Tricky_Dick

TL/DR - listen to this video and see if you think the crank sounds so slow it would stop it from starting.

YouTube Video:
This post is my about 2018 Jeep Wrangler Sport Unlimited S with the Pentastar 3.6L v6 in it, and I have just finished a complete rebuild on the engine following some excessive engine sludge build up noticed around 36k miles while investigating a rocker/lifter type noise.

Crank, block, heads were all sent to a machine shop and, even though within tolerances, I had the surfaces faced and the cylinders touched up, crank and cams polished, and the valves all redone at the machine shop. I got those back and put it all together with new bearings, all new hardware, piston rings, seals, o-rings, gaskets, timing chains, tensioners, oil pump, water pump, etc - if you could service it I made sure it was new.

I got the engine back installed, and now we have crank but no start. I did check for spark and see that, but only noticed a tiny drop of liquid and on the plug and it wasn’t flammable so that was kinda suspect but we wondered if it was condensation or assembly lube. My brother is on the standpoint that the starter is running slow and he’s convinced that is the problem. We have replaced the starter, the battery, jumped it with another car, hooked it to a wall jumper 100A box, load tested the battery, and everything seems fine but he’s still focused on the starter being our cause.

I finally convinced him so we could look over the basics and that’s when I confirmed spark and had some questions about the fuel. While I dig into fuel delivery and he digs into ground testing and voltage drops on the starter/wiring, if you could take a listen and let me know what you think that would be awesome!

YouTube Video:

Tricky_Dick

I pulled the plug and saw I did have spark, and despite the initial concerns about fuel… I pulled the intake and shot some throttle body cleaner in there and quickly slapped it back on and gave it a start to no avail.

At this point we’re going with slow running starter and continuing to trouble shoot that since we did confirm spark and even with a booster shot of fuel in the intake we still didn’t get even a studder so I’m going to say fuel is ok at the moment and continue trouble shooting.

I know there could be a million things, but any tips are more then welcome - this is my first major rebuild so I could have overloooked something simple but I did feel I was super diligent following the FSM for the entire rebuild.

Just wanted to drop that update, thanks!!

Jay2013jk

Do you have a Code Reader? Possible Crank sensor or Cam Sensor comes to mind. Good Luck, keep updating.

Tricky_Dick

So I did just that, and pulled the codes last night and got the following 4 codes.P0345
P0390
P0340
P0365
All four of those refer back to the cam position sensor not getting proper connection.

Since it’s throwing codes for both bank 1 and 2, I’m looking further up stream to see what they have in common. As of now I’ve checked the wiring for those sensors and see 5v on each of the three pins and the ground on pin 3 so that seems to be ok but that’s were I ended troubleshooting last night and still digging in more today.

Just from experience it’s not as common for both sensors to go out at the same time so that’s why I was looking further up stream or for common things between them both - but I do wonder if I accidentally got a magnet too close to the sensors and killed them during my rebuild. I did bag and tag them, but I had parts trays and alternator close by and could have made contact at some point or another on accident… so I’m not totally ruling that out either.

Tricky_Dick

After clearing codes and playing around with the same cam position sensor errors coming back, I really focused on the common denominators. I traced back the CMP sensors to the PCM bank-2 connector and was able to sniff down what pins handled signal and then found there are two common that share the ground in the 5 V supply.

I wrote the pin outs with the PCM connector pin, the circuit that runs on, the color of the line, a description of the line, and then the pin location on the sensor. Top 4 are the 4x cam shafts, mid 3 are crank sensor, and last two are the common shared ground and supply voltage the two cam sensors share and where I see my odd resistance reading.



They all showed ok… but I noticed when doing some resistance testing that with the battery, sensor, and PCM disconnected I got a resistance reading between the +5v supply line and the ground line.

I was able to replicate this on both cam sensors, and at the PCM connection - so if I’m reading this correctly I have a short between the common +5v line and the common ground line…. Can anyone confirm if I’m reading into that correctly, or is there some other reason why I have continuity between those two lines.

Thanks!

Tricky_Dick

Just a quick update, I started to pull shit off and check for any chaffing wires and whatnot - and the resistance went away.

After plugging stuff back in and out, it seems that the connection between the ground/ +5v supply is coming from the MAP (Manifold absolute pressure) sensor. When it’s disconnected the circuit is no longer grounded.

Trying to dig into if that’s normal or not, but I did chase the pin out and it uses the same K900 shared ground circuit and the F856 shared +5v supply circuit as both CMP sensors throwing errors so I think that’s worth me digging into more for now….

Jay2013jk

Thanks for the update and all the diagnostics .. very impressive and will be very helpful when you find the "root cause". Get ready for a "Big Snow" .

Tricky_Dick

Bahhh humbug!

I traced things down and found the MAP sensor was where the connection was coming from, but removing that from the circuit did nothing but add a P0109 (MAP sensor missing) and a P0113 (intake air temp sensor missing) which was from me unplugging them.

With the MAP unplugged that shares the 5v/ground with the CMP sensors, I was still getting some connection between the two and this time it was the PCM - but I don’t know enough about them to determine if that’s ok.

Since it was back together, I decided to try a Hail Mary and picked up a replacement CMP sensor (it was only $25 at local auto parts store) and with that new sensor in I was hoping to see one sides errors vanish but that was not the case and I still have P0345, P0365, P0340, P0365

ughhhhh running out of things to check! I don’t want to just throw tester parts at things - but open to any suggestions on other things to dig into!

Tricky_Dick

Im man enough to know when I’m in over my head, and im not afraid to ask for help when I need it… and that time may be getting here very soon - but wanted to give it one more good shot at diagnosis before shelling out money for honest help.

Before I try to hire a good diag tech to swing by and look at it with me, I decided to buy an account for AllData and went with the single vehicle option to save on the enormous cost of a full license. This thing is LOADED with details to chase down these DTC codes, detailed layouts of the circuits, pin outs, wiring diagrams, related parts and systems, and a detailed troubleshooting reference guide.

I finished up working on the Jeep early and decided to learn the software and make a game plan tonight. I’m going to outline all the steps in troubleshooting again along with the expected values and a place to write my actual values down in an excel sheet I can print out and keep tabs on. This way I can systematically go though everything that could possibly be the issue with those sensor errors and the slow crank.

I‘ll keep putting our updates as I make some progress or come along with something else - but am still open to any suggestions if you have them!

Thanks!

Tricky_Dick

After fighting this issue for weeks and weeks, I finally decided to pull the valve cover and check out the cams, the tone wheel, etc and see what’s up. I can’t find any electrical fault and everything pins out ok, but I’m still getting crank no start with all 4 cam position sensor circuit failure codes.

Well as soon as I got the left bank cover off, I knew we had serious problems. I had double checked timing and everything on the bench, but after I dropped it back in the car it appears the primary timing chain has snapped. The engine cranks, but the cams are all sitting still…. So the sensors were doing their job, it just wasn’t seeing any moment on the tone wheel and assumed it was a circuit issue.

Right now the primary chain is just a hunch, but the oil pump seems to be working as my filter is full and both secondary cam chains are nice and tight still, so we shal see once I get this timing cover off. I’m kicking myself for not going back and double checking the sooner, but I’m glad I at least have an idea of the problem and a direction to work towards a resolution and not just chasing down ghost electrical issues still. I’ll provide another update as I make progress, but figured I would share this for the record in case anyone else ran to a similar problem down the road!