View Full Version : Accelerator feels like it stays down after revving
Hello.
Can anyone tell me why after i put my foot down, say in first gear then lift off it feels as if the accelerator pedal doesnt lift as quick as my foot??? and engine keeps going for like a brief second...
or when I rev my engine it revs down slowly.... and yes ive checked the spring on the throttle :scratch:
could it be something to do with an exhaust valve or somthing like this?
Doubt it'll anything serious. As you say its prob something to do with either the spring (gone weak), linkage or cable. Make sure the bracket that holds the outer sheaf of the cable to the bracket on the carb is not loose, is the cable kinked, does the inner cable move through the outer freely etc...........
thanks mate.. il check that all out today.... js thought it might be a valve not opening or somthing... i tend to think the worse thing... so anything not so bad feels much better lol
In my case it was the throttle plate shaft in the carburettor that had developed a kink and was jamming slightly and not closing like it used to.
However it was a 'cut away' type. A normal type might not kink.
Could the carpet or under foam be sticking around the top of the pedal?
DISASTER UPDATE :cry: :
ok well.. my car is now dead. :( :cry: I put my foot down in first gear then tried to change to 2nd gear... but 2nd never engaged... and this accelerator problem killed my car. After foot down in 1st, the accelerator stayed on for a bit too long (even worse as it never went into second) so engine revved REALLY high..
wen i did put it into second... sounded and felt like only 2 cylinders where running. :( (luckily happend on my road)
struggled to get the car down the road to my house and parked it up. It cuts out. Ive checked all the basics.. thought it might be something on the rocker shaft.. but everything looks ok there.. :(
Ive taken out the plugs and on one of them the end looks like there is a 2mm chunk missing.. so im guessing somethings happening inside one of the chambers....
Any ideas? could be a valvue broken or somthin????
Tony Walker
20-02-2010, 19:02
Think a compression check will reveal your problems mate. my accel pump arm jammed a few times causing my throttle to jam open, ideally you need to sort the original fault before fixing the misfire. take the accelerator spring off and see how stiff it is to move or if any linkages jam, it does sound to me as maybe a bent valve (hopefully bent pushrod) fingers crossed mate :D and get a revlimiter about £100 but saved my engine the day my throttle jammed open.
well... im going to take the head off hopefully tommorw at some point and inspect.... :scared:
The linkages from accelerator to spring on throttle all seem fine and free moving. I think is some sort of carb fueling problem? posiibily???
with the engine off, while looking at the throttle.. pressing the accelerator pedal fully down and letting go.. looks fine.. with the throttle fully opening and closing...but when driving and foot down specially in higher revs.. seems like a ghost controls the accelerator for a split second keeping it down for a touch longer.. :S
Anyone know what this could be??? (other than linkage probs in the cable run)
valve prob? i dno :S :scratch:
If its fine when you operate the throttle by hand from the carb end but the problems arise when you press the throttle pedal, then the problems must lie between the pedal and the carb which would indicate a sticking throttle cable to me ????? :)
ok.. well il check the easy stuff to do with the cable after i do the difficulty stuff now! :mad: (taking head n stuff off)
Can someone please come round and do it for free?
Thank you very much.
Tony Walker
21-02-2010, 20:45
See if you can turn the engine over by hand first, big socket and ratchet on the bottom pulley, make sure nothings touching and turns over nicely, you should be able to feel the compression strokes while turning too. if it turns over ok and doesnt jam, dont just take the head off, do a compression test, see if a cylinder has a problem, if the valves are still sealing ok then u may just of bent a pushrod(best case scenario) the damage on the plug doesnt sound good, but without seeing it i cant really comment. are all your plugs well worn?? has the tip just corroded off?? or is the ceramic broken and come away?? Either way if your engine turns over by hand nicely then a compression test is your next step.
Scottish9Turbo
21-02-2010, 21:22
as above like tony says mate.... sounds like if its over-revved the engine, somethings spat the dummy
markey b
22-02-2010, 00:08
last time i over-revved mine i bent a pushrod... replaced it and back on the road again :agree:
could be the throttle cable freyed inside the sleeve, so even if the spring works with no cable on its got to fight against strands of cable when its all connected.
ok well.. couldnt take the head off today anyway due to the rain. But as ive just read.. better not to yet anyway..
It was just the one plug which had like a 2mm chunk off it.. not sure whats caused it.. as there not that old...maybe 1year? (but hardly driven car)
I will try and turn it over by hand.... so as far as i understand.... if it turns fine... then do a compression test next.. to see if its a valve? .... if it doesnt turn nicely?? what does that mean!??? :scared:
and im assuming a dummy is a pushrod??
in the mean time... today i bought: new dizzy cap and plugs. (although i know its nothing to do with them.. thought id get new stuff for peace of mind)
markey b
22-02-2010, 00:16
pushrod is a pushrod, spitting the dummy is just a phrase ;)
Tony Walker
22-02-2010, 00:37
Yeah turning it over by hand just makes sure its safe to flick it over with the starter for a compression test. if you feel like its jamming then you know either a piston is touching a bent valve of something broken inside the cylinder. it will feel quite dificult to turn when your compressing each cylinder but it should not lock solid. if it locks thats when you'll need to remove the head.
Yeah turning it over by hand just makes sure its safe to flick it over with the starter for a compression test. if you feel like its jamming then you know either a piston is touching a bent valve of something broken inside the cylinder. it will feel quite dificult to turn when your compressing each cylinder but it should not lock solid. if it locks thats when you'll need to remove the head.
If it locks il need to remove the head?, im sure il need to move the head whatever the prob.. im sure its a prob wiv either something in or todo with one of the chambers or something to do with somethin on the head.. valve or rod.
But rain strikes again.. gives me time to think... if i turned it over by hand the wheels will move right? that means i have to jack it up right? but when all this happend i tried to drive it home and put it on my drive which is a slope and put my hand brake up, but it snapped so now wat!! :cry::cry: i dno... il try something soon and update... can someone tell me why i shouldnt just remove the head anyway and inspect??? i have a feeling i want to do this..
They won't move if you put in neutral.
UPDATE:
Taken Head off,,,,, 1 Valve is snapped in Head :( The piston has a bit of a dent and score on the top under where the valve normally. :cry:
Is it still possible to leave this piston and maybe sand it? or smooth it or do i need to change it?? :sad: :hmmph:
OH: and can i re-use head bolts? if not.. anyone got some??
and valves? i need new valvues? where would i get them from? anyone have any? and valve springs? how can i tell if they are uprated..? i have a feeling they are not.. if they are not.. i need uprated ones as i have a 285 cam.. anyone can help.
Replace the piston as it's probably weakened the ringland.
Also get the rod checked, incase it's banana'd. And if you're really unlucky, it might have fecked the crank as well.
im pretty sure the bottom sounded fine tho :(
u sure il have to change the piston??? nooooooooooo
Fair do's. I'd personally be getting the crank checked, but it's your car.
At the least, I'd definitely pull the piston out to check the rod is true. If that's ok, just swap the piston over but retain the rings - You won't have to run anything in again then.
To answer your other Q's, for the sake of a few quid I'd fit new head-bolts. New valve(s?) from Renault (maybe even GSF might stock them) which either way won't cost the earth, and Piper for a set of valve springs.
thanks Mart. Could it ruin somthing or not work properly in some way if i try it without replacing the piston??
Because to replace the piston.. that means whole engine out right? :hmmph:
im no expert.. and im tryin to do things so the car is back on the road quickly.. cos im leaving the country soon :( so wana get it back on the road before then :sad:
If you've got the head off already, it's a half hour job tops - Jack the car up, stick it on axle-stands, clamp the liners down so they can't move, remove the sump, undo the 2 big-end nuts relevant to the piston/rod in question, pull off the lower half of the big-end shell (if it doesn't drop off when you remove the nuts), then just remove the piston & rod from the top (give the underside of the piston a nudge upwards until there's enough meat showing to pick it up/out from the top).
You'll more than likely have Tarabusi or Perfect Circle pistons in situ, which you should be able to source a one-off jobby from posting a 'Wanted' on here.
A local engineer shop will be able to swap the piston & rings over, then it's just a case of re-fitting it all.
Or if you're of the dishonest nature, ignore the piston issue, and just fit the new valve(s), refit the head, and say nothing more when selling the car (which I guess is why you want a quick fix, if you're off to pastures new soon?).
Rob@Backyardracing
22-02-2010, 23:03
It would just be a pain to build the car back up to find an issue, as said tho it could have damaged the piston within its cast, bent a rod, or even gave the shell (bearing) a beating, the softest part.. to change a piston its no huge deal just sump off (as said). BUT while your doing such a process you need to take care not to let ALL or ANY of the liners to lift while you rotate the crank as this can disturb the seals etc..
thanks guys...
reason im not wanting to do all this... cos ive never done anything with the bottom end before.. ive only done a head gasket before... and this would be not that difficulty for me to re do if i have to take the head off again if it doesnt work... :crap:
hmmm..
P.S
Im not or dont have any plans to sell the car. Ive had it for nearly 10 years! and have put alot of effort and hard work and money into this car (although i might know nothing compared to some of you guys.. but i like to believe i know enuf to understand pretty much everything) I love this car! although its like nothing but trouble! :mad:
In that case, do it right the first time around :agree: You'll only kick yourself if a few miles down the road after rebuilding it, the bottom-end starts knocking due to a fecked bearing/fudged crank journal.
sure ... I understand that Mart... I would love to be able to change a piston that quicly.. but reality is.. i cant and im leaving the country for a while very soon. When i get back i will rebuild it for sure. As i find it not too difficult to just take head off and on,,id like to try that incase it works. I just dont have enuf of an expertise opinion as to weather it will combust properly due to the chip in the piston...
but yes... i will (wen i have time) rebuild it properly. But for now.. its not possible :( if it works then great.. but il still rebuild it wen i get back... if it doesnt work.. then im carless. :dearme:
Alastair
22-02-2010, 23:36
sure ... I understand that Mart... I would love to be able to change a piston that quicly.. but reality is.. i cant and im leaving the country for a while very soon. When i get back i will rebuild it for sure. As i find it not too difficult to just take head off and on,,id like to try that incase it works. I just dont have enuf of an expertise opinion as to weather it will combust properly due to the chip in the piston...
but yes... i will (wen i have time) rebuild it properly. But for now.. its not possible :( if it works then great.. but il still rebuild it wen i get back... if it doesnt work.. then im carless. :dearme:
If your doing a quick fix make sure you dress the piston crown and remove any sharp edges, they are stress raisers.
I agree with Mart though, do it properly if you can mate, to remove the piston is really easy, whip off the sump and undo 2 big end bolts and away you go. You will need a piston ring compressor tool (v cheap) to drop the new one back in too. Dont forget to lap your new valves in properly too!:agree:
Either way good luck getting it back together. Any issues then shout up:)
Thanks alot mate :agree: :agree:
Quick qeustion.... Is it normal for a valve to brake because of very high reving? what can i do to avoid this.. other than a rev limiter?
Tony Walker
23-02-2010, 23:06
Depends how high the rpms, mine went to 8000rpm wheel spinning in the wet and not knowing there was no limitier, thats why i bought one. one of the best purchases ive made. luckily my car survived. depends what cam/springs you have. more lift + more duration is gonna mean its getting closer and closer to the piston. which is why u need the stronger springs.
ya ive checked and i have uprated springs :cooter:
Rev limiters are worth every penny, set it to 7k, would have saved your engine. I know mine has when wheelspinning/missing gears (cough kris m testing the van at the pod;))
:ashamed:, certainly made a nice pop for the spectators when i missed a gear :D
Ok... ive been doing some reading.. and apparently the valves seem more likely to snap with these uprated valve springs for a 285 cam.....
so why use uprated springs? whats the point? why not use standard ones? (sorry.. im very dumb :laugh:)
Ok... ive been doing some reading.. and apparently the valves seem more likely to snap with these uprated valve springs for a 285 cam.....
so why use uprated springs? whats the point? why not use standard ones? (sorry.. im very dumb :laugh:)
As quoted from above : depends what cam/springs you have. More lift + more duration is gonna mean its getting closer and closer to the piston. which is why u need the stronger springs :)
Tony Walker
24-02-2010, 21:51
As the cam lobe starts to move away from its fully open position the spring is what makes the valve return to its closed position so that the piston can reach TDC(top dead centre) without hitting the valves. at high rpms the valves open and close very quickly so the stronger spring helps the valve close quicker it also reduces the valves tendency to bounce.
i think i found out what contributed to this happening! .... one of the m7 bolts that hold the rocker shaft was loose! ... I remember when i put the head on last time and the middle bolt was quite short... and not much thread left to put the nut on...
on inspection.. the valve that broke is right next to this bolt that is/was totally loose!! :(
i think i found out what contributed to this happening! .... one of the m7 bolts that hold the rocker shaft was loose! ... I remember when i put the head on last time and the middle bolt was quite short... and not much thread left to put the nut on...
on inspection.. the valve that broke is right next to this bolt that is/was totally loose!! :(
:( quick question please for people in the know...
i have got a spare valve (exhaust valve) that i will be changing... but looked in the whole where you put the valve (sry for being not so technical) and it has 2 cracks now :'( do i need a new head???
If the crack is just in the valve guide then you maybe able to get the guide(s) replaced be a suitable machine shop. If it's in the head then :(
If the crack is just in the valve guide then you maybe able to get the guide(s) replaced be a suitable machine shop. If it's in the head then :(
Thanks Alex :) Indeed its the valve guide :) il need to replace that.... learning every minute :)
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