1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Cold advance/high idle drop in power when switching to low idle

Discussion in '6.9L IH & 7.3L IDI Diesels' started by thevanbulance, Sep 22, 2019.

  1. thevanbulance

    thevanbulance Registered User

    Posts:
    8
    Likes Received:
    7
    Joined:
    Aug 29, 2019
    Location:
    84098
    Hi guys,

    Lately I've been noticing my 1990 7.3idi is exhibiting a strange behavior when switching over from high to low idle. Here's the proceedure leading up to and including the symptom:

    1.) Cold start the engine and the high idle/cold advance appears to be working normally with my engine idling at a higher rate than when warm. No noticeable stutter or rough sounding idle.
    2.) Drive the van home from work at night with ambient air temps usually around 35-50°F.
    3.) About halfway home (usually 10ish minutes into the drive) the high ideal will abruptly switch off with an audible "thunk" noise coming from under what sounds like the drivers side fuse box. When this happens my headlights will severely dim and power to the engine drops significantly for maybe 1/4 - 1/2 second before recovering to normal operation.
    4.) After the recovery my lights and engine are operating normally and there does not appear to be any additional issues. It only happens when things switch over.

    Thoughts? I'm thinking either the high idle solenoid is going bad/has a bad connection but wondering if anyone else has experienced this.

    Thanks!
     
  2. chillman88

    chillman88 Supporting Member Supporting Member

    Posts:
    2,851
    Likes Received:
    1,799
    Joined:
    Feb 22, 2017
    Location:
    Central NY
    Mine has always done the same except no changes to engine performance other than the slight loss of advance from the cold advance dropping out. I always assumed it was just normal so I'm curious as well.
     
    thevanbulance likes this.
  3. BeastMaster

    BeastMaster Full Access Member

    Posts:
    174
    Likes Received:
    139
    Joined:
    Feb 7, 2017
    Location:
    Orange, California
    I note my engine sounds smoother after cold idle times out. No electrical anomalies noted.

    Is it possible some sort of noise spike ( inductive kickback ) from the cold advance solenoid is retripping a glow plugs cycle?

    But then your air conditioner clutch should be wreaking havoc.

    Just a thought.

    I am interested in what this turns up.
     
  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

    Posts:
    4,024
    Likes Received:
    2,339
    Joined:
    Feb 5, 2010
    Location:
    edmond, ks
    I doubt that it has anything to do with either a bad connection on the solenoid or the solenoid itself going bad. If it did, then it shouldn't do this when the solenoid kicks off. It's no longer getting power at this point. I would think that it has something to do with the pump itself since the timing advance also no longer has power at this point. I have no experience with this and have no idea if my truck does it or not. I try to let the engine run until the high idle kicks off no matter what the temperature.
     
  5. BeastMaster

    BeastMaster Full Access Member

    Posts:
    174
    Likes Received:
    139
    Joined:
    Feb 7, 2017
    Location:
    Orange, California
    Whatever is jumping on his electrical system is huge, judging by his description. Does the volt meter confirm this? Does this drag the battery buss down like glow plugs and starter motor?

    Sounds like 1000A or so for half a second? There's enough there to flat blow open most shorts. With smoke and light show. And ample evidence of the event left behind.

    Or is something stumbling the engine, and we are seeing the loss of alternator output?
     
    Selahdoor and thevanbulance like this.
  6. IDIBRONCO

    IDIBRONCO IDIBRONCO

    Posts:
    4,024
    Likes Received:
    2,339
    Joined:
    Feb 5, 2010
    Location:
    edmond, ks
    That's what I'm thinking. Timing maybe?
     
    Selahdoor likes this.
  7. thevanbulance

    thevanbulance Registered User

    Posts:
    8
    Likes Received:
    7
    Joined:
    Aug 29, 2019
    Location:
    84098
    Haven't caught the volt meter when this happens cause it's above the driver's side visor and it's not in my line of sight. This is an ambulance so I've got more electronics involved than most and most likely a higher power/output alternator.

    Last night I drove a different route that was mostly highway and it didn't happen to me. Most nights it's happened I've been taking back roads with low speeds where I'm almost at an idle RPM while driving. Wondering if that comes into play here too.
     
  8. Selahdoor

    Selahdoor How can I help you, or make you laugh, today? Supporting Member

    Posts:
    608
    Likes Received:
    311
    Joined:
    Oct 26, 2015
    Location:
    Index Wa
    I've kept out of this one because after it was postulated that some kind of heavy load kicked in, well I wasn't sure what that heavy load could be, or how it was being kicked in.

    But I wanted to ask from the beginning, what the idle was, once the high idle kicked off.

    Yes, too low an idle will mean less amps from the alt.

    Also could just be the alt going bad, and not even producing the normal amperage at the regular idle. Needs the high idle to keep up...
     
    IDIBRONCO likes this.
  9. chillman88

    chillman88 Supporting Member Supporting Member

    Posts:
    2,851
    Likes Received:
    1,799
    Joined:
    Feb 22, 2017
    Location:
    Central NY
    Almost "sounds" like there's a voltage drop, headlights dim, then the alternator picks up because of the voltage drop, then everything evens out?

    We both have a similar problem and nobody knows the answer haha.

    I recently swapped out my IP. Maybe I'll have to pay attention and see if mine still does it.
     
    thevanbulance likes this.
  10. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

    Posts:
    7,752
    Likes Received:
    5,940
    Joined:
    Jul 27, 2015
    Location:
    Bulverde, Texas
    Thats normal function with the 1G alternators. The solenoid pulls quite a bit of inrush amperage, less noticable with the better alternators. Its no 1000 amps, but with the 1G alt a sudden 20 amp draw will make a noticeable voltage drop, you can hook up the solenoid to a manual switch and manually trigger it each time and see the same result.
     
  11. IDIBRONCO

    IDIBRONCO IDIBRONCO

    Posts:
    4,024
    Likes Received:
    2,339
    Joined:
    Feb 5, 2010
    Location:
    edmond, ks
    I'm betting that you're on to something here.
     
  12. thevanbulance

    thevanbulance Registered User

    Posts:
    8
    Likes Received:
    7
    Joined:
    Aug 29, 2019
    Location:
    84098
    So this might be a stupid question but how do I tell if that's the type of alternator I have? Been under the impression since I'm rocking an ambulance that I've got some kind of upgraded/higher output alternator to help manage the increased electrical load from running lights and all the equipment in the back.
     
  13. Selahdoor

    Selahdoor How can I help you, or make you laugh, today? Supporting Member

    Posts:
    608
    Likes Received:
    311
    Joined:
    Oct 26, 2015
    Location:
    Index Wa
    Pictures would help. :D
     
  14. IDIBRONCO

    IDIBRONCO IDIBRONCO

    Posts:
    4,024
    Likes Received:
    2,339
    Joined:
    Feb 5, 2010
    Location:
    edmond, ks
    You're probably right on that one.
     
  15. BeastMaster

    BeastMaster Full Access Member

    Posts:
    174
    Likes Received:
    139
    Joined:
    Feb 7, 2017
    Location:
    Orange, California
    Does the glow plugs cycling cause the same kind of upset?

    On my E350, the glow plug draw is noticeable on voltmeter, but does not affect engine RPM.

    The cold advance seems to have no effect on voltage, but the engine changes it's sound a bit. Usually about two or three minutes after start
     

Share This Page