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Username Post: Code PO340 Cam Sensor        (Topic#271675)
98 Silverado 
Senior Member
Posts: 112
98 Silverado
Loc: Cedar Lake, IN
Reg: 02-27-05
11-06-11 05:09 PM - Post#2155159    

5.7 Vortec, 98k, runs strong. No issues. Set the SES and have PO340 code.

Not a thing has been touched on this truck for quite awhile, other than oil changes and a starter rebuild.

Is it likely just the sensor failed? Can it be replaced without pulling the dizzy?
Mike
98 Silverado 5.7 Vortec
94 Roadmaster LT1
71 Camaro SS clone
86 ZL600 Eliminator


 
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someotherguy 
Moderator
Posts: 25769
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
11-06-11 05:17 PM - Post#2155165    
    In response to 98 Silverado

The cam sensor is extremely easy to change out but I haven't seen a bad one yet. It's actually a pretty simple device. It's inside the distributor under the rotor; remove cap & rotor then it's just 2 more screws and a harness connector to get the cam sensor out.

I'd be more inclined to suspect distributor gear wear as there were a batch of them that were improperly hardened (GM's process is called melonizing) and wore quickly, causing ignition problems. It's not very easy to tell though without removing the distributor, then you have the hassle of getting it timed correctly again which can't be done with a timing light - needs to be installed in exactly the right position then fine-tuned using a scan tool that can read the cam retard number.

If you had more miles than 98K, I'd suggest checking for distributor top bushing wear but it's very unlikely with your mileage. Easy enough to check; remove cap and check rotor for lateral movement; sometimes you have to turn it a little and try again. If it flops side to side you've got distributor wear.

Check the harness going to the cam sensor to be sure there's no mouse nibbles or anything.

As always with these plastic Vortec distributors, be extremely careful with the cap screws as it's easy to break off the mounting tabs on the distributor body. If you install a new cap, use your old screws.

You could always try clearing the code and see how long it takes to come back.

Oh, and just for grins, check the wiring and connection at the crankshaft position sensor, which is at the front of the engine, bottom of the timing cover. You could be getting a false camshaft sensor error due to a crank sensor problem.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
98 Silverado 
Senior Member
Posts: 112
98 Silverado
Loc: Cedar Lake, IN
Reg: 02-27-05
11-07-11 07:31 AM - Post#2155383    
    In response to someotherguy

Wow, thanks for all the helpful hints Richard. This truck has been nearly trouble-free since I've had it, so not real familiar with the particulars.

The thing that strikes me as odd is you can still floor it and there is no hesitation, it takes off like a rocketship. I don't think it would run for crap if the dizzy was worn out, but what do I know.

I recently rebuilt the starter and I remember a wire going to a sensor in that area kept wanting to get pinched, but was careful to keep it free. Maybe I damaged it?

Can I just pull the batt cable to reset the SES? Odd that the light came on after a real low speed trip and after the truck was turned off for 5 or 10 mins.



  • someotherguy Said:
The cam sensor is extremely easy to change out but I haven't seen a bad one yet. It's actually a pretty simple device. It's inside the distributor under the rotor; remove cap & rotor then it's just 2 more screws and a harness connector to get the cam sensor out.

I'd be more inclined to suspect distributor gear wear as there were a batch of them that were improperly hardened (GM's process is called melonizing) and wore quickly, causing ignition problems. It's not very easy to tell though without removing the distributor, then you have the hassle of getting it timed correctly again which can't be done with a timing light - needs to be installed in exactly the right position then fine-tuned using a scan tool that can read the cam retard number.

If you had more miles than 98K, I'd suggest checking for distributor top bushing wear but it's very unlikely with your mileage. Easy enough to check; remove cap and check rotor for lateral movement; sometimes you have to turn it a little and try again. If it flops side to side you've got distributor wear.

Check the harness going to the cam sensor to be sure there's no mouse nibbles or anything.

As always with these plastic Vortec distributors, be extremely careful with the cap screws as it's easy to break off the mounting tabs on the distributor body. If you install a new cap, use your old screws.

You could always try clearing the code and see how long it takes to come back.

Oh, and just for grins, check the wiring and connection at the crankshaft position sensor, which is at the front of the engine, bottom of the timing cover. You could be getting a false camshaft sensor error due to a crank sensor problem.

Richard


Mike
98 Silverado 5.7 Vortec
94 Roadmaster LT1
71 Camaro SS clone
86 ZL600 Eliminator


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
11-07-11 07:37 AM - Post#2155387    
    In response to 98 Silverado

Believe it or not you can remove the CMP sensor and other than throwing a code, nothing bad will happen and nothing will change on the 96+ vortec motors. This is because the CMP sensor is not used for engine management but is a reference sensor. All it does is make sure the distributor is set within tolerances. It has nothing to do with timing at all and just makes sure that the distributor is set correctly to prevent a chance of crossfire. This is why everything drives the same.

As far as your starter question, I am almost 100% certain the wiring doesn't go down by the starter and rather runs with the main harness on top of the engine and through the firewall. Any other issues I could think of like maybe you broke a ground, would cause other issues as well and not just the CMP fault. I would start by checking the wire harness connection on the back of the dizzy and then reseat it. See what that does, I mean start cheap quick and simple first.

You may want to review the timing guide in the FAQ for 96 + vortecs, might shed a little light on what you are up against if you pull the distributor.
98 Silverado k1500 4x4 350


 
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