Click Here -> Please Consider Making a PayPal Contribution to the FordSix Forum!
2019 Contributors:
NJwpod, 1strodeo, mightynorseman, maxtrux, 6d7coupe, broncr, Phase3, 68Flareside240, bmbm40,
mustang6, WorldChampGramp, justintendo, BigBlue94, ags290, motorsickle1130, Rooster, ousooner919, ethanperry
rzcrisis, DoctorC, jamyers, Motorboy, fastpat, Silverback280, chad


<<< New Site Update >>>

Little bit of Dieseling at shut down. Hurting anything?

Moderator: Mod Squad

motzingg
Registered User
Posts: 815
Joined: Tue Apr 30, 2013 8:16 am

Little bit of Dieseling at shut down. Hurting anything?

Post #1 by motzingg » Fri Mar 13, 2015 5:19 pm

So I've seen this in a couple vehicles i've owned but inconsistent. Not super sure what causes it aside from the fact that something in the engine is hot enough to ignite fuel after spark has been shut off.

anyhow, my truck has done it a couple times now. Its not running hot and it doesn't have anything else wrong with it, that i can tell. It doesn't diesel on, it just kinda does a little after-cough thing as its turning off. Maybe fires once or twice and does a little rev up thing as its winding down.

Just wondering if this is a sign of a problem and what i should look at. Thanks in advance.

newly rebuilt 4.9L 1991 lower/ 85 head/ carb'd 2100 motorcraft/ duraspark

(if any of that is pertinent...)

User avatar
bubba22349
Global Moderator
Posts: 9131
Joined: Sun Jan 03, 2010 4:46 pm
Location: Flagstaff, Az. 86005 near the old Route 66

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #2 by bubba22349 » Fri Mar 13, 2015 7:19 pm

:hmmm: There are a few ways to fix that, one is to install a electric solenoid (like was used on lots of 1970's Fords with AC etc.) when it's on it holds throttle at idle RPM. Then when you shut it off the throttle blades are shut down tighter. Good luck :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

arse_sidewards
Registered User
Posts: 849
Joined: Mon Jan 21, 2013 7:18 am

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #3 by arse_sidewards » Fri Mar 13, 2015 9:40 pm

Try using hotter spark plugs.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

User avatar
mwilliamshs
Registered User
Posts: 215
Joined: Thu Apr 24, 2014 6:25 pm

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #4 by mwilliamshs » Sat Mar 14, 2015 1:11 am

Check the timing. Seen a loose distributor and retarded timing both cause that.

EFI don't do that stuff. Kinda nice that way. (joking)
1989 E-150 Extended Body SuperVan Sportsmobile Camper Conversion 4.9L, C6, 3.08 R&P

User avatar
THE FRENCHTOWN FLYER
VIP Member
Posts: 6093
Joined: Sat Nov 09, 2002 9:25 pm
Location: FRENCHTOWN

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #5 by THE FRENCHTOWN FLYER » Sat Mar 14, 2015 8:53 am

My '46 pickup w/ a 460 does that when it is hot - which is always. I just shut it off in gear and then move the shifter to PARK.

I never heard of an engine being damaged by it. If I had one of those solenoid gizmos when I built it I would have used it.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

1986F150six
Registered User
Posts: 315
Joined: Wed Oct 24, 2012 3:11 pm
Location: Northwest Alabama

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #6 by 1986F150six » Mon Mar 16, 2015 4:11 pm

Make certain the idle speed is not too high. Sometimes, it is amazing what difference ~100 RPMs will make.

motzingg
Registered User
Posts: 815
Joined: Tue Apr 30, 2013 8:16 am

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #7 by motzingg » Mon Mar 16, 2015 4:33 pm

interesting about the idle speed comments, yeah something hangs up in the throttle linkage and kicks the idle from 400-500 up to about 800 rpm's depending on how i let off the throttle. I could put in a stiffer spring and fix it, but i like having the throttle easy to push. Doesn't bother me except at really long stop lights i'll usually just give it a little stab and it drops right down.

well that is about what i figured. I'm due to change the break-in oil out any day now, and probably put in 6 new plugs while i'm at it.

I don't actually know the exact timing number, I set it by ear and vac gauge and it just barely knocks when i'm really into it. Probably could go retarded a scosh, which i'll do when i swap out the plugs.

Could the fact that it is pig rich have anything to do with it? Fuel combusts more readily just on the rich side of things, maybe hot plugs + a little rich mix is doing it.

User avatar
MechRick
Registered User
Posts: 877
Joined: Wed Jan 04, 2012 7:43 pm
Location: Las Vegas, NV

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #8 by MechRick » Mon Mar 16, 2015 10:20 pm

motzingg wrote:Maybe fires once or twice and does a little rev up thing as its winding down


When it does that, it's spinning *backwards*...

Engines that had worn timing chains or belts would often jump time while dieseling, creating a puzzling crank/no start. Thankfully the gear drive of the big six doesn't have this issue...

motzingg wrote:yeah something hangs up in the throttle linkage and kicks the idle from 400-500 up to about 800 rpm's depending on how i let off the throttle


Are you carbed? You should be able to rework the linkage to operate more smoothly. I've had to do it to brand new Holleys and Carters...I hate overly stiff return springs also...
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

motzingg
Registered User
Posts: 815
Joined: Tue Apr 30, 2013 8:16 am

Re: Little bit of Dieseling at shut down. Hurting anything?

Post #9 by motzingg » Fri Mar 27, 2015 5:47 pm

You know that is an interesting comment, because i thought the same thing at first (it actually sounds like the engine spins backwards... no idea how i would know what it sounds like?!), but once i let the clutch out too soon and the truck bucked forward as it did its little 'rev up'

Its only happened 10 times at most, and i've probably gone through at least 10 tanks of gas by now (fill ups, half tanks) haven't been counting mileage, so it is not often enough to get a good data sample.


I am going to get a new Duraspark box, as it is doing a bizarre cutting out almost every morning shortly after i start it. Not in the afternoon hardly ever and seems to be worse when it is humid.


Also working on redoing the entire electrical system, so hopefully that will purge some demons.

Who is online

Users browsing this forum: chad and 17 guests