Random Z34 Start

[Lyle27]

Hey Guys,
I just found your sight and have been doing some reading.

Here is my story (hopefully someone has had a similar situation...and solved it )

It's a long one.......

I found a really low mileage Z34 that is amazingly clean...and bought it as my winter/family car.
The guy said it had left his wife stranded and she made him buy a new car.......after a while he changed the Coil Packs (used) and voila..it started right up....but he no longer needed it.

Within a week I discovered the Volt Meter fluctuating and then eventually the alternator quit......car wouldn't start unless the battery was left on a charger all night.....

Long story short.....spent Christmas changing the alternator....it was freezing!!....and boy did I swear at GM....who puts an alternator down there???

So I thought that was it and still not a bad deal for a clean/fun car.

Well during the cold and sometimes moist days....the car will crank but not fire...battery sounds strong.....it is now brand new....but the volt meter lonly showed around 9v....so I would charge it and still no start....I pulled the air filter..I could smell gas.....I checked the codes using a paperclip...there were none......

It was very cold so I left it.....then a couple days later I try it and BAM.....it fires right up.......

I drove it around......it felt awesome...good...smooth power band.......nice idle...

Then one day it was raining....and wouldn't start again???

I assumed from what I have read the it is the Crank Sensor or the ICM or Coil Packs......

So today being a mild day...I decide to go check for spark.....and ofcourse it starts right up!!!

So obviously, I am afraid to go anywhere and be stranded....

Anyone else ever see this happen?

[GTP091]

It almost sounds like your problem is with moisture getting into the icm harness. You may want to inspect the seals on the harnesses that go into the ICM for tears that let moisture in and have caused corrosion to give you a glitch in the ignition module. The harness that goes to the crank sensor could be bad at the sensor end as well. If the crank sensor is bad it will just quit so your problem is likely in the wiring. Check the under hood electrical center for any corrosion at the ICM fuse as well. Don't replace the ICM until you test the wiring first you can get a free test at Napa if you take it out.

[Lyle27]

It almost sounds like your problem is with moisture getting into the icm harness. You may want to inspect the seals on the harnesses that go into the ICM for tears that let moisture in and have caused corrosion to give you a glitch in the ignition module. The harness that goes to the crank sensor could be bad at the sensor end as well. If the crank sensor is bad it will just quit so your problem is likely in the wiring. Check the under hood electrical center for any corrosion at the ICM fuse as well. Don't replace the ICM until you test the wiring first you can get a free test at Napa if you take it out.

Thanks GTP091!
I was hoping someone would help me rule the crank sensor out!
My first thought was moisture....but the first couple times it happened it wasn't raining....but it was zub zero temperatures and then the last time it WAS raining...but under the hood seemed really dry....and it took over a week before it fired up again....
I will have to take the ICM apart and trace the wiring harness like you said.....

[GTP091]

You will need a 5.5mm socket to take the coil packs off the ICM; anything else will strip them as they are likely a little rusty. you will also need to get right under the car to pull the coil pack off the engine. I believe 12mm. Three bolts to get it out and you will need a few different socket extensions to find the right angles. follow the socket head up to the bolt with your fingers and use your thumb to hold it on while you attach the ratchet. try just inspecting the harnesses before you pull it off tough. If they are clean inside and not corroded it may be time for a new ICM but i really think it's wiring. ICM shouldn't start and stop working like that. usually one of the coil outputs stops and then throws a code.

have you tested for spark when it doesn't fire??

[Lyle27]

You will need a 5.5mm socket to take the coil packs off the ICM; anything else will strip them as they are likely a little rusty. you will also need to get right under the car to pull the coil pack off the engine. I believe 12mm. Three bolts to get it out and you will need a few different socket extensions to find the right angles. follow the socket head up to the bolt with your fingers and use your thumb to hold it on while you attach the ratchet. try just inspecting the harnesses before you pull it off tough. If they are clean inside and not corroded it may be time for a new ICM but i really think it's wiring. ICM shouldn't start and stop working like that. usually one of the coil outputs stops and then throws a code.

have you tested for spark when it doesn't fire??

This sounds as though it is is going to be fun....

I am probably going to wait untill the weekend to get under there.......hopefully it is something obvious..........even if it costs a couple bucks....I would rather it just be fixed instead of leaving me stranded somewhere...

I didn't actually test for spark....it was raining the last time and I didn't have and extra hand to crank for me.........I know I should have done that...

I will let you know how it goes!