‘93 FZ80 Engine shuts down randomly only after it’s warmed up… (1 Viewer)

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Hey oh 👋…long time reader, first time poster for troubleshooting…anyways I’ve searched and read tons of mud posts over the last 3wks pertaining to engine shut downs but unfortunately I haven’t been able to solve my issue…looking for any advice to point me in new direction/focus within FSM…

Background: i’ve had my ‘93 FZJ80 for 2 years and i’ve slowly been baselining it and just recently completed a big road-trip: Austin to Telluride to White Sands back home with only real issue was at altitude fuel tank venting and soft brakes…drove great in the heat though!

However once I returned home three weeks ago I’ve been getting this random engine cutoff only once the car has warmed up and been driven for 30ish mins…it drives great cold and warm but once it’s warm the frequency of engine shut offs increases… you can drive it…it’s doing great and all of a sudden the engine dies or you can leave it idling for 5-10mins then it dies…check out video…sometimes it’ll fire right back up most times it needs to cool down for a few minutes then fires back up🤷🏻‍♂️

Engine parts I’ve replaced last 3 wks:
- FPR, EFI relay, distributor, dizzy, fuseable links, GM charcoal canister, vacuum hoses, deleted ERG valve, ‘94 ECU,

Replaced before Colorado trip over last year:
- brake master cylinder, radiator, thermostat, water pump, clutch fan, throttle cable, cats, 02 sensors, OEM new fuel pump

No CEL or codes currently, I’ve tested IAC and it passed, I’ve checked grounds and wires for a short nothing obvious…does VSV or hoses/check valves under the manifold cut the engine off? I need to test TPS…Thoughts? Thanks for any support!
 

Road Apple

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I’ve had a similar issue, which a new fusible link fixed. I’d still guess something electrical.

Sounds like you did a good job of troubleshooting. Did you test the ground wires with a multi-meter or just visually inspect them?
 
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baldilocks

Battle Ground, WA
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Bump

I’ve had a similar issue, which a new fusible link fixed. I’d still guess something electrical.

Sounds like you did a good job of troubleshooting. Did you test the ground wires with a multi-meter or just visually inspect them?
Were you able to view the video? I was not. Knowing in what fashion it dies would help.
 
Last edited:
Joined
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We’re you able to view the video? I was not. Knowing in what fashion it dies would help.
Link is working for me…in the thread and when it sends me to YouTube 🤷🏻‍♂️

Anyways, if I’m driving RPMs will drop straight to zero and then the xmas tree of lights comes on the dash a second or 2 later and engine is dead…I have to coast it to a safe spot. Another way is If I let it idle for 5mins it will die no sputter or rough idle…but one distinction is if the rig is starting cold it will run great for 30-40mins then start shutting down
 
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Bump

I’ve had a similar issue, which a new fusible link fixed. I’d still guess something electrical.

Sounds like you did a good job of troubleshooting. Did you test the ground wires with a multi-meter or just visually inspect them?
im thinking electrical too given heat being a factor…I only did a visual but will check with multimeter just to be sure. I did put a new fuseable link and checked all the wires to alternator and starter…no frays but the loom is crispy from 30yrs of heat, haha

What I don’t understand is why I don’t have a CEL…is my OBD1 just not advanced enough to identify it? Or computer keeps resetting?
 

baldilocks

Battle Ground, WA
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You said that you have done a good deal of work and parts replacements. Was this happening before you replaced the fuel pump? The OBD system is not aware that a fuel pump or filter exists.

I would retrace my own steps checking on components that the obd does not monitor. Have you ever removed and thoroughly cleaned the throttle body? If original, the wire harness is 1,000 dog years old now too. How about testing resistance through the ignition coil?
 

TomH

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Could be the fuel pump resistor. Next time it dies try jumping +B and FP in the data link box thingy under the hood. This will send 12V directly to the fuel pump.

1662958222194.png


1662958242478.png
 
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San Jose, CA
OBD1 is very, very basic.

Your ECU may be loosing power?
On my rig, I had a cracked battery clamp. The rig would die every time I hit a speed bump too hard.
One of the wires in the fusible link sends power to the ECU circuit.
Add test wires to the ECU power wires for the engine circuit. Then monitor with a multi-meter. See if voltage drops in concert with the engine turning off
Do you still have the ground wire from the engine to the firewall?
Loose alternator wire
Loose ECU connectors
Bad fusible link...
Random failing wire or wire connection.

Will your rig start after a shutdown or do you need to wait?
Does the rig die right away like turning off the ignition? Or does is sputter and die like running out of gas?

Fuel filter, and/or failing fuel pump depending on how the engine dies.

Did this happen before the ERG was removed?

Ahhhh, Please check your coil and coil wire to the distributor. If the spark plug wires (coil wire) are old they will lose performance (too much resistance (is futile)) as heat in the engine compartment heats up. Or maybe the wires are not seated correctly.
 
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Maybe check the fuel tank vent on the fuel pump? Could be pressurized once it heats up. Or a different cap if it's not OEM.

I'd check some of those crispy wires for kinks or fraying. Might even consider tearing off the old electrical tape to check and then replace with new tape or aluminum tape.

Could be a vacuum line that's clogged and is only used when up to temp.

All shots in the dark but weird issues require it.
 
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You said that you have done a good deal of work and parts replacements. Was this happening before you replaced the fuel pump? The OBD system is not aware that a fuel pump or filter exists.

I would retrace my own steps checking on components that the obd does not monitor. Have you ever removed and thoroughly cleaned the throttle body? If original, the wire harness is 1,000 dog years old now too. How about testing resistance through the ignition coil?
no this was not happening before the pump install, but its been a year since i've replaced the pump with a new oem pump and it drove great...all until 3wks ago. I've cleaned the throttle body it looks good...ignition coil testing is a great idea, i'll put that on the list to do after work! Question - would a bad ignition coil work sometimes then not other? thinking about the inconsistency of this problem and it being related to heat?
 
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I third the ignition coil and the grounding on that.

The fuel pump is signaled to operate once the engine shows rotation. On the 95+ years, that is done by a crank sensor, but the 93-94 use the signal from the coil / ignitor. I don't recall the exact method, but I'm sure someone else can assist.
 
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Could be the fuel pump resistor. Next time it dies try jumping +B and FP in the data link box thingy under the hood. This will send 12V directly to the fuel pump.

View attachment 3112492

View attachment 3112493
i will try this next time it shuts down...if it works this shows that i need a new FP resistor, correct? Meaning the old one is getting too hot and stops working until it cools down....random insight, i don't know know if its connected but i notice when i open the hood after a shutdown it restarts faster
 
Joined
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I third the ignition coil and the grounding on that.

The fuel pump is signaled to operate once the engine shows rotation. On the 95+ years, that is done by a crank sensor, but the 93-94 use the signal from the coil / ignitor. I don't recall the exact method, but I'm sure someone else can assist.
ok, i'm excited to swap this out and see if heat affects the new one! will report back!
 
Joined
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Messages
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Location
Austin, Texas
OBD1 is very, very basic.

Your ECU may be loosing power?
On my rig, I had a cracked battery clamp. The rig would die every time I hit a speed bump too hard.
One of the wires in the fusible link sends power to the ECU circuit.
Add test wires to the ECU power wires for the engine circuit. Then monitor with a multi-meter. See if voltage drops in concert with the engine turning off
Do you still have the ground wire from the engine to the firewall?
Loose alternator wire
Loose ECU connectors
Bad fusible link...
Random failing wire or wire connection.

Will your rig start after a shutdown or do you need to wait?
Does the rig die right away like turning off the ignition? Or does is sputter and die like running out of gas?

Fuel filter, and/or failing fuel pump depending on how the engine dies.

Did this happen before the ERG was removed?

Ahhhh, Please check your coil and coil wire to the distributor. If the spark plug wires (coil wire) are old they will lose performance (too much resistance (is futile)) as heat in the engine compartment heats up. Or maybe the wires are not seated correctly.
do you know if the OBD1 would identify a bad Coil pack with a CEL?

i recently changed my battery clamps, fusable links and cleaned up all the old wire loom and inspected wires to the ALT and Starter...they look good. Testing the ECU is probably over my head for right now...i still have the ground wire to the engine firewall. It will restart if its not too hot(ambient heat not coolant heat) right away if its hot...

yes this did happen before the ERG was removed and after.

coil pack is the next place i'm looking at, thanks!
 

80t0ylc

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I don’t think anyone has mentioned specifically the engine harness near the EGR. It becomes “crispy” with heat and age. But it’s also source for electrical shorts due to breakdown of insulation of wires routed together at that spot. Harness goes from engine to firewall.
 

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