I have my 97 f 150 4.2 at a garage, where the mechanic has changed out most items with new ones, but found the P0340 code triggers for cam shaft sensor.When the new parts did not help, he put the old ones back. Several burnt wires were re wrapped, continuities check good, checked with scope, checked timing, and after 1 week, nothing was found to indicate the problem. Did replace spark plugs, and truck idles smooth now, but check light will still come on, and same code shows. Alternator belt was removed to see if noise was factor, but nothing changed. Aluminum foil shield was put over wires and grounded at cam sensor, but that did nothing. Mechanic's computer showed a shield for these wires, but dealer parts said they did not see anything on their side.
Now he said I might order a new ECU to see if the old one has the code permanently embedded. Has anyone had success with changing the ECU and found a difficult to find problem, went away. I see rebuilt ones, and figure they would be a better bet than a junk yard part in this case.
thanks in advance

 

If there were burnt or chaffed wires that have been properly repaired and the code persist, it's possible that the PCM was damaged. If it were me and I had exhausted all other avenues (including clearing the KAM), I'd find a used PCM with the same calibration code and replace it.

No sense in spending extra money for a part you're not certain is bad.

 

Thanks EsJayEs... I was told to talk with the shop foreman of a local dealer repair, and find out what he thinks. I'm hoping he doesn't tell me to bring it in, as one other dealer did. I've done enough troubleshooting to explain what was done, so hopefully he'll listen to me. I'll let you know what I'm told.

 

The key in what EsJayEs told you was properly repaired wires. If you just wrapped them they may still be bad. Burning a wire will cause it to have more resistance, all the sensors operate on very low voltage, so that would be the cheapest thing to try first.

 

Thanks jgger after talking with a shop foreman for a local dealer, he said, if the sign wave looked good, grounds on various wires were present, and voltages were accurate, and the truck idled fine, then most likely the PCM was not getting a signal. I'll let the mechanic know of the burnt wire thought. When I saw it, the insulation was off on a piece about 1/2 inch, but the wire looked shiny. Contacted Rock Auto, and they have rebuilt units for about $100, if the core is sent back. Don't want to chance wrecking yard unit, for about the same price. I need to find the number on the present PCM, as there are several and with the California smog requirement, I need to be right the 1st time. If you know of a better place for purchase, please let me know.

 

Took out my computer, and thought finding a replacement would be easy. Mine is F75F-12A650-AYC. Rock said theirs was AVC, and it would not work. Does anyone know whether a computer with the F75F and auto trans would work, or do I need the numbers to match exactly. So far, I've only found some thru a wrecking yard on the East Coast. I'm in Ca.

 

Just occurred to me that you have the 4.2L V6. At any point, has the camshaft position sensor (aka "camshaft synchronizer" been adjusted? Over time as the timing chain stretches, it alters the position of the camshaft sensor. With enough slack in the chain, it's possible to cause the code.

Also worth inspecting the sensor for a crack while it's in your hand. It could still be the PCM, but I see that as a last-resort. I think you can rent the tools for free at AutoZone. The times I've replaced those sensors, the tool was included. They're different depending on the engine, but they look similar.

http://www.autozone.com/autozone/acc...er=979921_0_0_

It's easy to do. Bring #1 to TDC on the compression stroke, remove the sensor, loosen the bolt holding it in (exactly like a distributor on older vehicles), and adjust until the tool slips in. Once in, tighten the bolt holding the synchronizer assembly and reinstall the sensor.

This is why it's not a bad idea to change a timing chain at 100k-150k. They stretch over time and it retards the cam timing. It's overkill for many. Being an opportunist, I'd change the timing chain on a higher-mileage engine if the opportunity arose. Such as replacing the water pump since you'd already be halfway there.

 

Thanks EsJayEs-- The synchronizer and sensor were replaced, and then re checked with different parts, and the TDC was checked, and is correct. The mechanic I'm using has replaced quite a few parts with new parts to see whether something was bad, but when the code came back, the new parts were removed, and my parts were put back on. He has checked grounds, and actually installed a ground wire off the sensor, but still the code shows. New spark plugs did improve the idle. I drove it Sat, and it still has just a slight hesitation when you stop, and then hit the gas, but before, it would stall when at a stop sign, or stopping quickly, and then accelerating. I'm having difficulty trying to find the same ECM with the code on mine, so might send this one out to be tested for $75. That way, it could be rebuilt if needed, but at least, I'll know if it is causing the problem. Talked with a shop foreman, at a local Ford dealer, and he talked about various grounds, and what pins should have them, and they all check out. He also said, it could be the ECM.

 

Ordered a control module from J C Whitney. They guy I talked with ( India or ? ) said only one module would work, and never said it needed to be flashed. I called Cardone, the re manufacturer, and was told they had a plug and play module, and today the wrong one came, so now I'm on phone with a person from J C for the 3rd time, waiting while they figure this out. No one puts any notes in their system, to avoid the delays. So I most likely will have to drive to a Fed X store to send it back, and wait till next WED or Thur.

 

Yeah. A remanufacturered PCM has to be flashed for your calibration. The hardware itself is the same. All the more reason I'd have gone with a used one. Some local parts stores can flash them if you buy it from them. I remember a NAPA that had the machine from Cardone to do this.

 

Cardone told me, after the unit that needed to be flashed had been sent, they had a plug and play unit that would work, so it's on it's way now. Here is the response from Cardone ::: This will cross to the 78-8417F must be flashed, there is another part number that will not need to be flashed which is 78-6825. Sure hope it stops the P0340 code from coming back, and maybe help with the slight hesitation I have when I come to a stop, and then gas it. It tends to just about stall out if you don't come to a complete stop.

 

So after changing out quite a few parts, and installing extra ground wires, and making sure the timing was dead on, I replaced the ECM with a rebuilt plug and play module, that does not need to be flashed, and so far the P0340 code has vanished, and no service engine light. The truck seems to have lost the surge, and stall at the stop sign, and now starts and stops like a normal vehicle should. ... Guess that was the culprit all along.