Unhappy 360 (At idle)

[Stephan D]

"PS. Try to seperate the spark plug wires more if you can. it can reduce cross talk."

Good idea, will do!

 

[pt70]

Idle sounds high, but my ears don't do well on videos. There should be a hose routing decal under the hood. There should also be a decal showing the engine timing. A 1979 only factory truck service manual should also have it. This is a one year only engine/emissions set up.

-----------------------------------------------------------------------Sweet Ride------------------------------------------------------------------------

 

[Stephan D]

Idle sounds high, but my ears don't do well on videos. There should be a hose routing decal under the hood. There should also be a decal showing the engine timing. A 1979 only factory truck service manual should also have it. This is a one year only engine/emissions set up.

-----------------------------------------------------------------------Sweet Ride------------------------------------------------------------------------

The sound of the video is a bit misleading, but the idle is approx. 750 RPM in Neutral and 650 RPM in gear, there is a timing label under the hood that says 10 degrees +- 2 degrees at 750 RPM.
The hose routing sticker is there as well but outdated as most of the emissions stuff is gone, our domestic emissions regulations are quite liberal for vintage cars, not so for current vehicles.

 

[Mattax]

The sound of the video is a bit misleading, but the idle is approx. 750 RPM in Neutral and 650 RPM in gear, there is a timing label under the hood that says 10 degrees +- 2 degrees at 750 RPM.
The hose routing sticker is there as well but outdated as most of the emissions stuff is gone, our domestic emissions regulations are quite liberal for vintage cars, not so for current vehicles.

Stephan, The drop of 100 rpm indicates the engine has less power at idle than it should. It's prob too lean and slightly advanced.
There could be a big difference between setting 15° and 10° at 750 rpm.
Try 12° at 750 in neutral/park. You may have to fiddle with the idle speed (throttle stop). Then turn the idle mix screws until lean drop off, and then make them 1/4 turn richer.

It will be useful to see exactly what emissions was on the truck, and still is on the truck. If it had EGR, that would not come into play at idle. If it still has EGR, it needs to be correctly hooked up or it will be open at the wrong times. Not hard to do. If theair injection check valve or tubes are leaking, that can slightly mess up the cylinder mixtures especially at low rpm. What happens the exhaust leaving the the cylinder runs into near atmospheric pressure.

 

[Mattax]

There could be a big difference between setting 15° and 10° at 750 rpm.

If you have the shop manual, look up the advance specifications in the back of the ignition chapter. Otherwise will need to find someone with a specification card. Maybe @halifaxhops was one for a 79 360 in light truck.

The comment about softer distributor springs puts us on alert that the timing at idle might be extra sensitive.

For example, lets say the factory timing looked like this when set at 750 rpm to 12*BTDC.

With the mechanical advance as shown above, the spring force is high enough that advance only just begins around 700 to 750 rpm. Its not going to make much diffence whether the initial timing was set at 600 or 750 rpm.

But lets say the light spring was replaced with one that is 'softer.' If the initial tension was not increased, the weights will now have less restraint and start moving out at lower rpm. Timing at 650 rpm would be different than timing at 750 rpm.

 

[Stephan D]

Yes,I will try to adjust some more, but right now it idles better than ever before.

Originally it had catalysts, EGR and some more stuff, all is gone now.

Here is a picture of the original hosing diagram under the hood:

Timing instructions:

 

[pt70]

Check your carb to intake nuts. Snug is good enough. Readjust carb idle mixture screws as Mattax said.

Keep in mind that your engine has a hi-perf cam in it, so don't expect it to idle real smooth.

 

[Nat]

nice truck ! Good luck with it

 

[AJ/FormS]

What Mattax said;
Those are afterburners. Just exhaust powered, fresh air inhalers, to finish burning any misfires to save the cats. If your cats are gone, then you don't need them.

 

[Cudafever]

Do you know which port to put the vacuum advance to, on the carb
Do you know how to check the carb vacuum port to be able to us the right one............................

 

[Mattax]

What Mattax said;
Those are afterburners. Just exhaust powered, fresh air inhalers, to finish burning any misfires to save the cats. If your cats are gone, then you don't need them.

The air pump is gone. Even with cats, its now useless. I'm more concerned that the check valve is now two way! Really needs to plug that all off. Can put some high flow cats if he wants although maybe they won't last as long. Those things really improved in terms of flow when Fox body Mustang 5.0s came out.

My other concerns with the disconnect systems is the EGR and the idle stop solenoid.
I'd want to be sure the EGR valve or passage is plugged if the system is not being used.

Presumably the air snorkel vacuum motors are still hooked up. If not that could really choke the air flow, maybe even at idle?

 

[Stephan D]

The air pump is gone. Even with cats, its now useless. I'm more concerned that the check valve is now two way! Really needs to plug that all off. Can put some high flow cats if he wants although maybe they won't last as long. Those things really improved in terms of flow when Fox body Mustang 5.0s came out.

My other concerns with the disconnect systems is the EGR and the idle stop solenoid.
I'd want to be sure the EGR valve or passage is plugged if the system is not being used.

Presumably the air snorkel vacuum motors are still hooked up. If not that could really choke the air flow, maybe even at idle?

Regarding the EGR - the valve has been removed and replaced with a block-off plate, did it myself.

The vacuum motors for the snorkels are not hooked up, they now seems to be fully open all the time, I haven't checked if they can bounce around, will check that as well.

If they can bounce around, I will lock them in an open position.

Once again - Thanks for all ideas!

 

[Mattax]

Flaps open full time will work. It's a nice feature when they are functioning but not that important for what you want to resolve.

EGR block off plate I don't know whether that is enough or not. If it is great. There are a number of ways the EGR passages were routed. I don't know them that well and not your 360 at all.

 

[Stephan D]

Flaps open full time will work. It's a nice feature when they are functioning but not that important for what you want to resolve.

EGR block off plate I don't know whether that is enough or not. If it is great. There are a number of ways the EGR passages were routed. I don't know them that well and not your 360 at all.

The EGR Valve was a simple vacuum-operated device mounted on the drivers side of the intake manifold:

 

[Mattax]

Looks like the passage comes through the valve. On some the valve goes into passage.

 

[Tooljunkie]

I would check the gasket under the egr block off plate. They did burn out.
My 80 318 came factory with the egr blocked off. I remember a new plate hanging on the gasket pegboard at the old chrysler dealer in town.

 

[AJ/FormS]

A properly functioning EGR valve is no big thing. People get their underwear all balled up about it, because of it's status as a pollution device.
But our first generation devices, after 1973, were so well controlled and of such modest capability, that as long as they were working, you would never know they were there.
If you think about they do, and you might think about if you can put something into your 8/1 chamber that occupies space, but does not contribute to combustion, you know like the 79% non-oxygen molecules that gets inhaled together with the 21% oxygen, during every intake cycle; How can you make use of that?

Big cams have built in EGR, and it's worst at idle and low-rpm, far in excess of what those little intake mounted devices could ever do. Nobody ever pulls their big-cam EGR bumpsticks out, complaining about it. lol.

I wouldn't build an engine for use with EGR, but I wouldn't lose sleep over it , if my engine had an EGR system already on it.

One thing about defeating the existing EGR valve is that the hot under carb passage is still there, and if you take the intake off, flip it over and remove the splash-shield, that cavity is usually filled with coked-up oil. My guess is that it is acting like a heat transfer material, and to some degree cooking the A/F charge as it moves on by.

 

[crackedback]

If it's still acting up, isolate the intake tract from EVERYTHING else. Do not hook up any vacuum actuated items at all. Plug all ports off at the manifold/carb.

Runs the same, it's not any of the other crap hooked up. Runs better, hook up one thing and see if the performance changes. Cap that off, then go to the next item. You may find the culprit (PB boosters are a likely source along with PCV) until you narrow it down.

 

[pt70]

Another thing to check is the heat riser on the passenger side exhaust manifold. Make sure it is free of any binding and opens fully when hot. It is normally closed when cold [spring loaded].

 

[Stephan D]

Separated ignition cables as much as possible, might be a tad better in idle, but it could be placebo.

It's fairly OK in idle now, so I think I leave it for the time beeing, a dyno run is in the plans, hopefully they can find out some more there.

Some idle exhaust note in gear as well, 600 RPM:

 

[Mattax]

a dyno run is in the plans

If its a performance pull (not an emissions check which we used to do for state inspections) then you will get the most out of dyno session by having a goal and plans.
If you want to hook up an oscilliscope, discuss that first. Not many dyno shops do that. In fact most won't even understand why that might be useful. But that's what would be most useful for ignition diagnostic.
Find out what the dyno and the operator is capable of. An acceleration pull usefull for wide open throttle, full load. Use it for that.
If the dyno can be used for other things, and the operator knows about how to do it, you can do more.
But before all that, I suggest you measure and plot the mechanical advance.

Might skim through this thread
Need Opinions. Have nothing to compare to.

Engine dyno threads that have some relevance to goals and collecting useful data at WOT on a chassis dyno.
383 rebuild - kinda whimpy on the dyno?

2 different dynos,2 very different numbers.why?

 

[Stephan D]

The idle misfire investigation continues, did a compression test today, just to be sure that there wasn't any major issue with the engine, I think compression looks within limits.

Took a picture of a spark plug as well, they all look the same.

Any thougts on the findings?

 

[Stephan D]

A little bump...

Did the compression test with warm engine and throttle fully open.

Compression between 140 and 155 PSI as the graph shows.

Any thoughts on the compression test result appreciated!

Will create a timing graph as soon as I can persuade my wife to
push the throttle with me under the hood.