Intermittent Starting Problems

[1lejohn]

I had an intermittent starting problem for a few weeks. I haven't been daily driving the truck for a while. With the summer finally over here in Texas I was wanting to drive it to work. I use it for doing the dirty work at home and it's the high-water vehicle. On several occasions it would start fine. On other's it would just crank and crank. I have an MSD 6 box and coil. The HEI is gutted it has no coil or module in it. I got to thinking that had a bad ground going to the MSD. I checked them and no problems. The box had steady power. I checked for spark, and it was there, so I took it for a drive against my wife's advice. She was right I didn't make it far down the block. She's a good sport and helped me flat tow it home. We checked for spark, and it wasn't there. HUMM. I did some research and found a trouble shooting tip from MSD. I disconnected the wiring from the dizzy and checked the box and coil. Boom good spark. You do this by jumping the trigger wires that connect to the dizzy from the box. I bought a new FAST distributor from summit and installed it. The truck fired right up.
I spent yesterday fine tuning the spark advance. The combo is a Vortech headed GM crate 350 with the HT 383 roller cam. It has an Edelbrock 1406 square jetted with 98's and 73/47 rods. summit long tube headers, turbo 350 trans and the stock 3:08 gears. The motor didn't like a lot of timing, it pinged bad when given any throttle. I started with the vacuum advance curve set in the middle of the range, and the lightest springs on the mechanical advance. Wrong! I switched back to the stock springs, still alot of ping. Next, I adjusted the vacuum can all the way out. This setting still gives 18 degrees at idle but starts taking it out at lower vacuum levels.
After doing all this I was only hearing the motor ping at 2000-2400 rpms at 10 " of vacuum rolling into the throttle. WOW, WTF. I went back and replaced one of the stock springs with a heavier one on the mechanical advance. I drove it again and good deal it's not pinging anymore. The truck is running the best it ever has. It's idling at 750 with 16" of vacuum, the carb screws are only out 1/2 a turn. The idle is a little lean at 15.5. The initial timing is at 8 degrees, I'm guessing the mech is not all in till 4000. MY take is that the 3:08's are horrible they lug the engine down which causes the overlap in timing to occur resulting in the pinging. The truck runs smooth, the throttle response is not crisp to me. What's your all's take? Hope this book helps somone along the way.

 

[AuroraGirl]

I had an intermittent starting problem for a few weeks. I haven't been daily driving the truck for a while. With the summer finally over here in Texas I was wanting to drive it to work. I use it for doing the dirty work at home and it's the high-water vehicle. On several occasions it would start fine. On other's it would just crank and crank. I have an MSD 6 box and coil. The HEI is gutted it has no coil or module in it. I got to thinking that had a bad ground going to the MSD. I checked them and no problems. The box had steady power. I checked for spark, and it was there, so I took it for a drive against my wife's advice. She was right I didn't make it far down the block. She's a good sport and helped me flat tow it home. We checked for spark, and it wasn't there. HUMM. I did some research and found a trouble shooting tip from MSD. I disconnected the wiring from the dizzy and checked the box and coil. Boom good spark. You do this by jumping the trigger wires that connect to the dizzy from the box. I bought a new FAST distributor from summit and installed it. The truck fired right up.
I spent yesterday fine tuning the spark advance. The combo is a Vortech headed GM crate 350 with the HT 383 roller cam. It has an Edelbrock 1406 square jetted with 98's and 73/47 rods. summit long tube headers, turbo 350 trans and the stock 3:08 gears. The motor didn't like a lot of timing, it pinged bad when given any throttle. I started with the vacuum advance curve set in the middle of the range, and the lightest springs on the mechanical advance. Wrong! I switched back to the stock springs, still alot of ping. Next, I adjusted the vacuum can all the way out. This setting still gives 18 degrees at idle but starts taking it out at lower vacuum levels.
After doing all this I was only hearing the motor ping at 2000-2400 rpms at 10 " of vacuum rolling into the throttle. WOW, WTF. I went back and replaced one of the stock springs with a heavier one on the mechanical advance. I drove it again and good deal it's not pinging anymore. The truck is running the best it ever has. It's idling at 750 with 16" of vacuum, the carb screws are only out 1/2 a turn. The idle is a little lean at 15.5. The initial timing is at 8 degrees, I'm guessing the mech is not all in till 4000. MY take is that the 3:08's are horrible they lug the engine down which causes the overlap in timing to occur resulting in the pinging. The truck runs smooth, the throttle response is not crisp to me. What's your all's take? Hope this book helps somone along the way.

your truck has power mods and various changees... what is your tire size? I would think you would want a better ratio than 3.08.. especially with a th350. You could try a powerblast plate for your edelbrock to help with the throttle response. it being lean at idle sounds like that may be at play. Also, your advance weights, did you only play with springs? your distributor might just flat out need mechanical stops or different weights because of your cam and other mods. what port is your vacuum advance on?

 

[1lejohn]

The can is on manifold vacuum. The tires are 33's. I was thinking about adding a 1" spacer. The AFR goes rich whenever the throttle is opened. I can richen up the idle with a turn of the carb screws. I agree the 308's are the wrong application for this build. The truck originally was a 305 700R combo. Gears aren't in the budget at this time. What do you think 3:42's or 3:73's ? If and when I do them.

 

[AuroraGirl]

The can is on manifold vacuum. The tires are 33's. I was thinking about adding a 1" spacer. The AFR goes rich whenever the throttle is opened. I can richen up the idle with a turn of the carb screws. I agree the 308's are the wrong application for this build. The truck originally was a 305 700R combo. Gears aren't in the budget at this time. What do you think 3:42's or 3:73's ? If and when I do them.

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I Know conventional wisdom esp around here is manifold vacuum. but based on watching this, personally, Im curious if ported couldnt work a bit better for you? Only because you have modifications as well

That spacer idea and the powerblast spray add on kit are both likely to help!
Do you go on the highway? Do you pull things or do truck stuff? If you do, id say 3.73. if you changed nothing else but wanted all-around, 3.42 makes sense to me. But thats my brain balancing having 3 speeds and daily driver rather than "truck needs"

 

[1lejohn]

The pinging was above idle speeds and putting around driving. It was more pronounced when accelerating and under a load which makes sense. It was like at the cross over point when mechanical advance was coming in and the vacuum advance was falling off. I'm going to check the initial timing one more time and look at the timing tab versus the dampener marks. It's a degreed aftermarket one. Yes it's a work truck, not a lot of highway driving, but would like to be able to. Thanks for the response.