Volkswagen Polo (1981 - 1991) - mk2 1.3 violent judder/mifire under load diagnosis

Honest John Back Room » Technical matters
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Tue 23 Oct 2007 12:53
mk2 1.3 violent judder/mifire under load diagnosis - steveo3002
right weve got a polo mk2 1300 MH engine

over a couple of days it started to have a mild judder that turned into a violent jolt (maybe misfire not sure ) and its so bad its undrivable now

it starts on the button and seems to drive reasonbly at very light throttle...any normal to heavy throttle and it jolts like crazy...idles great and revs at standstill nicley

i thought it was the hall sender and fitted a new dizzy complete with cap and rotor, plugs, leads and coil are very recent as is the fuel pump and carb base

its got the dreaded pierburg carb that wasnt running to bad apart from cold mornings

any ideas what to do next? could it be the carb causing those faults (id planned to weber it when funds allow) no airleaks that i can tell

not sure what to do now , apart from replace random parts

Edited by Dynamic Dave on 23/10/2007 at 13:33

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Tue 23 Oct 2007 13:13
violent judder /mifire under load diagnosis - Screwloose

Test the voltage difference between battery positive and the feed to the coil at idle and when revved.

Any possibility of a blocked exhaust? What's the air temperature when it does this?
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Tue 23 Oct 2007 14:03
violent judder /mifire under load diagnosis - steveo3002
will check what you said in a min

cant see the exhaust being blocked...temps id guess around 60deg, im outside in a tshirt....i doubt its icing as it does it within a few yards of leavin the house
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Tue 23 Oct 2007 14:53
violent judder /mifire under load diagnosis - steveo3002
coil is getting battery voltage


a few more things to mention...if i dip the clutch and it get it flat out it goes ok with no misfire....would that confirm the spark and fuel pump is ok?

im thnking it could be a carb fault ...idle jet is okay ,but something else is not??
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Tue 23 Oct 2007 15:00
violent judder /mifire under load diagnosis - Screwloose
coil is getting battery voltage


That wasn't what I asked for.
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Tue 23 Oct 2007 15:17
violent judder /mifire under load diagnosis - steveo3002
hmm what are you askng..it gets the same volts as the batt at idle and when rev...no loss of volts between the two
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Tue 23 Oct 2007 15:41
violent judder /mifire under load diagnosis - Screwloose

Maybe it is a fuel issue then. Have you got a good flow from the pump? Is the restrictor in the fuel return still there?
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Tue 23 Oct 2007 16:58
violent judder /mifire under load diagnosis - steveo3002
not sure about any restrictors ? it hasnt been tampered with for some time so it hasnt caused any probs up till now

its a recent fuel pump ...the mech type, is there anyway i can test this? obviously its working as it will idle all day, it will also roar along well if i can get pst the stumble to wot
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Tue 23 Oct 2007 17:03
violent judder /mifire under load diagnosis - Screwloose

If it's had a recent pump, then check that there isn't any rubber debris blocking the flow into the needle valve.
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Tue 23 Oct 2007 17:51
violent judder /mifire under load diagnosis - steveo3002
someone on another forum has suggested its the tci unit

any thoughts on that? could it give those symtoms?
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Wed 24 Oct 2007 12:47
violent judder /mifire under load diagnosis - steveo3002
right for anyone intrested

ive took the loom of for the coil/tci/dist and poked it around ...i could find any breaks but i put it back and its fine now

so i'll either rebuild the loom or find a used one in better condition
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