84 60, 2F, starts and idles great cold or hot but loses power after 1-4 miles (2 Viewers)

[elripster]

So I have recently resurrected Mudhon, formerly Pisoschett, though is very close to earning back its old name, and am having an odd problem.

I have just brought the beast back to life. I have resealed the intake and exhaust as well has had a new exhaust fabricated. I have replaced all of the vacuum lines and verified the vacuum is excellent. I have plumbed in all of the smog junk and can electrically connect/disconnect at will. The truck has that Performance DUY distributor all timed up. When it is running right, it actually gets up and goes even with stock gears and 35's.

Today I attempted a drive on the highway and she started up on a 38 degF morning like a champ. She fell in to a nice idle I figured I was good go to. I got the highway and got up to 65MPH with no problem and was feeling the stoke. Then she started to lose power. As I pulled over she bucked a little and lost more power with each buck. Basically it took on an oscillation where each buck caused another. At the side of the highway I noticed it was idling perfectly but as soon as I tipped in the throttle it would sputter. While running I popped the hood and checked the fuel filter and it was full as always. Admittedly, maybe due to the light, I could not gauge how much fuel was in the carb via the sight glass. It might have just been that low.

So I run out of options and call the tow truck. After about 20 mins I pull the emissions junk fuse I installed and try again. Go figure it runs like a champ - again. I text the tow driver my status and give it a shot. I get about 1.5 miles down the highway to the next exit. As I leave the light it starts to act up. I then get on the highway going home hoping to reduce the tow bill. Unfortunately it bucked itself to a stop on the on ramp and purred gently as it rested there refusing to produce any useful power.

When I got home and off of the tow truck I started it up and it of course ran great to its truck bed in the back yard.

I am bit unsure where to go. The fuel filter is new. If I had a bad fuel pump I'd expect fuel starvation under all loads especially when the choke is on. If the fuel cutoff was not working it wouldn't idle or really run at all. I suppose I could have clogged jets but how do they clear when the vehicle sits of 10-20 minutes? With the emission "off" the EGR shouldn't activate but I guess that doesn't mean it can't. Still, if that was stuck open I'd expect major difficulty idling vs. the gentle lope it enjoys.

Thoughts?

Frank

 

[OSS]

In my experience-
Bucking was always a fuel starvation issue.

Things to consider:
If a fuel filter is plugged up, it'll still be full of fuel on the outer canister side that you can see. Since there's no way to visually know for certain if the filter is plugged, replace it.

There. -could- be junk floating around in the carb float chamber intermittently blocking the main jet.

The fuel pump -could- be spazzing out. Replace it with a Toyota pump if it's over 15 years old.

It's -possible- for the carb float to stick sometimes. Remove the carb cap & inspect. Also check the needle valve strainer.

Pulling the choke knob when the engine is the slightest bit warm will not richen the mixture like a normal choke. It will only speed up the engine exactly the same as if you were pushing down a little on the gas pedal. When the engine is warm, the choke knob only acts as a throttle positioner, not a choke.

 

[elripster]

The fuel pump is of unknown age and should just be replaced so that is on the list. Since fuel filters are cheap I will just get another new one for the heck of it since it might have caught a bunch of junk. I will pop the carb cap and inspect there as well.

Frank

 

[HemiAlex]

I would smoke test it first and make sure you don’t have a cracked intake manifold.

 

[elripster]

What is the smoke test? I sprayed for vac leaks and measured with a gauge and vac is good. If I had a bac leak I would typically expect poor idle but ok-ish higher rpm performance.

 

[HemiAlex]

What is the smoke test? I sprayed for vac leaks and measured with a gauge and vac is good. If I had a bac leak I would typically expect poor idle but ok-ish higher rpm performance.

Often times an intake manifold leak is a thermal activated crack. Mine only ran poorly when it was warm. Pull the carb off and make sure it’s not cracked in the intake directly below.

 

[elripster]

So when running poorly, did it idle ok and have hesitation under load?! Or how did it run poorly?

 

[HemiAlex]

Idled fine, drove fine for a few mins and would have a miss that came and went. The misfire would cause a bad carb cough.

My intake was cracked. Worth a check before you do anything else.

Also worth just changing your fuel filter or checking if the tank has junk in it. My 300k original fuel pump had no issues when I swapped it out.

 

[elripster]

I will recreate the issue and spray for vacuum leaks and hopefully that will help diagnose a cracked intake in the event one cannot visibly see the crack.


Frank

 

[dannyvp]

The fuel pump -could- be spazzing out. Replace it with a Toyota pump if it's over 15 years old.

In my experience-
Bucking was always a fuel starvation issue.

Things to consider:
If a fuel filter is plugged up, it'll still be full of fuel on the outer canister side that you can see. Since there's no way to visually know for certain if the filter is plugged, replace it.

There. -could- be junk floating around in the carb float chamber intermittently blocking the main jet.

The fuel pump -could- be spazzing out. Replace it with a Toyota pump if it's over 15 years old.

It's -possible- for the carb float to stick sometimes. Remove the carb cap & inspect. Also check the needle valve strainer.

Pulling the choke knob when the engine is the slightest bit warm will not richen the mixture like a normal choke. It will only speed up the engine exactly the same as if you were pushing down a little on the gas pedal. When the engine is warm, the choke knob only acts as a throttle positioner, not a choke.

Is it typical to need to replace the fuel pump every 15 years or so? I have no idea if mine has been replaced, but it does like to "buck" in second gear between 1000 and 2000 rpms....

 

[OSS]

I wouldn't say typical, but they don't last forever. I'm not a fan of running mission critical components (fuel pump) for decades to see how many miles I might get out of it. When fuel delivery problems crop up, I'm a proponent of the nuclear method of anything fuel related over 15 years old gets tossed regardless (if I can't figure out what's wrong)

 

[elripster]

Agreed. If i find a clogged fuel filter I will likely stock up them and just replace as they clog. They cheap, towing is not.

Frank

 

[elripster]

I have also read similar symptoms from a clogged charcoal canister causing vapor lock. Looking at the schematic I can see why. It looks like if the out vent control valve is closed and fumes from the bowl cannot get out and through the charcoal canister fast enough pressure could build and prevent the bowl from filling with fuel fast enough.

My canister looks old as sin so I will just replace that too.

Frank

 

[dannyvp]

I have also read similar symptoms from a clogged charcoal canister causing vapor lock. Looking at the schematic I can see why. It looks like if the out vent control valve is closed and fumes from the bowl cannot get out and through the charcoal canister fast enough pressure could build and prevent the bowl from filling with fuel fast enough.

My canister looks old as sin so I will just replace that too.

Frank

I thought those were discontinued now?

 

[elripster]

I ordered a Delco version I found on a thread here so we shall see how that goes.

 

[HemiAlex]

The Delco version will work great as long as you’re using a factory aisan carb.

 

[elripster]

Perfect, I have to use the factory carb due to Cali emissions pain.

 

[elripster]

I didn't quite get to the point of a test drive today but I did find a few things.

The line from the carb to the evap just past the switch was kinked which would explain vapor lock. I swapped out for the Delco and replumbed so that should take that oddity out of the equation.

I replaced the fuel filter for fun and dissected the original and it was spotless.

I have a new fuel pump but the existing looks rather new and I don't yet see signs of it failing. If the issue is gone I will keep the new one as a trail spare.

I swapped out the air rail as well as a load of other little things and ended finding that the thermostat is stuck open which is why the temp hardly moves off of cold. It's quite new but I will again swap it out...

I hope to test drive tomorrow.

Frank

 

[elripster]

Time for an update.

I drove today and while it ran well it did start to sputter after a hill on the freeway. It recovered at the light and figured I'd put the new fuel pump in for good measure. I did that, swapped abseal under the thermostat, and replaced the fan clutch since the red one I had would not unlock.

The engine still ran too cool with the radiator and thermostat housing warming together but it was warmer than before. I took it up a challenge hill, I15 north to Rainbow, and it pulled 65-70 the whole way. pretty good for a 60 on 35s and stock hearing.

When I got off of the freeway it stalled. It would not idle so got to a friends house nearby. It go worse to where I now have the opposite issue, runs well under load but won't idle.

I was able to clearly see fuel in the bowl centered in the sight glass. I removed the carb lid and found the bowl filthy. I cleaned it hoping that would help but no luck. I did not have my vac gauge to present hypotheses are clogged jet or vac leak....

Tomorrow I will spray out the jets and hopefully she will run well enough for a smog trip.

It looks like coolant is going around the thermostat so I will try adding a second seal under it.

 

[FJ60Cam]

Pull your fuel sender (access panel in your cargo area) and look in the tank for junk.

I had a truck (40) in the shop recently that was doing this. It had some fine silt in the tank that was clogging the pickup tube after driving a bit. After sitting, it would drain back out and run perfect til it clogged again.