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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: bake315 on May 12, 2018, 05:23:56 PM
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Hey guys. It's been ages since I posted anything here on the Forum, and since then I sold my '74 C20 and now I have this '87 R30. Anyhow, I was driving home oh, and I was running fairly fast, maybe 65 to 70 miles an hour, when all of a sudden it just died - almost as if somebody flipped a switch. I have yet to seriously dig into this truck, especially since I'm sitting on the side of the road at the moment, waiting for a tow truck. I'm trying to get a sense of what to start looking for as far as the cause. My initial guess is that a fuse is blown somewhere in the area of fuel delivery. I know I have plenty of fuel in both tanks, and I've tried starting on both. I did notice it seems to be a little bit odd sounding while I'm cranking, almost as if there's a dead cylinder. This engine has been super smooth and doesn't smoke, so I doubt if it's anything mechanical. I'm looking for a gut instinct from y'all. Thanks!
Oh, and one other thing - there seems to be an excessive amount of oily residue inside the air cleaner, so my second guess would be crankcase ventilation.
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welcome back, at this point it could be anything. need to check for fire and fuel, it could be anything from distributor, ecm, fuel pump, ecm or just a fuse. do you even hear the fuel pump prime when you first turn the key one? how about if you swap tanks? if no fuel pump sound check fuse ecm 2. if its good and if you have some spare wire just the little red wire on the fuel pump relay and see if you can hear the pump start then.
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welcome back, at this point it could be anything. need to check for fire and fuel, it could be anything from distributor, ecm, fuel pump, ecm or just a fuse. do you even hear the fuel pump prime when you first turn the key one? how about if you swap tanks? if no fuel pump sound check fuse ecm 2. if its good and if you have some spare wire just the little red wire on the fuel pump relay and see if you can hear the pump start then.
Hi Tim. Thanks for the welcome back. So here's what I have... I can't actually hear the fuel pump prime at this point (thanks partially to the warning buzzer - still works, surprisingly.) I thought I could hear the relay click over, but it could have been something else. Tested both ECM fuses under the dash - each tested good. Performed the ohms test on the external HEI coil - tested "0", confirmed good power getting to it. One of the very first things I tried was to switch tanks from R to L - seemed to make no difference.
Next test will be the direct hot lead to the relay and try for some joy there.
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OK... pump tested good. Relay tested good. Ugh. Starting to recall what I liked about pre-computer trucks. So, I think I can perhaps rule out fuel delivery at this point, other than checking the inline filter for an obstruction (which would have had to make it past the sock filter in the tank?) At the very instant it died - there was an audible "pop". I couldn't tell for sure, but it didn't sound like any sort of a backfire or anything like that. Is there any way to test for fire which doesn't rely on a helper being present?
I suppose I could "rent" a code reader from AutoBone and see if it can tell me anything helpful...
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Check both sides of every fuse using an incandescent test light. Give the three fusible links a firm tug to see if they stretch or separate. Make sure the distributor is tight and hasn't spun around.
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just because the fuel pump primes or runs doesnt mean the injectors are getting the signal to "fire" and that could be a distributor issue. im not sure theres much you can do without a helper turning it over for you.
after you do what BD suggested you can try other test by yourself if you have the right tools. i have used jumper cables to test for fire but pulling a plug wire and if you have a spare spark plug (or you might have to pull one from your block) and attaching one end of the jumper cable to a good ground and then the other respected end to the steel part of the plug and moving the plug to a visible spot from the driver seat and turn the engine over watching for spark.
the injector test you can do with a noid light and it will light up (also visible from the drivers seat )but most people dont have a noid injector tester. you can try to start it on carb cleaner or gas down the tbi but be careful of where and how much fuel you use.
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Give the three fusible links a firm tug to see if they stretch or separate.
Whoa! I think we have a winner! I didn't even need to tug on anything. This would account for that "pop" that I heard. Too late to fix it tonight - project for the morning. I'll let y'all know how it goes.
This place is so awesome. Great to be back!
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Trace it because fusible links don't just go for no reason. Most likely a wire on that circuit has made contact with bare metal.
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1987 Wiring Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/ST_350_87_1987_Chevrolet_GMC_Light_Truck_Wiring_Manual_Complete_11x17.pdf#page=171)
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Trace it because fusible links don't just go for no reason. Most likely a wire on that circuit has made contact with bare metal.
Yeah, I'm thinking it chafed against something as well. Finally getting out there to mess with it now.
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1987 Wiring Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/ST_350_87_1987_Chevrolet_GMC_Light_Truck_Wiring_Manual_Complete_11x17.pdf#page=171)
Thanks!
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Found the chafe. Pretty obvious this could have gotten ugly pretty fast.
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(sigh) Well, I replaced the section that fried between the fusible link and the block, verified good power above and below the link - still in a no-start status. I will replace that link anyway, since the condition of the wire going into it was a little bit sketchy anyway. I was hoping it would start and run, at least. :(
On to those wiring diagrams...
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Man, this is like trying to read Chinese...
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Did you check all of the fusible links and all of your fuses? What is it doing? Crank no start?
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Did you check all of the fusible links and all of your fuses? What is it doing? Crank no start?
Hey Vile. By the time I got the wire repaired between the link and the terminal block, it was getting dark, so I just tried it again (crank, no start), and gave up for the evening. I'm going to go back in and just replace that link completely - even though it seems to be good the wire going into it got cooked pretty badly. Going to check the others when I get home, while I still have sunlight. Fuses have all been checked twice, and are all good. Fuel delivery to the injectors is good. I'm going to focus on checking fire tonight, as I'll have someone there to crank while I watch.
If need be, I learned about the trick to check for trouble codes using the check engine light and a paper clip also.
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You do realize that the melted wire was the fusible link, correct? The cylindrical swell in the wire at the end of the fusible link ~6" from the junction block is just a molded splice connecting the original link to the factory harness. Replace the melted 6" link and splice with new fusible wire; see How to make a Fusible Link (http://forum.73-87chevytrucks.com/smforum/index.php?topic=11972.0) for details. DO NOT use regular primary wire to replace the link!
Once a new link is installed, switch the ignition on and listen for the fuel pump to cycle on for about 2 seconds before shutting off automatically. If the key warning buzzer makes too much noise, close the door before switching the ignition on.
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For background...a fusible link is a short section of wire that is smaller than the circuit it is protecting. Typically it is 4 AWG sizes smaller than the circuit it is protecting. So if you have 14 AWG wire, the fusible link protecting it is usually about 18 AWG. Now in newer years of these vehicles they switched to square millimeters (mm˛) of cross section for wire size. You can find converters online, but don't get confused with wire diameter in mm. The wire size that stated in wiring diagrams is cross sectional area or mm˛.
A fusible link is just normal stranded copper wire, but it is covered by a non-flammable insulation. Fusible links are there to protect high-current demand items on your truck, like electric fans, starters, etc. A normal fuse can't handle the high in-rush current that these devices usually demand at startup and over time will weaken the fuse and it will fail. The modern version of fusible links today are called Maxi-fuses. That is what new cars use now.
It can be hard to find fusible link in the right gauge at auto parts stores now, but you can get it easily online.
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OK, here's where I am. I made up a new 6" link using fusible wire (looks almost exactly like Vile's tutorial). It may be slightly heavy (14 ga.), but at this point I'm simply trying to get the truck to start and run, if only for a moment. Checked the link at the alternator, actually replaced the plug going into the alternator itself. Noted the distributor cap was pretty well worn and was contaminated with oil, so replaced it with a new one plus rotor. Reconnected the battery and tried to start. I am definitely getting fuel to the injectors to the point of flooding it. I have no spark. I have no idea why. I'm a troubleshooter by nature and by profession (not automotive), and this is really starting to get me down. Truck was amazing, now all of a sudden it's lawn art.
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Could it be the distributor itself? I'm desperately trying to avoid throwing a bunch of money and parts with a "hang them all to get the guilty" approach. Just don't have any solid leads. I need to know:
- which components would prevent spark in the event of their failure
- if it really was an overload on that particular circuit, what all resides on that circuit that could have failed
- whether or not those particular components are field testable by me, and what the procedure for doing so would be
If there is anything, no matter how remote the possibility, that you guys can think of, I would be very appreciative.
Thanks for all the input so far. Digging that V3500 crew, Erik!
bake315
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If you are getting oil inside the cap, replace the distributor. The pickup coil and ignition control module are inside the distributor. Your module is probably toast from the sounds of it. You can verify, start by checking for spark from the ignition coil while cranking
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If you are getting oil inside the cap, replace the distributor. The pickup coil and ignition control module are inside the distributor. Your module is probably toast from the sounds of it. You can verify, start by checking for spark from the ignition coil while cranking
Thanks, Vile. I'll let everyone know how it turns out.
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Okay. Running once again. I thought a lot about Vile's suggestion, but then I figured since the pickup coil is outside and in front of the distributor, and I'd already sprung for the new cap and rotor, that pretty much left the ICM. So, in this case, I gambled and bought/installed just an ICM, and she fired up quickly. So apparently, when the fusible link wire chafed through on the metal edge, it also fried what appeared to be the original ICM.
Now that I'm running again, I can spend time chasing my oil leaks.
Thanks again to everyone for their assistance!
bake315
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Glad you got it running. For clarification, the pickup coil is inside the distributor. This generates a pulse signal to the ignition control module which in turn controls the primary side of the ignition coil. The ignition coil is the device bolted to the intake manifold in front of the distributor.
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Glad you got it running. For clarification, the pickup coil is inside the distributor. This generates a pulse signal to the ignition control module which in turn controls the primary side of the ignition coil. The ignition coil is the device bolted to the intake manifold in front of the distributor.
Thanks for this. My apologies for the incorrect coil identification! Clearly, I continue to not always know what the heck I'm talking about. ::)