FJ80 3FE Surging/No Power (2 Viewers)

[Connorrw]

I was able to test fuel pressure. I get a consistent 40 PSI even during the surging.

I also plugged in a spare TPS and moved it by hand and the engine responded to the movement and tried to rev.

After reading some other posts, I started to suspect the AFM. I disconnect it while the problem was happening and the engine seemed to rev cleaner but hit a soft limit at 2K.

A previous owner shorted the idle switch of the AFM so the fuel pump didn’t shut off for that test.

Any further ideas? Thanks for the help.

 

[jonheld]

A previous owner shorted the idle switch of the AFM so the fuel pump didn’t shut off for that test.

That's not an "idle" switch. That's the flap switch that is the ground path for the secondary coil in the COR that fires the fuel pump.
I would reverse that ASAP. In the event of a collision, the fuel pump will continue to run even if the motor stalls. Not a good scenario.

 

[Connorrw]

That's not an "idle" switch. That's the flap switch that is the ground path for the secondary coil in the COR that fires the fuel pump.
I would reverse that ASAP. In the event of a collision, the fuel pump will continue to run even if the motor stalls. Not a good scenario.

I plan to. It’ll be an easy fix.

Any other ideas? I checked my intake tubing and it held pressure even as I gently flexed it.

 

[jonheld]

I plan to. It’ll be an easy fix.

Any other ideas? I checked my intake tubing and it held pressure even as I gently flexed it.

In an earlier post, you mentioned that the EFI MAIN relay was chattering.
Does this coincide with the surging?
This would cause all sorts of issues. The EFI relay supplies +12 to all the sensors as well as the fuel pump.

The ECU fires the EFI relay with a logic high on pin 3. Pin 1 should be a hard ground.
This is starting to sound like faulty/corroded connections in the relay box. Very common given its location directly above the exhaust manifold.

 

[Connorrw]

Thanks for the response. After testing more, I think the ECU isn’t allowing the motor to exceed 2000 rpm.

I checked the relay with just ignition on and got 12v. What is the pin on the ecu that controls the EFI relay? I can check it during the surges with an oscilloscope. I tried MREL as that seemed like but got no continuity regardless of the 12V either ignition.

I checked IGT on the ecu while the problem was occurring and didn’t see anything noteworthy. Just the frequency of pulses increasing during the surges.

I’ve attached two more videos of the problem, one of the exhaust puffing and then one showing the AFM being disconnected mid surge.

I think disconnecting it brings the rpm lower and below the point that induces the surging. If I add throttle while the AFM is disconnected, it will still surge.

It seems like no matter what the ECU tries to keep below 2000rpm. If I shift into first on a downhill it will still occur even when at no throttle. It still takes a bit of driving to induce the problem.

Thanks for the help.

 

[Connorrw]

Started to suspect that this was a sensor that was ignored until some threshold. In the FSM it describes warmup sequences. To me this seemed like open-loop control while the O2 sensors finished heating. I suspected this as during the first run of the day, it takes about half a mile for the problem to begin. After that, it depends on how long the car sat, but it can occur again as soon as 30 seconds of driving. Seemed like some heat threshold.

Based on the FSM, it seems like the ecu decides to enter closed-loop control based on the efi coolant sensor. I assumed that if that was unplugged, it would never enter closed-loop control and the bad sensor would be ignored. It didn't work. I also tried this with the two O2 sensors swapping them to see if either one was problematic.

No change in symptoms or time.

I also measured the temperature at the entry and exit of that catalytic converter as it was suggested it might be plugged. After the problem occurred, it was about 550F on the entry and about 615F on the exit. The muffler was about 420F on entry and 350F on exit.

Furthermore, I found the Vacuum diagnostic write-up. I measure within the normal range at about 19 inHg at idle and very stable. It lowers to about 0-2 inHg on full throttle and 25 inHg in the transient coming off throttle. It doesn't sag or change like there is an intake vacuum leak or an exhaust clog like the write-up suggests.

Any ideas based on this?

 

[Connorrw]

Jonheld do you know what is the minimum amount of sensors and other related things the ecu needs to run?

Something like injectors, O2 and AFM?

Want to disconnect as much as possible and slowly reintroduce things them in. Hoping to find out what side of the problem is on (sensor bad reading or ‘actuator’ not able to do what the ecu asks)


Not expecting it to run well, just run in the driveway enough.

 

[jonheld]

The EFI relay is fired from ECU connector E5 pin 3 (MREL).
That hits pin 3 of the EFI relay (coil) and the other side of the coil is pin 1 which is a hard ground.
This is all documented in the FSM and EWD.

As far as pulling sensors, you're going to have to field that one on your own. Remember that you're dealing with 1986 technology here. Removing any sensor that triggers a CEL will force the ECU revert to a base map for that input.

You should also clear error codes after each attempt.

 

[Connorrw]

I verified with an oscilloscope on the ECU pin while the surging was occurring that the relay output was constant and that it wasn't triggering by feeling it while running.

I then unplugged the sensors, trying to force the issue not to occur.
At first, I unplugged:
AFM
TPS
All temperature-related sensors
IAC
1/2 O2 sensors.
2/6 Injectors

The engine ran, and I was able to make it around the block. I do not think it was making enough power to have the problem occur but it was able to rev past 2k on flat ground. I pulled the injectors as I was suspecting their connectors to be inconsistent.

I next plugged back in the injectors and AFM, as that was the main cause of not making power and not running right.

After doing another loop around the neighborhood, the problem occurred even with no temperature sensors, no TPS, and no IAC. As soon as the problem started, I pulled over and disconnected the AFM. The problem was identical to before, now just with black smoke coming out of the exhaust. I plugged it back in after this and pulled the connector of the most suspect injector.

The problem went away temporarily. I would describe it as delaying the onset. I had the problem occurring, pulled other sensors, it still occurred, I pull the #1 injector connector, and the problem goes away for another 1/4 mile. I was able to rev past 2000 RPM. Unfortunately, when I got back to the hill, it still occurred.

After this, I swapped to the other O2 sensor and immediately got the problem after the normal amount of driving needed to cause the problem after the car was already hot.


Pulling the injector after this to confirm my test did not show any changes. On one of my test drives, I was able to get through the surging band and past 2000 rpm. After it was through, it made good power and ran well until it upshifted and was back into the problematic RPM band (~1500-2000). Reproducing this was difficult. I tried forcing a downshift on a downhill, and it would not go above 2000 rpm.


Pulling the injector stood out to me as I believe it will cause all other cylinders to run richer as the fuel trims are adjusted. (Assuming the O2 sensor works).

Any ideas? I'm not sure if pulling the injector and being able to push through the RPM band was just a fluke.

Thanks for the help.