92 Toyota FJ80 3FE - Limp Mode?? (1 Viewer)

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Hello. I'm new here. I have been working on vehicles most of my life, and currently do it for a living and holding 1 ASE cert (A4). I personally own a 1988 Pathfinder 4x4 and love going out on a good trail. More about that some other time.

Got doozy in the shop right now, a 92 FJ80 with the 3FE engine, thats got me pulling my hair out. Mitchell and IdentiFix have very limited amount of diagnostic information and not very many service manual bits.

CEL on. It's running rough with random multi-cylinder misfire, black/gray sooty exhaust indicating rich condition, and strong exhaust smell that makes your eyes water. I don't see any oxygen sensors in the exhaust piping? Performed vapor test, found a couple vacuum leaks, fixed them and no change. No exhaust leaks found. Have codes for AFM and TPS. Initially also had a code for IAC, but found IAC to be stuck open, replaced it and that code did not reset after clearing, but no significant change in running condition. More on TPS and AFM in a moment.

EDIT: Also when vehicle arrived it had TPS and IAC unplugged, and all the vacuum lines on the throttle body side of the plenum were disconnected completely and laying on valve cover. These issues were corrected first and foremost, but did not make a significant change.

Engine will crank, start and rev okay, revs up to about 3000 RPMs, then the engine will stumble violently, pop and shake and wont increase past ~3K RPMs. Verified fuel pressure, checked and replaced spark plugs (old plugs looked lean instead of rich???), wire set, cap and rotor, ICM, no change. Verified cold start injector is not leaking. No fuel coming out of fuel pressure regulator vacuum line. TPS and AFM look to be recently replaced.

If I unplug the TPS, engine idles just a hair better (exhaust still indicates rich condition), and when I rev up the engine there will be fuel cut (like a limp mode rev limiter) around 2800-3000 RPMs and will not go past 3K, if I plug the TPS back in it will do what I mentioned above and run a little worse. Noticed that TPS adjustment is maxed out to the left. If I try to adjust it even a little the idle just shoots up (not sure if that's normal for these?) Swapped TPS with a good part and no change, code returns after clearing with both TPS. Connector and wiring look okay.

If I unplug the AFM engine idle rises to about 2000 RPMs and stays there for a about a minute then stalls. If I try to rev with the AFM unplugged the engine stalls. (Again not sure if this is normal for unplugging AFM??) AFM looks clean and flap is not stuck. Connector and wiring look okay.

Before I just throw a AFM at this thing, (hard to find in the shop portals) I need to research and find information about the EFI system on these particular vehicles. So far not much is turning up... Where can I find a downloadable FSM? Does this EFI system even have a limp mode? Is it really as simple as a bad AFM??
 
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ppc

M Go Blue
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You can find a downloadable version of the FSM in the thread below:


Three things come to mind:

1 The TPS needs to be adjusted per the FSM. It is very sensitive adjustment.
2 The rubber intake hose from the AFM might be cracked on the underside letting in unmetered air
3 There are many cases where the ASM connector has been damaged by loosening the two screws damaging the connections inside the AFM. Some have success resoldering those connections

If you search on this forum there are lots of threads related to all three items.
 
Joined
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Three things come to mind:

1 The TPS needs to be adjusted per the FSM. It is very sensitive adjustment.
2 The rubber intake hose from the AFM might be cracked on the underside letting in unmetered air
3 There are many cases where the ASM connector has been damaged by loosening the two screws damaging the connections inside the AFM. Some have success resoldering those connections

If you search on this forum there are lots of threads related to all three items.

I had read about the TPS adjustment being fairly sensative, but can't find any documentation on how to properly adjust and what the readings should be. Perhaps the FSM and this will help with that.

I smoke tested the engine 3 times now and paid special attention to the intake hose between AFM and TB. (And all other rubber hoses on the intake) I removed the main intake hose and inspected, its soft, flexible and doesn't appear to have any holes or cracks, but will check all again to make sure.

I did notice that the black plastic cap on top of the AFM has silicone around it with a finger print on it indicating someone had it off? Maybe someone damaged and tried to repair the "new" AFM? The AFM literally looks brand new and still has part number and QR label on it, but I know that really doesn't mean a thing. Customer can't provide much history as they have not had the vehicle long.

I have been and will continue to do some searching here, but still so far not coming up with much, perhaps these new items will help. Thank you for your input.
 
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ppc

M Go Blue
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The thread below has some good pictures of the internals of the AFM starting at post #34 in the second page. There are most likely 20+ threads in addition to that one.

 
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You also make no mention of confirming timing.

It would be worthwhile to do this if you have not.

However, most of what you describe points to a bad AFM. (or VAF or whatever it is.)

Does @slow95z have any used AFM's for 92's?

Maybe @arcteryx ?

What codes are being shown on the CEL?
 
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I would check the FPR and listen to the injectors with a stethoscope. The fuel pump relies on the AFM for power when the engine is running. If you unhook it, the rail will empty of fuel shortly thereafter.
 
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3fe's do have a "limp mode". It limits the engine RPM to 2100 rpm after it encounters a prolonged WOT condition. If you de-power the ecu for 30 seconds it will reset back to normal operation.
 
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Okay with the help from you guys and of your service manuals I found that TPS was not installed properly being that it wasn’t lined up with the prongs on the throttle correctly. Put the new TPS back on and used the feeler gauges and checked resistence etc.

Runs better and TPS code is now gone and so is the “limp mode” it will rev all the way to red line with no issues, but exhaust is still indicating rich condition and still has a miss. Cleared codes and CEL comes on only getting code for AFM.

Before jumping deep into the fuel system I’m going to perform AFM resistence checks from the FSM and go from there.

PS I’ve tinkered with the ignition timing a little but mechanical timing is currently far down the list of considerations as I just put a long block in last week at customer request. It had the same running issue with both long blocks, that is off subject here as the customer wanted the long block replaced regardless of whatever else it may need. (He has made this a project to give to his wife once it’s all good to go. Lucky wife lol)

Reaching the end of the tunnel on this I think much thanks to all of you so far!!
 
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Joined
Jan 22, 2020
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Progress, pulled the black cap off the AFM. With engine idling the dial is way over towards the + sign. With engine idling if I move the dial it makes no difference in running condition.

With engine off, AFM unplugged and checking resistence on AFM terminals E2 to VS read nearly triple the ohms specified in the FSM, spec is 200-600 ohms I’m getting around 1500 ohms. Same with E2 to VC spec is 200-600 ohms and I’m getting around 1500 ohms.

E2 to THA reads about in spec for engine temperature, same for E1 to FC, in spec.

looks like I need an AFM for sure now. Hopefully thats the end of it. This thing is an awesome rig and I’m anxious to take it for a road test with it operating normally!

Thanks again guys!
 
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Looks like we get to play parts merry go round here.

Remanned MAF from Summit showed up today. Engine runs a hair better but still rich, still throwing code 31. When doing FSM diagnostics this time E2 to VS is 48 ohms. E2 to VC is 52 ohms. Spec is 200-600 ohms.

Where can I find a NEW afm and not a reman? Everywhere we check is only cardone remans and both of the AFMs I have are also cardone remans. I do not believe that the shop will be able to buy a AFM from someone here unless you can offer warranty and refunds.

Fudge.
 
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I bought a "new" MAF off of ebay for $100(not really new) but my problem for running too rich turned out to be a ground problem believe it or not. I now have a spare temp sensor, ecu, coil, MAF, injectors, and a few other things. Good news is that the old girl runs soo good I dont even mind the 3fe any more. Good thing because I have enough parts now to keep her running a loooooong time.
 
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I've read about ground issues as well, all the grounds I can find are clean and tight. Tho I'm still convinced that the AFM is part of this issue because so far both AFMs I've had failed their bench tests.

If I can ask what were the specifics of your ground issue?
 
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In the name of preserving information, the Cardone reman AFMs are, apparently, crap. The one that came in on the vehicle, as well as 2 more are these Cardone parts. Another one should be here Monday, but its all that can be found that is in stock, thru Summit. Of the 3 "identical" parts used, the vehicle runs a little different, but all like crap. The most recent one it had a worse sparatic misfire and super rich. (Previous part to this showed a little less rich exhaust) All 3 of these Cardone units show out of spec when performing the diagnostics in the FSM for the AFM. The original Cardone on the vehicle read well over spec for E2 to VS (spec is 200-600 ohms) and E2 to VC (spec is 200-400 ohms.) The last two Cardone units were well below those same specifications, as well as eventually setting code 31 for the AFM.

Also noticed the oxygen sensors tucked up under the driver floor board there, so did some diagnostics on those and found one sensor does not appear to be sending a signal. Not setting any Ox codes unless you unplug the sensor (obviously). Further testing will be done for that as well.
 
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If this were my truck, I would pick up a good used AFM from a 3FE equipped truck. FJ62/FJ80 had the same part number.
There are several folks on this forum who regularly part out Cruisers, and there is the entire classifieds section as well.
@arcteryx @slow95z
If you search a bit, there are several threads mentioning an AFM from a Camry or another Toyota car that has a drop in for the AFM.

You mentioned earlier that mechanical timing is "way down the list". Keep in mind that this is a tractor motor based on 1986 technology. If the mechanical adjustments are not to factory spec, the ECU and related sensors have a VERY limited window to bring things back. All mechanical adjustments must be done first.
 

slow95z

Always parting 80s
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Well I only have one 3fe AFM sitting around and thanks to getting tagged about this earlier in the week several are asking about it so if you need one let me know
 
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Did you ever locate the oxygen sensors? It should have two. They are just under the driver side in the exhaust pipe before the cats. If they are missing, they need to be added back in. It won't run right without O2 sensors.
 

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