Howdy y'all,

I could use your advice. About a week ago, the engine temp gauge, which has always heated up to the center of the normal range like the manual says it should, started only heating up to the bare minimum end of the normal range. I figured the thermostat was just stuck open, but I changed that today, and that wasn't the problem. Moreover, ever since it's been running cooler, it will randomly bog down. Not stall or die, but just give me a few seconds of bog like it's cold... but this can happen at the start of a drive, during the middle, or even towards the end of the drive, it's seemed random. The other day even, I started the truck, drove about 100 feet, and the truck died and wouldn't restart. Prayed about it w/ my GF, and a man showed up and God told him to turn the idle mixture screw on the carb a 1/4 turn to the left, and the truck fired right back up and was ready to roll. Not sure if adjusting the air/fuel carb mix was a bandaid... or if that screw had rattled itself too lean. Honestly, I'm lost. I'll detail the work it's had over the last two years for more info. I would really appreciate any advice y'all have.

Changed Today:
- Fuel Filter
- Thermostat

Last 6 Months:
- Valve cover gaset
- New gas tank
- New fuel sending unit
- New rubber fuel hoses
- New starter

6 - 12 Months Ago:
- New belts
- New carburetor
- New plugs, wires, cap, & rotor

12 - 24 Months Ago:
- New radiator
- New water pump
- New heater core & hoses

- and obviously, regular greasing and oil changes.

Looking forward to y'all's advice,
Duane Quade Jr.

 

Carb screw to the left, counter clock wise?, turning it out would make it richer, turning it in leans it out.
I cant see that making it start and run.

Being a 79 it would be running a DSII IGN system.
There should be a IGN box on the inner fender well.
Replace it with a top of the line unit not a cheap one.
If that dose not fix it you now have a spare for when it dose fail.

On the 80's truck's we have seen the box cause some crazy things.
Most of the time the motor just shuts off like with the key.
This happens when the box gets hot.Once it cools the motor will restart.
Aos seen it posted where the motor will loose power or run ruff at times.

I had 1 that you start the motor let warm drive down the road and stop for the light and would stall.
Same when coming home.I kept adjusting the choke as that was what it acted like.
This was on the wife's car but never happened when I drove it.
Once changed no more issues. This was on a 76 year car.
Dave ----

 

My thought was maybe the engine rattling caused the screw to slowly rotate to being too lean, and it finally quit. I had never paid any attention to the screw to see where it had been before. I'm new to engine work, so call me out if that sounds crazy, but that was just my thinking.

I hadn't thought about the ICM, I'll check the back of that tomorrow and see if it looks heat damaged at all.

 

UPDATE:

I took the truck for two, seven-mile drives today. The temp gauge has climbed from the coolest side of the normal range to sitting between the "N" and the "O," the problem being, it has always run between the "R" and the "M." Not sure how changing a thermostat I don't think was faulty and a fuel filter could cause slight improvement, but it did. The problem being, on the drive home (the second drive,) the truck hesitated for a few seconds about two minutes into the drive, then was fine the whole way home. I'm going to look into the choke tomorrow most likely, but I'm still confused. I'll check into the ICM as well, but any additional advice would be greatly appreciated.

 

Duane
I would listen to and try Fuzzface's ideas first.
In my opinion, he is one of the best trouble shooters when it comes to these 300's.
Very knowledgeable and tons of common sense.
Alex

 

I'll add as well, as maybe this is related, I'm not sure. The truck doesn't start right away when cold. (Having sat for a few+ hours) When I shut it down at the gas station, for example, it'll start back instantly, but after it has sat overnight, or any time extending beyond that, you have to pump the pedal a few times, crank, pump a few more times, crank, and then it will fire up. Maybe that's related? Or if anybody knows how to solve this problem... I'd love your advice... I'll likely make a separate thread regarding that here soon if nobody has any input. Thanks!

 

I appreciate your input... I'm certainly going to check it out tomorrow, and likely order the part. I just like to put my eye's on it before I spend the money... and it's dark out now.

 

To start these engines cold, mash the pedal all the way to the floor to set the fast idle before cranking.

Then after it fires up let it fast idle for @ 30 seconds (in this heat) longer when temps are cooler.

Then blip the throttle for normal (curb) idle.

You may have to experiment with the fast idle times for your particular motor.

 

Have not red the update yet.

If the carb screw would ever turn it would be out.
There should be a spring between the head and carb body this keeps the screw from turning.
The idle speed screw also has a spring for the same reason.

I think with the hood open and the tinkering done was enough to cool the box and it started back up.
I and other have had that happen. Open the hood to check everything hop back in the it now runs.
Dave ----

 

(check is in the mail for saying that LOL)
A lot has to do with age (63) and growing up with and working on this older stuff.

Todays gas blend may have something to do with it.
Mine will start up better if it sits over night with just a little pump and hit the key.
Now if I run it and stop for say 30 min it can be hard to restart and that is because of todays fuel.
Look up "hot restart" posts on this.

I dont blame you not wanting to throw money and parts at it but some times that's what it takes but you need to know why that part. On the ICM I have seen both posted and first hand it can cause crazy things that you would never thing it would.

I fixed it fore you to set the choke.

Now about the temp gauge.
Mine just makes it up to the line before the N.
I even changed out a new 190* stat, I forgot it was new, with another 190* and it still goes to the line.
Checking it the temp is 190*. I also changed out the sender with no joy.
So the gauge has to be off but I dont worry.
I do know it will go up if I sit for a bit, 10+ min, with the AC on and it being 90*+ out but once I start moving it comes right down.

Oh just remembered someone said to clean the push on connector and sender stud.
Then crimp the connector a little so it grabs tighter and that fixed his low reading gauge.
I keep forgetting to do this when under the hood and motor is cool.
It is on the right side down under the manifolds to the rear of the motor.
Hard to see but you can feel it back there.
Dave ----

 

Oh on the cold start after sitting over night, motor off, pull the filter and move the throttle to make sure the choke closes for 1.
2 Hold open the choke and look down into the carb and move the throttle you should see fuel squirt when it is moved.
If no squirt the accel pump is not working and a carb rebuild is needed.

It is not a hard carb to rebuild and the kit is cheap.
Might want to rebuild it just to clean the inside if it has not been done in a bit.
Dave ----

 

if you are running good air fuel ratios you are likely 12-13:1... if you lean that out to 14-15:1 it should run hotter rather than cooler. it isn't until you get past that where you start getting cooler but it wouldn't be running well at all. i'm not an expert but i think you'd have to have detonation above 15:1.

 

First off, the temp gauge reading low may not have anything to do with running or not. Temp gage reading low could be a loose wire at the sender or a low voltage from the IVR.

My '77 run until 2015 or so on it's original DSII box, then one day after work at my post-retirement gig, I drove through a drive through, got a sammich, cold drink, started home 15 miles. Only made it about 2 miles, truck died like out of gas. I had just sold one of these DSII boxes at work, it was fresh in my mind. I opened the hood after it would not start, saw potting had run out and on the inner fender apron. Poured my cold drink on the DSII, truck then started. I made it home, but without sitting in any more drive throughs.

I doubt the idle mix screw had anything to do with running or starting, but the time might have let the DSII cool off.