Jump to content

Dave WM

L28 misfire at idle

Recommended Posts

working on a misfire using power balancing and a color tune plug.

 

  • Like 1

Share this post


Link to post
Share on other sites

I am still having issues with getting the air out of the system, installed the overflow tank, and got it flowing and then topped up the rad. will keep an eye on it. I did another test this time after making sure the water was flowing thru the rad, sucked out some water with the turkey baster to make sure I did not suck up in water with the test kit. This time it did NOT change color at all.

I think I may have sucked in some rad water on the 1st test. Don't know why but when I did that I got a slight color shift toward yellow. Other things I noticed is there is a strong suction force after a few pumps which tells me the system is sealed which is also good since if gas was getting in I don't think I could do that. NO evidence of water in oil, I need to get some clean water/antifreeze in so I can keep an eye on it for oil slicks.

on the water temps I am looking for a quick warm up and opening of the thermostat, I think I keep getting bubbles in and then the stat does not open until soon enough. It does have a burp hole in it, I may open that up some with a drill bit.

 

 

Edited by Dave WM

Share this post


Link to post
Share on other sites

Is the engine "nose up" or nose down on your engine stand.  The pump will fill the engine with coolant up to the thermostat if it's nose up.  If it's nose down there could be an air pocket at the back of the cylinder head.  With a heater core installed that air pocket would end up there, instead of in the head.  Maybe you can "burp" it from the heater core supply port.

And, just curious, but is "air in the system" really a problem?   It's just heat transfer fluid, if it contacts the hot surfaces and absorbs the heat, then moves out to the radiator, all is good.  I've seen quite a bit of discussion out on the internets about what happens in the system, but , really, there's not much to them.

Share this post


Link to post
Share on other sites

in my case I am sure it was a problem, the T stat was not opening when it should, I just re ran it, this time all was good, came right up to 185 quick and stayed there. After shut down I was able to remove the cap, without any explosive burping or excessive overflow. Very little built up pressure with the temp at 185, I bet if I had a 160 in there it would have NO pressure build up. After removing the cap the water level was right up to the top of the neck. Before I am sure it was not cooling since the rad was staying cold way past when it should have been flowing water and cooling the engine down. Removing the cap was an invitation to a Mount St. Helens like event, even when the rad was cold after a short run.

I will have to take a look at the angle, will check it against my car. I still think I will drill that T stat, just to be sure. Its not a Nissan one, so maybe I will just get that instead.

 Next up will be to get some proper coolant in there, or at least a rust inhibitor.

Oh and I want to run it with the valve cover off (will have to plug the vent hose) just to see how well the oiling of the cam is going. I did NOT replace any of the gasket materiel that is in the oil squirt tube. Will do this out side of the garage since oil will go everywhere. I just like to see it working.

Edited by Dave WM

Share this post


Link to post
Share on other sites
3 minutes ago, Dave WM said:

in my case I am sure it was a problem, the T stat was not opening when it should, I just re ran it, this time all was good, came right up to 185 quick and stayed there. After shut down I was able to remove the cap, without any explosive burping or excessive overflow.

You removed it with the engine hot?  Should have had some overflow.

Anyway, carry on.  Just seems like being focused on seeing what the coolant is doing instead of what can't be seen.  The water pump is certainly full of fluid and will push it through the engine.  The only way out is the thermostat.  Air will easily make it through the tiny hole in the thermostat. 

Have to say though that the FSM is way behind in 1976.  My coolant level sits at the top of the filler neck after some heat cycles, with the reservoir working right.

image.png

Share this post


Link to post
Share on other sites
2 minutes ago, Zed Head said:

The water pump is certainly full of fluid and will push it through the engine.  The only way out is the thermostat. 

Actually, just remembered...if the heater core lines are looped, aka bypass mode, the coolant can make a loop through that path without entering the radiator.  At low RPM there might be enough flow through at path so that the thermostat sees very little.  Is your coolant port blocked or looped?

Share this post


Link to post
Share on other sites

I was careful to remove slowly so as to bleed off any pressure build up, Did have some overflow, but not explosive like superheat water converting to steam. Before it would literally blow out maybe a gallon of water and this is when the rad was not even hot. On my last fill up I just kept adding water while it was running (after it blew out a bunch) eventually topping if off. I thought I had been doing it this way all along, but seem like this last time it worked.

Share this post


Link to post
Share on other sites
1 minute ago, Zed Head said:

Actually, just remembered...if the heater core lines are looped, aka bypass mode, the coolant can make a loop through that path without entering the radiator.  At low RPM there might be enough flow through at path so that the thermostat sees very little.  Is your coolant port blocked or looped?

looped

Share this post


Link to post
Share on other sites

I can block them to see if that matters (will just clamp the hose).

Share this post


Link to post
Share on other sites
5 minutes ago, Dave WM said:

I can block them to see if that matters (will just clamp the hose).

It's been show to cause overheating.  It bypasses the radiator and the front half of the head.  

image.png

Share this post


Link to post
Share on other sites

I found another leaking injector (at the junction of the steel body to the plastic part with the connecter). I was also trying to see if I could further isolate the slight miss I still hear. I did the power test and while each cylinder would cause a slight drop in RPM when disabled, I noted the #2 also seemed to stop the miss as well as drop the idle. It happens to be the one that is leaking as well so will replace that one.

On the head gasket issue, I did the chem test on my 75 and it did not change the intensity of the blue color at all. While with this engine I could get a slightly lighter shade of blue (but never turned yellow). So I am unsure about the status based on the test. I have a 160f thermostat coming and plan to replace the one I have in there now. I used the 160 on my 75 and seems to work well. Will try it again when I have replaced the injector and the stat.

 

 

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.