#4 won't fire

fiatmonkey

fiatmonkey

Tim Hoover
Hi my homees

#4 not firing. Details:

Dual 40s with electronic ignition 1500
I have fuel and spark and even compression.

I have checked all my plugs and wires. #1 shows rich but 4 looked ok however I swapped it out anyway but no go.

Next ?
 
was is running fine before?

Then started missing? How do you know it's #4 not firing? I bought new plugs once and within a week, one of them quit firing. I ruled the plugs out at first because they were new and it took me forever to figure it out.

Check the condition of the cap first and clean the contacts in there with a flat head screw driver. Reinstall and check to see if that fixed it. If not, you'll have to check the spark plugs. You'll need to pull each plug (one at a time) and crank it over to see if it'll spark. Hold it to ground with a rubber handled pair of pliers so that you can see if it sparks. If no spark, hold just the wire close (not on) to a ground to see if it sparks. If the spark plug doesn't spark but the wire does, it's the plug that went bad. Do this for each cylinder. If this doesn't narrow down your problem, you may have a bigger issue than you originally thought.
 
Tom,

It's #4 since it runs and idles the same whether #4 plug wire is attached or not (for starters). I already confirmed I have spark for the cap to #4 and the plug I tested by swapping it with another cylinder that does fire.

I am about 99% certain #4 was firing but this idles so well even on 3 it is quite possible it never fired. I know compression is not 100% accurate to tell if there is an issue however it is good.

I will go over the electricals again as you suggest before I move onto the next logical possible culprit.

Thanks!

AngleT said:
Then started missing? How do you know it's #4 not firing? I bought new plugs once and within a week, one of them quit firing. I ruled the plugs out at first because they were new and it took me forever to figure it out.

Check the condition of the cap first and clean the contacts in there with a flat head screw driver. Reinstall and check to see if that fixed it. If not, you'll have to check the spark plugs. You'll need to pull each plug (one at a time) and crank it over to see if it'll spark. Hold it to ground with a rubber handled pair of pliers so that you can see if it sparks. If no spark, hold just the wire close (not on) to a ground to see if it sparks. If the spark plug doesn't spark but the wire does, it's the plug that went bad. Do this for each cylinder. If this doesn't narrow down your problem, you may have a bigger issue than you originally thought.
Click to expand...
 
Are you sure you have fuel?
As you're running twin 40 DCNF's, you have one choke per cylinder. A blocked jet to #4 would cause this problem.
John
 
Sounds like plug failure to me.... but to be honest Ive never had a plug let go on me so ..:huh: You said your getting spark at the coil, the cap the wires and plugs except #4 correct? Unless its an intermittent fault with either the ICM, or the internals of the electronic dizzy, I would imagine the plug its self is really your last possibility for an issue.
 
I've never had a plug completely fail either... I'd be dying to swap the number 4 plug with the number 2 or something and see if it really was the plug!

Heck, I've had cars run fine that were missing the copper (brass?) strip on the rotor inside the distributor! It was 100% gone and the little 81 Civic was bopping right down the road like nothing was wrong! You'd think it would run better with a new 'conducting' replacement rotor... but I couldn't feel any difference at all! Bit of a bummer because I was expecting wheelspinning hp after slapping a new one in there!

(I did have a plug shoot out of VW Vanagon once... that was pretty exciting!:doh:)
 
Eastep said:
Sounds like plug failure to me.... but to be honest Ive never had a plug let go on me so ..:huh: You said your getting spark at the coil, the cap the wires and plugs except #4 correct? Unless its an intermittent fault with either the ICM, or the internals of the electronic dizzy, I would imagine the plug its self is really your last possibility for an issue.
Click to expand...

I am getting spark from the coil down to the plugs on ALL 4 wires. I swapped the plug from #4 with a known working cylinder and no change (no better no worse).

Not ruling out the coil/dizzy out at all, just noting what I did thus far.
 
fiatmonkey said:
I swapped the plug from #4 with a known working cylinder and no change (no better no worse).
Click to expand...

and #4 is not firing... But has spark and fuel and compression? Swap plug wires with #3 if it's long enough to reach.
 
If i were you Tim, I'd throw a know good plug in #4 and see if it fires; if it does that's excellent & job done. If it still doesn't fire, then you know to start checking the distributor or ICM (Mr. Obvious here I know) Just sayin its best to rule out the simple stuff first.
 
EricH said:
and #4 is not firing... But has spark and fuel and compression? Swap plug wires with #3 if it's long enough to reach.
Click to expand...


#2's plug was swapped with #4 and #3's wire with #4 (as it was long enough). I did this to rule out the wire and the plug. The change made no difference. I am pretty confident the issue is upstream or downstream of the plug/wire.

Interesting: I just looked at the trigger in the dizzy very closely and one of the trigger arms looked bent so I checked the gap between the arm and the pole. It appears within proper amount and very close to the other 3

Thanks,
Tim
 
You need to get a known

working ignition system in there. You may have spark but it may not be big enough for a variety of reasons ( old cap, wire, coil, trigger, bad ground).
I think Bernice has a spare one she lent to someone recently to solve their ignition issues. Try sending her a PM.
 
Robert Mose said:
working ignition system in there. You may have spark but it may not be big enough for a variety of reasons ( old cap, wire, coil, trigger, bad ground).
I think Bernice has a spare one she lent to someone recently to solve their ignition issues. Try sending her a PM.
Click to expand...

I agree it would help to have a good working system that I can quickly throw on to confirm. I have a spare (on another motor) however it is a cam mounted type. If I get desperate I guess.

I will do some more testing tomorrow and see what turns up. Then Bernice a PM if I am still stuck ;)

Thanks,
Tim
 
Timing light

Interesting: I just looked at the trigger in the dizzy very closely and one of the trigger arms looked bent so I checked the gap between the arm and the pole. It appears within proper amount and very close to the other 3
Click to expand...

You could try putting a timing light on it. Use the timing marks on the crank or flywheel (not cam) and check timing with the pickup on on the #1, then #4 spark plug wires. If the distributor is fine, then timing should read the same for 1 and 4. If there is a difference perhaps the trigger wheel is the problem.
 
vacuum leak???

If it isnt firing at idle only it could be a vacuum leak on number 4. It also could be a bent throttle shaft not allowing air into the cylinder. You could also test by spraying a small amount of fuel into the throttle bore at idle. It could also be a blocked progression orifice since it adds air to the idle fuel circuit. Double check the idle jet also. A good test is to use a laser temperature unit on the header pipes to check the temperature at idla and high rpm's. If it isnt firing at high speeds then it sounds like the fuel jet on number 4 is blocked but this will not effect the idle. All this assuming the ignition is all ok. One other thing if it has the air blead adjusters and the other three are out somewhat and #4 is not then number 4 would be starved for air.
Good luck
Charlie
 
update...

ng_randolph said:
You could try putting a timing light on it. Use the timing marks on the crank or flywheel (not cam) and check timing with the pickup on on the #1, then #4 spark plug wires. If the distributor is fine, then timing should read the same for 1 and 4. If there is a difference perhaps the trigger wheel is the problem.
Click to expand...

I tried this test but #1 and #4 showed the exact same timing. Still missing, I decided to swap out the dual webers with another set I have already. Since they are already mounted on an intake mani it was pretty simple/quick swap. Sure enough, the car runs on all 4, at least for a little while. After letting the car idle for an hour so I could cycle the cooling system, I decided to take it for a quick spin. Well, sure enough a few blocks away it starts missing again.

I am somewhat perplexed at this point. I am leaning toward some kind of electrical/distributor issue but not sure what to test next.
 
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