Rick 12v CTD

so today I hauled my parts truck (92 d250 gas job) to the scrap yard to get it out of the yard and I pulled up to a light and my idle went to down to about 1000, then bumped up to 1200-1300 and hung for a sec, then settled at 900 like it's supposed to. idle has been set at about 900 for a few weeks now

15 minutes later at another stop light the idle does the same thing, but instead of it settling, it takes off and I yank my manual shutoff cable at like 1700-1800 rpm and it shuts down. I throw it in park, fire it up and drive home without issue.

What's the deal here? I've put about 800 miles on the new motor and IP without issue, then all of a sudden it does this? and does it randomly to boot. It certainly doesn't do it every time I stop at a stop light, and it doesn't hang if I free rev it while in neutral or park. Could it just be the new IP breaking in or what? seems odd to me, I didn't even know I was that close to runaway to begin with. like I said, it's been set this way for 800ish miles, and has never missed a step or hung AT ALL until now. The lock nut on the fuel screw was good and tight too, the screw hasn't budged.

I reset my idle to 750 and backed out the fuel screw 1/5th a turn when I got home. seems fine.


Thoughts?

As an aside, I'm glad my manual shutoff seems to stop runaway. When I broke the motor in after putting it in the truck and rebuilding it I had the fuel screw in too far initially so it ran away and the manual shutoff stopped it then too. Several times infact. Not the most ideal way to break in a freshly rebuilt motor, but it happened.

schamran

If it's actually "running away" you won't be able to shut it off by stopping fuel flow. This is why pulling trucks have intake shutoffs.

fatt

That would depend whether it is an oil runaway or something related to the injection pump.

mknittle

crap i got sucked in to responding to an old thread

patdaly

Eh, it's what us old men do........ You know, one step away from Dementia.

Lary Ellis (Top)

Glad that never happens to me....oh wait what were we talking about?

Rick 12v CTD

funny this thread got bumped. Back in May I had another interesting runaway experience.

The fuel screw was so far out that the motor wouldn't run, but it randomly fired and ran away on me. after shutting it down it wouldn't run again. It was very confusing. I ended up having to turn the fuel screw in 3 or 4 turns before it would run normally

1320Fastback

Might be a old thread but is still a relivent issue for some.

When I had my old C30 with a 4-53 Detroit, run aways were always a threat.
For conversions one would always put a knife blade air door to shut the oxygen off to the motor and usually this is how you would shut the engine down just to make sure it still worked properly. I took it one step further and plumbed a Co2 bottle into the intake just incase the air door wasn't sealing properly but never had to use it.

I have not experienced a run away with a cummins yet but the way our trucks are set up we could only shut down the fuel.

Jim Lane

Ocasionally my mind will also runaway, hate when that happens.

Detroits and runaways are synanmous.

I have probably had 4-5 6V-71 & 8V-71's runaway on me or be in the pit below one when it happened in my lifetime as a mechanic.

They will scream insanely before they explode,

I had a 6V-71 in a GMC transit coach had the crankshaft broken in 3 pieces and it was still running before it ventelated the block only seconds later.

searcher

I never even thought about a possible runaway with my Cummins, but it is always on my mind when driving my TDI.

Rick 12v CTD

the runaway us first gen guys are confronted with is fuel related. When you turn the fuel screw too far in it covers the spill port and causes the injection pump to do it's thing and runaway. In my experiences thus far, when that happens the FSS and/or the manual shutoff on the side of the IP has stopped it. I wouldn't want to rely on that alone though, just in case.

And obviously if it runs away by another means you're up poopoo creek

1320Fastback

My fuel screw is screwed in as far as it can go and then some. When I rebuilt the pump I couldn't for the life of me get it removed. I tried everything short of shearing it off or stripping out the threads of the pump.

Not sure why mine hasn't run away becuase of that but it had a cable to the manual lever under the dash and being a manual I could put it in gear and stand on the brakes to kill it.


From my Detroit days if you do have a run away for God's sake don't put your hand over the turbo. We had a 3' piece of 2x8 hanging on the wall but never had to use it, others suggested phone books and rags but I think a rag might cause damage to the turbo and the phone book would be a little hard to find now days!

Rick 12v CTD

not all pumps have a fuel screw long enough to cause a runaway situation.

My pump being one of them. I have removed the fuel screw and chased the threads with a die and it still bottomed out and hasn't caused a runaway. In fact, I don't even think it's close to runaway. I can only make 42 or 43psi and she burns clean as a whistle at WOT. I should be able to make a fair bit more boost at WOT but it runs really good like this so I haven't bothered

80lpm injectors, fuel screw turned, stock pin ground for full travel, 362/68/.7sxe etc (it's not the motor in my sig). No cam, no ctech head or hamilton springs. Old pump with 300k miles on it. block is out of a 95 and the head is off my old 91.5, same with the IP

E: actually I'm going to change my sig