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1996 Bronco XLT, 5.8, Auto Everything.
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Discussion Starter · #1 · (Edited)
I was driving, everything was good, and then the engine died like someone flipped a light switch. No stumbling, no idiot lights, just totally dead engine.

It cranks, the battery is good, but it won't start, although it does "cough" every now and then.

I'm trying not to panic (timing chain/rebuild/buy a jeep), so I'm working to come up with a list of things I can check to debug in an organized fashion.

The ford service manuals (I have 3 of the 4, 4th is on it's way) leave out a lot of possible causes, mostly considering themselves with the serious mechanical problems. I assume the relay/diode/electrical system fixes are in that 4th manual... so I'm doing my best to do this as an engineer, not as an idiot with some tools in his garage.

a "fishbone" chart is a list of all the possible causes of a problem, how to eliminate them from consideration, and how to tell if they are the problem. This is what I've come up with so far. The problem came on so suddenly and completely, I'm leaving out things that are likely to cause slow degradation of engine performance.

Potential CauseHow to testTest result if actual causeActual test resultNotes
2 diodes in the engine bay, if one is bad PCM may not be poweredtest diodes with meter, clean socket, reinstalldiode will indicate bad on meterboth diodes good. sockets cleanNot the problem
several relays in the engine bay controlling things like PCM, fuel pump, etctest relays or replace with stock-on-hand. clean socketsall relays replaced/verified, problem goes awayTest complete. All relays good.Not the problem
many fuses in engine bay, bad fuse on wrong circuit can kill vital engine systemscheck all fusesbad fuse needs replacement, engine startsall fuses goodnot the problem
timing chain brokencrank engine, observe distributor rotorrotor will not rotaterotor spinsnot the timing chain!
broken rotor in distributor, broken capinspect distributor/cap/rotorsomething will be brokencap and rotor are good, had truck tuned up about a year agonot the rotor
fuel pump not pumpingbypass FP relay, measure current to pump, listen for pump runningpump won't pump
other non-specific fuel system issuecheck fuel pressure per ford specfuel pressure will not meet spec
coil no make spark/weak sparkuse spark tester on coil wireno spark indicated with properly set spark testerNo spark at coilWINNER. Further testing reveals the coil, itself, is the problem. Will R&R.
coil wire to dist. badcheck resistance of coil wire to disthigh resistance3.7KOhms, which is correct for a cable 1.5' longnot the problem
something to be found in the OBD codesread codessomething enlightening will come outZero codes held in systemNot the problem.
check engine computer for damageremove and inspectdamage, exploded caps, fire, etc
 

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1995 5.8, 2.5" Rough Country Lift, Extended RA's, 4.10's, 33" BFG's
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Yo BIG,
If you have or can borrow a Diagnostic Trouble Code scanner, use it.
Inspect the air cleaner and inlet ducting. Check all engine vacuum hoses for damage, leaks, cracks, blockage, proper routing, etc. Check EEC connector & wiring harness for proper connections, bent or broken pins, corrosion, loose wires, proper routing, etc. Check the Powertrain Control Module (PCM), sensors and actuators for physical damage. TPS, ICM, DISTRIBUTOR, etc.
Check the transmission fluid; engine oil level and quality. Make all necessary repairs before continuing with Code TEST.
Engine Perpetrators:
  • Difficult Starting
  • Burnt valve.
  • REPLACE valve.
  • Worn piston.
  • REPLACE piston.
  • Worn piston ring(s).
  • REPLACE piston ring(s).
  • Worn cylinder.
  • Damaged cylinder head gasket.
  • SERVICE or REPLACE cylinder block.
  • Malfunctioning or damaged fuel system. And ignition system
    Rectangle Font Screenshot Software Parallel
    s

  • See table 3: will be back tomorrow
  • Font Rectangle Material property Parallel Screenshot



  • REPLACE cylinder head gasket.
  • REFER to Powertrain Control/Emissions Diagnosis Manual OBDII.
 

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1996 Bronco XLT, 5.8, Auto Everything.
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Discussion Starter · #4 ·
Updated the fishbone chart. All the relays are functioning properly, I still replaced a few just because I had them on hand, and the OBDII reader indicates 0 codes held in the system. I even cranked it and re-read the codes to be sure.
 

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1995 5.8, 2.5" Rough Country Lift, Extended RA's, 4.10's, 33" BFG's
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You need to see if the spark plugs are sparking.
 

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1996 Bronco XLT, 5.8, Auto Everything.
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Discussion Starter · #8 ·
You need to see if the spark plugs are sparking.
I figure, it's not going to be one or two plugs, because the engine is D-E-D dead... so I plan to start that process at the coil. Good chance I'll be able to check it tonight, in fact.

Frankly, now that I know it's not the timing chain, I expect whatever the issue is, I can find a way to handle. Even if it's soldering capacitors onto the engine computer or dropping the fuel tank, it'll likely be some kind of tractable problem.
 

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1995 5.8, 2.5" Rough Country Lift, Extended RA's, 4.10's, 33" BFG's
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I meant just checking for spark whether at the plugs or the coil not check all the plugs.
 

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You need to see if the spark plugs are sparking.
I figure, it's not going to be one or two plugs, because the engine is D-E-D dead... so I plan to start that process at the coil. Good chance I'll be able to check it tonight, in fact.

Frankly, now that I know it's not the timing chain, I expect whatever the issue is, I can find a way to handle. Even if it's soldering capacitors onto the engine computer or dropping the fuel tank, it'll likely be some kind of tractable problem.
I’m in agreement with @JScatt. An engine needs Air, Fuel, an Spark to run. The description of the engine dyeing sounds like no spark. So first thing you do is verify spar on #1 cylinder. If no spark, @miesk5 will post how to test the ignition system.

distributor turns, so not a broken timing chain, distributor drive gear, or seized engine.

Since you don’t have any codes that almost eliminates a fuel problem, but check the fuel pressure any way. If good fuel pressure, get a noid light and test the fuel injector harness to see if the injectors are receiving the signals to open and close.

Now I’m going out on a professional limb here. When the engine dies as if shut off by the key, usually 1 of 2 things happened. 1) The ignition Control Module Failed, or 2) the ignition switch has a problem (usually bumped out of adjustment or came unplugged, rarely burnt contacts but still possible).
 

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1996 Bronco XLT, 5.8, Auto Everything.
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Discussion Starter · #11 ·
No spark at the coil. Got me one of them fancy adjustable-gap spark testers, and tested it all the way from the mfg's suggested position to almost a dead short. Even tried the stick-a-screwdriver-in-the-wire move just to be sure.. As stated above,now I can make better use of the billion debugging paths in the manuals, and as presented by @miesk5 ...

Hopefully it'll be the coil, but since that is just a big coil of wire and insulation, my money is on the electronics.
 

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1995 5.8, 2.5" Rough Country Lift, Extended RA's, 4.10's, 33" BFG's
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Next you should check power to the coil. Here is a good trouble shooting guide for no start problems, scroll down and click "No start trouble shooting". If it is a bad coil replace it with a Motorcraft. These coils fail more often than you would think especially if its a aftermarket or non Motorcraft
 
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Check for power at the coil… like I said… it’s either the ignition control module, or a fault in the ignition switch… very rarely does the coil itself fail… and when it fails it’s obvious… smoked wires, bulging, split housing, ect…
 

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Discussion Starter · #15 ·

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Discussion Starter · #17 ·
I'll keep debugging this, because it's become an interesting exercise, but an interesting thought just occurred to me: whichever part it is I replace, all the other parts in the chain from distributor to ICM to coil, are 26 years old with over 200K miles on them.

Rockauto has Motorcraft replacements for all the parts, except the distributor. Depending on which distributor I choose, I could replace everything, from plugs to distributor, for about $350, and most likely a long weekend day of work. I even have a timing light around here... somewhere...

Given how terrifying it is that a single break in this chain can kill my car like a pissed off Chuck Norris, am I better off replacing only the broken part, or replacing everything?

(edited to add: a 2nd interesting thought: am I better off with a cardone/autoline distributor, or is there a way to get my OEM Motorcraft one rebuilt to try to get some more time out of it?)
 

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I haven’t had decent luck with Autolite Dizzy, but… if the distributor shaft doesn’t have any side to side play, you can rebuild it yourself… just get a new PIP sensor.

Coil- replace it if it’s bad
ICM- Replace it
Pip- Replace it

I personally would go aftermarket Mallory, Accell/Holey, MSD. If there was a problem with my Dizzy… Again this is coming from close to 30 years in the industry… throwing money at parts (distributor and coil) that typically last 300,000 miles (or more) just doesn’t make sense to replace them in a whim.

Check voltage at the coil, if no voltage present replace the ICM and check for voltage at coil again. If no power still at the coil, your engine control unit (ECM) is toast.
If voltage is present on the coil , then either the PIP or the coil is bad… test the ignition coil.
If Ignition Coil test comes back bad replace the coil
If Coil test good, replace the PIP.
 

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1996 Bronco XLT, 5.8, Auto Everything.
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Discussion Starter · #19 ·
Holy crap, I think I got through this about as lucky as I can...

The driver's side pin of the coil's 2-wire-connector had a steady 12 volts.

The passenger side pin of the coil's 2-wire-connector flickered a test light in a fast, steady rhythm when I cranked the engine over.

as I understand it, that means the coil must be bad.

I'll likely replace the ICM as well, since I've been digging around in here quite a bit for the past couple days, and I don't want to do this again if I don't have to. :)

Also, I checked the fuses in the power distribution box (all of them... with a multi-meter) and they were all good. One got a bit of a cleaning, but that's it.
 

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Testlight flickers when you turn the engine over… pip, ICM, Coil, ecu, are all good. Either bad coil wire to the distributor, or broken rotor
 
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