Power Loss Help (1 Viewer)

[prossett]

Hi guys, hope you can help out as I can't easily access a good mechanic.

1994 FZJ-80 auto gears.

Problem started with yellow check engine light coming after leaving the driveway in the mornings. When the light would come on, engine would lose power, some sort of safe-mode I guess. Turn off engine, wait a minute, switch it back on, and truck would drive normally.

Code was 26 - oxygen sensor or circuit, and confirmed by rich fuel smell.

After a few weeks, loss of power throughout the day even without engine check light. Exact symptoms are:

- from stop, accelerate and no power, engine hesitates, and then slowly the rev counter passes the 2,000 rpm mark, and the engine surges back to life.

- if accelerator pedal is kicked harshly at the start, no power loss issue

- when power loss happens, shifting into N removes problem and engine revs normally

- no issue in Reverse

- cruising at 50mph, depress accelerator without downshifting and there's no increase in power, until the Rev counter creeps up and passes 2500 rpm mark, after which it surges back to life.

Any and all advice welcome.

 

[jonheld]

Code was 26 - oxygen sensor or circuit, and confirmed by rich fuel smell.

Did you replace the O2 sensors?

 

[Tools R Us]

Check the O2 wiring, on the early rigs it's known to rub on the drive shaft, shorting and/or breaking it.

 

[prossett]

Thank guys - O2 sensor seems ok. Since there's no cat there's only one after the manifold.

Still can't find the problem

I'm hoping it's not the tranny. How could I tell if it's a sensor vs gear slipping?

 

[KliersLC]

You said that the problem goes away at WOT?

Maybe fuel pump relay? IIRC, it has a low side and a high side--could be corroded/degraded on the low side.

I don't think it is likely, but you might check the intake tube and the wiring harness by the EGR.

 

[jonheld]

Thank guys - O2 sensor seems ok. Since there's no cat there's only one after the manifold.

Still can't find the problem

I'm hoping it's not the tranny. How could I tell if it's a sensor vs gear slipping?

Is it still throwing an O2 code?

 

[Qball]

Thank guys - O2 sensor seems ok. Since there's no cat there's only one after the manifold.

Still can't find the problem

I'm hoping it's not the tranny. How could I tell if it's a sensor vs gear slipping?

Just curious on how you came to the conclusion that the O2 sensor seems ok? As far as I know there isn't a visual inspection or test for the O2 sensor in the FSM.

At the very least clean it.

 

[prossett]

Sorry, I wasn't clear - I was responding to the guy who suggested checking the O2 sensor wires, so I meant the wires are fine. I read that to check the oxygen sensor there's a procedure in the Haynes, seems like probing with a multimeter to monitor the voltage fluctuations. I'll try that this weekend and hopefully I can find which sensor is playing up.

First I'll start from the O2 sensor as you guys suggested, thanks!

 

[prossett]

OK, problem found. It was the wiring connector to the AFM (Air Flow Meter).

It was pure luck. The AFM tested out ok with the multimeter, but the wire connector clip was missing. So with tranny in D, foot on the brake, and accelerating so that the hesitation was clear, wiggling the wires showed the problem very clearly - wiggle up and the revs would shoot up, release and the engine would choke again.

Now I have a length of wire wrapped around it to hold the wiring connector tight in place, but it's iffy, of course - any ideas?

 

[95ToyCruiser]

Sounds like your shift solanoids, search and you should find some threads...

Next time, try to shift into "1" and then manually shifting through the gears, if it acts fine, it's your trans...

 

[inkpot]

You can probably get a new OEM plug with all retaining hardware and just re- pin it. John