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Do I possibly have a bad crank position sensor?

T

tom5170

New member
02 grand prix, 3.8 NOT SUPERCHARGED, 199k miles.

Today I was driving home from a restaurant a mile from my house. I stopped by a neighbors house to drop something off and then drove down the street to my house. As I was pulling in my driveway, I looked at the RPM needle and it was at the 0 rpm's line. I sat there in D for a bit and it ran just fine idling at 0. I put it in P, revved it, idled fine, but the RPM's never increased. When I turned the key off, the RPM needle dropped BELOW 0. I then went in my house, came back out about 10 minutes later, started car, it fired right up and the RPM gauge was working - Idling right at about 800 rpm's. I then drove around for about 10 minutes, RPM gauge was working just fine. I kept turning car off and on - the RPM gauge still worked fine. So WTH could it have been?

SO what could it be? I didn't drive it around when the needle was idling at 0 because I got scared and figured it was the CPS maybe. I didn't want to stall out anywhere.

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I've owned the car since August. And I've also had another issue. On startup, most of the time it fires right up. Sometimes it fires up, and the idle stumbles for a split second and then smooths out - the car will run and drive just fine after that. Then maybe 4 times now, I've had an extended no start crank problem on startup. The engine will crank maybe 5-10 seconds and then it will catch and fire right up and run and drive just fine. I have service records from 2013 saying spark plugs, plug wires, fuel filter, battery, MAF sensor, etc was changed. I recently replaced the MAP sensor because I had a code for that and I thought my start up issue could've been related to a bad fuel pressure regulator so I replaced the FPS and it's still the same as it was before. Yesterday was about the 4th time that I've had the extended crank no start problem and then it catches and fires right up. I've also cleaned the throttle body. I was thinking about the check valve on the fuel pump was sticking, but now that this needle issue dropped to 0, I'm thinking it could be CPS.

Any thoughts?
 


When I noticed it at 0, it ran just fine though but I didn't drive it (I got scared lol), I probably ran it for a minute before shutting it off. Is this common with a failing CPS to just idle at 0 without stalling or did I not run it long enough? I just drove it around another 10 minutes and the RPM gauge still works fine. Any guess on how much a shop charges to do the CPS?
 
no idea. id change it myself. hard part is breaking the crank bolt free, then rent a puller. buy a new sensor, tq it back on, and bam. its over.
 
http://www.grandprixforums.net/threads/60906-How-to-replace-a-crank-sensor bolts are listed

you want this style puller

45300_2F41593ECF48F.jpg
 


Can a dirty CPS cause issues? Like if it gets coated with oil/grease/dirt?

Does the RPM gauge get it's reading from the CPS?
 
So I'm at shop and they scanned it. A code came back for crankshaft position sensor and cruise control. The mechanic said that the icm and coil packs are on same circuit and those could be going bad. he advised me to change those first and see. I told him to go ahead and replace the cps anyways and I'll do coil packs on my own time. He also mentioned a camshaft sensor could be going bad.

I don't remember the code numbers for the crankshaft code but I saw it on the scanner.

Like I said last night the rpm needle dropped to 0 while idling.

How likely will it be the cps? The mechanic seemed condescending.
 
crank sensor is what makes the tach drop to zero. icm or coils you have misfires, they al do talk to each other tho.

if the code was there for the crank sensor chances are thats the issue, cause that code dont show 99% of the time when its bad, you get the code its bad for sure most of the time.

also have the guy check out the harness to the crank sensor, they get beat up over time, my 98 ate the harness, it was all chewed up looking with bare wire showing. that set the crank code on me.
 
Well it definitely dropped to 0. I even took pics lol. And it was definitely a crankshaft code. Past 6-7 months I've had extended crank no start happen a few times. But the most common is the car will stumble a second or 2 on startup and then smooth out and run fine.
 


Scottydoggs said:
no idea. id change it myself. hard part is breaking the crank bolt free, then rent a puller. buy a new sensor, tq it back on, and bam. its over.
Click to expand...

Side-question, if you don't mind.... if I'm already swapping the crank pulley for a top swap, would it be a good idea to replace the sensor at the same time (assuming that it's currently working fine).
 
Got new sensor in. Runs fine so far. Haven't gotten a hard or jumpy rpm startup yet. Rpm needle is working right too.
 
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