cylinders 1 and 7 are cold

Hey guys,

As some of you may know, I have been trying to track down this issue with my small block chevy for quite some time. The issue is that cylinders 1 and 7 are about 300 degrees cooler than everything else.

I think I have pretty much checked everything at this point. Heres a list of things that i have replaced or checked:
Compression test - within spec
Leak down test - within spec
Plug wires - repalced
spark plugs - replaced
distributor - replaced (including VR sensor and igntiion modual)
coil - replaced
injectors - tested and swapped
lifters - swapped
valley leaks - checked
vac leaks - checked

From my timing light, it looks like im getting a good signal on the wires to those cold cylinders.

I think this pretty much covers everything.

But one thing I haven't done is swap in a different heat range spark plugs. I am running older AFR 190cc heads and AFR recommend to run Champion RCY9C as a starting point. I recently learned that these plugs are considered fairly cold plugs.

I've been trying to track down this issue for so long now that I'm staring to explore some radical ideas. I'm wondering if its possible for the plugs to cause this large discrepancy in cylinder temps. From listening to the exhaust, its obvious its misfiring. I'm wondering if there is some sort of strange dynamic to the airflow entering these outside cylinders and that these plugs are not enough to get things going? Is this even possible?

Any input or suggestions would, as always, be much appreciated.
 
Hey guys,

As some of you may know, I have been trying to track down this issue with my small block chevy for quite some time. The issue is that cylinders 1 and 7 are about 300 degrees cooler than everything else.

I think I have pretty much checked everything at this point. Heres a list of things that i have replaced or checked:
Compression test - within spec
Leak down test - within spec
Plug wires - repalced
spark plugs - replaced
distributor - replaced (including VR sensor and igntiion modual)
coil - replaced
injectors - tested and swapped
lifters - swapped
valley leaks - checked
vac leaks - checked

From my timing light, it looks like im getting a good signal on the wires to those cold cylinders.

I think this pretty much covers everything.

But one thing I haven't done is swap in a different heat range spark plugs. I am running older AFR 190cc heads and AFR recommend to run Champion RCY9C as a starting point. I recently learned that these plugs are considered fairly cold plugs.

I've been trying to track down this issue for so long now that I'm staring to explore some radical ideas. I'm wondering if its possible for the plugs to cause this large discrepancy in cylinder temps. From listening to the exhaust, its obvious its misfiring. I'm wondering if there is some sort of strange dynamic to the airflow entering these outside cylinders and that these plugs are not enough to get things going? Is this even possible?

Any input or suggestions would, as always, be much appreciated.
Hi John, make sure the firing order is correct, twice if neccesary? cant tell you how many times I have seen it wrong! next thing is to check the valve lift on inlet and exhaust on those 2 cylinders, if you have point type ignition check the lobes in the distributor, the other thing i have seen over the years is a partially blocked exhaust or muffler, saw that stump so called experts a couple of times, hope this helps, let us know what you find, all the best, Neville Nesbitt.:idea:
 

Tim Kay

Lifetime Supporter
Firing order correct? Elementry but you never know. Certainly something I would do!!

Tim
 
These may be off the wall, but here goes. On the intake manifold have you measured the port on the manifold and the port on the heads. Are they all the same. One thing I did with my AFR 205 heads was to port match the heads to intake(by way of the gasket). the other thing I would suggest is that you need to check the software for the ECU and see if it allows you to retard or advance each individual cylinder. Something to get advice on for sure from the manufacturer and a shop owner that has experience with your system.
Have you got the distributor timing adjusted as it should. What I mean is, for example, with MSD you can allow the timing advance to be set with a set of springs and cams that you install yourself in the tuning proess. They also have a system that allows you to lock out the timing curve and set it at a pre determined setting on the crank shaft for the #1 cylinder. Then the advance curve is set through the computer for the amount of advance along the rpm range for what ever you want it. It is software set, and adjusted. That way you set the advance where you want it. You have to set the initial advance of the distributor to say 40 or so degrees for the #1 cylinder. This [uts it near one of the magnets on the crank trigger and allows the computer to know where the crankshaft is in relationship to the #1 cylinder, and it then fires the injectors and sparkplugs where ever you set your computer. 10-14degreees for startup and idle and eventually(every 200 rpms or so) up to 36 or so for full advance(just an example). Did you check for phase shift in your distributor? Find it on the MSD web site or on the distributor box. If not set correctly you will get the firing to swap cylinders randomly to the one in front or behind the cylinder that is suposed to fire on the distributor, which should be 90 degrees off and backfire.
Does it backfire during cranking or just at a certain rpm. Check the crank trigger and make sure you have a Chevy degree unit and not say a Ford. They have different mounting points and will give different values than what you need. You can't alter the computer to makeup for the difference. It cost me 4 ring gears for just those sort of things.
If you have an MSD distributor, go to their web site and look at their videos(they have about 15-20) on timing, advance, and initial setup. Even if you don't have an MSD, go anyway it is good info. It is done in simple english and is easy to follow.
The last thing I can think of is are your butterflys syncronized?? That is a biggie.
I know its a lot, but its all I could think of. Hope this helps you out.

Bill
 
Hi John, make sure the firing order is correct, twice if neccesary? cant tell you how many times I have seen it wrong! next thing is to check the valve lift on inlet and exhaust on those 2 cylinders, if you have point type ignition check the lobes in the distributor, the other thing i have seen over the years is a partially blocked exhaust or muffler, saw that stump so called experts a couple of times, hope this helps, let us know what you find, all the best, Neville Nesbitt.:idea:

Firing order is correct, this has been checked quite a bit, plus i have just redone all the of wire.

Distributor has been been replaced thinking that was the issue. It is a GM 8-pin HEI type.

Checking the valve lift is a pretty big deal. The engine has hydraulic lifters, and from what I understand, I would need a solid lifter to really check the lift. The short block is new with a new cam, i think its pretty rare that comp cams would send out a bad cam.

I don't understand why a partially blocked exhaust would cause only these 2 cylinders to be cold, unless the header primaries were plugged on them, which I know they are not. The car has a Y-pipe and a single exhaust.
 
These may be off the wall, but here goes. On the intake manifold have you measured the port on the manifold and the port on the heads. Are they all the same. One thing I did with my AFR 205 heads was to port match the heads to intake(by way of the gasket). the other thing I would suggest is that you need to check the software for the ECU and see if it allows you to retard or advance each individual cylinder. Something to get advice on for sure from the manufacturer and a shop owner that has experience with your system.
Have you got the distributor timing adjusted as it should. What I mean is, for example, with MSD you can allow the timing advance to be set with a set of springs and cams that you install yourself in the tuning proess. They also have a system that allows you to lock out the timing curve and set it at a pre determined setting on the crank shaft for the #1 cylinder. Then the advance curve is set through the computer for the amount of advance along the rpm range for what ever you want it. It is software set, and adjusted. That way you set the advance where you want it. You have to set the initial advance of the distributor to say 40 or so degrees for the #1 cylinder. This [uts it near one of the magnets on the crank trigger and allows the computer to know where the crankshaft is in relationship to the #1 cylinder, and it then fires the injectors and sparkplugs where ever you set your computer. 10-14degreees for startup and idle and eventually(every 200 rpms or so) up to 36 or so for full advance(just an example). Did you check for phase shift in your distributor? Find it on the MSD web site or on the distributor box. If not set correctly you will get the firing to swap cylinders randomly to the one in front or behind the cylinder that is suposed to fire on the distributor, which should be 90 degrees off and backfire.
Does it backfire during cranking or just at a certain rpm. Check the crank trigger and make sure you have a Chevy degree unit and not say a Ford. They have different mounting points and will give different values than what you need. You can't alter the computer to makeup for the difference. It cost me 4 ring gears for just those sort of things.
If you have an MSD distributor, go to their web site and look at their videos(they have about 15-20) on timing, advance, and initial setup. Even if you don't have an MSD, go anyway it is good info. It is done in simple english and is easy to follow.
The last thing I can think of is are your butterflys syncronized?? That is a biggie.
I know its a lot, but its all I could think of. Hope this helps you out.

Bill

Thanks for the suggestions Bill.

The intake is ports are matched to the heads.

I am running a factory GM HEI ignition which is controlled electronically. I dont think I can control each cylinders timing independently, i have never heard of that before with my unit (megasquirt 2). The engine doesn't backfire at all, it dose make some burbles and popping out the exhaust when held at a constant RPM. i figure that that those pops are the cylinders trying to fire or the unburnt fuel going into the exhaust.
 
Running a converted LT1 intake manifold.

Then that being a 180° manifold will have #'s 1746 feeding off the same runner, if its an old manifold check it has not 'rotted' thru anywhere in the integral exhaust hot box crossover which might be giving you a false signal, along with any other leaks it may have on that side, even between injector body/manifold base.
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
John,

I don't recall all the past details so bear with me...

Hydraulic flat tappet or roller cam?

Were the heads recently redone?

What has changed since the last time (if ever) it ran correctly?
 
Injector driver/computer?
Are all the injectors actually squirting?

Only skimmed this, so apologies if already covered.


Tim.
 

Ian Anderson

Lifetime Supporter
MS2?
I have read a lot over at the V* forum in the UK where people use this a lot.

Are all your earths on the injectors taken to a single point and is the same single point that earths the ECU

It appears that they are very sensitive to earthing

Ian
 
Then that being a 180° manifold will have #'s 1746 feeding off the same runner, if its an old manifold check it has not 'rotted' thru anywhere in the integral exhaust hot box crossover which might be giving you a false signal, along with any other leaks it may have on that side, even between injector body/manifold base.

I just had the manifold off and everything looked good. I took apart that bottom section to make sure everything was ok in there, and everything is fine. It does have those large bolts which I think act as plugs for the original casting holes, all of those are sealing effectively. Further more, the intakes's PCV vent has been sealed for our application since we have the vent on the valve cover.

The overall condition of the manifold is good and I saw no signs of any leaks. We also pull good vacuum. Also, I'm sure this isn't a 180° manifold, wouldnt that have runners that go up and over to the other side like an LSX or ford manifold? This intake has very short runners that go from the plenum directly to the head. 1,3,5,7 are all fed from the same side of the manifold that the cylinders are on.
 
John,

I don't recall all the past details so bear with me...

Hydraulic flat tappet or roller cam?

Were the heads recently redone?

What has changed since the last time (if ever) it ran correctly?

Hydraulic roller lifters. We just completed swapping them around from the bad cylinders to the good cylinders. There was no difference.

Heads have new springs, that's about it. The springs are the ones recommended by comp cams.

The car has pretty much never ran correctly. Before this short block, it did run the same heads, intake and headers, but it ran the old GM computer and was never tuned right. I'm only speculating, but i wouldn't be surprised if cylinders 1 and 7 were bad back then too...
 
MS2?
I have read a lot over at the V* forum in the UK where people use this a lot.

Are all your earths on the injectors taken to a single point and is the same single point that earths the ECU

It appears that they are very sensitive to earthing

Ian

Funny, I have never heard it called "Earths" before, across the pond we always say "Grounds". I have checked this and have redone the grounds. The thing is, the injectors are batch fired, so i have taken the connector that fires injector #3 and swapped it with injector #1. No difference was observed.
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
John,

Loosen up the lifters to Zero lash when on the heel of the camshaft lobes and try again.
Also - You may be having a couple valves that are hanging just a little. This would mean pulling the heads and examining valve stems and honing the guides for proper clearance.

Suck-squirt-squeeze-zap-bang-blow
Repeat.

Very simply put, something is not in the right sequence or not enough of it.

Next step would be to purchase or borrow an EGT gauge and thermocouple and start getting honest readings from each cylinder while under load. I don't trust the laser temp guages much anymore as I have found too much variation in the readings.


--edit--
I know your compression readings were good, but those are taken at cranking speed. Valves don't typically hang when running in slow-motion like that..
 
Last edited:
Hey Randy,

Before I put these heads on, I had a shop go through them to check out the guides. They said they were good to go. I also put the valve springs on myself and during the process, I didn't notice anything wrong with the valves.

I have checked and reset the lash 2 times now for the whole side, so I don't think that's the issue. Last time I did it was when I moved the lifters around.

I do have a high speed camera, i could possibly film the engine running with the valve covers off that one side to see if the rockers on those cylinders are closing differently.

Before I go pulling heads, there's a few more things I want to try. One of them is putting in a hotter spark plug. I found that the plug I'm using is for supercharged applications. I doubt this will have any effect, but who knows, its worth a try for 2 bucks.

I also have a different intake manifold, though, its needs some work and money before its ready to run.
 
Last edited:
John,
You said something interesting in that it was making a burbling sound. When unburnt fuel is in the exhaust you will hear a shotgun blast when it ignites. I can send you a video of mine doing that. Mine would burble on cranking when the wrong cylinder was getting the spark.The coil wires were jumping, to the wrong cylinder. I would bet it is an unshielded coil wire or a bad ground for one of the coils. then I would say to check the wires that are running together with the bad cylinder(s). I would suggest an unwrap of the coil wires for a better look at the runs. You have a backfire situation that is occuring on the intake stroke and the flow of gases into the cylinder is faster than the flame front. Remember that gasoline burns rather slowly. That is why we have to advance the timing before top dead center, so that the maximum force happens after top dead center. Most of your fuel is being burnt before it is getting into the cylinder, thus the cooler exhaust.I am not clear whether you are running a coil per cylinder or a distributor setup. If it is a coil setup then what I told you is happening. Or rather that is what was happening to mine. As soon as I changed over to a distributor it ceased to exist, and ran like it should. If you have a distributor, then ???

Bill
 
Bill, I am running a single coil and a distributor. I just put on a new distributor, wires and a coil and have noticed no difference.

At this point, I think its the intake manifold. I think the ports are so butchered that it destroying the airflow. I have a unmolested stealth ram I'm going to throw on top of of the engine (doesn't fit under the hood), but its going to take a while to set up. It, at the very least, needs a fuel rail and the proper fittings to fit to the fuel lines.

I did try the hotter spark plug today, I figured it would have no effect and it didn't...

Cylinder #7 is the worst and can barely make 300°...
 
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