Technical 4 banger dead miss on two cylinders, but no ?

Hey working on a 4 banger engine at work OHV

unit has a dead miss on 1 & 4 cylinders . But it dose not !!

pull 1 & 4 wires and the engine does not change , pull 2 & 3 and it gets more rough.

BUT have 1 & 2 connected and pull 2 & 4 wires and it will still run!! Like a bag of **** but it runs.

have good spark on all 4 plugs.
Compression is 150-140 across the board.
Leak down test was under 5%.
Pulled the front cover and timing chain is spot on and no slack.
Ignition timing is good .
Tune up is new .
Carb is rebuilt and good .
Oil pressure is good oil is clean.
Valve adjustment is good.
No vacuum leaks .

kind of at a loss at this point I had my guy pull the intake off as I have seen intakes runners get carbon up and plug up on cylinders.

not the case on this engine .

BUT intake valves on 1 & 4 where totally carbon up !!
Could this restrict air flow ? The plugs where not horrible , but they where replaced before this unit came to my shop.

if the valves where held open or burn , the compression test should have picked up on this I’m kind of stumped at this point but thinking pulling the head is my next step.

would it be worth my while to use some sea foam and soak the valves or run water through a vacuum line and put the engine back together snd see or start pulling the head.
Customer is cheap and his bill is getting larger and larger .

 

Broken valve springs?

***ume when you said 1 and 4 were carbines up, you mean the intake runners? To see the valves the head would have to come off.

Edit: thinking further, you probably were looking through the intake ports with the intake off.

 

Yes intake off looking at the tops of the valves

 

Pop the valve cover and take a look.

 

Does it like it to have the choke applied, how about when you spray some carburetor cleaner at it?

 

valve cover is off, squeaky clean no signs of anything

I’ll take a closer look at the valve springs if they broke , but I don’t think so.

 

It has no choke .
If I smother the carb with my hand it stalls out.
No vacuum leaks tested with carb clean and propane

 

That engine isn’t named after the letter Q is it?

 

? I don’t get it ?

 

It’s OT. I’ll PM you

 

That works , it’s a engine with an issue .

should not be O/T. It at this point I’ll take any help I can get

 

If it doesn't seem to make a difference that you pull the plug wires from the cylinders it seemed to be a misfiring, pull those wires. Put a spark plug on each one of them and leave them sitting on the manifold.

Run it briefly like that and see if those spark plugs are indeed sparking consistently.

Check everything in the ignition system. I have seen cheap distributor caps have issues in the towers that attach the spark plugs. Wiggle each one of the contacts on the cab and see if they move. I have seen broken ones. They were not visible from the outside.

Strange but true.

 

Dumb question, but is the firing order on the distributor cap correct? Is it possible that an ignition module is taking a dump? I’m guessing it’s a propane fueled unit, so fuel delivery pressure is out of the question? You mentioned that valve adjustment is correct, but possibly a camshaft going flat, do the rocker arm adjusting screws have roughly the same amount of threads showing above the locknuts? Swap plug wires around and see if the misfire moves with the wire position.

 

Oh goodie, that means I can put in my two cents Crossfire in wires, worn dist. shaft bushings, cracked/carbon tracked cap, worn points cam lobes, slipping dist. drive gear....?

 

I'd be curious about what an oscilloscope would have to say about the spark on the different cylinders, if it can show some consistent difference between them. May tell you nothing, may point you in the right direction.

 

Most are 1-3-4-2.

Now, which one is one?

 

If it's an inline engine and number one is on either end (and anything else would be crazy) 1-3-4-2 would basically be the same no matter what end the 1 is. Reverse the order of the cylinder and 1-3-4-2 becomes 4-2-1-3, if you put it in a longer sequence 4-2-1-3-4-2-1-3 you see that same familias 1-3-4-2 in the middle. So call one end cylinder 1 and know what direction the distributor rotates and you know where the cables should go.

 

That would be funny if the back of the engine was mistaken for the front.

 

If it has compression, spark and fuel, it should work. As mentioned, check for spark at the plug. If there's no spark try another plug wire. Any plug wire. We all have them laying around don't we? Wait until it's really dark in the shop and fire it up to check leakage in or between wires or to ground. Leaks will show up in the dark. Check the distributor rotor for burn through in the center. Check the cap and the coil tower very closely for carbon tracks inside and out. Often really hard to see. Just because a part, like plugs, are recently new does not mean they're any good. Swap the plugs from the cylinders that work with the plugs in the cylinders that don't. Any difference? Since the compression is good and it's obviously getting fuel that leaves only a couple things I can think of, flat cam lobes on the bad holes, severely worn, bent or broken push rods (if applicable), cam followers, Timing chain or belt, which ever applies, which can be easily diagnosed by turning the engine back and forth by hand while watching the distributor rotor to see how much it it takes to move the rotor from one way to the other. More than a few degrees (5 ?) at the crank is suspect.

 

If installed in equipment double check the firing order as mentioned, distributor rotation, and proper cylinder numbers, I've had forklifts that are numbered backwards from what is normal. If propane check that the engine coolant is full as it circulates through the evaporator to keep it from icing up.

 

I don't get where you guys are getting it is propane powered. It has a carb..... not propane. He said he checked for vacuum leaks using using propane.

Read before answering.

If it were propane powered, it also wouldn't have a ton of carbon on the intake valves.

 

Cylinders are numbered correctly
Timing is dead on
Firing order is factory spec
Good fat spark at each plug
New plugs
Swapped around a couple times by other techs and me
Swapped wires
Cap , rotor , wires are all oem parts and in good shape.( new , replace after this problem started and made no difference )

only thing is the excessive carbon on the valves.
But I think I’m reaching pretty deep on that one.

might try the leak down test again and take a good look at the cam and valve springs in the morning .

 

If it had a cam issue I wouldn't think the compression numbers would be good across the board. Carbon in the ports could cause a cyl to act weak. Maybe a leakdown test instead of a compression test. Lippy

 

Since the OP would not divulge what it is, I can only ***ume that it is OT.

For all we know it is a Honda Civic, or a Toyota forklift.

Out of our era, it is not unusual for #1 to be at an unexpected end.

Heck, IN our era Ford and GM did not agree on where #1 was on OHV V8's. They did not even number the banks the same. Never mind that positionally they have the same firing order.

 

Since I don't see anything about what engine this is I'll go out on a limb here and tell you that the Model A & B Ford engines had a different firing order than just about everything else. I have to look it up every time I need it because my memory quit working 20 years ago. I's 1423 or some such. I'll look it up tomorrow and post it if someone doesn't chime in.

 

One dumb thing to check: engine ground. Make sure that it is present, has clean contact, and is not frayed.

 

Is it a single barrel carb or two barrel?
My first thought is fuel mixture, but if it's a single barrel that would get ruled out.
Next thought is distributor bushing worn.
Just a thought, Good luck

 

so the intake valves are all coked up,what happens is the coke/carbon is absorbing the fuel and those cylinders are running lean.
Clean the upper end with seafoam or your choice of cleaner.

 

If it's that full of carbon I would just pull the head and clean/fix it right. A valve job while it's off is never a bad idea, too. If the two center cylinders (2&3) are at the top at the same time you could have a head gasket issue between them and still get compression reading. Put an adapter in the plug holes one at a time and put the air hose to it while listening for leakage. All plugs out, of course.

 

Ford always has had " exclusivity" issues , they built vehicles that had to use their accessories & only their accessories , their parts & only their parts , Henry always wanted a monopoly ! Wasn't ford the 25/32" wrench thing ?