Need help with Camshaft sensor error P0340

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Feb 4, 2018
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Guys, new to this site - thank you all in advance.
On my 98 4.0 OHV I've been working on a P0340 (camshaft circuit fault). So here's the deal...this fault existed before I recently changed the engine. I put another synchronizer and sensor on the engine. I could see the pulses on my oscilloscope going into pin 85 on the ECM; a nice square wave of about 13v. I figured it must be the ECM since all the right signals were there so I purchased a new ECM. There is no difference with the new ECM. So I have a new CPS, new ECM and the wiring checks out between them and I have a signal that matches whats suppose to be there (far as I know). There are no other codes. I've read in some forums that a bad alternator can cause this but I've disconnected mine but it didn't make any difference. After you clear the code, it appears immediately when you crank the engine up. The engine runs pretty smooth overall. So what can be causing this continual P0340? What else haven't I considered or checked? BTW, this is a 3-wire sensor (not 2 wire)

Mark
 
Its a continuous issue before and after new engine, new sensor and new PCM.
When you say the wiring checks out, can you be more specific? That's the only old part left in the system.
 
@ Dano - Yes, I checked continuity between the sensor and ECM. There wa no real need since I can see the pulses going into the ECM on pin 85. It's definitely getting a square wave into it per my oscilloscope. It's been hard to get a good wiring diagram but from what I can see on the web, pin 85 is the correct pin. I even pulled the ECM connector off to see if there was continuity from the back of the connector (blue/orange wire pin 85 and the pin on the ECM side. It's ok. So you would assume if you are watching pulses going into the ECM on your oscilloscope, everything is connected the way its intended.
Do I have the right Pin (85)? I don't have a good wiring diagram.
I didn't put on the new synchronizer - it was on the NAPA long block. I don't know 100% if it was installed correctly. However, the previous engine did the same thing.

Regarding the crankshaft sensor, I put a new another one on. Although I don't know how it would impact the camshaft sensor. The engine cranks ok and runs.
 
The crank and cam sensors have to be in time. Just having a signal is not enough.
 
ok, so the crank sensor isn't adjustable and the engine is running pretty good. If that's true, then you must be suggesting that the synchronizer is not in correctly since that's the only one you can adjust??
 
I have this posted on 3 sites (including therangerstation you mention) and no one is even attempting to answer, except this site. I guess I need to ask a simpler question like "how many miles do you get on your ranger" if I want to get help (LoL)
 
Originally Posted By: Rolltide6019
ok, so the crank sensor isn't adjustable and the engine is running pretty good. If that's true, then you must be suggesting that the synchronizer is not in correctly since that's the only one you can adjust??


If the engine is running well both sensors and ecm are working properly. The only thing of in that case (engine running okay) off the top of my head is the cam and cranks sensors are out if time.
It will run in any position you can get the plug on but throw a code if it isn't the right one (14T = 14 positions from what I am seeing here).

Edit: Did you use one of these?

https://www.amazon.com/OTC-6472-Camshaft-Sensor-Synchronizer/dp/B000VNFUJ2
 
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Trav - thanks. As I understand it, there are several Camshaft position codes as follows:
P0340 Camshaft Position Sensor Circuit Malfunction
P0341 Camshaft Position Sensor Circuit Range/Performance
P0342 Camshaft Position Sensor Circuit Low Input
P0343 Camshaft Position Sensor Circuit High Input
P0344 Camshaft Position Sensor Circuit Intermittent

The story I told myself is that if the sensor/camshaft was way out of sync, I might get one of the other codes - like p0341. But I could be wrong.

I've read on several forums that its quite common for the engine to run ok with the CPS not functioning since the ECM will use the Crankshaft signal in its place - although the fuel mileage and emissions may be sacrificed. As I read what others have written, the Firing is controlled by the Crank but the Injectors get controlled by the Cam sensor.

I have been assuming a few things that may or may not be right:
1) The new engine came correctly timed
2) The synchronizer was installed correctly (I put my own 3-pin sensor on it)

Is there a way I can tell whether the fundamentals or assumptions above are correct without tearing down the engine to check the timing chain? Is it likely to run down the road with the cam very much out of whack??
 
If the cam sensor was not working there would be no injector pulse on this system from what I can see. Its probably off a tooth as your not getting any of the other codes.
The first thing I would do if someone brought this to me is use the tool with the engine at TDC (insure #1 is at the top of its compression stroke).
The more I think about it could it be 180 off? No idea just thinking out loud, I will have to think about that one a little more.
 
Thanks Trav for the input. I can tell you for sure that the engine will run pretty good if you completely disconnect the CPS. From what I've read, the ECU seems to use the Crankshaft sensor to guess where the cam is. The injectors open and put fuel in the bank but its not at the ideal time and there may waste fuel or cause emissions issues. The part that frustrates me is that the previous engine had the same issue and I couldn't figure it out. Now the new engine does the same thing. I've changed most everything (not the wiring harness) and still getting the same results. New engine with different synchronizer, new CPS, new ECM. And not to mention, I'm getting pulses. It seems hard to reconcile that I'm getting the same results with practically everything different. Of course, someone may have put the synchronizer in a little off but I might have thought the code I would get is and "out of range" code instead of the circuit malfunction. I may have to start from scratch and check the synchronizer relative to Top dead center (TDC). If it were that, it would mean that the previous engine also had the same issue (hard to believe but maybe).

Trev - if I were to roll the crank around to TDC on the compression stroke (watching it with my meter or scope) should I see a corresponding pulse at the CPS at exactly time (probably not) I expect that you would open the injectors before you fire the plugs.... but I'm trying to see if there is a way to see it things are aligned without tearing it down again.

Any thoughts?
 
Does the cam sensor come out from the top on this engine it also drives the oil pump? Just trying to figure out if we are talking about thee same engine.
It would have to trigger the injector before ignition. Did you change this part?

 
The waste fire system with 2 plugs on each coil means the ignition will always work properly solely from the crank sensor, with or without a 180 degree uncertainty in cam position. Each coil has the two cylinders that are 180 degrees apart, so whichever one is on compression will fire and the other one just wastes a spark.

Without cam position information, the PCM must guess which group of 4 cylinders will open their intake valves on this revolution of the crank. In the interest of not stranding a loyal Ford buyer by the roadside, it will guess and keep going. The fuel injection won't be optimally timed.
 
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I am thinking you only changed the cap not the drive, if that's the case its probably not in that unit or its alignment but a wiring issue.
Let me look at a wiring diagram of this tomorrow.
 
Trav - yes, this is what I have, exactly. The lower part being the synchronizer and the top being the 3-pin hall effect sensor. The new engine came with the synchronizer so I didn't change it. I don't have a 100% guarantee that it was new but it looked good. It came with a 2-pin sensor so I put my 3-pin on it. The new engine was going to be put in a 98 Explorer which required the 2-pin sensor.
 
@ mk378 - I've read what you suggest say although my 4.0 OHV is a 6 cyl, not an 8. It runs so well your tempted to just ignore it but I've also read it will do long term damage. I'm not sure but I don't want to ignore it personally but its giving me a run for the money. I dropped the engine in in a day and have spent the past two weeks trying to figure out this dumb code. I think i mentioned it already but the former engine had this code also prior to it spinning a rod bearing. I had tried to resolve it on that engine with no luck.
 
Have you checked the power and grounds with a power probe? There appears to be a shield of some sort of the pin 85 wire that may also have a ground wire attached. Is the shield there?
It sounds like you probably have this already but here is the wiring.



Power probe ground to the pin 51 and 103 wire and probe + to the 71 and 97 wire.
 
Trav - I can't see a shield but it may have it. Up at the ECM connector there are no shields on any of the wires. It appears that there are 2 or 3 shields that come together and are tied to the chassis ground next to the ECM. Remember that when I put an oscilloscope on pin 85 I have a pulse signal - a square wave that varies in frequency when I rev up the engine. So it appears that this fact would eliminate wiring errors or omissions.

Some people have suggested that the ECM will throw this code if the CPS is out of sync with the crank signal but others say that's not the case. I'm thinking about pulling the whole thing out and starting over by putting the engine at TDC on a compression stroke and re-aligning. Part of me thinks that isn't going to help but its about eliminating the possibilities it seems.

Trav - do you have a wiring diagram for the whole ECM that shows all the circuits including the CPS? I could use one.
 
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