3f gremlin can't be found

[don runk]

I have a weird problem. Starting cold is not a problem, idles fine, revs without load fine. BUT if I try and rev under load (driving while engine cold) the engine will act like it is out of fuel/spark, goes from 3000rpm to 1000rpm in a heartbeat but doesn't die. It is rather dangerous since you pull out start to accelerate then all of a sudden the engine brakes come on!! The truck is on LPG but I get a similar problem on petrol checked fuel delivery and no apparent problems there. Of course once at running temp she's fine. Even if it has been running a few hours ago it won't happen. Has to be cold from overnight etc.

I have thus far replaced chasing this gremlin -
Leads and plugs
Dizzy cap and rotor
Pertronix ignition module and coil
LPG converter

It's a 91 with the 3f motor (not 3fE)

Hoping someone has some new ideas for me. (praying actually)

Thanks in advance guys best forum out there!

...via IH8MUD app

 

[don runk]

Any chance this could be a clogged catalytic converter??

be clogged up cold and free up when it warms up?

not sure if it fits but i'm grasping at straws at this point.

 

[angerhater]

motor mounts?

 

[don runk]

Thanks Shaun but mounts all look fine.

It is very temp dependent (must be cold from overnight) so things like mounts etc would present themselves at all temps

it's like the power is cut when under load at rev's. Yet idles fine and revs in neutral fine too. give it about 4 mins running and problem is gone.

could i have this in the wrong section as most here talk of the 3fe not the 3f carb?

 

[BILT4ME]

If this is a carbureted engine I would lean toward an automatic choke or heat riser issue. I have experience with Rochester and Holley carbs on GM products but not Toyota on this one. If it is OK once warm usually there is a heat riser off the exhaust manifold to warm the air to the intake of the carb and or the choke spring. Once warmed up the problem goes away. Can you convert it to a manual choke? If you know what you are doing they work better.

...via IH8MUD app

 

[don runk]

Thanks Bilt4me!

The 3f carb is factory manual choke and had a play with that and it functions correctly so i doubt that is the issue.

there is no heat riser fitted either, from top of carb it is straight air duct to air cleaner on opposite side of motor.

Thanks for the ideas!

 

[robertk61]

Could be a long shot but I have seen it before in my 30 years as a mechanic, the dizzy could be gummed up by the old grease lubricating the weights not allowing it to advance properly, but when it warms up it loosens up? may be worth popping the dizzy cap off when its cold and see how hard it is to move the rotor around, then try the same when it is warm.

 

[don runk]

nice one!

will definitely try that! i have been scouring the internet for months about this thing and another common comment is check vacuum hoses. perhaps vac advance hose aswell.

it's really doing my head in! and i only get one shot a day to try something new before the truck warms up and the problem is gone. then i have to wait till the following morning.

cheers any other ideas?

 

[don runk]

Thanks Robert,
i tried the gummed up dizzy and feels the same cold and warm.

i had a play with the carby to check all linkages were working and my vac hoses before taking off too.

all to no avail.

any other ideas guys?

thanks for the help so far.

 

[robertk61]

Don, it looks like you have covered the electrical part, so it has to be fuel related.
BUT have you done the basics, like valve clearances, timing setting etc first? Does the accel pump in the carby work correctly and have you checked the float level? I have seen a few threads on the fuel screen collapsing in the tank, but that should affect it all the time. Where do you live? I am in Boronia, so if you are nearby Maybe I could help you out?
Sounds like a weird issue though.

 

[voorland80]

You've done the ignition part. Try rechecking vacuum lines and routing, EGR, also check for leak at base of carb.

 

[don runk]

thanks robert and voorland,

rob - i'm in caulfield bit of a ways but may take you up on it if i cant sort out in mean time. i have alot to do - birfs,box etc in mean time but if i cant solve it i will deff take you up on the offer thank you heaps!

thanks for input voorland haven't checked for carb leaks. not sure about EGR but may replace vac lines just in case.

may look into the ignition switch not giving ignition module enough current also. have checked earth but not sure about ignition switch. at '91 it really could be anything hence the frustration.

 

[BILT4ME]

Fuel Filter? I had a GM once that wouldn't run up to highway speed, but would idle w/ no problems.

 

[red62]

.I may have missed it, but did you try adjusting the timing? It sounds like something that used to happen on an engine I once had. A mechanic could time it perfectly, but the only way to get it to run well was if I would time it by ear. It too only dogged while cold and more so if under load at the same time.

If you haven't already satisfied yourself it's not the timing, in your case, I would try adjusting it advance a few degrees before starting and while overnight cold, then take it out right away and see if it accelerates under load. It may take a few adjusts to get it right if this is the problem or part of it. Good luck.

Also, does your carb have jets?

Sorry, I see your timing comment now robertk61. I agree with the vacuum lines being a likely candidate too.

 

[don runk]

*update*

since i have checked -

running a jumper to the coil to eliminate ignition switch supply.

have found the only vacuum leak at the PCV point at the rocker cover, have sliconed up temporary to test - no difference (perhaps slight though could be imagining)

-

timing was checked not long ago and the engine doesn't have a history of changing timing, but will look into it. though i doubt that would be temp dependent.?

fuel pump is probably not the cause as i have problems with both fuels (LPG and petrol) though petrol will try and stall faster at take off and lpg will get to a few thousand rpm before shutting down.

i have read that the carby on the 3f is renound for the vacuum secondary playing up. so may look into this.


any thoughts on the secondary or any other ideas for me look at? thanks guys but it's still $hitting me to tears.

 

[BILT4ME]

don runk:
I think you're on the right track to look at the secondaries. As I stated before, the Toyota carb is new to me, however, principles are the same. There is a vacuum port that must draw vacuum to open the secondary butterfly based on the throttle position.

There is usually a piece of linkage that the primary must be in a certain position before it will allow the secondary to open. Then, a combination of springs control it's opening rate, based on vacuum. Look for clogged vacuum ports in the bottom of the carburetor. I would first give the carb a good soaking (while still on the truck) with carburetor cleaner. Spray in on the outside, and, with the engine running, spray it on the inside. You may need to hold the throttle open while you spray it into both the primaries and secondaries. If you happen to kill the engine, that's OK. If it dies, spray it all over inside and let it sit for a couple hours. Maybe even pull a few vacuum lines off and spray the carb cleaner into the port (not down the hose) Let it sit and try starting again later. It will start hard, but should clear up as it runs. If that doesn't solve it, I think a carb kit is in your future. Also run a screwdriver over all of the screws on the carb body to make sure they are all tight.

I assume you've read all these...
https://forum.ih8mud.com/60-series-wagons/135987-help-3f-carburetor.html

You may want to post in the 60 series section, as you are close enough that the 60 series may apply to your early 80 for the 3F problems. FWIW

 

[LandCruisinMy93]

I have a weird problem. Starting cold is not a problem, idles fine, revs without load fine. BUT if I try and rev under load (driving while engine cold) the engine will act like it is out of fuel/spark, goes from 3000rpm to 1000rpm in a heartbeat but doesn't die. It is rather dangerous since you pull out start to accelerate then all of a sudden the engine brakes come on!! The truck is on LPG but I get a similar problem on petrol checked fuel delivery and no apparent problems there. Of course once at running temp she's fine. Even if it has been running a few hours ago it won't happen. Has to be cold from overnight etc.

I have thus far replaced chasing this gremlin -
Leads and plugs
Dizzy cap and rotor
Pertronix ignition module and coil
LPG converter

It's a 91 with the 3f motor (not 3fE)

Hoping someone has some new ideas for me. (praying actually)

Thanks in advance guys best forum out there!

...via IH8MUD app

DON, is your cruiser Manual or auto? Maybe you're looking at the engine and not also at the transmission, If the problem happens under load, your transmission could be fighting your engine. My other thought is that if your timing is in fact correct then you should do a carb rebuild. Im not familiar with the 3f specifically, if its a timing chain system, not to much worry, if its a timing belt system, it could be loosing timing do to belt stretch from oil contact or from a bad timing belt tensioner.
hope it helps to prime the brain for diagnosing

 

[don runk]

hi guys just to update as i hate people leaving dead threads.

i have replaced the pcv valve and had a play (rattle everything around) on the carby

the gremlin has disappeared for now so thanks for all your input.

the gremlin did disappear before once and then raised it's head again so i'm not 100% confident it's gone but it could well be the carby that was the issue.

but i'm hoping it was a leak at the pcv valve and replacing that has fixed it for good!!

thanks again guys you're a godsend!

 

[Hootsmon]

hi guys just to update as i hate people leaving dead threads.

i have replaced the pcv valve and had a play (rattle everything around) on the carby

the gremlin has disappeared for now so thanks for all your input.

the gremlin did disappear before once and then raised it's head again so i'm not 100% confident it's gone but it could well be the carby that was the issue.

but i'm hoping it was a leak at the pcv valve and replacing that has fixed it for good!!

thanks again guys you're a godsend!

Hate to revive a closed thread but this has started happening on my 91 3F. Am in Melbourne as well funnily enough. Have ordered a PCV valve and grommet.

Did the problem stay sorted with the valve change?

 

[BILT4ME]

Hate to revive a closed thread but this has started happening on my 91 3F. Am in Melbourne as well funnily enough. Have ordered a PCV valve and grommet.

Did the problem stay sorted with the valve change?

Unfortunately, the OP hasn't been back since 05/2014. He may not reply.

What are you experiencing and what have you done so we can all go down the path.