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Ae71 misfire.


succulent eye

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Ok so the car was running pretty good for a while then started having a misfire, so I removed the plugs and checked them to see plug 1 ruined. I replaced it the misfire was good for a bit then it's back again. Checked the plug and it was pure black with carbon. Goes black after a day and I only drive like 10 minutes to work. Just trying to work out what might cause this, could it be a vacuum hooked up wrong ? Bad leads ? Bad dizzy ? I'm lost. So I've come to the gurus, I have attached a photo of the plug that was ruined. Also a photo of the only vacuum I've got hooked up.

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Hi Edward,

                   The real question is what do the other 3 off spark plugs look like ?  I'd remove all four (4), & clean them all.  Then put them back, & drive it as normal, then remove & review again.

If it is just no: 1 spark plug, each time, that is "carboning up", it can only be something wrong with no: 1 cylinder, or the control of it.

Directly after removing the plugs, whilst the engine is still hot, you need to do a compression test, on each cylinder & record the max reading. 

If they are all around 150 PSI, and within say 10 PSI of each other, then the bores, rings & valves probably acceptable.

If no: 1 cylinder has a low reading, then it could be burnt valves, broken or worn rings, or even a blown head gasket; or heaven forbid, a cracked piston.

Alternatively, if all cylinder readings look OK, then it is probably a HT lead between dizzy cap & spark plug no: 1.  Hope so, as that is an easy fix.

You might want to run the engine in the dark tonight, & have a look under the bonnet, & see if you can see any obvious arcs or glows, around the dizzy leads.

Another HV arcing area is down the inside of the dizzy cap. You can sometimes see these in the dark, through the dizzy cap. 

Really hope it is as simple as replacing a lead or dizzy cap, because if not, then it might just require the head to come off, for a "look see".

Best of luck, & let us know how you go, or what you find.

Cheers Banjo

          

Edited by Banjo
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Thanks for the speedy reply, so the update so far.

I have removed the vac advance to ensure it's nothing with that. I also cleaned the inside of the dizzy.

New leads , dizzy cap and plugs on the way

I done a comp test and this is the result,

Cyl 1 150 

Cyl 2 145

Cyl 3 148

Cyl 4 130.  I also read online that if it's lower to do a wet comp test, pour a little oil ( 1 tsp ) in the Cyl. After doing so it went up to 148. 

The odd thing is it was going amazing after removing the vac and cleaning the dizzy then yesterday it went bad again. I'm lost with it, goes great if ya smash the life out of it then just cruising it kinda splutters occasianly some days worse than others. I'll attach a photo of the plugs after cleaning and driving for a bit. The order is from left to right 1234

 

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Hi Edward,

                  Pretty common compression readings.  If you are going to have a cylinder that is down on compression, it will always be no: 4, as the back of the K Series head runs hotter than the front cylinders, as a result of poor coolant flow around the back of the head. You could have a broken or worn rings in no: 4, or maybe even a burnt valve seat.

Not sure what you mean by . . .  " it was going amazing after removing the vac".   Leaks into the induction system, can cause all sorts of air/fuel ratio issues, with variable & erratic performance. 

There are lots of places on the induction system where air leaks can occur.  Manifold gasket (common), gasket under carby, loose vac hoses (common), diaphram in dizzy vac unit broken, faulty PCV  valve, or hose fittings (common), vaccum brake booster & its hose.

Did you manage to get hold of a timing light, & check whether the centifugal advance mechanism in the dissy, it working properly ?

The good thing is, your compression test, indicates your motor probably hasn't suffered a blown head gasket.

After you have fitted new leads, dissy cap, & spark plugs shortly, if that doesn't fix it, you can bet it's an air leak somewhere, on the induction system.

Erratic performance due to an ignition component failure usually results in very sudden & sharp changes in the engine behaviour, whereas, air fuel ratio issues, don't normally have the very sharp & sudden changes. Does the engine feel, or sound like it is starving for fuel ?  The fuel system can easily be checked by removing all plugs; removing inlet pipe to carby, & feeding the line into a container.   Turn the engine over, & check that the pump & fuel filter are not impeding fuel delivery.

Cheers Banjo

 

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Thanks heaps for the reply, haha after I removed the vac advance that went from the carby to the dizzy it went fine for a few days not a single misfire then drove on the freeway and it started again. I've got a timing light and checked all tgat and it's good. It doesn't seem to be starving itself of fuel, it's kinda how you put it of sudden sharp changes. It doesn't big down at all. Imagine a heart and it misses a beat for a second then goes normal again :) alsalso have checked fuel filter and pump both are good. 

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Hi Edward,

                     You are doing well !  You will get there. 

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it's kinda how you put it of sudden sharp changes. It doesn't bog down at all. Imagine a heart and it misses a beat for a second then goes normal again 

 Almost certain that the issue is electrical, so head off in that direction.

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New leads , dizzy cap and plugs on the way

Once you receive these bits, & fit, your problems may be over.  It's always nice to know what it was that caused the problem, so change one part at a time, plugs, cap, & leads in that order, & test the engine inbetween each replacement.

That may not fix it, but if not, there are two other items that could be an issue.  If it is a points distributor, I would be changing the points & condensor also. Notorious for breaking down.

If all that fails; & I'm still placing my bets on it being electrical, I would be checking all the electrical connections in the ignition system, from fuse, starter key barrel, coil, ballast resistor, fuel cutoff solenoid etc.

Let us know how you go.

Cheers Banjo

 

               

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Thanks hopefuly I get there :)  I got sick of waiting for the new plugs so went to the local auto store and grabbed some. I just put them in so I'll see how it goes now. I also thought id check something and had the timing light hooked up. As it was idling you could hear it miss and a little pop out the exhaust so I watched on the timing and it drops from 10 down to 5 when it misses. Hopefully the other bits get here soon. 

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  • 2 weeks later...

Well guys I thought it was fixed but turns out it's not, cruising to mannum today and guess what happens. I'm pretty well lost with this, I pulled the plugs a few days ago just to check em and see what they are like and plug 1 and 4 were very black, cleaned em and put em back in not thinking much of it as the car was running mint. Today I have replaced the 4 plugs with bosch instead of ngk and I'll monitor further each arvo. The car also has the stock carby with the pain of a thing ( auto choke ) so I wound the screw for that out as far as I can so it won't come on. My reasoning is as follows. 

I installed a new radiator ( mishimoto ) a while ago which is big and on the freeway the car sits on cold, like very cold the lowest it can go which I'm not sure but might be bringing the choke on as it thinks it's cold and causing trouble. If I'm wrong or should be trying something else don't hesitate to say so as I'm rather confused by all this. 

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It doesn't matter how big the radiator is the thermostat should regulate engine temp to an even 80-90 degrees at all times, so fit a thermostat as yours is faulty or missing.  That will help you establish a hot running condition that is consistent and wont affect your test results.  Engines wear prematurely if they never get to an even up to temp state for general use, as the pistons need to expand with the heat of the system to give ideal tolerances.

Fouling plugs is usually a symptom of too much cold enrichment, a general rich state or incomplete ignition in that cylinder leaving the sooty deposits that block or insulate the spark from occurring in the correct way.  So from what I can gather the issue was with cylinder 1 and now its with cylinder 4 as well.  If it was a choke issue specifically you would see all cylinders affected in a similar way.

Is your rotor button worn?  Do you have the correct points gap?

If its worse on the freeway then your issues might be being compounded by the rushing of air or the extra motion based forces that occur in this state.  I once had a car cutting intermittently as I approached 100klm/hr.  If I drove under 90 no issues, but if I drove over 95 I would experience misfires.  I stopped on the side of the highway and saw that the wire attached to the ballast resistor was faulty, so I wandered over to a nearby house, asked for some tape, taped it on and drove home no worries.  So look for loose connections in the ignition system, and check that your engine grounds and battery to body grounds are clean and well attached.

I think were past expecting this to be a basic service related problem and its going to be something more obscure.

Edited by LittleRedSpirit
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Buy a thermometer and check the guage against a real temperature with it just idling from cold for 20minutes.  We blew a head gasket with the temp gauge reading half and no water left.

That will tell you if the water is up to 80deg, if the thermostat is working, and the choke should or shouldn't be working.

As the Spirit man said, the choke would affect all cylinders equally.  A more interesting outcome would have been from swapping the plugs from 1 & 4 into cyls 2 & 3 and seeing what happened.

All you can do is drive it and see how the new plugs look in a week.

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  • 5 weeks later...

Sorry for the slow reply, been giving it some time to see if it's fixed and finally all issues solved. It was the thermostat somehow keeping it too cool or getting stuck open. Replaced that and it's been mint ever since, runs without an issue now. Well apart from a decent coolant leak behind the timing cover area. Anyways thanks heaps for all the help.  

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Second happy ending to this story !  Top marks for Altezzaclub & The Spirit Man for getting this one right.

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Buy a thermometer and check the guage against a real temperature with it just idling from cold for 20minutes. 

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so fit a thermostat as yours is faulty or missing.

 Cheers Banjo

 

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