Ford F700 '79 Dump Truck won't start

[Ditivec]

I've been having a problem getting her to start starting about a week ago. I was up in the engine compartment filling the brake fluid and bleeding some lines. After that, she wouldn't start. Turning the ignition and pressing the accelerator causes the engine to rev, but once you disengage the starter, it putters out. See this video:

https://photos.app.goo.gl/cQRrrX75Bh1BFRyH8

I was able to get it started last weekend after 30-40 attempts and it started easy the rest of that day. When I went to try again after a couple of days, same symptoms. I checked the air filter and made sure fuel was getting mixed into the carburetor. I checked the spark plug connections and they were all fine. Any ideas of what I could check next or what could be the problem?

 

[Theweldor]

Look carefully and see if you didn't disturb some vacumn lines somewhere.

 

[DMiller]

If will run with starter engaged it is running off the crank side ignition circuit, there is another to feed off the ignition switch and you have likely broken a connection or a wire in the process of working in the engine compartment. Does this have a retro fitted Points ignition or still the Big Blue Cap distributor with electronic?

By the spaghetti mess hanging under that dash I would seriously start there.

 

[Ditivec]

Came like that I do need to dedicate a weekend to tracing them out and tidying up though.

I'll check out the vacuum lines as well.

Anybody know where I can find a service manual? Quick google search didn't fish out too many promising leads...

 

[DMiller]

Not many were out there when this was new, mostly limited to Dealer mechanics. Try Fleabay but would be a longshot.

Under a Google Search on IMAGES try entering this:

1979 ford F700 truck basic ignition wiring

I got a number of hits that you could likely use. Also showed a couple other Ford Specific Truck site access points.

 

[funwithfuel]

See if you got an electric choke. Once you've figured out what type of ignition you got. It kinda sounds like a bad ballast resistor. Check hot side of coil with key on, should be like 9 volts or so. When cranking , it should be battery voltage. Hope this helps.

 

[Wes(MI)]

It's a 1979, Ford went to the Dura Spark II that year in medium duty trucks. Should be either a 370 or a 429. He has a manual choke, if no one has swapped the carb. Check all of the pigtail connectors going into the control module on the driver's side inner fender. The Dura Spark II's need an extremely good ground. You may have inadvertently stepped on one of the wiring harnesses. I also agree with funwithfuel about checking your coil power. Also, there's no ballast resistor for the ignition in these trucks. However though, they ran a fuse-able link wire from the ignition switch out to power the (IIRC) Dura Spark II. If you had smoke come out from under the dash, it needs to be replaced. It's rather frangible at 41 years old too.

 

[Ditivec]

The engine is a 429, manual choke.

I was able to find and order and electronic copy of the manual and have been researching the problem. Ignition switch checks out just fine.

I checked the hot side on the coil and am showing 12V. I'm also showing 12V on the tach side in the run position. Didn't check in the start position since I didn't have a second set of hands. Is that to be expected or is there a ground problem?

I dug into the dash and there were certainly problems there. At one point in time in its 41 year lifespan, somebody had a short and a lot of the wires in the bundle going out to the duraspark II module had melted insulation. One wire was an absolute mess, no insulation at all. See picture.



I replaced that wire. It was the 12V line from the run position on the ignition switch going to the 2-connector on the DSII module. Still no change, however. I'm still seeing the same symptoms. She will run for as long as I keep the switch in start position and immediately revs down and dies when I switch to run position.

Also, one wire going to this was broken. Anybody know what that module is? It's directly attached to the brake pedal mount

 

[funwithfuel]

Pics are showing as a red Xs

 

[Ditivec]

Pics are showing as a red Xs

Should be fixed now.

 

[funwithfuel]

The last pic looks like a brake light switch for hydraulic brakes. Maybe a throttle delay valve switch.

 

[Ditivec]

The last pic looks like a brake light switch for hydraulic brakes. Maybe a throttle delay valve switch.

Ok, so not related to my problem here.

 

[DMiller]

It is starting on the CRANK Side of the circuit, that tells me it is in the wiring to the Ign Module, should be able to put a spark plug tester on and start it then release the key, if spark stops the RUN Circuit to the module is bad and needs chased down.

 

[DMiller]

One other point, have you replaced the ignition module yet, they are NOT pricy. BTW Bad grounds and heat were killers of those.

 

[Ditivec]

One other point, have you replaced the ignition module yet, they are NOT pricy. BTW Bad grounds and heat were killers of those.

Just bought an aftermarket one today. I traced the run line from the ICM to the BAT connector on the primary coil and am getting 0.1 ohm, so it seems there is no ballast resistor here? But definitely continuity.



Based on that, and the fact that it will intermittently run, I'm going to try to replace the ICM tonight and see how that goes.

 

[DMiller]

Might surprise
Would still be cleaning up rats nest

 

[Ditivec]

Might surprise
Would still be cleaning up rats nest

I have cleaned it up _significantly_. I'll post pictures when I get the dash put back together.

 

[Ditivec]

It was the Duraspark II module apparently. Replaced it with an aftermarket and she fired right up and stayed running for 5 minutes.

 

[DMiller]

Good, next problem.

 

[Truck Shop]

Duraspark, one of fords better ideas.