Running on three cylinders

[danzo]

My car has a dead #1 cylinder and I feel really stupid that I can't figure this out. It runs rough and when I pull the plug wire off #1 there is no change in how it runs. An inductive timing light will shine when hooked to #1 wire, and that plug wire will arch ferociously when within a half inch of any ground. New plugs, wires, cap 'n' rotor, and the ignition coil and ignitor check out via the FSM.

I initially thought I had a stuck valve, but the compression in that cylinder is 185 and the rest are about the same. Makes me think there is a carb prob but the other cylinders are not effected, i.e. when I pull another plug wire the car runs even rougher. It's been awhile since I've had a carb'ed car. It's almost like it has a dead plug, unlikely, but when the car cools off I'll slap in a known good one.

Is there some strange "Terc only" malady I need to know about? I really want to get this sorted before I go on a 550 mile trip Monday. Thanks for any help!

[Neu]

Could your intake be plugged? I'd pull off your intake and take a look around, make sure there's nothing in there.

[Petros]

Danzo.

You have spark, you have fuel and air to the other cylinders. Check the camshaft. pull the valve cover and check the no. 1 intake and exhaust valves and cam lobes for function. Turn the engine over (either by hand with the spark plugs out or with the starter) and watch the action. Sometimes a cam can be so worn it will not open the valve at all, or not much. If either valve is not opening it will still compression test okay, but you will not have power in that cyl. If so replace the camshaft with a good one, it will restore power to all of the cylinders, especially the one with the worn out lobes. It is possible that a broken valve spring could do this too, though this seems less likely, but inspect these too when the valve cover is off.

Also, it is possible the carb swallowed something and is blocking the intake runner (though not likely, it can happen). To clear any blockage, position the crank so the intake valve is open, with the throttle and choke open (or much better, remove the carb all together, not too difficult) and blow compressed air in through the spark plug hole, it should blow anything out.

With the carb off you can also try fishing a wire down into the no. 1 intake runner and work free anything that air will not blow out.

I can not think of anything else that could cause this. Good luck.

report what you have found.

[danzo]

Yesterday I did install a new valve cover gasket, and was planning to adjust the valves and r & r the timing belt/water pump. I was pleasantly surprised to find that the t-belt was almost new and the h2o pump was in good shape, so I left well enough alone. Also the valve clearances were OK, slightly tight, but close enough.

Concerning #1 cylinder - I did not notice the cam lobes to be worn, they all looked normal. I know the springs are not broken. At idle this cylinder is dead, but it may be operational when at speed. The car runs much rougher at idle, but it really smooths out going down the highway - I can't detect a misfire. Maybe I should verify the top speed is what it should be?

But today, thanks to a slackluster Jerry Jones and his minions, I will hopefully have time to check all the possible "rough idle causes" as per the FSM. God love whoever posted that sucker online. Will check for vaccuum leaks, HAI, EGR, HAC, MC, etc. If I cannot find a fault, then I will employ my carb rebuild kit. Of course if I do this I will remove/inspect/clean the intake manny. If this doesn't work I'll just slap on a Weber and four turbos .

Thanks for the help, I'll let you guys know what happens.

[sdoan]

Danzo,

Sounds like you've done all the sensible things, but what about a bad sparkplug? I've heard of it. try replacing it or swapping it with another cylinder.

Or how about an air leak at the little vacuum port on the top of the number one runner (one or two vacuum lines depending on the year) of the intake manifold. (this might be a Tercel specific issue)

An leaky valve (too tight or burned) can cause a miss at idle that will go away at higher rpm if not too bad.

Can you see the timing mark on the pulley when you hook the timing light to the number one sparkplug wire? You should be able to - if not bad distributor cap or wrong wire order.

I wouldn't think a carb problem would cause a miss on only one cylinder because the intake runners all draw off the mixing chamber under the carb.

Let us know what you find.

[danzo]

I did slap in a brand new plug into #1 but it didn't make any differnce. However, after I did this I sprayed some carb cleaner into the carb and then drove it. It did make an improvement, but it didn't seem to run consistently perfect.

Since I felt I was on the right track I then ran the car on two straight cans of Berryman B12, and it seemed to run as it should. I'll know more when I drive 'er down to Houston and back (500+ miles) to get my new-to-me gearbox. I did not check for vacuum leaks, but I will as soon as I can find my blasted gauge which is temporarily lost in a moving box.

I wouldn't think a carb problem could do this, but what the hey, if this works then I'm happy. I did time the car correctly, it is at 5 BTDC and advances properly.

Thanks for all the suggestions and I'll let you know if the car is fixed.

[Petros]

This sound like it could be vac leak right at the no. 1 cyl. intake port. I think on the front intake manifold runner is a vacuum module (it has either one or two vac lines going to it, depending on year), if this is cracked or leaks it would act like a vac leak only in the front cyl. of the engine. I would check that, it would not harm anything to remove it and plug the hole (and the vac lines going to it) and do the test again.

A minor vac leak into the number one intake port could behave this way, at higher demand the vac leak becomes less important. Also check the manifold gasket by spraying carb cleaner or propane gas in the area and see if the engine speed changes. Did you try tightening the bolts on the intake/exhaust manifold? they tend to work loose because of temp cycling.

If it is a vac leak it likely will not cause any harm for the sort term. But I would want to find out what is causing it no matter what it is, then you will know if it needs to be fix right away or cause more damage later.

Good luck.

[danzo]

Thanks for the tip, Petros, I will check out that #1 vacuum port. I should have looked closer and saw it before - chalk it up to beer goggles.

The funny thing is that the car ran as smooth as glass this morning after running it on B12 last night. Then today I took on a 550 mile trip and periodically it would idle rough, but not consistently. Made me think I should bite the bullet and rebuild the carb, but I guess I'll check the simplest things first as you mentioned.

I have not retorqued the manifold bolts, but I definitely will if I find a vac leak. I do have another in/ex manifold gasket handy in case I need it. I'll let you know what happens.

[ARCHINSTL]

When I first got Goldie in '05, and in trying to trace the various vac leaks, after PITA retorquing the manifold to no avail, I wound up installing a new gasket, which solved it (well, at least the manifold leaks...). Dunno if the 3AC is particularly prone to this, but a number of members have mentioned this.
Tom M.