Code 42, backfiring and stalling under boost

[89mulletbird]

My car has been intermittently having this issue, mainly it starts happening when I give it full throttle after it is warmed up.

After driving for a few minutes, I punch the throttle and the car starts backfiring and the tach jumps downward and back upward quickly.

(what supplies the tach signal?)

The car is now backfiring when I press the gas, and sometimes stalls. I pull over and get the car started up again, it runs fine for a little bit then this issue repeats itself. I can limp it home with very little throttle.

I swapped the ignition module, but the problem persists.

The car finally threw a code 42, which says Ign. module or ground. But I've already changed this..

I've also found this thread:
Code #42 - TurboBuicks.com

 

[89mulletbird]

I wanted to update this thread. The root cause of my issue was the crankshaft pulley bolt was loose and at higher RPM the pulley was moving forward and disrupting the crankshaft sensor. I torqued down the crankshaft pulley bolt and problem solved.

 

[longball]

Cool. Glad you fixed the problem. Also glad you updated thread - been reading too many threads about problems and most
don't finish with a solution! (pet peeve of mine )

 

[Chuck Leeper]

I wanted to update this thread. The root cause of my issue was the crankshaft pulley bolt was loose and at higher RPM the pulley was moving forward and disrupting the crankshaft sensor. I torqued down the crankshaft pulley bolt and problem solved.

May/may not be "solved". Suggest you pull the balancer, and inspect it closely.
The bore and/or the crank surface may be fretted, keyway knocked out, balancer cracked, etc. This will eventually cause another failure.
Also, look closely at the threads on the bolt, and in the crank.

 

[longball]

^^^^^^^^

that's what I meant to say.....