tb42 misfire

Submitted: Monday, Jan 27, 2003 at 13:38
ThreadID: 3107 Views:6040 Replies:10 FollowUps:10
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i have a1991 ford maverick ,auto,petrol/gas which has a misfire when at idle and in gear (approx 750 rpm). seems to be worse when on lpg, temp doesn't seem to make a difference . tb42 is carby and has about 145000 km .any ideas ?
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Reply By: stephenj - Monday, Jan 27, 2003 at 13:47

Monday, Jan 27, 2003 at 13:47
forgot to mention have replaced , plugs ,points , rotor , cap , condensor ,plug leads , coil.
AnswerID: 11921

Follow Up By: Oziexplorer - Monday, Jan 27, 2003 at 14:06

Monday, Jan 27, 2003 at 14:06
Have you checked the compression on each cylinder?
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FollowupID: 6815

Reply By: stephenj - Monday, Jan 27, 2003 at 16:04

Monday, Jan 27, 2003 at 16:04
no , i have not . but misfire not always there
AnswerID: 11925

Follow Up By: Oziexplorer - Monday, Jan 27, 2003 at 16:34

Monday, Jan 27, 2003 at 16:34
That does not matter if the misfire is not always there.

Shock horror, could also be a head gasket with a very small water leak. Are you using any water at all?

A compression test is always a must, especially with everything else you have done. I always like to keep an annual or twice yearly check on compression on petrol engines. Really gives you an indication when that rebuild is getting imminent.
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FollowupID: 6821

Reply By: ThePublican - Monday, Jan 27, 2003 at 17:58

Monday, Jan 27, 2003 at 17:58
If around Brisbane get your vehicle of to Hycraft Auto at Clontarf on the Redcliffe peninsular, gas experts, dyno reports pre and post tune,4way gas analysis ect.
AnswerID: 11932

Follow Up By: Stephenj - Tuesday, Jan 28, 2003 at 09:03

Tuesday, Jan 28, 2003 at 09:03
live in north qld, about a hour north of townsville , but thanks for the reply
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Reply By: stephenj - Monday, Jan 27, 2003 at 18:02

Monday, Jan 27, 2003 at 18:02
not using any water,i'll get a compression test done and go from there,thanks for the suggestion
AnswerID: 11933

Reply By: tour boy - Tuesday, Jan 28, 2003 at 06:52

Tuesday, Jan 28, 2003 at 06:52
Another operator had this problem. Turned out to be the head.
AnswerID: 11970

Follow Up By: Stephenj - Tuesday, Jan 28, 2003 at 09:18

Tuesday, Jan 28, 2003 at 09:18
thanks for reply tour boy . i'll go and see my local mechanic and get him to do a few checks. i actualy spoke to the nissan dealer about this little problem and the only things they could come up with was replace the rotor , because they thought the rev limiter was faulty , and they also said to disconect the tacho as it might have a short. both of these things did not work , so they said learn to live with it
. not saying all nissan dealers are like this , with the learn to live with it attitude. went to ford first ( being a ford maverick) as soon as i mentioned maverick ,went no further got told go to nissan.
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FollowupID: 6860

Reply By: Rowdy - Tuesday, Jan 28, 2003 at 18:39

Tuesday, Jan 28, 2003 at 18:39
Possible cause could be valve recession as LPG is a dry fuel and valve seats wear more rapidly than when on petrol and valve stems are more prone to sticking. If valves have recessed into the head they can cause a miss or hesitation at or just above idle, especially if hardened seats and valves are not fitted. This was a problem in the early years of LPG conversions before unleaded fuel was used and valves and seat quality was not as good.
Rowdy
AnswerID: 12016

Follow Up By: Stephenj - Tuesday, Jan 28, 2003 at 20:06

Tuesday, Jan 28, 2003 at 20:06
thanks rowdy, i'll get the mechanic to check that as well.
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FollowupID: 6926

Reply By: kezza - Tuesday, Jan 28, 2003 at 23:27

Tuesday, Jan 28, 2003 at 23:27
Ill go with rowdy - valves!!
kes
AnswerID: 12039

Reply By: Member - Steven - Wednesday, Jan 29, 2003 at 19:22

Wednesday, Jan 29, 2003 at 19:22
stephen
does it backfire if under load .i have an 89 patrol same motor brother in law a mechanic spent hours trying to find problem came home from alice springs 2002 bloody thing backfired every 40 ks finally went to a place called performance ignition nunawading melb web site as above i think i will look it up and post an addon any way they sold me an extended rotor button $55 also guy behind counter said if on gas open tappit settings normally .32?mm open to .5 mm we settled on .42 mm have not had 1 backfire , miss, burp , fart or other hiccup since installing and getting better fuel consumption
steve
AnswerID: 12095

Follow Up By: Stephenj - Thursday, Jan 30, 2003 at 15:50

Thursday, Jan 30, 2003 at 15:50
sometimes under load around the 80 - 90 khm range and i'll try the tappits at that setting.
thanks
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FollowupID: 7055

Follow Up By: Member - Steven - Thursday, Jan 30, 2003 at 20:50

Thursday, Jan 30, 2003 at 20:50
stephen probably better to trythe extended rotor button i think this is the main part as it shortens the distance the spark has to jump to fire steve
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FollowupID: 7067

Follow Up By: Stephenj - Thursday, Jan 30, 2003 at 21:08

Thursday, Jan 30, 2003 at 21:08
steven , i have sent a email to performance ignition regarding the rotor and waiting for reply , thanks for the information and reply.
regards stephen j.
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FollowupID: 7068

Follow Up By: Stephenj - Thursday, Feb 13, 2003 at 10:50

Thursday, Feb 13, 2003 at 10:50
final word , had mechanic do compression check , check for head crack, and also check valve recess . all ok . i have installed extended rotor from performance ignitionmelb , no more misfire at idle under load or at 80-90km .so far so good .the rotor seems to have fixed the problem , but when the budget allows a electronic conversion will be put in place . so thanks to everyone who replied your advice was extremly welcome.
regards stephenj.
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FollowupID: 7624

Reply By: Ferret - Wednesday, Jan 29, 2003 at 23:16

Wednesday, Jan 29, 2003 at 23:16
Toss the dizzy and replace with electronic ignition
AnswerID: 12119

Follow Up By: Stephenj - Thursday, Jan 30, 2003 at 15:52

Thursday, Jan 30, 2003 at 15:52
ferret ,can i use a nissan one from an electronic ignition model , or do i have to use a conversion of the aftermarket type ?
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FollowupID: 7056

Reply By: Member - Steven - Thursday, Feb 13, 2003 at 21:11

Thursday, Feb 13, 2003 at 21:11
stephen hopefully you will find economy increases as well glad you found problem and cure i have had my rotor in about 3 months and no problems (touch wood ) see you on the road steve
AnswerID: 13067

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