93 FZF80 Code 26. Stumble at Idle and No Power (1 Viewer)

[Kylackey]

Alright I've been troubleshooting everything I can think of and am still stumped...

Details on my issue and background:
I've recently had the engine rebuilt and during this process I've replaced just about everything that goes on, or around a 1FZ. I wasn't aware that the injector connectors have issues on these older engines and upon first fire we noticed the engine was misfiring. I found out that the #6 injector terminals on the harness were messed up and not making contact. I split the manifold, replaced the injector connector (with new terminals) and no longer have a misfire. At first, the engine started up great with no issues, however when I let it sit and idle the truck runs rough and stumbles when you try to drive it.


It has thrown a Code 26 and upon reading multiple threads seems to be the result of the engine running rich. The truck did not have this issue even when it was misfiring. The code is new, and prior to the changes has not come up.
E
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Items that have been checked/and or replaced: ALL NEW OEM
- Checked all vacuum lines are properly connected and in the right position (ALL lines have been replaced and checked with carb cleaner to see if any of them are leaking. No leaks.
- 02 Sensors were replaced, they're Denso unit and have less than 5k on them
- Plugs, wires, coil. New. No issues with any of these from what I can tell
- EGR valve is new OEM from Japan, EGR Solenoid New
- I have unplugged all the connectors on the throttle body (including air filter) and cleaned them with contact cleaner. They all properly seat and don't appear to have any issues
- Replaced all of the available solenoids inside the intake manifold that are still able to be purchased


All of this leads me in the direction that I am missing something easy to fix and the result of user error.... I have taken pictures of everything I've taken apart and everything seems correct?

I would appreciate the knowledge of other forum members to point me in the right direction to resolve this issue.

- Thanks, Kyle.

 

[OffRoadScott]

I would double check your O2 sensors, the FSM calls for 5.5-6 ohms. My O2 sensors were newer and had similar mileage as yours do and were bad.

Not sure what year your vehicle is but have you checked the air meter and tested per the FSM for the proper year?

Mine 94 was experiencing similar issues but wasn't throwing codes and the above items were the issues.

 

[Kylackey]

I would double check your O2 sensors, the FSM calls for 5.5-6 ohms. My O2 sensors were newer and had similar mileage as yours do and were bad.

Not sure what year your vehicle is but have you checked the air meter and tested per the FSM for the proper year?

Mine 94 was experiencing similar issues but wasn't throwing codes and the above items were the issues.

It's a 93 so I'm assuming the same.
VAF tests within spec at 226 ohms
02s test at 5.8 & 5.6 so those are both good.

Appreciate it

 

[OffRoadScott]

It's a 93 so I'm assuming the same.
VAF tests within spec at 226 ohms
02s test at 5.8 & 5.6 so those are both good.

Appreciate it

What were the readings across the THA - E2 at ambient temperature?

 

[Kylackey]

What were the readings across the THA - E2 at ambient temperature?

2.81. FSM Says 2-3 is within spec?

 

[OffRoadScott]

2.81. FSM Says 2-3 is within spec?

Correct for about 70 degrees F.

When the motor was out did you have the injectors cleaned? Might have a leaky injector.

 

[Kylackey]

Correct for about 70 degrees F.

When the motor was out did you have the injectors cleaned? Might have a leaky injector.

Injectors have all been out, cleaned and installed properly. (RC Fuel Injection)

Truck doesn't misfire since I replaced the #6 injector connector as well as splicing on 2 new terminals. Just runs like s*** once high idle goes down.

The truck also has a new oem FPR and lines along with it.

Spent a few minutes spraying every single vac line, egr lines, intake manifold split, and air filter hoses with starter fluid and it did not change how the engine runs..

I haven't pulled them since instalation but I'm not sure what problems would arise if they appear to be firing and cleaned.

Ohm checked all grounds as well per the FSM and no issues. They're tight.

 

[OffRoadScott]

Injectors have all been out, cleaned and installed properly. (RC Fuel Injection)

Truck doesn't misfire since I replaced the #6 injector connector as well as splicing on 2 new terminals. Just runs like s*** once high idle goes down.

The truck also has a new oem FPR and lines along with it.

I haven't pulled them since instalation but I'm not sure what problems would arise if they appear to be firing and cleaned.

Ohm checked all grounds as well per the FSM and no issues. They're tight.

Then I am at a loss of ideas. Hopefully someone else chimes in.

 

[Kylackey]

Then I am at a loss of ideas. Hopefully someone else chimes in.

Okay!

So even after testing the ohms I unplugged each sensor with it running.. Instantly cleared up my rough idle and seems to have power again..

I'm suspecting you're correct with it being bad O2s.. That's crazy to me knowing I don't even have 10k miles on these!

 

[OffRoadScott]

Okay!

So even after testing the ohms I unplugged each sensor with it running.. Instantly cleared up my rough idle and seems to have power again..

I'm suspecting you're correct with it being bad O2s.. That's crazy to me knowing I don't even have 10k miles on these!

Mine were about the same and were bad. Did you use the correct O2 sensors?

With the 94s the NTK O2 with the longer tail is only available now but can be used on in both locations.

I used the Bosch O2 sensors and passed emissions. People on the forum will say the Bosch ones are garbage, there were things I did not like about them but Bosch has been in the game for awhile.

I did not like the fact they were separate flanges for the O2. Meaning they screwed into a flange and that flange mounted like the OEM ones.

 

[Kylackey]

Mine were about the same and were bad. Did you use the correct O2 sensors?

With the 94s the NTK O2 with the longer tail is only available now but can be used on in both locations.

I used the Bosch O2 sensors and passed emissions. People on the forum will say the Bosch ones are garbage, there were things I did not like about them but Bosch has been in the game for awhile.

I did not like the fact they were separate flanges for the O2. Meaning they screwed into a flange and that flange mounted like the OEM ones.

I used NTK replacements. I'm assuming when it blew a headgasket about a year ago it spit coolant out of the overflow bottle and might have drenched the exhaust.

Either way just grabbed a bosch pair at oreilys here locally and it seems to have resolved my issue! Fingers crossed. I really appreciate the help and knowledge. Enjoy your weekend!

 

[OffRoadScott]

I used NTK replacements. I'm assuming when it blew a headgasket about a year ago it spit coolant out of the overflow bottle and might have drenched the exhaust.

Either way just grabbed a bosch pair at oreilys here locally and it seems to have resolved my issue! Fingers crossed. I really appreciate the help and knowledge. Enjoy your weekend!

My pleasure and enjoy that LC.

 

[Kylackey]

Well... I'm here again. Let me recap what I've done and what I've checked so far. I replaced both O2 sensors since blowing the head gasket and going through a rebuild
I've driven about 1500 miles since the last time the truck has given me an issue.

The truck now has a fresh set of Bosch O2s (I know, but they're all I can currently get my hands on at the moment for my 93 ), and the truck is back to idling rough and shuttering. I can't get it to throw any codes at me, but I unplug one of the brand new O2s and the idle clears up and it seems to run fine.

I have tried the old NTKs and it does not clear up.

Checklist of items I looked at this morning:
-EFI Relay functions to spec.
-Ohm'd the fresh O2s they are within spec.
-Injectors are all firing. They've been rebuilt and don't seem to be causing any issues.
-Engine grounds (battery cables are new, engine grounds are new and tight)
-Checked for vacuum leaks. Found nothing. All new vac lines anyway.
-Input/Output temp on the CAT, seems to have a difference of 100 degrees which seems fine.
-Removed PAIR reed valve and function tested. Works properly.

I'd really appreciate anyone's recommendation/information on what could be a potential cause of my issue. Both O2s have less than 2k miles on them, but when I removed them they seem to be gunked? Not entirely sure they're supposed to be this covered in soot after such a short period. Looking at them has me think the truck is running rich.

 

[Malleus]

Have you checked the IAC?

 

[Kylackey]

Have you checked the IAC?

Just checked it with a stethoscope, I can hear it click.

Checking it out it appears the range is 10-30 ohms.

S1-S3 reads at 40

B2-S2 reads 20

Last one says to check B2 & S4? Also reads at 20?

Reading at 40 isn't within spec? Is that suspect?

 

[Malleus]

There are two tests, one electrical and one mechanical; the mechanical test is visual.

A high impendence would tend to indicate the motor is stuck and isn't moving the piston.

The IAC has to be removed in order to verify the correct piston extension/retraction. It could be moving, but not enough to completely block/unblock the throttle body bypass. When I hear of hot idle failures, this is the first item I check.

It's very easy to disassemble these valves and clean the piston bore; this was all it took for mine. The motor worked fine, but the piston bore had a very small amount of crap in it, and with the very little clearance in the bore, that's all it took to bind it. 20 seconds with a piece of crocus cloth and it was done.

 

[Kylackey]

There are two tests, one electrical and one mechanical; the mechanical test is visual.

A high impendence would tend to indicate the motor is stuck and isn't moving the piston.

The IAC has to be removed in order to verify the correct piston extension/retraction. It could be moving, but not enough to completely block/unblock the throttle body bypass. When I hear of hot idle failures, this is the first item I check.

It's very easy to disassemble these valves and clean the piston bore; this was all it took for mine. The motor worked fine, but the piston bore had a very small amount of crap in it, and with the very little clearance in the bore, that's all it took to bind it. 20 seconds with a piece of crocus cloth and it was done.

Yeah. Just took it out and cleaned it. When I rebuilt the whole intake got cleaned and looks pretty fresh. Unfortunately all the electronic stores around are closed at the moment so I'm not able to build leads to actually bench test it or else I would.


I'm just stumped. Truck will run perfectly fine once I Unplug that O2.. There's a problem just not sure where to look.

 

[Malleus]

My guess is that the unplugged 02 sensor is causing the throttle plate to stay open enough that, when the ECU thinks it should be closed at idle, there is sufficient airflow to prevent the A/F mixture from becoming too rich.

You don't need anything exotic to bench test the IAC. Two short pieces of bell wire will do. You're only supplying voltage to the motor. If you can confirm the motor turns through all four positions, with the piston installed in the valve body, it's OK. If it doesn't, then the piston is stuck for some reason, most likely carbon buildup in the bore. Once that's removed, it'll function as designed.

The way this motor works, if it turns at all, it'll turn the entire 360°. So, if it doesn't turn the entire way around when the load (piston) is connected, it's the load binding and not the motor.

FWIW, if you do verify the IAC isn't working properly, and you can't fix it, the later ('95-'97) versions are direct replacements. The '93-'94 version is NLA. A used IAC will work and is much cheaper than a new one.

 

[93yotasr5]

My major stumbling issue was fixed with a new (used) IAC. It only passed half of the tests per the FSM.

 

[Kylackey]

My guess is that the unplugged 02 sensor is causing the throttle plate to stay open enough that, when the ECU thinks it should be closed at idle, there is sufficient airflow to prevent the A/F mixture from becoming too rich.

You don't need anything exotic to bench test the IAC. Two short pieces of bell wire will do. You're only supplying voltage to the motor. If you can confirm the motor turns through all four positions, with the piston installed in the valve body, it's OK. If it doesn't, then the piston is stuck for some reason, most likely carbon buildup in the bore. Once that's removed, it'll function as designed.

The way this motor works, if it turns at all, it'll turn the entire 360°. So, if it doesn't turn the entire way around when the load (piston) is connected, it's the load binding and not the motor.

FWIW, if you do verify the IAC isn't working properly, and you can't fix it, the later ('95-'97) versions are direct replacements. The '93-'94 version is NLA. A used IAC will work and is much cheaper than a new one.

My major stumbling issue was fixed with a new (used) IAC. It only passed half of the tests per the FSM.

Okay. I think I bench tested it right. Constant power to stated terminals and then tapping ground wire to each stated terminal in order? Am I doing it right? The valve did not open or close when I did that.