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Hopefully someone more experienced in the electrical side of things can chime in on this one.
My mom just bought a 96 ram 1500 with the 5.2, it wasn’t running when she bought it, but it was a clean truck, and for what the truck has and what she paid for it, it was a good deal to jump on.
Anyhow, the guy she bought it from said he thought the crank position sensor was the issue, ok $70 bucks, worth a shot. well I turned the key to the ON position and listened for the fuel pump to prime and it didn’t, checked for pressure at the rail and there was none. so I checked the 20A fuse under the hood for the fuel pump and sure enough it was blown. so I swapped it with a slightly higher amperage fuse just to test it and the fuel pump primed and the truck fired up, then shut down. now when you turn the key to the ON position, the fuel pump just keeps running, and the relays in the underhood block click like crazy until you turn the key off. and it won’t start back up. anyone have any ideas? I’m leaning towards a short in the circuit, or a bad ECM possibly, but before I start really getting into this thing I wanted to get some suggestions. thanks in advance.
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I think the larger problem is likely to be a very simple circuit integrity problem. And I’m kinda banking it’s going to be a main power with a bad or weak connection or a ground wire maybe back feeding somewhere. Start with the basics and make sure your battery has a good charge, the terminals & battery posts are clean, the cables are tightly clamped to the posts, and the cables are also clean and tight at the other ends. If that’s all good, then move on to checking primary power and ground connections at the fuse block for the same conditions.
Start with that and then we can dig deeper if we need to.
Good luck.
I’ll give that a shot. I did run the battery pretty dead last night messing with it, jumped it off my truck and it cranked good and had full power at least according to the gage. but I know Chryslers especially are really weird about low voltage. I’m gonna stop by the parts store after work this afternoon and grab a few of the 20A fuses and make sure it has all its fuses because I was doing some google-fu this morning, and it seems that the circuit controlling the fuel pump has a lot of parts to it that require proper voltage, I may have created an open connection somewhere by swapping fuses around and not having all the fuses it calls for in that distribution block.
so I did some more investigating with the multimeter and did a few other tests. and I’m 99% certain the ECU was fried. I pulled it out of the truck to inspect it on the bench, noticed the smell of electronics that’ve seen better days, so I cracked it open and 2 out of 3 capacitors were bulged and the coatings were melted nicely. so either tomorrow morning or Monday I’m gonna be visiting the auto yard and grabbing another ecu to try. I’ll post back when I make some more progress.
alright, went to the parts yard today and grabbed 3 ECU’s to try. when I got home I stuck one in the truck and fiddled with it a bit and still won’t start. however, I noticed something, if the auto shutdown relay is in and you turn the key on, it blows the 20A fuel pump fuse every time..as soon as you turn the key to on. if the auto shutdown relay is pulled out, it doesn’t blow the fuse, but it also doesn’t prime the fuel pump. also jumping the fuel pump relay to bypass it doesn’t help. I’m thinking the problem is in the ASD side of the circuit, but I’m at a loss on what to check or how to check it.
also, if I pull the fuse in the underhood distribution block that’s for IGN/RUN/ACC it doesn’t blow the fuel pump fuse either.
does it have an aftermarket security system? Some of them disable the vehicle by intercepting the power to the fuel pump and if it is fried it could explain all the issues your having.
nope, had an aftermarket radio, CB, and CD changer, none of which were installed 100% right, but I yanked all of those and still no Bueno. thing the ignition switch or fuel pump itself could be doing this? or maybe ignition coil with a short in it? dude I bought it from replaced both of the body modules that sit in the front end on the inner fenders, I have both the old ones that still work. maybe one of the newer ones are defective? I’m really at a loss on this one, electronics are like brain surgery to me.
What type of Battery are you using? What kind of draw is the system showing? I have a 96 Ram 5.2l, I would do an electrical Diag to see if it has any shorts or look for exposed wiring under the dash or hood.
its got an AC delco battery in it, the batterys in good shape. what do you mean what kind of draw? I’ve been tracing wires and looking at grounds. ground to chassis, engine, and battery all read between .5ohm and 1.5ohm. nothing looks chafed, burned, or damaged.
paracidic draw on the battery, due to a short circuit could be causing the amp to pop and draining the battery.
Just guessing I would say it is the pump or wiring to the pump grounding out and popping the fuse. Putting the higher amp rated fuse is prolly what fried the ECU. If a fuse blows it is generally a good idea to figure out what is causing it before replacing it. If it were my truck I would get a wiring diagram and figure out EVERYTHING that is on that circuit and do a continuity test from the load to the NEG batt terminal for everything on that circuit. Hopefully it is JUST the fuel pump on that circuit and that makes it much easier to troubleshoot. I can almost guarantee something on that circuit is shorting and causing all the issues. Getting the wiring diagram is the key.
If you are looking to change out the fuel pump on that truck, There are a couple of ways to do it.
First, lift the truck in the air high enough to drop the tank.
Second: unbolt and remove the bed to access the fuel pump.
ok, unplugging the fuel pump and (assuming I find the wiring back to it to be up to par) turning the key on, I can see if the fuse blows and if it does, its not the pump, if it doesn’t I’m on the right path. and getting the tank down from underneath won’t be an issue, its got like 6-8″ of lift on 38’s. I’d probably still lift the bed though, easier to get to everything all at once.
and I’m about certain that putting the 40A fuse in place of the 20A for the fuel pump is what did the ECU in, didn’t have any of the issues with the relays going nuts before I did that. so I guess tomorrow, I’m gonna start unplugging components and see if blows the fuse. if I get one that doesn’t, I guess I’ll be looking closer in that area.
The PCM is going to prime the fuel pump when you cycle the key on but it’s the ASD relay that controls the fuel pump circuit so it’s only natural for the fuse to blow under the current conditions you’ve mentioned. The power side of the fuel pump circuit itself seems to be the likely culprit for a short to ground. It’s also possible that the fuel pump itself is shorted out.
Disconnect the electrical plug from the fuel pump and then try cycling the key on with a new 20 amp fuse in place and make sure the ASD relay is also installed. (No more fuses with higher amperage or you’ll probably get a chance to use all three of those PCM’s you picked up.) If the fuse does NOT pop with the pump disconnected, you have found your short and you’ll need to replace the fuel pump.
If the fuse still pops, there’s more likely a problem in the wiring before it gets to the fuel pump. The fuel pump power wire is dark green with a black tracer on it and it’s the same color from the relay all the way to the pump if I can trust my wiring diagram. The first place I’d look for a short is at any main harness looms that get close to the exhaust manifolds. The only reason why is I’ve had a couple experiences with burnt harnesses off the manifolds specifically on the 5.2’s.
I know the Mitchell diagram I’ve been doing some research with has some misprints so just work with what I gave you for now and if you can’t find your answer in that, then I’ll try to find the OE diagrams and sort it out a little better where to look next.
EDIT: I see I’m a little late with my answer but still look at that harness near the manifolds.
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