3FE- Loss of power/mild stumbling/at mid RPM range

[lelandEOD]

I've been trying to diagnose an unusual problem with my 3FE for over a year. I've replaced almost all ancillary components that could cause this problem and have yet to find a solution.

Here's what it's doing: Warm or cold, I notice a slight hesitation/stumbling/sputtering as I accelerate through the RPM range. This isn't a violent loss of power or obvious miss but rather a subtle degradation of power that occurs from about 2,400 rpm all the way to 3,500rpm. At a very specific point, usually right at 3,500 rpm, it's almost feels like I flipped on a supercharger or something because the engine really comes alive. The loss of power is only noticeable under load (it free-revs fine) and is usually accompanied by a barely audible change in the exhaust note that can be best described as a mild buzzing or fluttering sound.

For the longest time, I was convinced this was a fuel pressure/supply problem. Last week, I bit the bullet and replaced my entire factory fuel system in favor of an aftermarket Tanks Inc. pump set up in the Con-Fer tank I've added to the rear. I've simplified the plumbing and am confident I'm supplying the needed volume and pressure (free of leaks that could introduce air into the lines) and I'm still getting the same hesitation symptoms at mid range.

Has anyone ever experienced something similar in their 3FE?

 

[woytovich]

You replaced the fuel filter, right?

 

[vipergrhd]

Check distributor cap and spark plugs for carbon tracking. It could be jumping spark across terminals and insulators do crack at times.

 

[LAMBCRUSHER]

egr CIRCUIT/// LOOSE VACUUM LINE...>BYPASS EGR AND REPORT BACK

 

[bigdaddychud]

My sons 62 does the same thing going up hill, usually he just mashed the pedal to get it to accelerate, still have not been able to fix it

 

[lelandEOD]

Mark,
the fuel filter is less than a year old but I ordered a new one just to be sure. Also, this engine has been de-smogged so there's no egr circuit. I have sprayed WD40 and used a map torch (gas only) at every gasket/junction/vacuum port to look for leaks. I haven't been able to find any.

Thanks for the leads, gents. Keep 'em coming!

 

[60Works]

My '88 has a dead spot between 1,200 and 2,500. If I can coax her to 2,500 she takes off like nothing is wrong. Only under load, in any gear, even in low range, at any temperature. No codes. Not MAF or EGR.

Lately she's started overheating, but only if on the highway.

 

[jcj_78FJ40]

egr CIRCUIT/// LOOSE VACUUM LINE...>BYPASS EGR AND REPORT BACK

x2
This has happened to me a couple of times (although mine is a 91).

1st time it was a clogged cat. 2nd time it was a clogged diverter valve to the EGR vlave.

Took me forever to figure out the 2nd one

 

[cruisermatt]

x2
This has happened to me a couple of times (although mine is a 91).

1st time it was a clogged cat. 2nd time it was a clogged diverter valve to the EGR vlave.

Took me forever to figure out the 2nd one

He is de-smogged so it is probably neither of these.

Have you had your injectors looked at? Often overlooked on this forum.

 

[lelandEOD]

I had the injectors rebuilt and flow-tested last year.

I'm also experiencing another unusual symptom that maybe someone can chime in on: The engine randomly cuts out or bucks momentarily when driving under very specific conditions. This only happens for a split second and it actually took me a while to recognize it as something wrong as opposed to just hitting a bump in the asphalt or rut on the road (it feels like a subtle jerking or bucking motion). I get this occasional jerk ONLY when I've barely got my foot on the gas (like when coming up to a stop sign or coasting to slow down for a speed zone) and the throttle is just barely cracked open. When it happens, the engine blips for just a moment and I can see a puff of smoke from the tail pipe that corresponds to the blip.

Ideas?

 

[jcj_78FJ40]

Did you remove the cats with the desmog? I had similar issues when a piece of the honeycomb broke off and was floating around.

Also, you might test the TPS.

 

[LAMBCRUSHER]

last symptoms sounded similar to when the ignitor took a nap on my 2F...first symptoms also sounded like how my old camaro would do when it had eaten another ignition module...you might look hard at your ignition system, from Key switch out...

 

[rjonesiv]

I've been trying to diagnose an unusual problem with my 3FE for over a year. I've replaced almost all ancillary components that could cause this problem and have yet to find a solution.

Here's what it's doing: Warm or cold, I notice a slight hesitation/stumbling/sputtering as I accelerate through the RPM range. This isn't a violent loss of power or obvious miss but rather a subtle degradation of power that occurs from about 2,400 rpm all the way to 3,500rpm. At a very specific point, usually right at 3,500 rpm, it's almost feels like I flipped on a supercharger or something because the engine really comes alive. The loss of power is only noticeable under load (it free-revs fine) and is usually accompanied by a barely audible change in the exhaust note that can be best described as a mild buzzing or fluttering sound.

For the longest time, I was convinced this was a fuel pressure/supply problem. Last week, I bit the bullet and replaced my entire factory fuel system in favor of an aftermarket Tanks Inc. pump set up in the Con-Fer tank I've added to the rear. I've simplified the plumbing and am confident I'm supplying the needed volume and pressure (free of leaks that could introduce air into the lines) and I'm still getting the same hesitation symptoms at mid range.

Has anyone ever experienced something similar in their 3FE?

Have you replaced your throttle positioning sensor?

 

[Trollhole]

Mass air flow is getting stuck or has an issue. Cant remember if fuel pump relay has a low and a high for fuel pump. Don't think so. BUt it would be good to measure voltage driving at fuel pump. Spec out TPS. Willing to bet it's mass air sensor.

 

[lelandEOD]

Thanks for the suggestions, fellas. I'll look into the AFM this weekend as I really get into this thing.

I did find something puzzling last night when I tried to confirm the O2 sensors were operating as designed. When I followed the FSM procedure for checking them (warm engine, install jumper at diagnostic port, maintain 2,500 rpm for 2 minutes, and count 5v pulses to ensure they are in range), I don't get squat. I'm using an analog voltmeter that I bought just to replicate tests specified by the FSM since my Fluke RMS can't give the same results (no needle to deflect).

I'm getting a steady 5v on VF1 and no voltage at all on VF2. So something is definitely wrong here. I'm going to do some more o2 diagnostics tonight. What a nightmare.

 

[STICKP]

@lelandEOD - Ever get your problem sorted out? I'm having similar issues.

 

[lelandEOD]

Not exactly solved but I was able to identify one problem. The cut-out/bucking symptoms that I described in Post #10 was a TPS out of adjustment. I replaced it and that issue went away.

The hesitation mid-RPM was still a problem through last September, when the engine blew a head gasket. That prompted a complete rebuild so I am cautiously optimistic that the problem was related to worn valve guides/seals allowing too much oil to be sucked into the combustion chamber. My theory is that if it was burning a good amount of oil that it would confuse the O2 sensors and the ECU would try to lean out the mixture. I'll know soon enough...

 

[STICKP]

Good luck with the rebuild. I'm about to take my throttle body off to adjust the TPS. I did so with it on, but from other threads it seems that getting it dialed in correctly is best done with the TB off. Do you agree?

 

[Neils4him]

Did anyone ever solve their issues on this? Mines doing the same thing. I had the valves adjustes, new plugs, new wires, new rotor and cap and MAF. Idles beautifully, put the pedal to the floor it accelerates great (as much as one can anyway...) but slow accelaration in the 1st to 2nd and 2nd to 3rd gears... it will cough, sputter, sometimes buck. Next steps?

 

[Seth S]

if you've verified all ignition components, checked timing, have good filters, and fresh oil change:

1.) Verify all grounds are clean and no broken ground wires
2.) Verify all vacuum lines are connected and none are broken
3.) Make sure the battery cables are in good condition, the terminals are clean and tight.
4.) Make sure your battery is good
5.) start the truck and hold a cloth over the end of the exhaust....is there good pressure build up and do you hear any air escaping under the vehicle? A leak before an O2 sensor could cause issues.

6. I'd next verify the Temp sensor is working properly. You should be able to check the resistance on it when cold, when warming up, and when hot and see three different values. (a mud thread on the sensor: FJ62 Water Temperature Sensor) I dont have the FJ62 FSM but I'm sure someone on here can post the test procedure and measurement range (usually a pot of hot water and an DVOM).

7. Verify O2 sensor operation. Best way for this is to use a scope to look at the O2 sensor pattern. You want to see a nice variation of voltage indicating a rich/lean/rich/lean mixture. If its a flat line it might be a bad sensor which could lead to a rich or lean condition and can effect running conditions.

8. TPS's are not usually the problem but when they go bad the engine might run well enough on the other sensors to hide the issue. Again you want to measure the sensor to make sure it returns a range of values as the throttle plate opens and closes.

9. Air flow meter: I think the toyota system uses a flap style air flow meter. If so it could be dirty or the electrics could be wearing and leading to a confusing reading at certain throttle positions..which drives confusion in the computer and that translates to performance issues. Easiest way to check is by putting in a known good meter...but there is a procedure without that and need to see what the FSM calls out

10. I've experience engine cutout under hard acceleration in my road car that was due to a fuel hose on the fuel pump kinking. So the car would start and run but under high fuel demand the flow would choke and the card would stumble.

some ideas, hope its useful