No action in two of four cylinders

2480 Views 17 Replies 6 Participants Last post by La Voce, Apr 1, 2008

gprocket

Discussion Starter · Sep 14, 2007 (Edited)

I am awakening a 1750 SPICA motor that has been asleep for twenty years. Rather quickly we were able to get it running but I am not developing power. When I pull the plug wires I get no rpm drop in two and four. I am getting spark. Even so, I have replaced the plugs and the wires but no change. Next I cracked the line at the injector to verify that I was geting fuel - I am. Then I pulled the injector and connected it back on the fuel line to see if I was getting fuel out of it - I am. (Pulled the plugs and #2 &#4 were wet - the others were perfect). Then I did a dry compression test. All cylinders came in at between 170 and 175. Not super but nice and consistent. I don't have a set up to do a leak down test but that seems to be the next step. A flashlight down the spark plug hole didn't reveal anything unusual.

There are no unusual noises that would lead me to think that I've got a valve floating around. In fact, it idles quite nicely and even revs freeely without under load.

I can't think of anything else to do other than to walk back through eveything again. Anybody got any suggestions? If I can't find anything wrong my next step will be to pull the head. I really hate to do this because the motor appears to be nice and tight, no leaks, no smoke out the tail pipe.

Thanks,

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Bill S

· #2 · Sep 14, 2007

If you have good compression I can't see any reason to pull the head. Were the symptoms EXACTLY the same before you changed the plugs and wires? Put your timing light on each of your plug wires to confirm that the plug is consistantly firing in the cylinder. Do you have one of those spark gap arc measuring devices that lets you measure the distance of the spark? ($5-$10 at autozone). How's the distributor? Those Marelli distributors often don't get the points changed because it's such a hassle. If it's on just 2 & 4 maybe the cap? Keep us posted!

Bill

Urbana1750

· #3 · Sep 14, 2007

Sounds curious. How strong was the spark on 2 and 4? I would recheck the ignition timing and for correct firing order. A couple of other things that I would check are; the injector pump timing, the idle circuit pumbing to make sure it is not clogged, and the throttles to make sure they are opening and closing appropriately. Before pulling the head I'd also check the valve clearances and watch the valves open and close when cranking the engine. Good luck.

rogerspeed

· #4 · Sep 14, 2007 (Edited)

could plug wires be mis-ordered on the distributor cap as suggested above? Should be 1=3=4=2; 1-3-2-4 would cause the symptoms you describe. If that isn't it, check the inside of the distibutor cap and rotor. If those are good, what plugs and ingnition do you have. Unless electronic, you should have a conventional (non-platinum) plug. Old trick taught to me by a well-known alfa mechanic years ago: Don't secure the sparkplug wires to the plugs on the ones that don't fire, in fact peel back the boot and hold the end about 1/4 to 1/2" from the plug (leather gloves, rubber shoes, dry floor) have an assistant crank the car, you should see the spark arc from the wire end to the plug, it will often get the dead cylinder/plug to fire. One more thing, check the engine ground.

gprocket

Discussion Starter · #5 · Sep 15, 2007

HAHA, I stood there indignant that my helper would question my superior knowledge of Alfa ignition systems. "The firing order is 1-3-2-4" , says I. Its a good thing its the weekend so I can sneak into the office and make the switch.

Great call Roger! How did you know that 1324 would run but not fire on 2 & 4? I will try to think this through if my head doesn't explode first!

Thanks again. I will make the change in the morrow!

rogerspeed

· #6 · Sep 15, 2007

Occasionally I have a moment of clarity and get something right; I've played with so many cars it gets very annoying when remenbering a mistake made on a previous car then repeated. Your firing problem to me was a matter of deduction. Theoretically I know the diagnosis to be true, but it was your description of the situation that led me to postulate the answer.

The damage to your car by the transporter is very distressing, this is the second car on the BB in a month to suffer damage from transport. I guess this is why some use an enclosed carrier, when my BMW 1600 purchased by AMS Motorsports of NE, they did it this way.

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gprocket

Discussion Starter · #7 · Sep 15, 2007

Man if I were transporting that car I think I'd cover it in bubble wrap too. Love that color!

gprocket

Discussion Starter · #8 · Sep 15, 2007

Roger, you are the man!! Swapped two and four and it's running like it never sat for 20 years. Now I'm depressed about the car getting smashed because I never thought the motor would run that well...

Thanks again.

rogerspeed

· #9 · Sep 15, 2007

You are welcome, glad that worked out. Depression is over-rated, you should be very pleased with compression of 170-175psi, my understanding is, very near the absolute theoretical compression a stock 1750 motor would make

gprocket

Discussion Starter · #10 · Sep 17, 2007

I agree, Roger. I think anytime you are compressing a gas things get very fuzzy. My understanding is that the consistency between cylinders is what to look at. As I recall, one should be happy with +/- 5%. Also, there is tale to tell when you compare dry and wet readings.

My logic in peforming a compression test was to see if I had a stuck valve that would not allow any compression and hence to combustion. I figured if I saw 175,0,175,0 the jig was up...

Thanks again.

La Voce

· #11 · Mar 19, 2008 (Edited)

The mystery of the squeaky clean spark plug

What a great read! The reason I have jumped in is that I need some advice. I suspect my #2 cylinder in my 2L (weber conversion) is not participating. The engine idles OK, a bit of a stumble from idle but not too bad, and under full throttle pulls well, but seems a bit anemic under a load, such as going up a hill. I have been cleaning and tweaking the carbs since I got the car running after many years, as she was running rich when I did get her running. I finally have #1, #3, and #4 plugs a perfect light brown color, but the #2 plug appears as it just came out of the package at the parts store, even after several hundred miles of driving. I confirmed good spark by grounding the plug to the engine with the motor running. Adjusting the mixture for #2 has no effect on idle speed, even full down, and there is no fuel or even the smell of fuel on the plug when I pull it after extended idling. It's just hot and like-new clean. I pulled the Marelli distributor and set the gap on the dual points using a feeler guage but have not put a dwell meter on it yet. I have confirmed the carb throat that feeds the #2 cylinder is pulling an equal amount of air as the others using a float type syncrometer. I suspect no fuel is reaching the combustion chamber?

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Bill S

· #12 · Mar 19, 2008

La Voce said:
I suspect no fuel is reaching the combustion chamber?

Sure sounds like it. Most supposed carb problems are really ignition but it seems like you've narrowed it down pretty well. You might double-check the #2 plug firing by putting a timing light on it at idle.

La Voce

· #13 · Mar 23, 2008

hmmmm

OK, pulled the carb and it's squirting fuel just fine from both throats. Pulled the plug, rechecked visible spark, reinserted the plug, then pulled the plug wire with the engine idling- no rpm change noted. I swapped plugs with #1 cylinder, and the problem did not move. I then reached over and pulled the plug wire on cylinder #1 with the original #2 plug installed, and it resulted in a noticeable drop in engine rpm, confirming the squeaky clean plug fires OK in a compressed fuel/air environment. Moved the plugs back to their original orientation, and I'm scratching my head. I have fuel squirting from the carb, I have a plug that fires, and according to a carb synchrometer and that sucking sound, the #2 cylinder is pulling in air, indicating to me that the valve train is operational. What the heck? She runs pretty well on three cylinders, can't wait to see how she'll do on all four.

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Bill S

· #14 · Mar 24, 2008

I believe that fuel squirting just means your accel. pump is working. Idle jet could still be clogged.

La Voce

· #15 · Mar 24, 2008

Thanks and concur, but I pulled the idle jet (along with the others) and confirmed visually and with air pressure that the jet was clear. I then poured Sea Foam ( a carb/fuel/engine cleaner) directly into the idle jet well, and it all drained down and away instantly. Also, I'm thinking even if only the accel pump worked, would there not eventually be evidence of combustion on the plug after a few hundred miles? It's still as clean as the day it came out of the package. I pulled the plug wire off of the plug both at idle speed and about 3,000 rpm, same results- no effect on engine speed or smoothness.

La Voce

· #16 · Mar 31, 2008

Found It

Just got back from a weekend of camping and finally had a chance to poke around some more. Valve train was working fine, carb throat was wet with fuel and sucking well, tried directly spraying fuel into the carb throat with no change in rpm, and swapping plug wires did not move the problem with the wire. Then, as I accelerated the engine from idle speed using the throttle linkage directly, I noticed a spark arcing from the bottom of the #2 plug boot at the distributor cap plug tower. The higher the rpm, the bigger the spark. Up until this point the plug boot must have been hiding it, but as the crack propagated down the cap tower, the spark finally became visible. That would explain the spark visible at the plug but not enough to support combusion. (Thinking back the spark was a bit weak looking, but how does one measure other than the measure of experience). Rummaged around the box of spares that came with the car and found another cap, cleaned it up, installed it- and Basta! She's running great! This must be the first time all four have been contributing, as there's a huge difference in low end torque and acceleration now. I'm impressed and delighted. My next goal is preparing her for a trip to Road Atlanta for the Mitty the first weekend of May, that will involve replacing radiator hoses and all the driveline flex couplings. Thanks to all!

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gt601

· #17 · Apr 1, 2008

My next goal is preparing her for a trip to Road Atlanta for the Mitty the first weekend of May

Ahh.. so you are going. We will be there. (Fetta78 and crew, Me and the wife.)

I do hate the simple fixes that take a long time to figure out. I had a new cap out of the box do that to me last week on a car I was working on.

Paul

La Voce

· #18 · Apr 1, 2008

Yes sir that's the plan. Between now and then I must replace the rear motor mount, all radiator hoses, and all three flex couplings. Should make it! Don't know who, if anyone, will accompany me on the journey. Is everyone camping?

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