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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29520
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Changed harmonic balancer and crankshaft position sensor on

Customer Question

changed harmonic balancer and crankshaft position sensor on 2001 Monte Carlo 3.4 liter, LOW END idle good,HIGH END backfires at 2000 - 2500 rpm, do I need to reteach and if so how do I go about this?
Submitted: 1 year ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 1 year ago.

Hi there, I am Cam, Can I get your first name? Also can you tell me if the check engine light is on?
The crank relearn is only initiated with a scanner. It then asks the driver to rev the engine quickly to a preset value, usually around 4000 rpm. It would set a code suggesting that the relearn needs to be done.

Expert:  GM Tech (Cam) replied 1 year ago.

Attached is the document outlining that.

Customer: replied 1 year ago.
Hello my name is***** have no check engine light on, did not start doing this until engine warmed up to operating temp.
Expert:  GM Tech (Cam) replied 1 year ago.

Is it always at higher RPM or does it do this only if you rev it higher faster? How does it drive? Also does it do this if you unplug the EGR? Mass Air Flow sensor (MAF)? Map sensor? Without codes it does make this a bit more difficult to find.

Also prior to the replacement of the parts you listed, is this the same reaction it had/

Customer: replied 1 year ago.
it is always between 2000 -2500 in park and while driving, did not unplug EGR,MAF or Map sensors, daughters car so the back story is weak, I did not drive it prior to work, Serpantine belt was bad, when I went to change belt I saw balancer was coming apart so I thought while changing the balancer I may as well change out crank position senor at same time.and I threw in a new set of plugs and wires.thought I was being proactive and now I think it going to bite me in the Ass.
Expert:  GM Tech (Cam) replied 1 year ago.

OK, so in park I am not as concerned but does it drive then now Scott? And if not then lets look at the position of the crank sensor. Is there a chance the balancer is hitting it? Wires chaffed? If no then it may simple be that the new sensor is not good. It happens.

Customer: replied 1 year ago.
it does drive, if I do not let the tach go above 2000 while driving all is good, it is when I get on the gas that it pops and cracks, it does recover and gains speed.
Expert:  GM Tech (Cam) replied 1 year ago.

Ok so then it did not do this before the belt/balancer/sensor replacement so it stands to reason that one of those is bad. Belt I doubt, sensor possible but if the balancer is out or the reluctor is not aligned properly it would cause this. Myself I would take the sensor and put the original back in and try that. IF it does not change then I would consider calling the balancer you got bad.

Customer: replied 1 year ago.
Well I just had my daughter drive it and she said it was doing this before the parts were changed.
Expert:  GM Tech (Cam) replied 1 year ago.

Ok so then we need to see what the fuel pressure is doing, I am surprised there is no check engine light. Can you see when the last fuel filter was replaced, consider taking it off and checking it and even replacing it? Also unplug the map, Mass Air Flow sensor (MAF) in turn and see what that does.

Expert:  GM Tech (Cam) replied 1 year ago.

Scott, I am stepping away from my computer for a bit, I will check in with you in an hour or sooner.

Expert:  GM Tech (Cam) replied 1 year ago.

Any updates?