‘93 FZ80 Engine shuts down randomly only after it’s warmed up… (2 Viewers)

RodrigzCrzr

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yes, but that negates the 2yrs i had the rig in ATX without these issues, before heading to CO...so i wouldn't think altitude is a factor. Reminder i drove +1000miles back to texas without issues plus a few days once i returned
Yeah, your right and do remember.
Just seems odd how intermittent it is.
 
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you think it could be a bad connection or deep cycle battery messing with old fzj80 electrical system?

It sounds awfully coincidentally with electrical work performed. I don't think the 80s are sensitive enough to care about the specific type of battery you use, but I have heard bad things about Optima. I don't have in-depth knowledge of how batteries are constructed. Is it possible to have an intermittent connection inside? One that opens (or just has significantly increased resistance) under vibration or heat?

I'm far more suspicious of anything done with the terminals, wires to/from the terminals, and even fusible links. Are the links torqued down adequately? Also, it's uncommon but not unheard of for brand new parts to be bad.

Additionally, to my knowledge you still haven't checked the harness where it passes through the firewall on the passenger side. When you checked the harness near the EGR you said you looked for frayed wires when you're supposed to be looking for discoloration from heat. Ideally, you would check for continuity on each wire while manipulating the harness, but as the wise lady says, ain't nobody got time for that.

I would also look at the vacuum system (carbon blockage and/or leaks), personally, but since you say it will die while driving rather than only at idle, I think it's almost certainly related to the electrical system.
 
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As I’m waiting for a new COR relay and IAC thought I would retrace my steps directly after our +2500 mile trip to CO/NM where I didn’t have this issue🤔

After I got back to ATX, I changed the below items within 5days of being back:

- Charcoal canister and associated vacuum lines that led into the VCV for the evap…why, cause I boiled my fuel at the summit of Ophir pass (engine shut down)… pulled the venting tube that leads from the tank to the CC and drove for another week all the way back to ATX

- Changed my fuseable link which looked corroded and nasty but didn’t fail

- Changed my terminal posts on my battery for new ones

- Changed my battery to a new Optima yellow top 27 deep cycle battery… in Colorado my battery failed and they had an Optimum red top starter battery, so I took it…but I wanted a yellow top so one day I could move it to a dual battery set up, when I got to ATX I exchange the red for a yellow at O’Reilly

I can’t remember exactly but after a few days I started to get more of these engine shut downs and shutting down at idle after a few minutes

Anyone think these changes could drive my issue/related or is it just coincidental?
Just clarifying.
You changed the battery terminal posts or the battery terminal clamps? Or your battery cables terminate with large eyelets that you bolt to the battery?

You have done a lot. The engine dies gracefully, no coughing, and no stumbling. Just turns off like the key was turned. As someone already mention it is electrical.
I do not think the IAC does anything when driving at speed. However, the ECU is in control. I believe an IAC loss of signal would flag the CEL. Maybe set the engine at 2000rpms and disconnect the IAC... just to see what characteristics occur. I think the CEL would flag. Look at the list of CEL codes in your FSM. Also, not all DTC codes trigger the CEL.

Sorry dumb question...
Your check engine light (bulb) is working. Momentarily lights when the key is first turned on.
 
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What does "boiled my fuel" mean. I have never heard of this.

1663863760087.png


Your engine over-heated at the Ophir summit which did something to the fuel system or fuel delivery?
 

ChaseTruck

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What does "boiled my fuel" mean. I have never heard of this.

View attachment 3121050

Your engine over-heated at the Ophir summit which did something to the fuel system or fuel delivery?
Boiling point for gasoline is dependent on temperature AND atmospheric pressure. FI systems typically run with excess fuel delivery to the injectors, where the fuel delivery to the engine is metered; the rest is returned to the gas tank. But in that way, the fuel has a chance to absorb heat from the engine compartment. Add to that the lower atmospheric pressure high up on a mountain pass, and the fuel in the tank can get past the initial boiling point. Venting of vapors usually goes through the vent canister, but you can end up with considerable fuel vapor pressure in the tank when the line to the canister can't handle the volume. Can be quite dramatic.
 
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Just clarifying.
You changed the battery terminal posts or the battery terminal clamps? Or your battery cables terminate with large eyelets that you bolt to the battery?

You have done a lot. The engine dies gracefully, no coughing, and no stumbling. Just turns off like the key was turned. As someone already mention it is electrical.
I do not think the IAC does anything when driving at speed. However, the ECU is in control. I believe an IAC loss of signal would flag the CEL. Maybe set the engine at 2000rpms and disconnect the IAC... just to see what characteristics occur. I think the CEL would flag. Look at the list of CEL codes in your FSM. Also, not all DTC codes trigger the CEL.

Sorry dumb question...
Your check engine light (bulb) is working. Momentarily lights when the key is first turned on.
Sorry I should’ve been more specific…I installed new battery clamps that you bolt to the battery.

Yes CEL bulb is working - it lights up during ignition and goes off, even pulled pulled TPS plug while running and CEL popped immediately, plugged back in and it went away.

Update new COR installed, no change…however, some progress was made today - yes, i definitely think it’s electrical, related to heat build up, and affects fuel delivery, at the pump I think!

Given the sporadic nature of my shutdowns it’s been tough to troubleshoot and I’m a noob…but I’ll post my logic in a fresh post😁
 
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Boiling point for gasoline is dependent on temperature AND atmospheric pressure. FI systems typically run with excess fuel delivery to the injectors, where the fuel delivery to the engine is metered; the rest is returned to the gas tank. But in that way, the fuel has a chance to absorb heat from the engine compartment. Add to that the lower atmospheric pressure high up on a mountain pass, and the fuel in the tank can get past the initial boiling point. Venting of vapors usually goes through the vent canister, but you can end up with considerable fuel vapor pressure in the tank when the line to the canister can't handle the volume. Can be quite dramatic.
What does "boiled my fuel" mean. I have never heard of this.

View attachment 3121050

Your engine over-heated at the Ophir summit which did something to the fuel system or fuel delivery?


Thought I would upload the video of my rig 100ish feet from the summit…my engine shut down and I heard this bubbling coming from the tank. Then pooped the hood and pulled the line from the tank to the CC…drove back to texas with it vented thru my fender…didn’t happen again 🤷🏻‍♂️
 
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Ok I think we’re narrowing in on what’s going on…maybe🤞🏽

So for context the shut downs are very sporadic and hard to troubleshoot… but the hotter it is the more frequent they occur today was high of 97 in ATX

So we decided to get back to basics and try to confirm spark and fuel again - we had already done this previous last week after a shutdown and confirmed we had both…BUT…

We always did spark first and would crank a couple of times and got spark☑️…then we pulled the return line on the FPR and crank and would get fuel…well today we got lucky and it shutdown in the garage and this time did fuel first…cranked 3 times no fuel…4th time fuel everywhere🤔. We repeated this on another shutdown,, and same thing, no fuel, until 4th try…did it again with B+ bypass and same thing, no fuel until 4th crank…

Actually I could prime the pump 3 or 4 times without crank and it would fire up…

So we changed the fuel pressure regulator for a new one this evening…since it was cooler it took longer to shutdown, like 40mins of driving…we actually thought we solved things but nope, lol… before it failed though RPMS dropped and there was a jerk then 7 seconds later engine shutdown.

So I’m thinking either wire harness short at EGR affecting fuel delivery, fuel pump wire short issue?

Anything else that would make the pump stop working or make the FPR not shoot out fuel🤷🏻‍♂️

Sorry for the long post just want to be detailed…also hoping this points us in the right direction
 
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Ok I think we’re narrowing in on what’s going on…maybe🤞🏽

So for context the shut downs are very sporadic and hard to troubleshoot… but the hotter it is the more frequent they occur today was high of 97 in ATX

So we decided to get back to basics and try to confirm spark and fuel again - we had already done this previous last week after a shutdown and confirmed we had both…BUT…

We always did spark first and would crank a couple of times and got spark☑️…then we pulled the return line on the FPR and crank and would get fuel…well today we got lucky and it shutdown in the garage and this time did fuel first…cranked 3 times no fuel…4th time fuel everywhere🤔. We repeated this on another shutdown,, and same thing, no fuel, until 4th try…did it again with B+ bypass and same thing, no fuel until 4th crank…

Actually I could prime the pump 3 or 4 times without crank and it would fire up…

So we changed the fuel pressure regulator for a new one this evening…since it was cooler it took longer to shutdown, like 40mins of driving…we actually thought we solved things but nope, lol… before it failed though RPMS dropped and there was a jerk then 7 seconds later engine shutdown.

So I’m thinking either wire harness short at EGR affecting fuel delivery, fuel pump wire short issue?

Anything else that would make the pump stop working or make the FPR not shoot out fuel🤷🏻‍♂️

Sorry for the long post just want to be detailed…also hoping this points us in the right direction
Yes. The temperature sender. There are two. One for the gauge and one for the ECU.

When the engine temperature comes up, the ECU goes into closed loop and the fuel pump changes speed. Think of it like part of using the choke on the old carburetor trucks.

If the temperature sender is giving poor or no signal it may cause the fuel pump to stop.

Just a guess based on the latest information.

It's not uncommon for the wiring or plug to break.
 

TomH

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…did it again with B+ bypass and same thing, no fuel until 4th crank…

Actually I could prime the pump 3 or 4 times without crank and it would fire up…

I'm no expert on this and still trying to learn but if you look at the schematic you can see that if you have 12V to +B and you connect that to FP then you have essentially hard wired the fuel pump. If the fuel pump isn't working under this condition then my opinion is you have a fuel pump problem.

The things in the way of powering the fuel pump under these conditions are connectors IH2, ID2, BO1 and splice E12.

Have you checked the ground at BF?

I'm also curious how you are priming the fuel pump.

1663948602806.png
 
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The things in the way of powering the fuel pump under these conditions are connectors IH2, ID2, BO1 and splice E12.

Have you checked the ground at BF?

I'm also curious how you are priming the fuel pump.

View attachment 3121864
I’m very green with electrical and learning too!

So when hardwired (+B to FP)…is it safe to say those connectors and the pump work to an extent…then something happens (ie. maybe a short due too heat) that kills the pump…causing the rig to shutdown…then once I restart the car it takes a few cranks to build up pressure and get fuel in the lines - which is why I don’t immediately see fuel from the FPR return line, right?

Another question, if the pump is hardwired (+B to FP) can the VAF cut fuel to the rig and cause my sane symptom?

Any other sensors that can cut the fuel pump off when hardwired (+B to FP)?

I primed by just turning the key off and on 4 times…and I haven’t checked ground at BF, but I will on Sunday.
 
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then something happens (ie. maybe a short due too heat) that kills the pump…causing the rig to shutdown

Personally, every time I've seen a fuel pump fail, it's blown the fuse. Maybe someone else has had a different experience or can think of a plausible scenario where it could happen.

Have you inspected the pump and wiring at the pump? It's really easy to get to on these vehicles. Well, relatively anyway. Pull the rear seats, lift the carpet, and remove an access panel.
 

TomH

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I’m very green with electrical and learning too!

So when hardwired (+B to FP)…is it safe to say those connectors and the pump work to an extent…then something happens (ie. maybe a short due too heat) that kills the pump…causing the rig to shutdown…then once I restart the car it takes a few cranks to build up pressure and get fuel in the lines - which is why I don’t immediately see fuel from the FPR return line, right?

Another question, if the pump is hardwired (+B to FP) can the VAF cut fuel to the rig and cause my sane symptom?

Any other sensors that can cut the fuel pump off when hardwired (+B to FP)?

I primed by just turning the key off and on 4 times…and I haven’t checked ground at BF, but I will on Sunday.

Jumping +B and FP is intended to test whether the fuel pump is working and based on what you've written you haven't convinced me you verified it works. I saw that you have recently replaced the pump.

If you look at what @gummycarbs posted, with +B and FP jumped and key on, the hose from the fuel filter should be pressurized and you should hear the fuel return. This tells me that fuel should be flowing to the fuel rail and returning to the tank. If at any time you have +B and FP jumped and there is no fuel pressure then you have a problem with the fuel pump. There is nothing to stop the fuel from flowing. You shouldn't have to get fuel in the lines, it shouldn't be draining out.

A couple snips from the FSM showing the fuel lines are direct from tank to fuel filter to fuel rail to fuel return.

1663994797812.png


1663994855451.png


I don't think VAF can cut fuel flow with +B and FP jumped. Neither can the fuel pump relay or circuit opening relay.

The only thing I can think of that will stop fuel flow with +B and FP jumped is if +B loses power from the EFI main relay.

If you have the +B and FP jumped then you shouldn't have to turn the key on and off. +B and FP jumped with key on should pressurize the system.

…did it again with B+ bypass and same thing, no fuel until 4th crank…

If this statement is correct and you had 12V to +B and it took four tries to get fuel pressure, then I agree with @gummycarbs that inspecting the fuel pump wiring would be a good next step.

If you don't find any wiring problems, at the next no start I would immediately check for 12V at +B and then jump to FP and verify fuel pressure. If you have pressure then that likely rules out the fuel pump.
 
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Edited:
Jumping the pump at the check connector will bypass the VAF fuel pump trigger. You should be able to feel pressure in the fuel lines, and/or hear the fuel pump hum if you go to your gas tank and listen. Running the pump at the check connector will not energize the COR relay (you need the VAF to open).

Your analysis is good. The VAF opening/moving at starter crank energizes the Circuit Open relay (COR), which also feeds the Cold start injector. The COR also energizes the EFI pump relay. The EFI relay sends power to the IAC. The water temp sensor tells the ECU when the engine is warm to reduce the extra fuel sometimes needed at startup (to turn on the cold start injector.) There is also a water temp gauge sensor (unrelated to the cold start injector circuit).

Did you swap/replace the COR relay? Relays get hot, build up carbon on the contacts and get tired.
 
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Jumping the pump at the check connector will bypass the VAF fuel pump trigger. You should be able to feel pressure in the fuel lines, and/or hear the fuel pump hum if you go to your gas tank and listen. Running the pump at the check connector will not energize the COR relay (you need the VAF to open).

Your analysis is good. The VAF opening/moving at starter crank energizes the Circuit Open relay (COR), which also feeds the Cold start injector. The COR also energizes the EFI pump relay. The EFI relay sends power to the IAC. The water temp sensor tells the ECU to turn on the cold start injector. There is also a water temp gauge sensor (unrelated to the cold start injector circuit).

Did you swap/replace the COR relay? Relays get hot, build up carbon on the contacts and get tired.
You're describing the fuel pump logic from a 3FE.
The 1FZ-FE uses slightly different logic. The ECU runs the show and has no cold start injector.
 
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You're describing the fuel pump logic from a 3FE.
The 1FZ-FE uses slightly different logic. The ECU runs the show and has no cold start injector.
Yes.
I realized after I hit reply
I edited the post.
 
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For the GM canister replacement...
Next time your troubleshooting, Remove the gas prior to starting.
 

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