Chasing a no run situation, need to verify a few things.

[mopar346]

Good evening all,

It seems I am involved in another 1 ton square body, This is a 87 2WD 3500 tow truck, hydraulic boom and wheel lift, FI454 & SM465 (I think). Fairly solid truck but it hasn't run in about 2 years, pulled into the shop one evening and when they went to back it out the next day it was blowing the ECM2 fuse. They replaced a bunch of iginition stuff and never figured it out. My son in law is interested in buying it but we wanted to make sure it woul run first. A quick list of parts replaced: ECM, dist module, coil, fuel pump relay, fuel pump, rotor and cap, best I can tell that is it. He brought it to me late yesterday and I began to play with it. I jumper wired a 30 amp circuit breaker in the ECM2 fuse hole and it didn't trigger so I knew I wasn't dealing with a hard short. I primed it and got it to fire and run with a little gas to dribbling from the injectors. After that the fuel stopped dribbling, since I knew I wanted to clean out the tanks before I went any further we stopped at that point it we closed the hood and started figuring a game plan. Today I began to track down the fuel issue, found the tank selector switch bad and a bad connection inside the driver's tank at the fuel pump. I repaired all the wiring, cleaned the tank out, jumped the switch and made sure I had fuel at the back of the throttle body. I also removed the injectors, cleaned and tested them. After reassembling everything I have no fire and the injectors wont pulse. I verified power to the coil, swapped out the dist module with a known good one and still nothing, same with the coil. On the off chance my known good module was bad I had the original tested and it was good. Tomorrow I am gonna replace the stator.

Here are my questions.

Is there a good woring diagram posted somewhere on the forum?

Should the injectors pulse once when the key is turn on like the fuel pump relay energizing? Where does it get its signal for this pulse?

Does the injector run pulse come from the stator like the firing pulse does? If not where does the signal come from.

Keep in mind I am an old car guy use to very simple electrical systems and carburators, my electrical test equipment consist of a test light and jumper wires but I'm pretty proficeint with them, not sure I even know how to operate a ohm meter.

Thanks in advance, for reading the whole story and for any advice you can give, Kevin

[slug]

The fuel pump will only run a short time without the truck running. Check the wiring coming from the distribution block on the fire wall and the small wires goong to the starter. They are fusable links.

[Gregski]

Originally Posted by mopar346

Keep in mind I am an old car guy use to very simple electrical systems and carburators...

Kevin

Well Kevin that's why I bought a '74 all you need is spark and fuel (I know guys say air too, but unless the truck is under water it always has air, LOL)

wish I could help you but your truck is about a decade too young for me to wrap my mind around the electronic carburetor that I'm sure is in there

did you just take one spark plug out and ground it to see if you got spark at the plugs

when you replaced the cap did you put the wires back on in the proper firing order, don't mean to insult you but sometimes it's late in the day sometimes you are too frustrated to double check, mistakes are made

just trying to help

[D13]

The ecm needs to see ignition pulse to fire the injectors. The fuel pump just runs to prime until there is oil pressure.

Based on your symptoms you have an issue in the ignition circuit. Modules are most common, I used to use ONLY Delco as the aftermarket did not have the same level of internal circuit protection. Worn distributor, back pick up coil, or a loose wire would be next.

My quick and dirty check was to dump a little gas down it, hold the throttle open and crank. If it started at all the fuel system, if it didn't ignition.

[mopar346]

Thanks guys for the input.

Slug, Fuel relay energizes and kicks out at about 3 seconds as it should, fuseable links are something I haven't thoguht about.

Gregski, I'm with you, my square body is a 88 C&C with a carburetor with the older style HEI so it up my alley. Yes, actually used a spare plug ground to the exhaust manifold, sparked on Friday night, didn't yesterday after I went throught the fuel system. Plug wires were never off in my possess, all the parts were replaced on the previous attempt to get it running before I put my hands on it, so if it busted off Friday night should've done the same Saturday. I'm not one to get frustrated with these things anymore, I know it accomplishes nothing and clouds my thinking.

D13, D13 is the option code for a 3 speed floor shifted manual trans on 69 and up Mopars. Priming was the first thing I did Friday night when I busted it off, so that with knowing that the fuel system had set for 2 years is why I first addressed the fuel system. After I put the fuel system back together and didn't get a spritz when I turned the key on I primed it again, no start, tracked it down no spark, so definitely ignition at this point.


I am thinking that with some of my picking and poking on the electronics of the fuel system with the test light or jumper wires I shorted something in the ignition. The other thought is that due to me having a 30 amp breaker in the ECM2 fuse slot instead of the 10 amp fuse it uses, I may have smoked something, although it would surprise me that 30 amps would smoke anything.


Follow up question:
Would a intermittent/bad stator cause the ECM2 fuse to blow? What is know to cause them to blow?

Thanks again, keep the suggestions coming, I'm gonna start back on it here in a little bit.

[mopar346]

I checked the fuseable links they were all good, I pulled the distributor and replaced the stator and it started right up. Moved it around and into the shop since I had been in the yard where the moron wrecker driver dropped it with dragging brakes. Went to work on the brakes and replaced the front hoses and after awhile of sawing the steering back and forth for bleeding it blow the ECMB fuse (the one I have been calling ECM2). Hmmm......wonder if it has any relationship or just coincidence. Once I worked around that by putting my circuit breaker back in it doesn't have fuel pressure again.

I don't think I am gonna work on it again til Tuesday evening, I know the steering column has issues cause the from tilt column has a band around it like a rubber PVC clamp and no lights other than the high beams so I'm gonna pull it apart and see what the wires in there look like. I know I have somethings to solve in there so maybe it'll fix more stuff in the process.

[mopar346]

I'm sure hoping someone is still looking at this thread and can verify something for me. The tan w/white tracer wire coming from the fuel pump relay is the power supply wire for the fuel pumps correct? It runs through the buckhead connector to the hot fuel module and the fuel tank selector switch correct? And with the selector switch and module unplugs and it pulled out of the fuel pump relay connector it should be an open circuit with no connection to anything correct? So if it is a hard ground it is shorted somewhere in the wire correct?

It went back to blowning the ECM2 fuse as I said Sunday night and in the process of tracing down the short I disconnected the pumps, the selector switch, the switching valve under the truck and still it blow. I disconnected the hot fuel module and it still blew, I disconnected the ECM it didnot blow, I reconnected the ECM and it blew, I disconnected the relay and it didnot blow. I reconnected the relay but removed the tan w/white wire from the connector it didnot blow, tested that wire and found it was a hard ground. I threw power to the test lead and where the wire would connect was hot, I turned the key on and it energized for 3 seconds and went out as it should when the relay cycles. I threw power to the tank side of the selector switch connector and it energized the pump I was on. I am convinced that there is a short in tan w/white wire. What do you think?

[buddy_1]

Here are some electrical diagrams for the power train.

[buddy_1]

Here's a couple for the fuel system.

[mopar346]

Thank you, I have the one similar to the top fuel system one you posted except it is for dual tanks. With that said, I am really looking for someone with a lot more knowledge than me to confirm that I am reading the diagram correctly and their is no other place the tan w/white wire can get ground except to be shorted. Again, it is unplugged from the relay, the hot fuel module and the selector switch, so the in cab and under hood section is isolated and it is showing a hard ground. In the diagram it shows the atn w/white as being a power wire and should not go to ground under any circumstance, correct?

Thanks again, Kevin

[mopar346]

Well I found it! The answer to my wuestion was no it should not be grounded. I traced it down to the wiring that goes back to the tanks, there is a wire loom above the driver's tank and it was pinched at the tank bracket, not sure how I missed it when I had the tank down but that is why it quit blowing the fuse for a few minutes after I dropped the tank to clean it. Fortunately I was able to loosen the tank and move it although outbaord to get the wires down to repair them properly. The illusive part of the wiring was that the dual tank selector switch plug in the cab runs back out the firewall and back below the truck. I did pull the instrument cluster to gain access to the dash harness and once I could see where the switch plug was routed I realized it went outside and then the tracing was basic. Fired it up after the repairs, runs fine. I have some reassembling to do tomorrow night but I feel good about what I found. Now onto the inop tail and running lights, the headlight switch was real loose so I am starting with that and the then I check the turnsignal switch if that doesn't cure it.

Wish me luck!