Weird intermittent power loss

[antiacus]

Today was slightly different. It actually made a sort of "bogging" noise and i was able to feather the throttle (more like pump) and nurse it home. I would get about 1/2 second of power before it lost power again but if i pumped the gas it was enough to maintain speed.

 

[antiacus]

Also, because it's intermittent it's tough to diagnose but i was able to get under the hood and manually activate the throttle. Didn't help.

I also noticed when it bogs down at idle, something clicks and it revs up to normal idle. Like there is some sort of bypass to whatever system is failing that idle can control. Not sure how well i'm communicating this.

 

[BILT4ME]

I'm thinking fuel pressure drop. Since the throttle body movement does not increase the RPM, then it must be limited by the fuel volume/pressure. Possibly the fuel pressure regulator or the fuel pump not getting a correct signal for the two speed. Possibly a dirty sock or filter. Although the fuel problem would be RPM based or distance based, if it reaches its limit, it may limit the response.

Jonheld: Brain storming: Is there a vacuum line that if it came off or moved and leaked, it would limit fuel pressure? Fuel pressure regulator? My first thought was the TPS, but the mechanical movement should override it. What if the throttle lever was slipping on the shaft of the throttle butterfly? Remove the intake hose and observe the movement of the butterfly with the throttle cable movement? Detached throttle cable? It would move with the pedal movement, but may not actuate the butterfly.

OK: Shoot holes in my thought process....

 

[Chupacabre]

Mine is doing the same thing... also a 91, I have desmogged, replaced tps, removed cats, rewired and cleaned maf, replaced spark plugs and wires, replaced one O 2 sensor (the other one will have to be cut out probably), I've run several injector cleaners through it and still no dice. I'm thinking I'll change fuel filter and sock along with the distributor cap and rotor when I get time unless there are any better suggestions or you found a solution antiacus. Mine also doesn't seem to clear the check engine light or display the codes. Cel just stays on solid all the time no matter what I do.

 

[antiacus]

Today i installed a new cap & rotor and discovered i had a vacuum hose loose https://forum.ih8mud.com/threads/anyone-know-what-this-hose-does.839201/

I can't say for sure when that thing came loose. I drove it about 5 miles symptom free after fixing the hose and the new cap & rotor but i've been duped into thinking it was fixed before

We shall see.

 

[antiacus]

Started cutting out again on the way home from work last night.

I was thinking of replacing the fuel sock, fuel filter and maybe ignition coil next?

Actually I haven't checked all the connections between the alternator and coil yet so I guess that's next.

 

[Oscar Witte]

I'm not an expert in the least , but to me it would definitely have something to do with fuel pressure. This would explain how the Revs build only for a second then die down. The fuel filter would be the next most logical step in my opinion.

 

[Kaid000]

Today was slightly different. It actually made a sort of "bogging" noise and i was able to feather the throttle (more like pump) and nurse it home. I would get about 1/2 second of power before it lost power again but if i pumped the gas it was enough to maintain speed.

EXACTLY! HELP
I changed Fuel filter
Fuel pump
TPS
RAIDIATOR 3 times this month!
(It keeps cracking in the same spot)
Air intake hose

 

[jonheld]

I'm thinking fuel pressure drop. Since the throttle body movement does not increase the RPM, then it must be limited by the fuel volume/pressure. Possibly the fuel pressure regulator or the fuel pump not getting a correct signal for the two speed. Possibly a dirty sock or filter. Although the fuel problem would be RPM based or distance based, if it reaches its limit, it may limit the response.

Jonheld: Brain storming: Is there a vacuum line that if it came off or moved and leaked, it would limit fuel pressure? Fuel pressure regulator? My first thought was the TPS, but the mechanical movement should override it. What if the throttle lever was slipping on the shaft of the throttle butterfly? Remove the intake hose and observe the movement of the butterfly with the throttle cable movement? Detached throttle cable? It would move with the pedal movement, but may not actuate the butterfly.

OK: Shoot holes in my thought process....

The fuel pressure on a 3FE should be constant. There is no fuel pump relay that controls pump speed like on the 1FZ-FE. The only fuel pressure regulation comes from the vacuum operated FPR and the fuel pressure damper.
I have been thinking about this one for a while and I keep coming back to the TPS. The fact that the engine "smoothly returns to idle as if you let off on the pedal" is telling me that the ECU is not getting the correct information or the throttle is disengaging. It could be mechanical or sensor related. Without physically inspecting the linkage and testing the TPS and throttle body, there is no way to rule that out.
In any case, mechanicals need to be checked out first.
Fuel pressure can be easily monitored off the cold start injector feed line as a diagnostic.

 

[jonheld]

Started cutting out again on the way home from work last night.

I was thinking of replacing the fuel sock, fuel filter and maybe ignition coil next?

Actually I haven't checked all the connections between the alternator and coil yet so I guess that's next.

Does the issue occur only after driving for about an hour or so, or is it bad at startup?
Your inline fuel filter and fuel pump pickup filter are original? I'm thinking after 24 years of service you may want to take them out to dinner and a movie.
If your ignition coil was faulty this motor wouldn't run.
If your charging system or alternator was faulty there would be a 3 light display on the dash.
There are no direct connections between the alternator and ignition coil. The distributor pick up coils generate pulses that are fed to the ECU, processed, and then fed to the igniter which generates a pulse that feeds the primary of the ignition coil. None of this has any effect on controlling engine RPM, it just makes fire. The ECU controls injector pulse width/timing, ignition timing, etc. and it's all based on the feedback it receives from various sensors.

 

[antiacus]

Thanks jonheld. Today I'll replace the fuel filter. By the looks of it it's the original. I'm assuming i won't be able to find the fuel sock locally, if not I'll order it.

The condition has worsened. On my way home the other night i nearly had to pull over to the side of the highway. It started cutting out about 2 minutes after start up. It cut out off and on for about 6 or 7 minutes then suddenly ran great for the last 5 minutes of my commute.

I don't work until Monday so I'm really hoping to get this sorted by then.

Weird that there are three people on here with the exact same intermittent symptoms.

 

[Oscar Witte]

If you get stuck somewhere disconnect the filter and shake it around a bit. Sometimes to unclogs some of the holes.

 

[jwilber]

I had the same issue or at least very similar to what you describe. I checked my fuel pressure and it would bounce up and down. To make a long story short i replaced my fuel pump and have been issue free for months

 

[taccruiser97]

That is what I was wondering, would a fuel pump going out act up intermittently or do they just quit?

 

[antiacus]

I've heard lots of accounts of intermittent problems before finally quitting.

 

[antiacus]

So after changing the fuel filter, cap, rotor, and inspecting the fuel sock it's run perfectly for about 100 miles of city driving. Last night i started her up to go home from work and it started to stumble. I fired up the camera phone asap.

Not sure how helpful this will be but here it is: at about 0:15 it starts to stumble. At 0:30 i start feathering the throttle. Around 0:50 or so it starts running great and ran terrifically all the way home.

The loud rattle is from a ghetto exhaust hanger someone installed (on the list to fix) and the oil pressure gauge has always read low. There's no valve clatter or other signs of low oil pressure.

 

[antiacus]

Ran fine all the way to work today. In the last 100 miles i've only had a couple hiccups, none worse than the video posted above.

If i had gotten a bad tank of gas would it take a few tankfuls to flush it out?

It does seem to have gotten better since the new fuel filter.

 

[Oscar Witte]

Yeah could have been bad gas.

 

[Relstcruzr]

I'm having this same issue with my 96. Just started today. I found if I could sit for even 30 sec it would run fine again for a spell. What was the resolution of this issue?

 

[MyCrush]

OP
1yr later, I'm wondering if all is still well?

I've a 94 showing the same random symptoms.