Cranking but wont start, just replaced heater core...

[Burton85 0]

Replaced my heater core last night, which was oh so fun, and came out to flush the coolant and refill this morning and now the truck will not start. It just cranks and cranks...When I dropped the dash I unhooked the 2 wiring harnesses from the column, the vacuum lines from the hvac controls and the 2 heater fan connections. Under the hood I had to disconnect and remove the computer on the passenger firewall to get to the heater box bolts. Other than that I can can't recall any other wires that may have been missed in re-assembly. Currently truck is sitting 80% drained of coolant with the lines off, fuel pump is working fine. I kicked on the heater controls to check and it is stuck on the defroster but shuts down when I turn the knob to off. :shrug:Hopefully a rookie mistake that's an easy fix! Any ideas???Thanks,Josh

[dripley 3,175]

As one who will be doing this soon, I cant help. But from your descriotion of what you disconnected I would almost have to believe it is in one of the harnesses you disconnected from the steering column. I sure someone with more knowledge of this will be along shortly. I will be watching this thread a learning with you.

[Burton85 0]

As one who will be doing this soon, I cant help. But from your descriotion of what you disconnected I would almost have to believe it is in one of the harnesses you disconnected from the steering column. I sure someone with more knowledge of this will be along shortly. I will be watching this thread a learning with you.

The biggest hassle of the replacement was all of the parts that had to be moved to get to the core. Aside from that it is a relatively easy repair...well, minus the not-starting-when-complete part... My first thought was that I tripped something in the computer module on the firewall (exterior pass. side) but I have done every reset sequence that I can track down with no luck and no codes are coming up on the pcu/ecu test. Ill try popping the column harness again just for grins I guess...10th times the charm??

[dripley 3,175]

Have you cracked one of your injectors open just see if any fuel is getting to the engine? Possible you popped the fuel system relay? If you are getting no fuel swap the relay with the another relay in the pdc and see what happens.

[gassernomore 15]

How are you checking for codes? On an 01 the key trick is un reliable for getting the codes. What is your fuel PSI? I was thinking along the same lines as Dripley, Check the fuel system from front to back. I believe it is a 40 amp fuse in the PDC.

[Burton85 0]

I have not cracked any injectors yet. As for fuel pressure, I have not put a gauge in the truck yet so I dont have a clue on that. I will check the lift pump and injectors after I look at the fuse block. Kind of frustrating as it was running perfectly before I started working on the heater core, aside from the leak...

Thanks guys. I will let you know what I find out.

- - - Updated - - -

How are you checking for codes? On an 01 the key trick is un reliable for getting the codes. What is your fuel PSI? I was thinking along the same lines as Dripley, Check the fuel system from front to back. I believe it is a 40 amp fuse in the PDC.

I just used the key trick for the codes. I called Oreilly about a scanner and they said theirs only works when the rig is running.

[dripley 3,175]

i understand the frustrattion. I have many knots on my noggin from:banghead::banghead::banghead: and more than a few from:doh:.

[Mopar1973Man 6,889 5 Vehicles]

Check error codes it might give a clue to what's wrong. A lot of different wires will cause error codes if there are still unplugged.

[Burton85 0]

Well, I know it has been a bit but I fixed the problem somehow. Rookie mistake I guess but once I refilled the coolant it just started up and works great now. Engine must have a coolant level sensor or something. I felt rather dumb after that was all it took. Thank you everyone for your ideas and help. Heater works great now!

[Mopar1973Man 6,889 5 Vehicles]

Actually there isn't a coolant level sensor on these trucks. http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/26-engine-systems/87-dodge-ram-turbo-cummins-24-valve-engine-wiring There is only a handful of sensors a few temperature sensors (ECT and IAT), few speed sensors (Crank and/or Cam), Oil pressure and basically thats it...

[GSX455 6]

Same problem, replaced heater core, but did not unplug the PCU, just moved it out of the way. Hooked everything back up, and went to start, something popped and now the batteries, dash light are dead. Where could the short be? did I burn out the PCU, when I hooked up the battery? I looked at the fuses and relays, and none of them was burned up. One blue relay in the drivers side fuse panel clicks a lot when I tried to jump it.

[king3500 0]

Im doing my heater core soon.. I guess I need to be extra careful

[YabbaDoo 70 3 Vehicles]

I live in Florida and I bought the truck with a bad HC... Really in no rush to fix it either:cool: After all, the HC in my GMC has been bad for about 16 years and I seem to do fine without it in Florida... The only thing that is mandatory for Florida would be the A/C:thumb1: Even while on vacation up here in Virginia I seem to be doing fine without the HC... I have a from Harbor Freight that keeps the windows from fogging up..

[IBMobile 1,748]

One thing I've learned, if you'r going to unplug ecm's pcm's ecu's or another control unit in a vehicle is to disconnect the battery. I've seen voltag spikes over 100voltes when a control unit is pluged back in with battery voltage going to it. The newer vehicles with the can system (combined area network) are even more sensitive.

[Ilikeoldfords 189 5 Vehicles]

Whenever I am doing any work with electronics on my truck, I always unhook the batteries for this reason. Even if I'm just installing a gauge with a light or anything. Its not worth shorting something out somewhere and having to fight those headaches.

[GSX455 6]

When you do your heater core, make sure to route the black vacuum line outside to engine compartment near the evaporator outlets. Unhook the steering wheel harness, too. The negative battery cable was corroded, a replacement cable fixed the problem.

[santan40 11]

Check out my post's in 2nd gen power train -----At the end of my rope, At the end of my rope (more) and the most interesting At the end of my rope Victory!  I replaced the lower dash and the heater core. Would crank but would not start. Ended up being a wire that got pulled out over by the emergency brake that I had removed to drop the dash.