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Discussion Starter · #1 ·
I have an 01 Intrepid with a 2.7 vin R that is not starting, I changed the cam and crank sensor and the timming chain, still wont start. I tested fuel presure and ignition pulse both are good. the car has a black key. The inresting thing about this problem is it stars and runs good when I unplug the cam sensor. I cant figure this one out, has any one seen this before?? Thanks for any help.
 

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Seen it many times. Either the new sensor is bad, and it happens all the time, new sensor, defective right out of the box.

OR the timing is not right in some link of the chain. Either the trigger wheel is off relative to the cam, or the cams are off relative to the crank, or one or more of the four cams is off relative to each other and/or the crank.

I would start with the sensor first. The fact that it starts and runs well when unplugged tells me it is either the sensor or the trigger wheel. And we have heard of a lot of failed sensors.

Jim Snover

I have an 01 Intrepid with a 2.7 vin R that is not starting, I changed the cam and crank sensor and the timming chain, still wont start. I tested fuel presure and ignition pulse both are good. the car has a black key. The inresting thing about this problem is it stars and runs good when I unplug the cam sensor. I cant figure this one out, has any one seen this before?? Thanks for any help.
 

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Seen it many times. Either the new sensor is bad, and it happens all the time, new sensor, defective right out of the box.

OR the timing is not right in some link of the chain. Either the trigger wheel is off relative to the cam, or the cams are off relative to the crank, or one or more of the four cams is off relative to each other and/or the crank.

I would start with the sensor first. The fact that it starts and runs well when unplugged tells me it is either the sensor or the trigger wheel. And we have heard of a lot of failed sensors.

Jim Snover
Yes,, double check the new sensor first by replacing it with another new one...If it is not the sensor the most likely cause is the timing chain was installed 1 tooth off by not having the crank mark lined up perfect..

The only function of the cam sensor is to make the fuel delivery timing more precise with the intake valve timing... It only monitors the position of the left intake camshaft..The other 3 camshafts are kept in sync by the chains... There relative position will not have any effect on it trying to start(if they are too far out of sync mechanical damage will occur, but electrically it will try to start..

An 01 will start with no cam signal and will run if the cam signal is lost..But it will not start if the PCM determines that the cam signal does not match the crank signal when it is trying to start...When this happens it "thinks" that the timing chain has slipped and activates the auto shut down to protect the engine..
..

Also make sure that the sensor wheel on the cam is not bent or damaged and do not rev the engine above 2000rpms...

Good Luck!!
 

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With respect, I have to disagree with you on your second paragraph. Several folks have inadverently mis-timed one or more of the cams on second-gen 3.5's and 2.7's, and suffered no physical damage, but were also unable to get the engine to start.

You are dead-on about the sensor only actually monitoring one camshaft, but the underlying assumption in the PCM's program is that the other three cams are correctly within their appointed positions relative to the one actually monitored camshaft. The physical reality can be wildly different, and result in no damage, but also result in an engine that will not start or run.

And yes, I know this because I have learned it the hard way.

Jim Snover

Yes,, double check the new sensor first by replacing it with another new one...If it is not the sensor the most likely cause is the timing chain was installed 1 tooth off by not having the crank mark lined up perfect..

The only function of the cam sensor is to make the fuel delivery timing more precise with the intake valve timing... It only monitors the position of the left intake camshaft..The other 3 camshafts are kept in sync by the chains... There relative position will not have any effect on it trying to start(if they are too far out of sync mechanical damage will occur, but electrically it will try to start..

An 01 will start with no cam signal and will run if the cam signal is lost..But it will not start if the PCM determines that the cam signal does not match the crank signal when it is trying to start...When this happens it "thinks" that the timing chain has slipped and activates the auto shut down to protect the engine..
..

Also make sure that the sensor wheel on the cam is not bent or damaged and do not rev the engine above 2000rpms...

Good Luck!!
 

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With respect, I have to disagree with you on your second paragraph. Several folks have inadverently mis-timed one or more of the cams on second-gen 3.5's and 2.7's, and suffered no physical damage, but were also unable to get the engine to start.


Jim Snover
You are right..I did not mean that the engine would actually start only that it would "try" to start, meaning the PCM will send fuel and spark, as long as it gets a cam signal that matches the crank signal with some degree of tolerance for wear(this keeps the fuel delivery timed exactly with the intake valve opening even if the chains wear or stretch a little bit because the sensors can monitor any differences in the crank and cams and adjust accordingly making the assumtion that the chain will stretch uniformly accross its entire length); and it will also "try" to start even if it gets no cam signal as long as it gets a crank signal (possibly to prevent stranding a bunch of motorists because of a common cam sensor failure)...If any of the cams are off by more than about 5-10degrees it may not start due to not having enough compression because the valve timing is off or because the fuel delivery is at the wrong time, but it will typically still get fuel and spark and "try" to start...And if the crank gets ahead of the valve timing by much more than about 25degrees the pistons will hit the open valves and cause damage...So if the PCM senses that the left cam signal is off by somewhere between 10 and 20 degrees compared to the crank signal, it prevents the engine from starting to avoid damage..In the unlikely event that the cam sensor quits at the same time as the timing chain slips a few teeth you could have some major damage..

And the PCM has to "assume" that the chains are installed correctly...But it only needs to monitor the 1 intake cam sprocket because after 1 full revolution of the chain the relative position of all the other cams as they relate to the left intake cam is determined by the number of chain links since all of the slack in the chain gathers on the non driven side of the chain, and the exhaust cams are driven basically by solid chains from their intake cam..Assuming that all the chains are installed correctly, the other 3 cams will always "follow" the first monitored cam(untill the water pump goes or the chain jumps, but that is a whole diferent story:crying:!)..If the main chain is installed 1 tooth or even 1degree off from the crank to the left cam then all of the other cams will be off also..

Given that he has replaced the cam and crank sensors and the timing chain, I think we agree that the logical order of diagnosing the no start is to rule out yet another defective cam sensor then check the sensor ring (especially if it seems to run well with the cam sensor unplugged and does not start with it connected)then check to make sure chain is installed properly..Could also be one of the small chains has slipped, causing the exhaust valves to be out of sync with the crank, but that is not that common..

We wish him luck with diagnosing it..
 

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Discussion Starter · #6 ·
Hello everyone Thank you for all the info. There is more to this situation. I was just told the car ran fine for a few weeks after the timming chain was installed. After it stopped running is when we put the cam and crank sensors in. Very strange symtoms
 

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Hello everyone Thank you for all the info. There is more to this situation. I was just told the car ran fine for a few weeks after the timming chain was installed. After it stopped running is when we put the cam and crank sensors in. Very strange symtoms
If you have ruled out another bad cam sensor,and is getting fuel , compression and spark, and it still runs with the sensor unplugged... I would pull the valve covers and verify that the timing chain has not slipped a tooth or the sensor ring come loose...If the tensioner was bad or not reset properly it can work for a while then it will let the chain jump when you start the engine..

I have also seen metal dust from a loose chain hitting the front parts gather on the sensor and cause it not to work..But you would notice this as you replace the sensor..
good luck!
 

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Discussion Starter · #8 ·
thank all for your input, I tore the front of the engine down today and found the problem to be the timming chain crank gear was spinning with no key inplace.
 
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