Wicked issue with 4AC

[el_camino]

Hello guys, I am trying to build love to a good condition AE86 with 4AC and keep it original for the moment. 

There is not logical issue however and being out of ideas I am reaching out for help.

The cylinder one refuses to work, no matter what.

There is spark, a good one. Distributor revised.

There is fuel. Tried with different carb from working 4ac.

There is good compression on all 4 (12).

Valves have been adjusted 3 times and are in spec.

The car is running smooth on the other 4 otherwise, starts first try. Runs rich, I assume due to the not burned fuel in cylinder 1.

I am really out of ideas what to do next. Anyone had a similar problem and ideas for testing please?

 

 

Edited yesterday at 08:37 PM by el_camino

[altezzaclub]

Tricky... So is the cylinder ID from pulling a spark plug lead off when running? Number one didn't drop the idle speed?

What were the compression readings?

Is the spark plug black or clean? Colours of the other 3?

..and Cyl 1 will fire a spark plug in its lead resting on the head?

 

 

[el_camino]

All leads are new and all spark plugs are new as well as the distributor cap. 

Indeed, pulling the cable off the cylinder 1 doesn't change the work of the engine, while pulling any off the others would nearly stall it (two cylinders left).

Swapping spark plugs or leads always keeps the first not firing. 

The spark plug on cylinder 1 turns wet and black. The one on #2 is rather black with a bit of brown, the others are rather brown 

Cold compression test reads 11.7 on #1 and 12 on the rest. Warm compression shouldn't be as far from this to the point to fully not ignite cylinder one.

Edited 18 hours ago by el_camino

[altezzaclub]

have you checked this one- '..and Cyl 1 will fire a spark plug in its lead resting on the head?'

Just to make sure the plug does fire on the lead, which it probably does.

So, has fuel, has spark and has compression.. The compression is the worry, a broken ring would drop that compression before stopping the plug firing. A head gasket might drop it enough to misfire but you would expect to see that in the compression test. Sort of 110psi for a dud cylinder, and your #1 is only 5psi down.

No oil in water or water in oil?? They usually fail between 2 and 3 or 3 and 4 but maybe cyl 1 is leaking out somewhere... Which is what the Brave AI didn't specify.. 

"The Toyota 4AC engine is notably prone to head gasket failure even from minor overheating events, without necessarily reaching the red zone on the temperature gauge. "

I didn't know they were prone too HG failure until I thought to check.

So, check a definite visible sparking of a plug on #1 lead. No water in oil, oil in water or bubbles in the radiator on cold start... and list anything else you can think of.

How did it start? Just one day never ran on that cyl, or were there oncoming signs of misfire?

  

[el_camino]

It sparks amazingly when held to the block, it was the first thing to check before doing all other effort. 

There is no oil on the water. 

I bought it with not functioning fuel pump and I found the issue after I installed the fuel pump. Actually I installed another one just to be sure this is not the reason. 

So, head gasket might be the only option left and I will need to take the head off to check? Would this be possible with this compression? 

 I am too tempted to get rid of this head as I have a GE one and this is the reason I was hesitating doing it. I was hoping for an easy project.

[altezzaclub]

Is fitting the G head an easy job? The block is the same but the crank/rods/pistons are different I think. Low compression and weak internals.

However, I've run out of ideas if you've checked everything we've talked about.

The head gasket could leak into the water jackets, that's common, so you get bubbles in the rad when the motor is cold and the motor loses the top inch or two of water each day, but then hardly loses more. The bubbles are the compression being forced into the water system and when the thermostat is closed they push down to to the bottom of the rad and push the water out. So if you have a full radiator and the cap off when you start it and watch for a minute or two, a bad head gasket will overflow the water then suddenly burp some bubbles out and the water level drops an inch or two as the thermostat opens, allowing the compression to escape. You can buy test kits that look for carbon monoxide in the rad water to check this.

The other side is that at night after a run the motor cools and that cyl sucks a little water in, which condenses on the spark plug, and when you start the next morning that cyl doesn't fire. Eventually the warm-up drives the water off the plug and away it goes, so the motor runs on 3 cyl at first startup, then runs OK during the day, just short of power. You could try fitting a new spark plug to #1 before starting it in the morning and see if it starts up on 4 cyls.

A warp in the head often leads to oil in the water and vice versa, but that is usually cyls 2 and 3.

A bent valve or a burnt valve will drop the compression, especially at cranking speeds, but a leak-down test really shows that. A compressor hose on a drilled out spark plug should hold pressure against the rings but drop pressure passed a bad valve or a broken compression ring. That is a more positive test than the compression meter while cranking.

So, let it idle with a full rad and no cap until the water suddenly heats up, or buy a test kit and check the rad coolant. that would eliminate the head gasket. Then drill the center electrode out of a spark plug and clamp a compressor hose on it. Even a tyre compressor with a  gauge would do, just blow it up to 100psi and turn the compressor off, and watch the gauge.  Do all the cyls and note how fast the pressure drops. The motor will turn over half a turn as you pressurise it, its a surprise the first time! I think this is the most likely reason for it not running now, everything else seems fine.