Crankshaft position sensor mess! [Archive] - Forum


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12-27-2009, 07:52 PM
hey everyone. im new here so please bear with me... i still have my first 99 grand am coupe with the 3400 and she has 190,xxxx and hopefully many more to go. ive done a lot of work on this car but this last one is leaving me scratching my head... ok... drivin home... check engine light...WTF, (well at lease my computer is sensing something) take it in to get code, it happens to be the CPS (crankshaft position sensor)

now the 99 3400 has two of these in some not to nice, but not so nice places. we have the 24x sensor that measures 24 times per turn. this is right behind the crankshaft pulley. now online it says this sensor is responsible for RPMs and timing. now my car was kinda sputtering every once in a while and sometimes the tack would get squirrely. but it would have maybe a 1 to 2 second time period when it wouldnt function correctly, then all would be normal, and this was only when i was at full running temp. ok so replaced it like two nights ago, and had to get new crank pulley unfortunatly for not using the right tool. so i have a new 24x sensor and crank pulley on. now tonight when i came out to my car from walmart... started it up turned on the ipod... died... so now what could it be? ugh.... start her back up and start driving. rpm guage bounced a few times and she starts sputtering... then while dies. throw it in neutral, start it back up and keep going. now keep in mind the check engine light didnt come on... it blinked for bout a second when my tach bounced and then it shut back off. like if you blinked you would have missed it. over the period of driving home the car died 3 times on me. all times were under 4000 rpms. when i would stop at a stop sign it would be all good til i let off the brake, then sputter sputter die. now ASSUMING i havent changed the 7x sensor im guessing this may be the actual one i have to change.

However right after i changed the 24x sensor, my check engine light went off within the first 5 minutes of runtime, so i figured i fixed the issue...

now on the site i got my info off of, it said that without the functioning of the 7x sensor, the ignition system would fail, which may explain the dieing. just wondering if anyone on here has had this issue before. if so got any ideas? thanks!

12-28-2009, 07:08 AM
wow sounds like a pisser of a time but on a ga with 190k your lucky it even turns over lol

12-28-2009, 11:37 AM
Not at home right now so I can't check my manual for some of the stuff, but I can give you some information.

The 24x crank sensor only controls ignition timing up to 3000rpm. Above 3000rpm the pcm uses the 7x sensor to control timing, and I believe it always takes the rpm signal off this too (not 100% sure on that). I do know the tach signal for the gauge cluster comes straight from the pcm, so any tach issues and running issues will be the result of a sensor signal problem going to the pcm.

If you replaced the 24x sensor and the crank pulley, you need to get a crank position learn procedure done (known as a CASE learn). The only way to do this is with a tech2 at a dealership, or if you can find someone local with a DHP or HPtuner who will do it for you. There is no way to do it yourself. That may fix your issue... it may not. If it doesn't then it's possible it is a problem with the 7x sensor, but I would think it would have a dtc code for that. There may still be a code stored in the pcm but it just hasn't tripped the SES light yet, so you might want to get it checked for codes. If you do need to replace that sensor, it is on the back of the engine block (firewall side) above the oil pan and transmission. Kind of tough to get to, but you should be able to see it from under the car. Hope that helps a little.

12-28-2009, 12:46 PM
yea thanks. i will try to replace the 7x however do i need to pull anything off like the oil pan or more(hope not) to get to this sensor?

12-28-2009, 12:49 PM
you would be surprised at how long a car will last if it is properly maintained

12-28-2009, 03:25 PM
well i went out and put out maybe 25 city miles today. no issues unless i put i to the floor... then it would hesitate. and right before i got home it would start to act up at 1500 rpms. it would die only when i let it and not hit the gas. this was only when the car was in park. i really dont understand why this is going the way it is. i ran to get the codes checked and it is still the CPS. like i said the crank pulley and 24x sensor were replaced and the car idles and runs flawlessly on and off. so the 24x sensor cannot be the issue. like you said up there... it may need to relearn. but how and why is it on and off instead of constant crappy running. it sounds to me almost like a connection issue. so im going to try the connections. ill test the 7x and the 24x and see if they are corroded or coated with anything. if all looks good, what should i do next? this one makes me scratch my head...

12-28-2009, 04:53 PM
i also have ses light on with crank shaft position sensor as the code coming up along with a small evap leak.. i was told by the mechanic that i need to replace my crank shaft position sensor only which i checked with autozone thats only 30 dollars... from time to time my car sputters but never thankfully has shut off... mine only has sputtered when taking off...

12-29-2009, 06:45 AM
Don't need to remove the oil pan or anything to replaced the 7x sensor. It's on the outside of the engine block. It's just kinda hard to get to since it's on the back and you've got the steering rack and transmission down there and the exhaust manifolds up top. It's the only thing plugged into the side of the block back there though so you can't miss it when you see it.