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

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I will check my spares to see if I have an IAC.
 
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For the IAC, see if the out of spec Ohm readings are repeatable. Clean the contacts, etc.

It is a stepper motor. So every time power is applied (pulse) the IAC will open or close about 1mm. A traditional motor would run until power is removed. The IAC will only open or close by repeated power pulses. Maybe get the IAC to fully open by tapping (adding) power to the contacts. Once fully open. Install it again. The ECU will close it down to control your idle. Try this a couple of times to exercise the full range of motion. You don't need to re-install, just plug the harness in and switch the ignition to on.

Sorry, long winded. Maybe the IAC has a dead spot. If the IAC fails the FSM testing and the failure is repeatable. You need to replace the IAC. This would eliminate the IAC as the root cause.

I do not have a spare IAC for the 80 series.
 
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Joined
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It is good to see your idle back were it should be (check).

I do not remember all your posts. Did your rig die at idle or while driving at speed as well?

The VAF sends a fuel pump on when air is pulled into the engine. The flapper opens and turns on the fuel pump via the "Circuit Open relay". Please swap the Circuit open relay. I think at least 2 of the same relay. So just swap them around. They are in the driver foot well.

No change, go for the TPS adjustment or install your new one.
Thanks a ton for this reco/insight! I’m still a newbie to troubleshooting, I thought by bypassing with B+ and FR jumper that confirmed relays in the chain we’re essentially g2g (maybe it dies for just fuel side🤷🏻‍♂️) but per your note and links didn’t know the COR provides some type of input with the VAF…anyways I was out of town this wknd but I’m excited to at least try this tomorrow!

Question - I’ve ordered a new Denso relay…won’t come til Wednesday - it’s good PM even if this isn’t the solve. Anyways, does anyone know which other relay is interchangeable with the COR relay?

I plan to pull the other block relays but just curious…I searched mud didn’t see any swap lists just in case🤷🏻‍♂️
 
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It is good to see your idle back were it should be (check).

I do not remember all your posts. Did your rig die at idle or while driving at speed as well?

The VAF sends a fuel pump on when air is pulled into the engine. The flapper opens and turns on the fuel pump via the "Circuit Open relay". Please swap the Circuit open relay. I think at least 2 of the same relay. So just swap them around. They are in the driver foot well.

No change, go for the TPS adjustment or install your new one.
Sorry forgot to answer your question - it does at idle after a few minutes and randomly when driving
 

TomH

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Thanks a ton for this reco/insight! I’m still a newbie to troubleshooting, I thought by bypassing with B+ and FR jumper that confirmed relays in the chain we’re essentially g2g (maybe it dies for just fuel side🤷🏻‍♂️) but per your note and links didn’t know the COR provides some type of input with the VAF…anyways I was out of town this wknd but I’m excited to at least try this tomorrow!

Question - I’ve ordered a new Denso relay…won’t come til Wednesday - it’s good PM even if this isn’t the solve. Anyways, does anyone know which other relay is interchangeable with the COR relay?

I plan to pull the other block relays but just curious…I searched mud didn’t see any swap lists just in case🤷🏻‍♂️

Jumping +B and FP bypasses the circuit opening relay and the fuel pump relay. Did you verify 12V at +B when you did the jump? +B originates at the ECU and powers quite a few other things. It's all in the EWD which you can find in the resources section if you don't already have it.

I thought I'd post this from @jonheld as a reminder.

How about starting with the basics before using the parts cannon.
During a no-start are you getting spark?
During a no-start are you getting fuel?
 
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Jumping +B and FP bypasses the circuit opening relay and the fuel pump relay. Did you verify 12V at +B when you did the jump? +B originates at the ECU and powers quite a few other things. It's all in the EWD which you can find in the resources section if you don't already have it.

I thought I'd post this from @jonheld as a reminder.
No didn’t verify 12V at B+ but will do this today👍

As for verifying spark and fuel….yes we did after NS but I’ve noticed the longer we have the hood open and setting stuff up to check it always restarts first time (if that makes sense)…if I try to restart after NS right away it’ll crank and crank, so time/heat is a factor I guess🤷🏻‍♂️
 

jfz80

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EFI main should be same relay as COR. I was having a cutoff while driving in ambient heat issue and suspecting COR. Was going to mention but different symptoms. Mine turned out to be the dizzy.
 
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Jumping +B and FP bypasses the circuit opening relay and the fuel pump relay. Did you verify 12V at +B when you did the jump? +B originates at the ECU and powers quite a few other things. It's all in the EWD which you can find in the resources section if you don't already have it.
I thought I'd post this from @jonheld as a reminder.
Confirming I have 12volts at B+
 
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Messages
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For the IAC, see if the out of spec Ohm readings are repeatable. Clean the contacts, etc.

It is a stepper motor. So every time power is applied (pulse) the IAC will open or close about 1mm. A traditional motor would run until power is removed. The IAC will only open or close by repeated power pulses. Maybe get the IAC to fully open by tapping (adding) power to the contacts. Once fully open. Install it again. The ECU will close it down to control your idle. Try this a couple of times to exercise the full range of motion. You don't need to re-install, just plug the harness in and switch the ignition to on.

Sorry, long winded. Maybe the IAC has a dead spot. If the IAC fails the FSM testing and the failure is repeatable. You need to replace the IAC. This would eliminate the IAC as the root cause.

I do not have a spare IAC for the 80 series.
So did the full range testing with the IAC, it did fine and moved a bit, plus I heard it clicking after shutdown. Ive tested multiple times and only one pair of terminals fail out of spec S1-S3 at 42ish ohms…I’m not sure if it matters given it’s a step motor but the FSM says it’s out of spec so I’m assuming it does…I’m currently trying to source one just in case, but given everyone’s advice it’s probably not my problem…

Question - does the IAC play any role while driving at speed? Thought I’d ask given I randomly stall while driving too not just at idle….
 
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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?
 

baldilocks

Battle Ground, WA
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you think it bad connection or deep cycle bat messing with old fzj80 electrical system?
The yellow top is not a true deep cycle. They call it a “combo” battery for stating and deeper discharge. I ran one in a 1978 dodge Ramcharger for ten years with nary a problem.
 
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Jumping +B and FP bypasses the circuit opening relay and the fuel pump relay. Did you verify 12V at +B when you did the jump? +B originates at the ECU and powers quite a few other things. It's all in the EWD which you can find in the resources section if you don't already have it.

Confirming I have 12volts at B+
B+ at the diagnostic connector comes from the 15 amp EFI MAIN fuse through the EFI MAIN relay. The ECU energizes the EFI MAIN relay.
 

RodrigzCrzr

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It sounds like while you where at a high altitude no symptoms came up.
once you dropped they popped up. Hmm.
 

TomH

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B+ at the diagnostic connector comes from the 15 amp EFI MAIN fuse through the EFI MAIN relay. The ECU energizes the EFI MAIN relay.
Thanks for the correction. I understand now how that works.
 
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It sounds like while you where at a high altitude no symptoms came up.
once you dropped they popped up. Hmm.
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
 

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