GQ TB42s bad misfire problem

LUX253
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GQ TB42s bad misfire problem

Unread post by LUX253 » December 21st, 2010, 7:44 pm

Hi guys, having a problem with my patrol 4.2 carby motor. It's got a bad misfire at any revs under any load and seems very inconsistent. It actually affects the tacho enough that it look like you are turning the key on and off quickly, and the engine stumbles, the tacho flicks around.

Now I have replaced the following
Plugs
Leads
Dizzy cap
Rotor button (standard)
Points
Fuel filter

And have adjusted
Points gap
Set dwell to 38degrees
Set timing to approximate 12degrees (it's on gas too but prob is on both fuels)

Have checked the coil and ballast resistor. And yet the problem remains!

Looking for any suggestions! I had the problems ages ago but It seemed to be gone when I did the tune up, and I was running on gas most of the time,
However I have recently decided to use petrol more so have a brand new original carby just gone on and need to get it running perfect on petrol before I get a gas tune up done please help I'm lost for ideas I have had the other mechanics at work look at it and we are out of ideas!

R&R
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Re: GQ TB42s bad misfire problem

Unread post by R&R » December 22nd, 2010, 9:52 pm

when you checked the timing was the timing mark steady or did it jump around a bit.
recheck the dizzy make sure there aint any sideways movement just grab it where the rotor button goes on ant try move it side to side to see if there is any movement there.

budha066
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Re: GQ TB42s bad misfire problem

Unread post by budha066 » March 11th, 2011, 6:52 pm

I had same problem with my GQ on gas Mechanic tracked it down to a push on wire termanal on side of coil had corrsion. replaced it now runs fine.

Jaymes
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Location: Parkwood Queensland

Re: GQ TB42s bad misfire problem

Unread post by Jaymes » July 25th, 2011, 2:52 pm

Did you find the problem? I'm having a similar problem with mine now. Have replaced all the same things as you also checked the lead from coil to engine everything's fine there. I'm guessing it's my carby as when the overhaul kit was put in I noticed that the diaphragms were starting to give out. However at the time no one in my area was able to source them not even ford or Nissan. Now that I've moved to the gold coast I hope to find someone down here who can order them in for me.

paulie0735
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Re: GQ TB42s bad misfire problem

Unread post by paulie0735 » July 25th, 2011, 8:11 pm

Float level, will just about guarantee it’s to low and or you have fitted a non genuine needle and seat that don't suit the Australian carbs. Don't ask me why they are different, they just are and you will never get it right. Go to a Nissan dealer and order a genuine needle and seat than reset the float level using a piece of Perspex cut to size to put in the front of the carb as a temporary way to view the level. Fuel level needs to be almost at the top of the viewing glass, adjust the needle until you get it right.

macca1981
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Re: GQ TB42s bad misfire problem

Unread post by macca1981 » July 26th, 2011, 4:32 pm

Hey guys i had the exact same problem in mine and it is a very common problem in the gq where either the dizzy shaft wears excessively and the points start to chatter causing the miss and backfires and the tacho jumps around as well. Also the top plate in the dizzy wears where it joins to the advance diaphragm causing the same problem
mine was getting to the point where it was getting undriveable every time i went up hill or took off from the lights it would backfire or miss...it was a pig!!

i went to performance ignition on mitcham vic they do a changeover fully rebuilt dizzy with crane electronic ignition setup for $440 sounds expensive but its never ran better and no points to change. the only thing that upsets me about it is i bought a timing light when i bought this car and now ill never have to use it again ;)

Jaymes
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Location: Parkwood Queensland

Re: GQ TB42s bad misfire problem

Unread post by Jaymes » July 26th, 2011, 5:05 pm

Thanks for the info guys, car ***** itself today. Managed to get my boy off to school which is only 10 minutes down the road, ran like a dream and I said to the missus hey the cars running well today. Got to the hill at the bottom of our street and it started playing up again by time we got to the top of the hill she stalled. Now it will start then stall right away unless its held at 1100RPM and will idle steady, at about 1000 - 800 RPM with the air box off you can hear it sucking air iregularly and its idling up and down between 800 - 1000RPM once you drop it down below 800RPM it stalls again and wont start untill you pump the gas at the same time as turning the key. Ill start by buying doing the following tomorrow.

genuine needle and seat
checking the float as stated in the above post
Ill then replace the dizzy cap
points
condenser
leads
plugs
and ballast resistor all over again to genuine parts instead of the after market ones i have on there.

paulie0735
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Re: GQ TB42s bad misfire problem

Unread post by paulie0735 » July 27th, 2011, 4:21 pm

Have you fiddled with the vacuum lines at all recently? If as you say it’s sucking hard at a fast idle you may have inadvertently plumbed one of the main vacuum feeds up to the control solenoid that is connected to the carby, the one I'm talking about is fitted to the carby on the rocker cover side. If that solenoid gets full vacuum it will cause a very erratic idle, it will be a pig to start and when (if) you do get it running you get a loud induction noise at idle. The other thing that happens is its actually ok when its cold as the fast idle cam compensates for the overly lean condition caused by the solenoid, but when it warms up it’s a pig!!! Worth a look before you throw a heap of coin at it trying to hit the target! You can leave that solenoid free of vacuum, it’s not actually needed in our climate. If there is a vacuum line connected to it just pull it off and block it up.

I think its time I put up a vacuum line diagram and carb adjustment post.

Re the distributor, yes its true they wear and the rotor button is actually too short from new but its rare that this will cause serious issues, its more lazy starting (they still start ok, just a few more cranks than normal) and a poor idle, but never seen one cause as much drama or as bad as what’s described in the posts above.

Jaymes
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Location: Parkwood Queensland

Re: GQ TB42s bad misfire problem

Unread post by Jaymes » July 27th, 2011, 8:26 pm

Thanks for the post paulie and to answer your question no i hadnt changed any vaccum hoses prior to the issue, it just appeared out of the blue 2 days ago and crippled the car within that time.

I actually threw bit over $500 plus a few new parts i had laying around at the car today after a phone call to a carby rebuild shop in clontarf and he told me by what i was describing that it was most definatley spark related. So I went and got a new coil, ballast resistor, condensor, points, platnium ngk plugs, new leads didnt touch the dizzy cap or button because at inspection there was no indication of damage to these as they were only done about 3 months ago. While i was at it i checked that there was no intake vaccum leaks by checking the manifold, and carby was seated correctly, replaced the fuel filter even though that was replaced 2 months ago, I replaced the thermostat as ive been meaning to do this for a while and just hadnt got around to it, also replaced the rocker cover gasket, none of which has fixed my problem. So guess tomorrow ill be checking i have no collapsed or blocked fuel lines, checking the fuel pressure, and fuel pump, also noticed that i have unusually high oil level so im going to check that i dont actually have fuel going into the crack case from the internal diaphragm on the fuel pump. Im convinced that its a fuel issue dispite what the carby rebuild shop tells me because i pretty much illiminated the electrical side of things today and still have the problem. If all else fails i guess it will be a trip to the mechanic on friday to see if they can find the issue.

Jaymes
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Location: Parkwood Queensland

Re: GQ TB42s bad misfire problem

Unread post by Jaymes » July 29th, 2011, 2:56 pm

Tool it to a carby specialist yesterday he had a good look spent 45 minutes on it and didn't charge me told me I had a clogged idle jet go home remove the idle screw and spray a can of carby cleaner down it leave it an hour put it together and come back Monday if it don't work. Guess what it worked. Also found I have a faulty petrol pump, it's pumping fuel into my crank case.

paulie0735
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Re: GQ TB42s bad misfire problem

Unread post by paulie0735 » July 29th, 2011, 7:52 pm

good news, not so good about the fuel pump.

Jaymes
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Re: GQ TB42s bad misfire problem

Unread post by Jaymes » July 30th, 2011, 7:30 pm

Spent the day working on the truck today, replaced the fuel lines as they were looking worse for wear, renewed the thermostat just cos it was convenient to do sosince the car was pulled apart, changed points and condensor full oil service, changed fuel pump for a spare one I had on another motor I have in the shed, did a few other small bits as well just for the hell of it. The car thanked me for it and is running better than it's ever done in the time I've owned it.

xxxpat
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Re: GQ TB42s bad misfire problem

Unread post by xxxpat » August 6th, 2011, 8:17 pm

I had that exact same problem on my old patrol was a tb42 on gas and petrol i replaced everything with no effect, Found out was the carby needed a rebuild, the plunger and all the seals had sh*t them selves put a carby kit through it took bout an hour and a half and cost bout $90 including some fuel to clean everything with and whe i was done was like a new car ran awsome on both gas and petrol.

Bourke Patroler
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Re: GQ TB42s bad misfire problem

Unread post by Bourke Patroler » August 8th, 2011, 12:54 pm

mine had the same issue and i bought a carby kit for about $110 and some carby cleaner it fixed the prob then but now the car is only being used on the weekends it has returned although not as bad.
I had fun that day and smelt great because of the carby cleaner!

diesel_boy87
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Re: GQ TB42s bad misfire problem

Unread post by diesel_boy87 » August 9th, 2011, 5:58 pm

hi xxx pat.... it wasnt to hard to put the carby kit through was it... im having this same problem and just want to get it over with...

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