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Dieseling causes

dremu

dremu

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My K5 is starting to diesel again when I shut it off, and I'm tired of killing it in gear ... time to fix it.

Here's a list of stuff I know can cause dieseling and what to do about it; chime in with any others you know?


  • Timing (check, reset.)
  • Extended idling (goose the gas for a bit 'fore shutting it off.)
  • Idle speed too high (set properly)
  • Running too hot (fix cooling system)
  • Crappy/old gas (fresh gas, treatment for what's in the tank)
  • Carbon in the heads? (caused by heat, maybe, but how to check and what to do about it?)

In this instance, timing should be dead on, and she diesels even after actual driving (as opposed to idling in my driveway.) There may be a heat issue, as I had to trim the fan shroud when I did the Doubler and I think the cooling has suffered since. I'll break out the infrared thermometer and double-check, as the factory gauge may be off. The gas is suspect, as it's oooold, so I'll get some fresh gas and/or dump some treatment goo into the tank.

Other than that, what else should I be looking at?

-- A
 
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Do you have any "idle kicking" devices on the engine?

My '83 had some sort of issue with a throttle kicker (AC maybe?), dieseled like crazy once that started acting up.
 
Idle set too high. Believe it or not, it doesnt take super high RPMs to cause dieseling. Just 900rpms can do it. Ive got my RPMs at around 600now.
 
dyeager535 said:
Do you have any "idle kicking" devices on the engine?

My '83 had some sort of issue with a throttle kicker (AC maybe?), dieseled like crazy once that started acting up.
Click to expand...

There is a fast idle, originally for the AC, which is now wired to a switch on the dash to bump the idle up for the OBA or for winching. At least by the sound, though, she's idling nice and low, and I don't *think* the solenoid is doing anything. At the very least it only engages (plunger out, to stop the idle at a higher RPM) when it's powered, i.e. when it's unpowered it springs back out of the way. (In fact, I have to engage the solenoid and then manually goose the throttle in order for it to engage, as the solenoid doesn't have enough push power to move the throttle on its own ... just enough to hold the throttle linkage from going any further down.

ANYWAY ... it's something to look at, thanks.

-- A
 
Atleast with my old boat during the summer, the engine would diesel for a long time but during the winter it wouldnt do it at all. Not sure why outside temp would affect this but it did, granted the boat was kinda quirky
 
Aaron, chevy vehicles of your vintage had an anti dieseling solenoid on them. Basically it is a solenoid that when not activated allows the throttle blades to close further than when the engine is running. Basically once you start the engine the solenoid is activated and this is when you set base idle RPM's, when you shut the ignition off the solenoid deactivates and the throttle closes further shutting off all air to the engine and prevents the engine from dieseling.
 
4X4HIGH said:
Aaron, chevy vehicles of your vintage had an anti dieseling solenoid on them. Basically it is a solenoid that when not activated allows the throttle blades to close further than when the engine is running. Basically once you start the engine the solenoid is activated and this is when you set base idle RPM's, when you shut the ignition off the solenoid deactivates and the throttle closes further shutting off all air to the engine and prevents the engine from dieseling.
Click to expand...

Duh ... I'll double-check the action on mine, but unless it's the fast idle solenoid, I don't know about it and I would *swear* I don't have one. This would go on the carb, right, and act on the throttle linkage?

-- A
 
dremu said:
Duh ... I'll double-check the action on mine, but unless it's the fast idle solenoid, I don't know about it and I would *swear* I don't have one. This would go on the carb, right, and act on the throttle linkage?

-- A
Click to expand...

That is correct. Some people have called them a fast idle solenoid but that's not what they are really.
 
I'm not sure where the wire originally went but yes, keyed out to activate the solenoid. When you turn the key off the solenoid will deactivate and close the throttle plates completely.
 
We're assuming that this is stock for the K5 and not the solenoids installed on some one tons (unsure of years, early 80's I know) that OPENED the throttle at certain times.
 
So the solenoid I'd put on there had maybe 3/16" gap at idle, i.e. between it and the eccentric on the throttle.

However, my ears have been telling me for a while that the tach on this truck is off, and a quick check with an external tach verified that. I gotta remember to use The Force, Luke. Anyway, the idle was too high, and yep, at a lower idle it's better behaved. (I think the gas is still crappy and the timing may have slipped, but I have enough projects for today =))

The tach in the dash is a factory tach, and it's worn out -- in fact, a quick run through my spares says they're all mildly inaccurate. Time for me to go read up on replacing the capacitors and such on a 30-year old circuit board =))

-- A
 
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