200 ci dieseling?

Discussion in 'Ranchero Tech Help' started by 66Ranchero, Jul 16, 2017.

  1. 66Ranchero

    66Ranchero In First Gear

    Messages:
    11
    Hey guys!
    I'm loving my Ranchero but I've noticed that it diesels pretty bad after turning the key off. The whole truck rattles and then engine sounds like it's winding down. I'm running 91 octane in it and it always starts up instantly no matter it's temp and it runs like a sewing machine! Where should I start? I'm new to owning a classic car so I apologize if this has been posted before.
    Thanks!
    -Hayden
     
  2. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    5,131
    Location:
    Everett, WA
    Usually, 'dieseling' can be caused by either having the throttle stop screw turned in too much (sometimes to mask other problems in an attempt to get an engine to start or run better), or the engine has run rich for a long time, and carbon buildup becomes so hot, that as the turning engine will still pull fuel and air into the cylinders, that heated carbon 'flashes' it, which causes the engine to continue turning after the ignition is turned off.
     
  3. pmrphil

    pmrphil In Fourth Gear GOLD MEMBER

    Messages:
    459
    Also check the ignition timing, if it's too far advanced that can cause it to "run on", as can too high of an idle.
     
  4. ribald1

    ribald1 In Maximum Overdrive PLATINUM MEMBER

    Messages:
    16,577
    Location:
    California
    How can advanced timing play a role? The spark circuit is off.
     
  5. tony o

    tony o In Third Gear

    Messages:
    168
    Location:
    orange, ca. usa
    I'm with Handy Andy. The first thing that I would check is to verify thr vacuum advance is connected and working. If it's not, fix it. When I worked for Ford as a mechanic back in 70-73, the great state of California, in it's ultimate wisdom, decreed that a NOX reduction kit had to be installed on 1966 and earlier vehicles on change of ownership. The major constituent of this was to disconnect the vacuum advance. The theory behind this is that it would reduce combustion temperature and thereby reduce the formation of NOX. Later vehicles were equipped with EGR to do the same. When you disconnected the vacuum advance you had to crank the throttle plates open more at an idle to compensate for the loss of advance. This created all kinds of dieseling complaints.
    If all is well with the vacuum advance I would try one of the decarboning chemicals.
    If that doesn't help. I would connect the vacuum advance to manifold vacuum. This will give you full vacuum advance at an idle and allow you re adjust the throttle plates more closed to to get the idle speed back down. This will reduce the tendency to diesel. Ported vacuum from the carb only lets the vacuum advance to see full manifold vacuum once the throttle plates start to open. By connecting to manifold you get full vacuum advance at idle, off idle the vacuum advance functions the same as it did when connected to ported vacuum.
    If this is a modified engine running centrifical advance only. As a base line I would get the initial timing up to the 12 to 14 degree range and curve the distributor to 34-36 degrees total, all in by 2800-3000 rpm.
    I have had zero success reducing the tendency to diesel by retarding the timing as this forces you to open the throttle plates more and increases the tendency to diesel.
     
  6. ribald1

    ribald1 In Maximum Overdrive PLATINUM MEMBER

    Messages:
    16,577
    Location:
    California
    Ah, the ported vs manifold discussion.
    Tony, I think your memory is a bit off. What CA required was a temperature controlled vacuum shutoff. (I also was there at the time) The retrofits were installed on the upper radiator hose. Ported advance was put into the carbs around the same time to resolve drivability (poor throttle response off idle) in the newly required low compression engines.
    Almost every engine will perform better off idle with ported rather than manifold vacuum. That is because when the carb is tuned for the extra timing it becomes too lean the moment you crack the throttle and the timing retards. High compression engines don't crater the vacuum when the throttle is opened, so they are more tolerant of manifold vacuum. On the other hand, with a serious build the base timing is going to be 18 degrees or more and idle timing of 28+ degrees brings its own set of challenges to tuning.
    That said, there are valid reasons for using manifold vacuum. If your engine heats up while waiting on the tree, manifold vacuum will make it idle cooler and you really don't care about part throttle operation anyway.
     
  7. Sophie948

    Sophie948 In Overdrive

    Messages:
    569
    I've heard that using the wrong spark plugs can also cause dieseling.
     
  8. tony o

    tony o In Third Gear

    Messages:
    168
    Location:
    orange, ca. usa
    Well Ribald, I do remember installing systems like you describe. Ford had a factory system like that, but it was $$$. We only inststalled that on cars with a 4bbl or multiple carburation the Lincoln- Mercury dealer that I was working for. Everything else got a Kar-Kit NOX reduction system. Cheep as you could get that was approved by CARB. It consisted of 2 vacuum caps and 3 stickers. To install you disconnected the vacuum advance and capped the carb and the advance canister on the distributer. You the installed 1 sticker that said Kar-Kit NOX reduction system was installed on the air cleaner. Sticker #2 went on the fender next to the factory Idle speed and timing sticker and said to reduce base timing to 1/2 the recommended by the factory. Sticker #3 was supposed to go on the speedometer inside the vehicle (which we were told to never install) that said not to drive the vehicle over 60mph for extended periods. There was another kit we used sometimes that had you completely remove the vacuum advance canister and install a plastic piece tha locked the breaker plate and cap the carb. There were variety of NOX kits at the time. They all basically worked the same in that they removed the functionality of the vacuum advance. The high end one added the temperature related defeat if the car overheated.
    The first thing I told him to do was check and make sure the the factory vacuum advance was connected and functional. Even with ported vacuum you will have some vacuum on the canister at idle, just not full manifold vacuum. As I am sure you know that is why you have to remove and plug the vacuum line to the vacuum advance when checking the base timing. The only reason I mentioned the retrofit NOX systems was if he had one installed he should consider removing it and restoring the vacuum advance to it's original factory configuration. If the vacuum advance was non functional then repairing it and resetting the carb may completely cure the problem.
    Connecting to manifold vacuum was a last resort to try and solve the problem. In the description of your expierience with using manifold causing an off idle stumble. Would I be correct in assuming that it was a performance application with a large carb? If so, could you been forced to close the butterflies so much to get the idle down that you where on base circle of the accelerator pump cam and not the ramp? That may be the source of the tip I stumble.
     
  9. 66Ranchero

    66Ranchero In First Gear

    Messages:
    11
    Thanks for all the great replies guys! I'm gonna start with the vacuum advance and work my way up from there. I'll update you on the progress!
     
  10. pmrphil

    pmrphil In Fourth Gear GOLD MEMBER

    Messages:
    459
    With all the high performance stuff you do, you've never had an engine that would run on from either lack of octane or too much timing? Get one that rattles and back off the timing and now it shuts off too. I can show you with the Ranchero in the pic, it does it.
     
  11. ribald1

    ribald1 In Maximum Overdrive PLATINUM MEMBER

    Messages:
    16,577
    Location:
    California
    Actually no, I haven't. Considering that the cylinder fouling caused by too much timing at idle is wet fouling due to the flame being put out at near TDC running on in that condition would indicate to me a separate underlying issue, especially as you describe it as "rattling". Possibly an overheating exhaust valve rocker (or rockers) denying oil to the valve or chain firing through the intake due to improper configuration.
    The method I use for setting timing involves retarding the timing about 10 degrees, removing the springs from the mech advance, setting the timing (36-42 BTDC depending on the engine), locking down the dizzy, shutting it off, then reinstalling the springs. At that point I restart and note base timing.
    Never had one diesel doing that.
     
  12. ribald1

    ribald1 In Maximum Overdrive PLATINUM MEMBER

    Messages:
    16,577
    Location:
    California
    There must have been different rules in different areas. In San Diego what was done was to install a temp controlled vacuum switch so that the advance didn't work until the car was up to operating temp.
    The stumble can be tuned out easily by adjusting the secondary butterfly. The issue is going lean during the transition when not depressing the pedal fast enough to actuate the accelerator pump, a situation that usually only occurs during stop and go driving that can cause a pause or even dying. It is true that it can be tuned out by altering the air bleeds, but no car manufacturer was going to do air bleed tuning on every car.
    What happens is that when the carb goes into transition the vacuum falls, leading to retarded timing further lowering vacuum, thus denying the signal to the main jets. Pressing the throttle a bit quicker solves the problem as the accelerator pump kicks in, but when the car in front of you is only 10ft away, not a good option.
    Personally, I find tuning for crisp throttle response to be far easier with ported vacuum as the signal is more predictable and plots with load and RPM the same way regardless of driving conditions.
     
  13. ribald1

    ribald1 In Maximum Overdrive PLATINUM MEMBER

    Messages:
    16,577
    Location:
    California
    Yes, running too hot a plug is a common cause.
     
  14. pmrphil

    pmrphil In Fourth Gear GOLD MEMBER

    Messages:
    459
    Maybe you misunderstood - rattling, pinging, detonation, different words for the same issue.
    I wonder how you set timing before MSD distibutors - did you remove the breaker plate to remove the springs? Seems like a lot of work.
     
  15. ribald1

    ribald1 In Maximum Overdrive PLATINUM MEMBER

    Messages:
    16,577
    Location:
    California
    I understand that all those words mean the same thing, but none of them mean dieseling. Dieseling is the engine running on after the ignition is turned off.
    Yes, working with older dizzys is more work, but it is especially important with them as tolerances were larger and it is the only way to find out exactly what the total timing will be. You only have to do it once, from then on you know what your base timing needs to be with that particular dizzy, and can curve it properly.
     
  16. pmrphil

    pmrphil In Fourth Gear GOLD MEMBER

    Messages:
    459
    Of course none of them mean dieseling.
    I owned a 67 XKE that would run on (dieseling) if you didn't run a high enough octane fuel in it. This was back in 1978, when Sunoco had good fuel at the pump still. If I stopped and fueled with Gulf, you could shut off the key, get out, and walk away, it wouldn't stop dieseling. Turned off perfectly when using higher octane Sunoco. I drove that car for a bit over a year and it repeated both symptoms, both ways, every time. When I couldn't find a Sunoco, I was screwed.
     
    Last edited: Jul 17, 2017
  17. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    5,131
    Location:
    Everett, WA
    BTW, 66 Ranchero, is yours equipped with power steering? A quick trick on dieseling is to turn the wheel all the way to the lock, one side or the other, doesn't matter, but just turn the key to 'OFF-UNLOCK' then turn and hold the wheel against the stop. The drag of the P/S pump can help to stall the engine.
     

Share This Page