3100 Will Not Start

[bluebomber]

Finally put together the motor again today after installing the new camshaft. Motor started, but idled high (2000) and one of the pullies was squeaking really bad, we assumed it had gotten some coolant on it. We attempted to restart the motor but now it will not start and appears to be firing back into the intake (popping out of PCV line and intake hose)! Anyone have any ideas? We are out, everything seems connected and are about to try a compression test to see if things came out of time...

[Chris88CL]

If it passes the compression test then check out the ICM.

[geoffinbc]

Well are you getting BOTH fuel and spark? Thats always the first to check.

[bluebomber]

We discovered the problem. When the CPS is plugged in, the engine does not start due to the fact that it thinks its in a different cycle. When unplugged, and the car is running in closed loop mode, the engine will start and can be convinced to idle, it just runs like crap because the computer doesn't know what cycle the crank is on. So now I'm looking for a new CPS, crank pulley or both to remedy the problem.
Thanks guys!

[geoffinbc]

HUH? It doesn't matter so long as you lined up the timing marks on cam gear with the mark on the crank gear then the motor it good to go. Just get a new sensor. Oh and the cam sensor ring on the new camshaft matched the old one right?

[ouch1011]

Hi, I'm bluebomber's brother. I've been helping him out with the cam swap.

The timing marks on the crank gear (under the front cover) and the cam gear lined up perfectly. However, I think while we were trying to remove the crank pulley we either damaged the "teeth" on the pulley itself, or the sensor. In any case, it runs acceptably with that sensor unplugged, which would lead me to believe that one or both of these parts were damaged in the process. I think the sensor itself may be to blame, since I washed off the front cover with some solvent not thinking to remove the crank sensor before doing so. (D'oh!)

And yes, everything on the new cam matched everything on the old cam. We checked this to make sure since the new cam came from a different year Grand Prix, and I knew that the timing ring on the cam changed a couple times...

I've got a question as well. I know there are two crank postion sensors on the 3100. A 24x one and a 6x one IIRC. Which is the one mounted on the front cover, and what is its purpose (a little more indepth besides the obvious "it determines the crankshaft position) What does the one on the front cover do or not do that the other one does/doesn't?

[bszopi]

The other one is a 3x sensor. The 24x sensor is the one mounted on the front cover (count the openings on the reluctance wheel... 24 ). The only reason for the 24x sensor is to give a more precise crank position at low RPMs (<2k I think), therefore allowing for a smoother idle.

[ouch1011]

Thank you, that explains alot (hard starting, rough idle, hesitation off the line, loss of power below about 2500 rpms)

This new cam really brings the engine to life, tho...

[bszopi]

Yeah, the cam profile you got is just under what I used to run. It was just awesome after 3k rpm. How does your's idle though? Cause I had some major idle issues (I have a video around here somewhere). Oddly, I founf that my car idled best with a small vacuum leak (there is an extra vacuum port on the plenum I left unplugged).

[ouch1011]

It definately has a lopey idle right now, and sometimes it tries to stall immediately after hot starting or putting it in gear, but I'm not sure how much of that is the cam and how much is the fact that the 24x Crank Position sensor is unplugged...

We are hoping to get the car to the Woodburn dragstrip on the 30th to see what kind of improvement the cam and upper intake modifications did. It was running a solid 16.3x before...