So, this truck has been an ordeal since it started to lose compression and leak coolant at 130k miles. I decided to rebuild the engine instead of just buying a crate motor because it had been my uncles truck and for some reason I wanted to keep the original block for him. (left it to me in the will years ago, absolutely he wouldn't have cared if I'd just bought a crate but here we are).

I basically followed Hughes' guide on how to build up a magnum engine except I didn't stroke it. I've got it all back together after the mechanics that I tried to have do the job either couldn't/wouldn't finish the job. 3 guys quit,1 died (rest in peace buddy), the last guy ran out of time because the owner of the shop sold the shop. So, after two years of them occasionally working on it, losing almost every single bolt from the engine bay and many parts (lost parts include: cats thieves cut off, oil tube and dipstick, oil pump, oil pickup tube, distributor gears, battery, two oil filters, the coolant overflow bottle, all of the sensors on the throttle body and the flex plate (and someone broke what was left of my dash stealing the aftermarket stereo)), it's back in my driveway. The good thing is the engine was assembled and turned smoothly when manually spun. (I was there a lot pushing them to finish it and helping them the last few months so I know it was turning smooth.) I had sent the block to be bored, decked, honed and the crank balanced by a race motor shop. Set of EQ heads that I had polished for good measure. It was in the truck and was nearly finished being hooked back up when the shop shut down for good.

I finished making sure everything was bolted up, the grounds at the back and front of the motor are attached. I drained all the oil and filled it with break-in oil just so I would know the correct amount of oil is really in there. (dipstick being lost and the replacement not sliding in and out properly so I'll fight that later) I filled the other fluids, put my other truck's battery in it, gave it enough power to update the computer to the tune I purchased. Then I jumped the fuel relay to drain the tank of the old gas. Put in 5 gallons of fresh 91, waited for a warm day and rolled the motor over by hand a few times. I turned the key and waited a few times to let it pressure up the fuel system. Then tried for real and it started to crank and then sputtered out, did this a few times getting less life each time but was able to verify I had fuel pressure at least.

Pulled my code reader: P0031 O2 errors (from the cat theft), P0505 (IAC was missing, didn't realize), P1391 (they couldn't get the crank position sensor to clip in fully so wasn't surprised). Got and installed an IAC, put on a replacement o2 sensor even though its just hanging there since there's no exhaust past the headers yet. Clipped in the cps until it snapped in. Cleared codes.

Started again, started weakly a second then puttered and died. Now code P0123, uninstalled and reinstalled throttle position sensor. No change. Bought new one to replace the one the shop bought, installed it, truck started weakly but responded to the gas pedal, for 30 seconds.. puttered died. Would not start other than just to weakly puttering and only as long as I have the key cranked to keep the starter engaged.

Got Code 1391 again, replaced crank position sensor, cleared code, stronger starting but not really starting still. No codes.

Went to check the fuel pressure at the rail, realized I didn't have a valve, ordered one from Hypotech, and installed it. Fuel pressure sits about 50psi when trying to start. I pulled the bed, cleaned the tank, replaced the fuel pump just in case it wasn't able to keep up after initial pressuring. Maybe it was starving for fuel. Tank was surprisingly clean, filter wasn't clogged but whole assembly was yellowed with age and I had a new delphi anyway so I swapped it. 10 gallons of 91 just to be sure.. turned the key, roared to life for the first time, instant throttle response, running real smooth, was elated.. and then it puttered and died. And wouldn't start the start next time.

Another 1391 code. I cleared the code, tried it again, roared, responded, backfired and died in 15 seconds and wouldn't start again.

Getting code 1391 again. Pulled the distributor after checking the order of the plugs was correct. Removed the distributor ignition pickup (tps and cam sensor are the code), put in the stock one since I still have the original distributor. Tried to start it, puttered, checked the distributor cap fit, it was loose. Removed the cap and made sure the rotor was fully seated and nothing damaged from being loose. Put it back together tight. Tried to start, putters at me but won't actually fire up.

Replaced the coil pack since it was still original thinking maybe its starting to go and can't generate enough spark. Seemed to try harder but still won't really start. Tried a few times but can't even get it to fire up anymore. Just sputtering and dying. No codes, my scanner can't see if the TPS or the pickup are sending information but since I don't have a code I'm assuming they are.

Put the stock flash back into the computer just to see if the new tune was the problem. Zero change. I know the stock tune won't drive it but figured I'd see anyway.

Give me another set of eyes and some advice, please. I'm losing ground. After the fuel pump replacement start up I was sure I was almost there. Could 8an fuel rails on stock fuel lines be the issue? My head says no, shouldn't matter once the system is full and if the pump is keeping up but I'm to the point I'm just looking for any next step.

 

What brand crank sensor???

These trucks really don't care for the aftermarket fellers.

 

The Crank position sensor is Duralast. The cap and distributor are Blue Streak but I pulled the distributor ignition pickup from the stock distributor and put it in. The throttle position, airflow and iac are all duralast as well. I used a duralast IAC on this truck about 20k miles ago and didn't have any issues with it. I hadn't replaced any of the other sensors before the rebuild so felt comfortable using DL. As i'm reading more and more people have trouble with any after market sensors though.

With no error codes at all now I'm hoping those are CPS and DIP aren't the problem but I'm open to the idea they are. I'm trying to get my hands on a better scan tool to see if the fuel sync is lined up correctly or if I need to take this to the dealership and have them set it and get it running finally. The mechanic did set it to top dead center on one, I went ahead and verified it myself this morning just to see. I figure it should at least fire up at least and then shut down with sensor issues but if something isn't reading consistently then yeah, no joy at all.

 

Still have the old sensors? I would be tempted to reinstall the old crank position sensor.....

Verify you have power at the coil while cranking.....

 

I do have the old crank sensor still but it was in there at the start and was throwing the P1391 code which is why I replaced it. I guess I could put it back and see if maybe the code was from the distributor ignition..

 

Worth a shot, though, I know how much fun that is to change.......

 

I went ahead and ordered a new one from Mopar, I won't have a chance to work on this until next week anyway so we'll hope its a 'just one more time' situation for swapping out the CPS. I can't find a MOPAR distributor ignition pickup but I can go to the junkyard and get one if the CPS doesn't improve the situation.

 

Mopar couldn't make up their mind what they wanted to call it. Sometimes, it's cam position sensor, other times, its pickup-coil.... They *should* still be available, but, it isn't quite as critical as the crank sensor..... It only changes state once per revolution.

 

Okay, new MOPAR crank position sensor in.. zero change, zero codes. Still can't get that good fire up even once.

 

Are you getting spark? Injector pulse? Does the fuel pump run while cranking?