The Camaro made loud noise and shut off as I was driving about 20mph the other day. I thought I had run over something; my wife was in another car behind me and thought she heard a backfire. In any case, the car would not start again. I towed it to the mechanic, who said the crank position sensor was bad and would need to be replaced.

He replaced it (turns out the old one was sheared off!) and the engine fired right up. But now it has a loud knocking sound and the #4 cylinder is not firing. My mechanic is not sure how the two are related -- he said the position sensor is down low in rear and the knocking sound is from up high. There is spark to the cylinder (arcs if you pull the plug). Car sounds and runs like crap. Maybe a stuck valve/lifter? Thrown rod? Thoughts?

I have not had him open up the motor to figure it out -- the car has a 157k on the clock and I don't want a $1k bill to determine that the motor is junk. Any thoughts on next steps?

 

compression test on that cylinder to start with. Check the injector for that cylinder as well, make sure its getting fuel.

 

"[QUOTE=Jeremy1;5397747]The Camaro made loud noise and shut off as I was driving about 20mph the other day. I thought I had run over something; my wife was in another car behind me and thought she heard a backfire. In any case, the car would not start again. I towed it to the mechanic, who said the crank position sensor was bad and would need to be replaced. "

where is the crank position sensor on your engine?

 

The cylinder is getting fuel.

I could do the compression test. What would that tell me?

 

If a lifter or valve is stuck open, a compression test will show up very low on that cylinder.

 

camaroLevi: there are two crank position sensors. haynes describes them as "on the engine front cover behind the damper" and the second one "on the right side of the block near mid engine near the crankshaft relucter ring". The sensors read the timing mark to control the timing. apparently, if the sensors contact the interrupter rings on the vibration damper it gets damaged and the engine shuts down. so we replaced mine and the egine restarted. but I am still not sure how this killed my #4 cylinder. Any thoughts?

 

95camaroinok: I'll pick up a compression gauge and test the cylinder. assuming it is low, does that indicate i need a valve job? Or what do you think?

 

If its holding pressure, and the valves arent sticking, then your looking most likely at bottom end. Pull the pan and check the rod, bearings, crank, etc. If its not holding pressure, pull the valve cover and see if you valve springs are moving right on that cylinder. You could pull the head, and check further. Chances are it'll have to come off anyway if it has low compression or if there is a definte knock. Then you can diagnose it farther and if its in the head, you can rebuild the head yourself if you have much mechanical knowledge, and save a good chunk of change. If its that specific piston, then you can drop the oil pan and get in the bottom end and push that piston out. Check the crankshaft for wear or gouges on that journal, and possibly get away with replacing just that rod and bearing or piston, rod, and bearing. I do however recommend, if you pull one head, pull them both so you at least have new headgaskets on both sides while your in there anyway. Give you a chance to clean up the top end and you'll know whats goin on in there. If it will still start and run, and isnt pouring oil out, it should be fixable without total replacement.

Do the compression check, pull the valve cover off that side and inspect it and let us know what you find. We'll guide you from there.

 

ran into a weird issue will running the compression test (seperate thread). In the mean time, here is a video so you can hear the sound it is making. Any thougths?

http://www.youtube.com/watch?v=A_uEu02gzmc

 

ran the compression test. here are the results:

passenger side
#5 = 175
#3 = 178
#1 = 175

driver side
#6 = 180
#4 = 0
#2 = 180

so my next project (hopefully next wk) is to take off the valve cover and have a look at number four. any preliminary thoughts?

anyone have thoughts on pulling the cover? (looks like the air intake plenum has to go?)

 

Ok, so I finally got the time to pull the valve cover. I turned the engine over by hand and watched the rocker arms/springs. Everything appears to be working fine. There does however seem to be some extra play in the rocker arm on the #4. When I turn the engine so that the intake/exhaust rocker arms on #4 are level with each other, I can wiggle the rocker arm that is closest to the front of the car.

I am pretty sure the valves on the 3.4l are not self adjusting, so does anyone have good instructions for adjusting the valves? I am thinking the loose rocker arm COULD be the source of the noise (check out the video link earlier in this thread and let me know what you think). But is my compression problem related? Or do you think it is something more serious?

 

any thoughts on next steps?

 

Set the cylinder to TDC, then while spinning the pushrod with your fingers, tighten the rocker arm nut just until your pushrod stops spinning. If I remember right, that's all there is to it. Pretty good explanation in the Hayne's manuals.

 

Thanks. I can do that. I guess a bigger part of my question is whether I should try adjusting the valves, or if I should do something else while I have the engine opened up. I am hopeful that adjusting the valves will take care of the problem, but I am worried that I may adjust the valves, close the engine up, and still have the same problem. Any advice would be helpful. I may post a new thread and ask for thoughts on next steps.