. Replace as necessary.

kornfox
12-20-2009, 06:27 PM
Ah, vacuum leak, didn't think about that one.. I'll try to take a look for leaks tomorrow or tuesday if it's not freezing out.

Will a vacuum leak happen that quickly? Where I would have no issues then all of the sudden on a normal start a hose/seal is shot?

Also, I didn't know a vacuum seal would significantly impact the startup process, thought that was more of an idle variable.

KhellendrosxS
12-20-2009, 08:05 PM
It could.

If one of the larger hoses cracked or split for some reason then you get an instant leak. Others may start slowly and get larger causing more issues as it grows but it is certainly possible to get one overnight.

It might not hurt to also check your IAC valve on the throttle body and clean it if its sticking.