FJ80 3FE Surging/No Power (3 Viewers)

[Connorrw]

Hello,

I am coming here after being stumped on my 1992 FJ80 with the 3FE. Here is a youtube video showing the problem.

The main issue that the engine surges about 200-400 rpm under little load and the problem is getting worse.

Initially, I thought it was a torque converter lockup issue but I have now forced the issue to occur even in neutral -- not the transmission.

The problem is definitely worse when the engine is hot. If I hold the pedal at about 20% down, it will struggle, but will make it. If I go past that, it surges and bounces. It feels like an on the power off power surge. When its not making power, I can push the pedal all the way down and get nothing.


So far, I have checked the TPS sensor - I measure about 0.7v when at idle and about 3.8v when wide open and the idle switch works.
The AFM I have checked with an oscilloscope and can see a smooth sweep of position.
I have done the FSM check of the ignition coil - I get 0.4 ohms on the primary, about 13.5k on the secondary.
I tested fuel pressure a few weeks ago and saw 40psi continuously. I'll be checking again tomorrow.
When shorting TE1 and E1, I see code 15 -- ignition fault.

Any ideas or good next troubleshooting steps?

 

[Connorrw]

I should also add that the video above is at constant throttle. That is the engine, in the diagnostic mode (ie locked timing?) revving by itself. I brought it to about 2000 and it does that.

Here is a video of what it looks like during driving.

 

[jonheld]

When shorting TE1 and E1, I see code 15 -- ignition fault.

I assume you mean code 14 as there is no code 15.
You're looking at a wiring issue between the igniter and the ECU or the igniter is failing.

 

[Connorrw]

I assume you mean code 14 as there is no code 15.
You're looking at a wiring issue between the igniter and the ECU or the igniter is failing.

Looks like it was code 14. Counting can be hard sometimes.

I took a good look at the wiring last night and got some interesting results I'm not sure what to make of.

Some background - I'm looking at the igniter primarily as that is the code per above. There is a 5-pin connector on the bottom and a smaller 2-pin above. Additionally, coming out of the harness at the same place, there is a 1-pole connector. Is that normal? This goes into a small capacitor to ground. This wiring (the 1 pole + capacitor) all looks like it was done by a previous owner, and not well. Is the capacitor normal in this area?

My results from checking stuff:
I went in assuming that I would get either no signal good signal on the 5 pin connector. When looking at the FSM that seems to be the signal from the ECU.

What I got though was 5v, 0v, 12v, GND, and 0v when probed with the key in the ignition position. I was assuming that one of the 5v or 0v was a signal from the ECU which led me to probe with an oscilloscope to see check for signal under cranking.

This led to 5v, 5v, 12v, GND, 0v all with static, non-transient voltages. This leads me to why I'm stumped. I was assuming to get nothing or signal, not something but no signal.

Is my guess right that one of those pins on the 5 pole connector is a ECU signal? Is my ECU not giving signal when the 5 pin connector isn't in? The car can run so some form of signal must be getting somewhere?

Does this make sense or should I look elsewhere to diagnose?

 

[jonheld]

The igniter and coil on the 3FE are mounted together on the right fender in 1 bracket, but are 2 separate items. The igniter is grounded through the mounting bracket. Make sure there is no corrosion on the ground points.
The igniter (89621-30010):

The ignition coil (90919-02185):

Ignition spark is developed by the pick up coils inside the distributor. Those pulses are fed to the ECU and adjusted for timing and duration based on sensor inputs.
The ECU feeds pulses to the igniter, which in turn feeds the primary of the ignition coil. The secondary of the ignition coil feeds the distributor rotor.
A snip from the Toyota EWD:

There are no other parts attached to either the igniter or ignition coil. Both of these items have been discontinued years ago.

 

[Connorrw]

Been traveling and finally got a chance to look again. I installed a new igniter and got no better results. Start checking wiring? Is there a common fault point? Any more advanced tests I can do with an oscilloscope?

 

[Hornd]

I'd look for a Bulged Capacitor on the ECU.

ECUS are No Longer Available but can be Reworked.

Once you watch this you Never Forget:

 

[Connorrw]

Finally got time to work on the truck. I had a spare ECU that came out of a running parts car, and so I swapped that in. I also took out the old ECU and didn't see anything concerning on the board.

The newly swapped-in ECU did FAR better. It took longer for the problem to develop and I was able to drive the truck around the neighborhood for about 20 minutes. Only on the way home up a very steep hill did the problem redevelop. After it started, I just parked the truck but it was occurring even after the hill ended. Before this hill, I had gone to full throttle a few times just to see if the problem started.

I'll pull the codes tomorrow. Any ideas based on this? My initial thought is that some sensor is throwing some garbage value and the old ECU was still calibrated for the old car's sensors. My understanding is that the ECU learns the sensors' normal ranges over time.

 

[jonheld]

I'd be willing to bet that if you swap in the old ECU, the exact same thing will happen.

By removing the ecu, it now has to relearn all the sensors. Same idea as pulling the EFI fuse or removing a battery terminal.

 

[Connorrw]

Yeah, I might try that after I pull the codes. To me this points to a sensor doing weird stuff. Either intermittent bad values or a continuously bad value. Any ideas on what sensors would be likely?

 

[jonheld]

Yeah, I might try that after I pull the codes. To me this points to a sensor doing weird stuff. Either intermittent bad values or a continuously bad value. Any ideas on what sensors would be likely?

ECU feedback for fuel trim would be the TPS, AFM, and O2 sensors.
Read the code(s) and follow the FSM.