Firing Order?

[jon8christine]

I went to check the compression and timing of the engine on my '76 1800 today and while making notes of my current spark plug wires and checking the firing order in my Haynes manual I think it's messed up. I've never changed plugs or messed with the distributor so it's my first time really paying attention to it sadly.

I understand the firing order to be 1-3-4-2. With number 1 cylinder being closest to the radiator, working back to number 4 by the windshield. The 5 wires on my distributor cap are labeled (clockwise) 1 3 Bobina (on the coil input) 4 2, so that matches the firing order. My concern comes where my spark plug wires are currently connected. #1 on the dizzy runs to #4 on the engine (closest to the windshield), 3 runs to 2, 4 runs to 1, and 2 runs to 3, as if someone once thought #1 cylinder was at the windshield.

My question is how is this engine even running? Is it possible that something else is swapped so this is now wired correctly? I'm not sure I know what a misfire sounds like, but it doesn't run terrible.

If I swap the wires around so they're correct, does the length of the wires matter?

Here's the photo.

https://drive.google.com/file/d/1sH8jEY ... p=drivesdk

[18Fiatsandcounting]

My concern comes where my spark plug wires are currently connected. #1 on the dizzy runs to #4 on the engine (closest to the windshield), 3 runs to 2, 4 runs to 1, and 2 runs to 3, as if someone once thought #1 cylinder was at the windshield.

My question is how is this engine even running?

This will work fine, although I agree with you that it's sorta weird. As you note, the firing order is 1-3-4-2, but you could also say the firing order is 4-2-1-3. Or 3-4-2-1. Or 2-1-3-4. All those are the same firing order, and the only difference is which plug you are labeling as the "first" one. But the engine doesn't care which cylinder is "first", and it will just fire on the next available cylinder that has fuel, compression, and spark, whichever cylinder that happens to be, and then it proceeds from that point in the firing order of 1-3-4-2-1-3-4-2-1-3-4-2-1-3-4-2 etc.

My guess is that someone connected the plug wires this way because the wire lengths matched better. And, as you note, it works although it is confusing.

-Bryan

[wetminkey]

Wow, I'm impressed! I never would have though it possible, nor did I figure that I see what is going on,...
Your wires are swapped around, but your engine is still firing in the correct order - check the firing of each numbered cylinder, as you follow the supply to your wires, while the distributor rotates in a CW manner.
I'd guess that you are finding your timing mark in an unusual spot,...or perhaps you have the same problem as mine - no marker. 'Course, only if you are using #4 wire for timing,...

[jon8christine]

Makes perfect sense now. Thanks

[18Fiatsandcounting]

Note that you could in theory set your ignition timing using any spark plug wire you want. However, since the mark on the crankshaft is set to the point at which cylinders 1 and 4 are at TDC, most people put their timing light on either of those spark plug wires. You could also put the timing light on the plug wires for either cylinders 2 or 3, but then TDC on the crankshaft would be 180 degrees away from the timing mark (and there is no mark at 180 degrees), so that's why people don't set ignition timing using 2 or 3.

I just put my timing light on the wire from the coil to the distributor, and then you don't need to worry. This also has the advantage of being able to see "misses" as the timing light flashes are almost a continuous stream, and so a "miss" is more evident. Of course, the challenge then is to find out which plug/wire is skipping a beat now and then.

-Bryan

[jon8christine]

Cool thanks.

For checking compression just want to make sure of my "to do" list?

- pull the wire from the fuel pump so I don't flood the cylinders
- pull the ignition coil wire leading to the distributor off the top of the coil so I don't fry it
- pull the spark plugs
- install the compression tester and crank 4-5 times
- repeat

[18Fiatsandcounting]

Your first two items (fuel pump wire and ignition coil wire removal) are not strictly necessary, but on the other hand, it can't hurt.

I would add one other item: As you are cranking the engine, hold the gas pedal all the way to the floor. Don't pump, just hold the throttles open. Lets more air in.

I crank until the compression reading stabilizes, which does usually take 4 to 5 cranks, but it could be a couple more.

Also, I can't remember is your engine is stock, but I would expect somewhere in the range of 120 to 150 psi, depending on engine condition. If you have high compression pistons, it would be more. In any case, I usually look for consistent numbers between all 4 cylinders rather than fretting too much about the psi values. Unless they're super low of course.

-Bryan

[jon8christine]

Ok, tested the compression and got horrible numbers. It's a new untested compression tester form Amazon, so I'm seriously questioning it right now. I'm going to go borrow a friends to double check.

Started with a COLD engine
1 - 66psi
2 - 74
3 - 50
4 - 74

Not only are they really low, but there is a 39% difference between 3 and 2/4

I wanted to try them with oil, so added a tsp to each cylinder and ran then in for a few seconds and got the following COLD w/ oil
1 - 78
2 - 76
3 - 58
4 - 81

still abysmally low. Next I wanted to check them HOT, so I put all the plugs (which were carbon fouled...need to get this carb tuned better) back in the same holes and wired the plugs correctly (1-3-4-2) and it will not start. I started worrying about frying the coil, the oil etc. but after switching back to my weird ignition wiring / firing order (4-2-1-3) it fired right up. Now I'm seriously wondering how well this engine is really running. I should probably just fork out the cash for a Colortune and 'look' into each cylinder as it's running.

[SteinOnkel]

Yeah that's completely roached if that's correct.

You can borrow a compression tester from Autozone or OhReally Auto for free to compare. I don't trust Amazon tools.

Colortune is not as helpful as you might think. It's okay for roughing it in, but the fine tuning ability is just not there.

[18Fiatsandcounting]

...so I put all the plugs ... back in the same holes and wired the plugs correctly (1-3-4-2) and it will not start. I started worrying about frying the coil, the oil etc. but after switching back to my weird ignition wiring / firing order (4-2-1-3) it fired right up.

If my theory is correct about your engine plug wiring being set up to fire in the order 4-2-1-3, then your distributor rotor is likely 180 degrees out of phase. You could try again to set it back to 1-3-4-2, but you would need to rotate the distributor rotor (just the rotor, not the body) exactly a half rotation (in either direction; it won't matter).

Yes, those compression numbers seem very low, but my suspicion is the same as Steiny's in that the tool is, well, not sufficiently accurate for our work here today.

Also, is the compression tester the type with a hose and fitting that you screw into the spark plug hole, or the type where you mash the rubber tip into the spark plug hole while the wife/kid/friend/helpful neighbor cranks the engine? If the latter, I never could get those to seat very well, with the result being that the numbers were low.

-Bryan

[jon8christine]

My tester was the screw in type. Borrowed my buddy's name brand tester and it was only a couple pounds higher. He said some of the american classics he works on run in the 70s and 80s, but from reading here these engine should be 120 to 150. That and the big delta between cylinders tell me the engine need rebuilt.

[18Fiatsandcounting]

Well, with those compression numbers, it's definitely time for some engine work. But how does the car run in general? Still peppy, or kinda anemic? Does it burn oil?

It could just be that you need a good valve job and new head gasket and head resurfacing, or it could be that you need all that plus new piston rings. But, since the numbers didn't go up that much when you added a teaspoon of oil, I'm kinda thinking it's an issue with the valves. It could just be that they are all crudded up and not seating properly.

Have you tried the Italian tuneup? Drive at 4000 to 6000 rpm like the sheriff's coming to put you back in the slammer, for a half hour or so (driving time, not time in the slammer). Some people swear by this method, although evidence is mixed whether it actually works or not.

-Bryan

[aj81spider]

Apart from being low overall I'd be a little concerned that #3 is significantly different than the rest. It's cheap to try Bryan's tuneup, and if it works you thank the Italian gods and move to the next project. If it doesn't I'd pull the head and get a good look at what's going on with the valves and the head gasket.

[redcars]

OK having looked at the picture and read the post. I would say your distributor is in 180 degrees off. Now for the compression did you do it with the throttle completely open and crank it 5 or 6 times at lest . I crank until it quits going up. You are correct in that 39% different is bad. It should be less than 10% , less than 5% is real good. If your numbers are correct that engine shouldn't run or run poorly with a miss. My stock 2Ls have about 150psi and my 1608 with high compression has 225psi.

[jon8christine]

Thanks for everyone's response. I've done the Italian tune-up several times this year, I call it driving on the interstate, these cars seriously need an overdrive instead of 5th that is right next to 4th. I also tried holding WOT while cranking 6+revolutions and the needle has quit moving. Holding WOT made very little difference, 1-2 psi maybe. This spider is the only classic car I've ever owned and the only spider I've ever driven, so I don't have a good base line. It revs fine once it gets going past 2,000rpm, but makes no power. Hitting 60mph is like 18 seconds. Seems like it should be 10-12.

I've been doing all this engine testing (oil pressure is at 12 psi hot at idle) to see if it's time to upgrade to high compression pistons and bigger valves, so it sounds like a good winter project.