BUICK LACROSSE, V6 31,950 miles

This was a car that had zero problems, ran flawless! 10/22/16 completely shut down while exiting a gas station. Towed it home and looked to be an obvious problem, a smoked coil pack (primary side) before realizing the core problem was shorted ignition control module (ICM). Replaced ICM and coil pack, again. After replacing first ignition control module (AutoZone), started throwing oil pressure sending code P0520. Replace sending unit, no change in code. Drove it 2 days and on the freeway entrance ramp. RPM spiked then dropped to zero. Changed ignition module with second AutoZone part. No change. Towed it home. replaced the other two coil packs. Replaced ICM with a NAPA part then started throwing crank position code; rapidly, to the point I had trouble driving I on a 5 mile loop back to house. Replaced the ICM with a GM part. Still the crank position code but, way fewer episodes. Also started throwing misfires, a total of over 100, on 2 cylinders probably from my frustrated driving. Replaced crank position sensor and checked wire harness to crank position sensor and oil sender unit. Found no problems.
At this point, took to dealership. Lead mechanic assigned to car with all background information above. Catalytic converter was replaced because plugged. Cleaned and checked engine grounds, added redundant ground load test wires to ignition module to crank and cam sensor and ignition module to PCM (with incandescent light tester). Wire in 12 volt bypass harness from ignition module to batter volts. Bypassing ignition switch and fuse panel. Still, RPM blips, while driving. Sometimes no codes and sometimes phantom codes…..

PARTS (some parts used to prove original part wasn’t bad)
• Ignition module (AutoZone 2, NAPA 1, GM 2)
• Coil packs (AutoZone 2, Advanced Auto 2)
• Oil pressure sender
• Crank position sensor (NAPA 1, GM 1)
• Camshaft sensor (GM 1)
• Harmonic Balancer (GM 1)
• Catalytic converter (GM 1)
• PCM (GM 1)
• MAF (GM 1)

GM Tech Support have been called twice; first said PCM and second said Harmonic Balancer. Neither have resolved the RPM instability. Brought car home, drove the car 3 days and lost RPMs on the freeway. Waited 30 minutes on the berm, started and drove home. ANY SUGGESTIONS TO FIX THIS ISSUE ARE SURELY APPRECIATED!

This really drives me crazy, when a GM shop can't fix a GM problem.....calling TAC is like the last line of defense.....

Waited 30 minutes on the berm, started and drove home. ANY SUGGESTIONS TO FIX THIS ISSUE ARE SURELY APPRECIATED!

Just a few questions.......

Was this vehicle acting up while the GM Tech was working on it, or was he guessing on the fix, because it never happened for him?

Too many parts were replaced, without fixing the problem....

Did he ever take a Snapshot of vehicle data, when the problem occurred?

What was the EXACT code that was set?

So the car died on you while on the road.....it started 30 minutes later? Does that mean it wouldn't immediately restart? If that was the case, that was the time to check for spark, injector pulse, and fuel pressure.....

I had an Olds 88 with the 3800 engine that would strand me in the afternoon due to a no-start condition. I would wait 30 minutes and THEN it would start. I replaced the fuel pressure regulator and that solved my starting issues. Has fuel pressure been checked?

TECH II Answers: The car was acting up when the Tech was working on it. No Snapshot. The exact codes were P0520 then P0336. The car would not immediately restart.

Here is a little more detail for your analysis:
Only since the ICM issue: Driving the car and randomly the RPMs spike to 3,000-4,000 then drop right back to 1500-1800. Intermittently, spike to 3,000-4,000 then drop right to zero. The car will not immediately restart but will restart eventually.

This is what the Dealership Mechanic wrote: Has power but intermittently stalls and will not restart. Found no spark when acts up. went through diag for crank no start. tested wiring at ICM. All ok. removed harness to crank and cam sensors and inspected harness. ok. Called tech assist and advised to try a new ECM. replaced ECM and programmed. still acts up. tried new ICM. still acts up. tried running second ground and power signal to ICM. still acts up. removed CAM sensor and inspected. now no cam signal while running. tested all terminal tension and pin fit at all related connectors. all ok. checked wiring between ICM and ECM. all ok. called tech assist again. advised possible bad harmonic balancer. removed balancer and inspected. looks ok. replaced balancer, crank sensor and cam sensor. reassembled. still acts up.

Wow, it does make you wonder........

When it doesn't start, there is no spark....and the first thing they do is replace the PCM? Seriously?

If no spark, you pull a coil and you attach a test light to the input leads to the coil to see if you get a flashing light during cranking....if you get no flashing light, we are talking either crank sensor , ICM, or wiring....

I assume that the ICM, and crank sensor were new parts, and apparently, they did a drag test to check the connection of the female contacts in the wiring harnesses.....you do not need a a cam signal for spark....they did a redundant ground and power to the ICM circuits....

That leaves the wiring....I would have done an ohm check on the crank sensor wiring between the crank sensor and the ICM, while flexing and moving the harness, for a possible broken wire inside the harness, causing an intermittent condition........

Did they do a crank variation relearn? You need to do this if a crank sensor is replaced, or a PCM is replaced.....

TPS replace and MAF clean fixed a very similar issue for me. Also swapped the IAC while I was in there. Just a thought