Bought a non running 94 fzj80 need help (1 Viewer)

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Aug 23, 2016
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Rocklin, ca
Hey guys I'm new here and new to 80 series. I've always wanted one so I sold the crawler and found one.
Got a great deal on a super clean 94 that wasn't running. The po said it was running great until it died at a stop light and wouldn't restart.

His mechanic replaced the fuel pump and fuel filter. No fix. Sweet I have a new fuel pump and pita to change filter! I trailered her home.

I'll check the mechanics work once running. At this point there was no spark, fuel pressure or CEL. Tried B+ to FP. Had fuel pressure still no spark or CEL with key in run. Checked EFI relay it's good. Coil checks out, has power and good ground but no signal to fire. Cranked it over forever trying different stuff.

Here's where it gets weird.... Unplugged the air flow meter CEL comes on engine fires right up runs smooth as silk for 3 seconds and dies. Will fire up and run 3 seconds every time. Plug AFM back in nothing again. Ok I need a new AFM so I pull the cap off and sure enough there's a safety switch inside with bad contacts. Clean the contacts fires up runs great! Drove 15 miles or so very happy. CEL is on but it's running great. Shut the motor off restart and it's running horrible. Stumbling mildly backfiring and acting like its starving for fuel. WOT and rpms take 15 seconds to climb from idle to 3500. Shut it off start again runs great. Shut it of start again stumbling. Every 7th start or so, it's running well enough but pinging like the timing is way off.

Check OBD 1 Morris code. 2 codes: 12 and the code for intake air temp sensor inside the AFM. Code 12 is my concern loss of signal from the crank position sensor to ECM. Test distributor air gaps and ohms. Slightly out of spec. New distributor and still the same problem. Have a new AFM on the way. What a nightmare finding one. I know the AFM is part of the problem but I've never seen one have such a drastic effect. Checked O2 sensor it's in spec TPS is functional but could use to be replaced.

AFM should be here by the end of the week however I'm doubtful it will fix the main problem. I don't know where to go from here. Any help would be greatly appreciated.
 

baldilocks

Battle Ground, WA
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I don't think a 94 has a crank position sensor. Have you inspected your engine harness right where it passes close by the egr tube? It gets heat damaged over time, wires become bare and weird stuff starts happening. Key on with no CEL means the ECU is unpowered or its bad. These problems are tough ones and call for a good inspection of all engine associate wiring.
 
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I think you've found the issue. A faulty AFM will give the ECU false information regarding intake air volume and temperature and the ECU will set the A/F trim accordingly. This will cause a rich/lean condition that the O2 sensors will feedback to the ECU causing more problems as the ECU tries to correct.

It will never run right without a good AFM. Make sure the large intake tube is in good shape without cracks that will allow unmetered air into the system. This will also cause poor idle.

Used OEM parts are available from @arcteryx Jason@Cruiseryard.com as well as the parting out section of the forum.

You should also pull the 15 amp EFI fuse in the underhood fusebox for about 10 minutes or when doing any engine work. It essentially reboots the ECU and clears out any error codes and allows the ECU to "relearn" the sensors in the system.
 
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Joined
Aug 23, 2016
Messages
126
Location
Rocklin, ca
I don't think a 94 has a crank position sensor. Have you inspected your engine harness right where it passes close by the egr tube? It gets heat damaged over time, wires become bare and weird stuff starts happening. Key on with no CEL means the ECU is unpowered or its bad. These problems are tough ones and call for a good inspection of all engine associate wiring.
There's no sensor I know of at the flywheel as a crank sensor but the manual is calling the sensors in the distributor crank and cam sensors. I will check the wiring near the egr when I get home from work later thanks!
 
Joined
Aug 23, 2016
Messages
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Rocklin, ca
I think you've found the issue. A faulty AFM will give the ECU false information regarding intake air volume and temperature and the ECU will set the A/F trim accordingly. This will cause a rich/lean condition that the O2 sensors will feedback to the ECU causing more problems as the ECU tries to correct.

It will never run right without a good AFM. Make sure the large intake tube is in good shape without cracks that will allow unmetered air into the system. This will also cause poor idle.

Used OEM parts are available from @arcteryx Jason@Cruiseryard.com as well as the parting out section of the forum.

You should also pull the 15 amp EFI fuse in the underhood fusebox for about 10 minutes or when doing any engine work. It essentially reboots the ECU and clears out any error codes and allows the ECU to "relearn" the sensors in the system.
Thanks for the info and links. I've been pulling the EFI fuse after each set of tests. Sometimes it fires up nicely and sometimes not. Still throwing the same codes though. I'm going to wait for the AFM before going any further. I've worked on 2 trucks with bad AFMs one a 22re and the other 3.0 v6 and thinking back, you're right. One wouldn't run at all and the other would run but had 20hp tops.
 
Joined
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Installed the AFM ran fine for a while then back to crap again. If I reset the ECM by pulling the EFI fuse it runs fine for about ten miles then starts stumbling pinging and won't idle. It seams to be running rich as there was black smoke coming from the exhaust when it started running bad again. I could floor it and no rpm gains just rough idle. TPS? Had to pull the fuse and reset to make it home. Still throwing code 12.

Do I need to pull the whole intake plenum to access the wiring harness near the EGR?
 
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So Cal
 
Ah man, I was gonna say good year and good find but then I read the issues you're having with your rig, sorry to hear. But look on the bright side, you've got a great vehicle. My 94 was giving me issues not so long ago, and just two weekends ago, it left me stranded on the freeway. Mine, hopefully, is the AFM, so i sent it in to get reman'd for the second time. Looks like you've done a fair share of work and hope you find the culprit.
By the way, where in the world did you find an AFM? I waited almost 2 months for one from carid.com for them to tell me later that they were not going to get anymore for a while. I looked almost everywhere, except dealer, and thought I lucked out when carid said they had some in stock.
 
Joined
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Rocklin, ca
Ah man, I was gonna say good year and good find but then I read the issues you're having with your rig, sorry to hear. But look on the bright side, you've got a great vehicle. My 94 was giving me issues not so long ago, and just two weekends ago, it left me stranded on the freeway. Mine, hopefully, is the AFM, so i sent it in to get reman'd for the second time. Looks like you've done a fair share of work and hope you find the culprit.
By the way, where in the world did you find an AFM? I waited almost 2 months for one from carid.com for them to tell me later that they were not going to get anymore for a while. I looked almost everywhere, except dealer, and thought I lucked out when carid said they had some in stock.
I got an AFM from a wrecking yard. A parts house said they can send mine in to have it rebuilt but it could take up to 3 months. So I bought a used one off of a running vehicle that will be my spare when I get the reman back. It was a nightmare finding one from a wrecking yard! Had to order it from 2000 miles away. I'm really happy to have an 80. It runs great when it runs and everything is in good working order besides the distributor wiring. A mechanic friend said it may be a bad ECM, but referred me to a Toyota tech he's friends with. I'll keep you posted on what he finds.
 
Joined
Aug 23, 2016
Messages
126
Location
Rocklin, ca
Ah man, I was gonna say good year and good find but then I read the issues you're having with your rig, sorry to hear. But look on the bright side, you've got a great vehicle. My 94 was giving me issues not so long ago, and just two weekends ago, it left me stranded on the freeway. Mine, hopefully, is the AFM, so i sent it in to get reman'd for the second time. Looks like you've done a fair share of work and hope you find the culprit.
By the way, where in the world did you find an AFM? I waited almost 2 months for one from carid.com for them to tell me later that they were not going to get anymore for a while. I looked almost everywhere, except dealer, and thought I lucked out when carid said they had some in stock.
Oh and new factory AFMs are out there. They're going for between $800 and $1100 usd. I searched for weeks online to find any new units and found 10 or so . I can share the links if you're interested.

Sorry to hear about the problems with your rig. Is the CEL on? Apparently the only thing in the AFM capable of completely shutting off your motor is the safety switch. The two pins on the AFM furthest to the left will have no continuity with the motor off and the flap inside the AFM closed. They should have continuity with the flap pushed open. The contacts on mine were corroded causing the ECM, fuel pump and coil not to turn on.
 
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After you reset the ECU does it throw code 12 immediately or does it only do that when it starts running poorly?
Is the poor running related to engine temperature?

My thinking is that the ECU is likely good but it is getting false signals from sensors and it is trying to correct.
There have been many many reports of the wiring harness melting next to the EGR pipe causing all sorts of interesting things. Another trouble spot is where the ECU harness passes through the firewall. It has been known to chafe wires.
 
Joined
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Messages
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Rocklin, ca
After you reset the ECU does it throw code 12 immediately or does it only do that when it starts running poorly?
Is the poor running related to engine temperature?

My thinking is that the ECU is likely good but it is getting false signals from sensors and it is trying to correct.
There have been many many reports of the wiring harness melting next to the EGR pipe causing all sorts of interesting things. Another trouble spot is where the ECU harness passes through the firewall. It has been known to chafe wires.
I will have the 3 day weekend to start trouble shooting the wiring harness thank god! Thanks for the info it's helpful to know where to start looking. I also read that it can chafe under the dash near where the ECM is mounted.

It throws the code before the engine fires so I don't think it's heat related and I can reset the ECM with the motor warmed up and drive. Seems like it runs ok with factory parameters on a reset but then is thrown off by a bad reading. I checked the distributor wires and 3 have voltage with the motor running while the forth, furthest toward the firewall has nothing. I doubt this wire would be a ground as the distributor is grounded. I can't find anything related to operating voltage of the distributor sensor wires only resistance specs. Does anyone have an ECM wiring diagram, distributor diagram or wire color knowledge? I don't know if this wire runs from the distributor straight to the ECM or passes through another sensor or fuse on the way to the ECM and connects to the ECM in a different color.
 
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Riverside, CA
 
Check the wire harness at the back of the engine by the firewall. This is a known failure point and could cause issues if you have some broken wires. Heat could be causing them to expand just enough to ground out on eachother but be fine when cold.
 
Joined
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So Cal
 
916rock - yeah kep me posted on what your mechanic friend finds. And to answer, my rig has no CEL or any other failure light when on. The bulbs do work cause CEL turns on upon startup but goes away w/in 1 or 2 seconds. I'm gonna stay tuned to see if you are able to figure something out. Hopefully my AFM will be back soon to see if the fixes my issues.
 

baldilocks

Battle Ground, WA
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Where did you get the AFM and how much was it? When I replaced mine last year I saw prices ranging from $600-$1200. I lucked out and found a part out in my area that was posted that day! I paid $40 bucks! I'm not usually that lucky. LOL
 
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Good find baldilocks! I'm never that lucky. Possibly due to impatience? I paid $120 for mine and it's surprisingly clean for being original oem. Wish it was $40. I found it on car-parts.com a lot of body and mechanics shops use it to locate hard to find parts.
 

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