360 running on 4 cylinders

-
cudamark said:
The odd thing
Click to expand...
Not odd at all if the carb is very rich at cold-idle.
At cold idle your engine might require 2,3 or 4 times as much fuel, than at hot/warm. This falls nicely into line with your black plugs, and destroys the rags in the plenum theory,lol. What I can't see is both carbs doing it.
 
AJ/FormS said:
Fixed it for ya,lol
Click to expand...
Everyone always forgets to add timing to that list. You can have all those things but if they don’t happen at the correct time, then **** don’t run.
 
One thing that changes as the engine gets up to running temperature is valve lash (clearances). The carb settings don't change?? The intake doesn't change unless it's developing a leak (on one side) when it gets warmed up from heat expansion?? If the problem gets worse as the engine gets up to running temperature doesn't the problem have to be related to engine temperature rise??
Exhaust heat riser??
 
Things like gas tank, timing, fuel filters, etc. are not going to effect just those 4 cylinders. It would also be extremely rare for the spark plugs on those 4 cylinders to not have a problem cold, but, to have one when up to operating temp. Same goes for valve adjustment on a hydraulic system. As has been mentioned, you need fuel, spark, and compression (along with the correct timing and fuel/air mixture!) so, this is something specific to these 4 cylinders that changes as the engine gets hot. Either these 4 are not getting fuel or the right mix, not getting spark, or losing compression for some weird reason.
 
Thanks, wow that's a lot of suggestions to respond to. I'll try to here;
  1. The gas tank, it's new along with the sending unit and pump. Only the fuel line is original. We replaced the fuel filter with the Holley install.
  2. Timing is good, 12 degrees initial and 32 degrees all in.
  3. Spark gap check, I stuck a screwdriver in the boots and measured a good healthy spark about a quarter inch from the engine as ground. The spark plug gap is .035" I also checked to see if I had good spark with the plug grounded to the engine.
  4. Compression is good cold and hot. Leakdown is ok I think, not really sure how to measure that properly other than watch the gauge after the compression test.
  5. The ignition system is bone stock except the coil is a MSD Blaster. Even the distributor is stock. Popped the cap and inspected it, no issues noted.
  6. Nope, no rag in the plenum. I did check while I had the carb off for the second time.
 
If hot compression test results was similar to the cold results you listed, that rules out all cylinder sealing problems.
You cannot do a leakdown test with JUST a compression tester.
 
Spent this rainy Sunday troubleshooting some more.
  • Changed the coil, no change
  • Changed the cap and rotor, no change
  • Changed the plugs, no change
  • Switched back to the Carter, no change (it does run smoother with the Carter probably because it's not running rich and fouling the plugs like the Holley was)
  • Removed the ECU and sanded all the paint off the mounts and fender wall. Reinstalled with dielectric grease, no change.
I also used my timing light to check all the plugs for spark. All seemed to be good steady flashes except for #6 it was flashing really intermittently or multiple times per stroke. Think it could be the ECU?

Appreciate everyone who has made suggestions. I still need to get a leak-down tester and prove each cylinder.
 
Find someone willing to run your carb(s) on their engine. if you havent dismantled either to check for goo, that would be my next step. Buddy had me chasing timing on his small block chevy and i finally got fed up and looked in carb...
Immediate improvement.
 
If you have a significant leak down problem, you'll be burning oil. If it has the compression you said it does, that's enough to run smooth. I like to keep a spare module in the trunk along with a ballast resistor, just in case one craps out at an inopportune time. I'd get a spare to try and keep. I have an extra distributor in the garage for the same reason. It's rare a reluctor or pickup coil will go bad, but, not unheard of. I'd still try dribbling a bit of fuel into the carb to see if the idle smooths out or not. First one side, then the other. You may be getting some weird vacuum leak once it warms up. I know some of the stock intakes (like the '73-8 440's) would crack through the bottom, and sometimes into the EGR port. They would sometimes run fine cold, but, once fully warm, that crack would open more and they would lean out, idle rough, and run hot. Maybe you have something like that going on.
 
Tooljunkie said:
Find someone willing to run your carb(s) on their engine. if you havent dismantled either to check for goo, that would be my next step. Buddy had me chasing timing on his small block chevy and i finally got fed up and looked in carb...
Immediate improvement.
Click to expand...
Thanks, I've rebuild the Carter twice in the last 3 months. The Holley I took it apart and blasted with it with carb cleaner, lots of crap ran out of it. I'm not confident the Holley is any good, but the Carter was running nice and clean, exhaust wasn't nasty at all and the plugs were a nice light gray. I'm pretty confident in the Carter.
 
you can disable spark by putting little pins in the cap wire boots that extend out of the edge of the straight boot. They were little brass brads when supplied by Mallory in their 1985 Supershops $8.00 7mm blue cut to fit spark plug wire set. The you just take an insulated ground clip and touch the pin and it'll divert the spark right to ground killing that cylinder. Wrap the coil in a wet rag and see if it does anything. If the coil is going south, I think it gets hot itself.
 
cudamark said:
If you have a significant leak down problem, you'll be burning oil. If it has the compression you said it does, that's enough to run smooth. I like to keep a spare module in the trunk along with a ballast resistor, just in case one craps out at an inopportune time. I'd get a spare to try and keep. I have an extra distributor in the garage for the same reason. It's rare a reluctor or pickup coil will go bad, but, not unheard of. I'd still try dribbling a bit of fuel into the carb to see if the idle smooths out or not. First one side, then the other. You may be getting some weird vacuum leak once it warms up. I know some of the stock intakes (like the '73-8 440's) would crack through the bottom, and sometimes into the EGR port. They would sometimes run fine cold, but, once fully warm, that crack would open more and they would lean out, idle rough, and run hot. Maybe you have something like that going on.
Click to expand...
I'm going to buy a leak down tester to prove it out. I remember my dad always had a spare ballast resistor in the glove box, on hots days, it usually gave out right after parking somewhere. If I can find a ECU I'll keep the old one, I now have spare a cap and rotor, need to find another dizzy. The intake is a Edelrock dual plane, seems to be ok up top. Sprayed water everywhere on it to see if there was a change. Vacuum gauge is still hunting all over the place, useless.
 
pishta said:
you can disable spark by putting little pins in the cap wire boots that extend out of the edge of the straight boot. They were little brass brads when supplied by Mallory in their 1985 Supershops $8.00 7mm blue cut to fit spark plug wire set. The you just take an insulated ground clip and touch the pin and it'll divert the spark right to ground killing that cylinder. Wrap the coil in a wet rag and see if it does anything. If the coil is going south, I think it gets hot itself.
Click to expand...
Thanks, I'm sure I have spark at all the cylinders, tested spark jump with a screwdriver in the boot, tested with plug grounded to engine, and tested with timing light. The only anomaly is #6 with the timing light was flashing erratic, sometime many flashes per stroke. Brand new coil installed, no change.
 
start pinching vacuum hoses with a pair of needle nose pliers while watching the gauge. If everything is pinched off and nothing changes vacuum wise......? reluctor gap changing due to a bad bushing? Its odd, that the dead cylinders are staggered evenly with the firing cylinders. a misfire will play havoc on a vacuum gauge.
 
Last edited:
I'm going to see if I can post a video of it running along with vacuum gauge. It's bouncing so wildly, I don't think pinching vacuum lines will show much difference. I did pull the dizzy line and plug it to see if idle changed, nope.
 
Bl1zzard said:
The only anomaly is #6 with the timing light was flashing erratic, sometime many flashes per stroke.
Click to expand...
Make sure that plugwire is not running next to another, separate it out of the loom. If it still sparks the same way, then throw that plug away and put a new one in.
No it's not the Ecu, not the ballast, not the wiring. It has to be between the rotor and the plug, and my money is on the plug.
BTW
just to be sure, #6 is passenger side, Third from the front right?
 
Bl1zzard said:
vacuum gauge. It's bouncing so wildly,
Click to expand...
In order for that to happen;
Firstly the gauge is not properly damped.... but if it is telling the truth, then;
Secondly, you have some cylinders that are pulling vacuum, and some others that are not only not pulling, but are actually sending a pressure spike up into the intake............... after the engine reaches operating temp.
To me this points to sticking intake valves or intake valves not closing, which I might interpret as lifters pumped up, or pushrods too long, but I can't think of anything else.
If you opt to do a LD test. you MUST do it HOT, when the engine is in the failed mode. If you wait until it has cooled off, you will miss it.
But, IMO, the gauge is already telling you about the problem, and a LD test is a lotta work. There is an easier way; just pull the plugs out of all the cylinders that you know are faulty. Plumb your gauge, and start it up. If I'm right, the pistons in those cylinders are now gonna pump the pressure out the plugholes, and the vacuum gauge should settle down. Altho, with 4 missing cylinders, I would expect the actual reading to be quite low.
With those cylinders now not upsetting the Idle fuel mixture, the richness should also disappear.
It's gonna be loud.
Yes I'm guessing, but this is IMO, a logical interpretation of the symptoms you have detailed, that began at cruising speed, lightly loaded. Why those 4 just happen to all be on the same plenum is a mystery to me. or
Thirdly that one-side plenum could be receiving multiple pressure pulses from some other source, like say a floorjet into a cracked or broken cross-over passage. But I think that's really stretching it.
You only need one bad cylinder pumping into the dual-plane intake, to mess it up for the other 3 om the same plenum, so I might be tempted to run it on all seven others, with only the #6 plug removed, and see what the vacuum gauge says.

.
 
Last edited:
After warm-up, running bad, - I'd undo each rocker shaft bolt one turn, and see if it ran any better.
If it did, I'd tighten one side, then the other, to determine which valve isn't closing.
jmo
 
It's #6, the leakdown test proved it right away. As soon as I pressured up #6 @tdc, air started blowing through the crankcase via the oil filler on the opposite side of the engine. If I plugged that, it came out the dipstick tube. Also with all my running and testing, I found oil in the intake manifold now and it's burning blue out the passenger side all the time. I took a video of it running with the vacuum, but it's not needed now. Time to investigate whether I want to spend the time and money for a bottom end rebuild or go a different route. I've replaced rings on a Honda 750 motorcycle and a Dodge Colt 4 banger, just not sure if I want/should keep this. I've already poured what I paid for this car to get it on the road and safe to drive. Now it a question of replace or rebuild.

BTW thanks FABO for all your helpful suggestions. The leakdown test should have been the second thing I tried, not the last.
 
You won't really know the extent of what the engine needs until you take it apart. Maybe just a refresh of bearings and rings. Maybe a complete overhaul.
 
Was #6 at TDC...... COMPRESSION?
Not that it matters......
cuz, in my experience, from the chamber, cylinder pressure at TDC compression, can only get into the CC three ways, namely
thru the piston,
around it,
or out past a ruptured headgasket..
But that doesn't explain the Vacuum gauge action, cuz the CC ain't connected to the intake, except via the PCV I guess. ..... but that would have corrupted both plenums.
This is getting interesting.
 
Last edited:
Yes, it was on the compression stroke. I was fighting to keep it from turning with the socket wrench on the crankshaft when I applied the air.
 
cudamark said:
You won't really know the extent of what the engine needs until you take it apart. Maybe just a refresh of bearings and rings. Maybe a complete overhaul.
Click to expand...
I've lost complete confident in the PO's abilities. It was supposed to have been rebuilt but never run (still had assembly lube in the plug holes, etc.) We found so much stuff that was done wrong, timing chain installed 40 degrees out, wrong transmission (early 60's 904 that didn't mate up to the engine), various other electrical problems, took me and my son almost 2 years to get it running and safe. At this point, I'm almost sure we'll uncover more bad/wrong stuff inside it.
 
You must log in or register to reply here.
-

Back
Top