I’ve scoured the boards, google, and YouTube. Not finding any new/helpful information on my specific scenario. Any help offered would be greatly appreciated!

I drove my son’s truck this morning. Ran great, was in and out of it a couple times. I was about to head home and started truck up with no issue. Remembered I needed to make a call first, so shut engine off - 5 minutes later I tried starting it up with no luck. Had no issues leading up to this, truck has ran great for quite a while.

I had truck towed home and checked easy stuff first. 12.8V at battery. Inertia switch had not been tripped. I checked Schrader valve at fuel rail and had fuel w/ good pressure. Tried the 50/50 method w/ some ether just to make certain - no luck. Pulled a plug wire and checked for spark coming in from coil. Nada. I happened to have a spare coil so swapped that out - no luck. The starter sounds strong when cranking. So seems like the culprit was probably a bad crankshaft position sensor. Ran down to O’Reilly and grabbed one - they only had the aftermarket version in stock (Standard Ignition Products) so decided to chance it. Replaced when I got home with no luck. Oh, I also went through fuses and checked anything related to ignition, pcm, fuel, etc..

I’m banging my head against the wall. What are the chances the cheap aftermarket sensor is bad out of box? If it’s not the sensor, I’m left to assume it’s a PCM issue. Which, I’ve never dealt with.

My only other thought is if PATS could be to blame? I have two programmed keys. I’ve tried them both. I even waited two hours in between to make sure I hadn’t been locked out due to the 90 minute setting after two many attempts. Still nothing. The theft light blinks once every 3-4 seconds while vehicle is off. It turns solid while cranking for about 3-5 second and then goes away…?

The CEL light stays on while cranking, and tachometer isn’t registering any RPMs. So, I feel like all indications point to the sensor. But again - replacing it didn’t help (unless bad out of box). If sensor is fine how do you explain the PCM just suddenly going from working to fried within one ignition cycle?

 

Update - I probed the harness at the CKP Sensor. It reads between .9-1.1V AC while cranking. So, that seems to indicate the new sensor is fine.

I have power into the ignition coil. But no spark coming out of it. As mentioned yesterday, I’ve tried swapping the coil with no luck.

I have good compression.

Scan tool shows no DTCs.

Is the PCM the only other possible source? Is there a way to test mine to confirm?

What about camshaft position sensor? Would that play into it at all?

 

check power from the cam sensor? when trying to start, turning over motor does the CEL go out?

 

From recollection:
The plug which powers the coil has one hot and I believe the other 3 connections are grounded.
The "shade tree test" involves seeing the tester flash as each of the 3 'doubled up' coils grounds.
I've never done this test, but I believe the PCM does the grounding.

 

not sure but makes sense like the old days with points. and I think the cam sensor tells the PCM when to fire them. there 3 coils one for 1-5 2-6 3-4 its a waste system 1-5 are at tdc the same time but only one of them need spark at that time.

 

I thought I would go ahead and close this one out. I know it's nice in the future, when someone needs help troubleshooting, to have a resolution.

As previously mentioned in my initial post, I was unsure if the Cam Position Sensor (CMP) played a role in creating spark. After a ton of reading and scouring of diagrams, I was fairly certain it does not. Purely out of curiosity, I did check the resistance of the CMP with my Fluke. It showed around .485 ohms. I also probed the backside of the harness to check voltage during the crank/no-start. I don't recall the specific voltage it showed, but it was enough to make me confident it was working. So with all of that information, I made the determination the CMP was probably not the issue, and opted to save the $60 O'Reilly's wanted for an aftermarket CMP.

This crank/no-start situation was unlike any of the ones I was finding in old threads on this forum (or the others). More specifically, unlike the others, my Check Engine Light (CEL) was staying illuminated as I cranked. I was also NOT registering any RPMs on the tachometer. It was for those reasons that my first knee-jerk reaction when this all started was to assume a faulty CKP. As we now know, replacing it didn't solve squat. As I began to actually troubleshoot, I verified resistance of the new CKP as well as the output voltage. I had good voltage from the battery through the starter and up to the coil. But no spark out of the coil. Further diagnostics showed the harness into the coil had 12V but DID NOT pulse ground while cranking. With all other known conditions (ie, fully functioning CKP and CMP sensors) it seemed to indicate a bad PCM. But from my understanding, a truly bad PCM is a rarity. It further confused me that truck had been running totally fine leading up to this: no check lights, misfiring, prolonged cranking, or anything else abnormal. It literally went from working perfectly to not working at all in the span of one ignition cycle. So I was skeptical to say the least.

The only other possibility I could find was where some folks with crank/no-starts were finding their harmonic balancers were to blame. But in all of those scenarios, the truck had not been running prior to troubleshooting (ie, engine replacements and/or trucks purchased in non-running condition). Mine had been running perfectly for months. I had also replaced my harmonic balancer with the newer version last winter when I replaced a blown engine with this low mile engine (along with everything else: timing chains, harmonic balancer, water pump, gaskets, belts, hoses, plugs, wires, etc, etc, etc...). So it seemed unlikely that the engine ran perfectly for months after doing all of that, and then one day decided to reject the harmonic balancer.

With all of that in mind, I opted to go the PCM route. Interestingly enough, when I pulled out the old one I noticed a "remanufactured" sticker on it. It also failed to have any of the normal part number information. That seemed note-worthy to me. With no part number to go off, I wasn't exactly sure which PCM version I needed - so I didn't feel confident in shopping the junkyards. It made my decision even easier when a search of car-part.com showed nobody seemed to have a PCM for a manual transmission, 4WD, 4.0L Ranger. With that, I opted to go through Flagship-One out of New York. They flash secondhand cores based on your specific VIN. They sold the PCM w/ a set of chipped keys for $265. I opted to pay another $65 for 2 day shipping, as this all happened 8 days before my son turned 16 - and is itching to get behind the wheel on his own. Flagship One took like 6 business days to actually ship the item out - which was frustrating. I received the new PCM this afternoon, ran down to town and had the blank keys cut, and back up to the house to throw everything back together. The new computer came with easy directions for pairing the new keys to the PATS system without having to take to a dealer or locksmith for programming. As soon as I had that done, I cranked her over. Started right up and runs/drives perfectly.

Moral of the story... I guess a computer actually CAN go from perfectly operational to completely non-operational in the span of one ignition cycle for seemingly no reason. I'd be interested to know if it had something to do with the old PCM being a remanufactured unit. The good news if that was an issue, is that the Flagship One purchase comes with a limited lifetime warranty. So if it does ever lose it's programming or whatever in the future, I can send it back to be re-flashed for free. But, I'd prefer to just not have to deal with it again. LOL. Anyway - I hope this helps somebody in the future.

 

huuuum but no codes? I dont know how to know how to ck for that. you have an OD2 reader and an APP to see whats going on ?

 

One other thing, could it be the PATS if I’m right it turns off the fuel. I was just trying to think of other things that might be

 

Not sure if you saw my most recent post, but the problem was resolved. It was the PCM.

 

sorry, im not much of a reader. so how did you figure it out or did you just guess ? glad you got it fixed.