77FJ40_79PU

Hey I have a 79 pick up with an 83 engine, Ive been experiencing very violent bucking and then loss of power once i let off the gas and push in the clutch it stops bucking I try to step on the gas agian while letting out the clutch and it dosent do anything no power at all. The only way to get power back is to take it out of gear and then put it back in but then it just does the same thing. Some times it will run fine for a while but other times once it starts it just keeps happening. Never had this problem before... very confused. please help. Thanks.

IndustryYota

I have had some similar "bucking" action in my truck but no major loss of power. When it would happen I could usually power through it by stomping on the gas, or putting the clutch in. All I could figure was that the motor was suddenly getting a shortage or uneven amount of gas at some point. I couldn't find any fuel line leaks or clogs. I read somewhere that possibly a fuel hose may be pinching closed when the right amount of suction occurs. There also could be some vacuum leak or something else that is letting extra air in, but not extra fuel.

I'm rebuilding my truck right now and hopefully I fix this problem with new fuel lines, but we'll see. It is sketchy though, especially when it happens in traffic.

Scooby098

did you try replaceing all the fuel filters?

77FJ40_79PU

yea i just cleaned my fuel filter and i took it around the block and it ran good... I almost think it might be something with the engine running hot because it happens more when the trucks been running through out the day. maybe its a vacum leak. thanks for the advice though. ill keep pluggin away at it.

scooper

I know you can get a loss of power when you overheat, but the bucking im not quite sure of, unless you have warped the head or a gasket here somehow and the air/fuel mixture is not quite right. The bucking however, makes me think more of a fuel problem.

83

I'm still trying to figure out a similar problem. Thought it was fuel filters but I don't think it was. Only happens at highway speeds, and not reliably. Drove all the way to Phoenix (from Montana) and it didn't happen once. On the way back it happened twice. I'm thinking either a vacuum leak (but why only sometimes?) or maybe I need to replace all the rubber hoses in the fuel lines.

So yeah, try fuel filter, if that doesn't help make sure your carb is good, and fuel pump, and if those are good and don't help the issue, check fuel lines. Also the chance that it's vapor lock. Sounds a lot like my issue and I'm 99% sure it's a fuel issue, and I've got a new carb, fuel pump, I'm on my 5th filter in 1 year (kept changing them when the issue came up but I think that just pulling over and messing with the fuel lines made the problem go away, rather than the new fuel filter solving the issue...), and it's still been happening to me. I never see any debris in the the filter, either, so I don't think my tank is gunked up. Let me know if you figure out! I'll do the same.

IndustryYota

I tried new plugs too, Bosch Platinum, didn't do a thing. Also a new fuel filter, and nothing. The motor still always ran fine.

77FJ40_79PU

yea i cleaned the fuel filter i had on it and it ran ok for about two miles then it got really bad and now does it sometimes when im starting in first. im pretty sure all the hoses are fairly new because the engine was swaped in with only 7000 miles on it. I just got a name of a mechanic in town that knows toyotas pretty well im going to go see if he has any answers.

83

Cleaned the fuel filter, not replaced it? If it's happening for you at slow speeds, like in first, I'm guessing it's not the same as my issue, but I'd still like to know what you find out. It may help me!

ajoebob

have you looked at your clutch?

77FJ40_79PU

No i havent looked at the clutch i was kind of thinking it might be something to do with that since i have to take it out of gear to get power back. What do you think could be wrong with the clutch to make that happen?

83

Usually if loss of power is due to a clutch your symptoms will be the engine reving really high with no power associated to it, because the clutch is slipping. A slipping clutch can also "chatter" when you're first letting of it and give you bucking, but, if the engine is getting gas, it will rev high. If it's reving high and you're not going anywhere, then yeah, clutch, but if you're giving it gas and the engine isn't reving high, then it seems more likely to be a fuel issue, whether too much or too little.

I'm trying to think of other clutch problems that would just cause bucking and no slipping but I've never experienced any (doesn't mean it doesn't happen, though), so I can't help there.

I see you're in Bozeman! If you ever decide to give away your FJ I'll be happy to take it off your hands.

77FJ40_79PU

Yea i've experience a slipping clutch before and im sure its not that and i've experinced lack of fuel in my cruiser due to cloggin but i dont think its that. this is a tough one... i have driven that past two days and havent had the problem once, its just strange. Yea i just moved to Bozeman, my 40 is back in Vermont for I think i might be keeping that for a while tho haha. There are a few for sale around town in Bozeman tho and they look pretty good.

gsb15

i would say fuel, not clutch. i had almost the exact same problem in my '79(with an '83 motor) and it ended up being a bad fuel pump.

Scooby098

do you have a electric fuel pump ? When I got mine it seemed to give it a more constant flow, and when I got the bucking/ it was only when one of the 2 fuel filters on it were bad I have 3 on my truck. One at the gas tank. one on the fender, and one just before the fuel pump thats cause for warrenty is has to have it.

83

Yeah...I can't remember...read Marlin talking about what early model Toyotas came with electronic fuel pumps. Mine is definitely mechanical and I only have one fuel filter, but I'm not sure about a '79. If it's a mechanical fuel pump I'd have a hard time believing that it would come & go like that. They seem to either work or not work.

gsb15

when it happend on mine i was a new pump that was deffective. and changing the pump again deffinatly fixed the problem