Hesitation, stumble, flatspot

[humper99]

I have been trying to track down why my completely stock FJ60 has a erratic stumble on acceleration. It only happens about 25% of the time regardless of throttle opening and usually occurs between 1800 - 2600 rpm. I've noticed that it tends to happen more when the engine is hot, but it's done it when the engine is cool as well. Almost acts like it's droping cylinders but I don't feel or hear a miss. Frustrating part is that it will be completely fine one second then down on power the next or vice versa. Idles perfect and runs out on the highway fine.

I've replaced the cap, rotor, wires, plugs, PVC, vaccum advance, and rebuilt the carb. Everthing is tuned spot on including the timing and valves, and the EGR is unhooked.

What else should I look for and does this sound like a fuel problem or an ignition problem? Heck could it even be an emission problem? Please help I love my 60, but this is getting annoying!

 

[IDave]

Compression leak or head gasket leak under load?

I assume you checked the fuel filter(s) for plugging.

 

[Cruiserhead05]

i had the same problem in my late model 40. spent 800 putting in a new carb, that didnt fix it. turns out i fixed it myself with a 2 dollars fuel filter. my 40 had two of them one was hidden. i had to learn the hard way. follow your gas lines and replace any and all filters you may have.

 

[swank60]

If your EGR is unhooked, it seems like that could cause a problem. Also, check and make sure everything that's unhooked in that system is plugged up and that there are no vac leaks.

Might also check the charcoal canister and see if it's plugged up. Sometimes that can cause weird things to happen.

My money is on the fuel filter though, if you haven't checked it.

 

[swank60]

Oh, and have you checked your air filter? (just in case)

 

[vtcruiser60]

This is not an uncommon problem with the 60's. The topic has been covered several times here, though each time seems to uncover a new solution. For example, see the following threads:

https://forum.ih8mud.com/showthread.php?t=6934

as well as.....https://forum.ih8mud.com/showthread.php?t=16417

Seems like you are going about it correctly, tuning and fixing the cheap stuff first. Do take a look at the EGR downpipe and check for leaks there. My rig ran great and did not stumble at all after I cleared up that leak.

Keep posting too, we'll try to help.

 

[humper99]

I've changed alll the fuel and air filters I could see. The problem was also there before I unhooked the EGR, made no difference. I'll have to check for that EGR pipe leak. Couple other symptoms that may or may not be related is a fuel smell every so often while driving and when cold starting with choke after a day she will fire then die. I must repump and she'll fire again stumble then start running correct.

Also when I removed the fuel line from the carb just 30 min. after she ran I didn't get any fuel spill from the line. Kinda espected to see some there but none. Normal or check valve problem.

 

[swank60]

Hmmmm. Could it be the fuel pump? Seems too random for that, but I'm usually wrong when it comes to fuel pump diagnosis.

If it's pulling gas away from your carb, and you're getting a fuel smell - those symptoms would have me looking at the charcoal canister and the vent lines to the tank. The only thing that I've ever heard that causes the fuel smell is the charcoal canister (unless there's an obvious leak) - for whatever reason, if the vent lines are stopped up, vac pressure builds up and gas gets either sucked back into the tank or into the charcoal canister.

One quick check on the vents, I think, would be to loosen up your gas cap while you drive and see if that makes a difference. It needs to be loose enough so no vac builds up.

Also, pull the chacoal canister and see if it smells like gas. It shouldn't. If you have the FSM for the emissions system, it has a complete test for the charcoal system.

Speculating here, but you've done everything else...

 

[dogboy2]

I second Swank60 on the charcoal canister and the fuel smell. Strong fuel smell under hood is indicative of a non-functioning canister or one that is partially plugged, short of a leaky fuel line, etc...

Suffering from a similar problem with our '60, there are other components to the EGR system that affect the vacuum operation of the system and it's overall function, regulating the timing and duration of the EGR valve opening/closing. Check out your BVSV, the VSV, and the EGR Vacuum Modulator as well as all of your vacuum lines. HIGHLY recommend the Toyota Emission Control Repair Manual for troubleshooting.

HTH,
-dogboy- '87 FJ60