Hesitation just off idle (and only in gear)

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Hesitation just off idle (and only in gear)

ckuske
Administrator
Hi Everyone,

I know this horse is pretty black and blue via other posts, but your advice always points me in the right direction, and my symptoms are a little different (I think) Let me break down the symptoms, and what is done and what I maybe think is the next thing to look into.

Then, you can let me know if it makes sense or if I should go do something else with my spare time.

My recurring symptom is as follows:

My truck starts easily, and drives well for the most part. But, it has one symptom that is gnawing at me. And, my son wants to start driving it (3rd generation in the same truck!) but I'm hesitant for this one issue.

When the truck is at a stop (and in drive), if you give it let's say 1/4" to 1/2" of pedal travel (to slowly pull away), there is a dead spot adding a little more travel doesn't translate to more power or RPMs. And, if you leave the gas pedal at that area, the engine will stall about half the time. My son is nervous (he JUST got his permit) about this happening, although I showed him how to shift into neutral and restart as you're rolling down the road...

If you are a little more generous with the gas pedal (let's say 3/4" to 1" of travel), you basically skip the symptoms and pull away nicely. But, you definitely have to have a feel for the right amount to give it. My kid definitely doesn't have that feel yet. If you try to glide away or pull up with a small amount of gas, you run the risk of stalling the truck.

Once you're going down the road, there is no hesitation or delay. If you're idling in park, you can't make it do the same thing even with the same amount of pedal travel.

This problem has existed since I bought the truck back. The carb has been rebuilt twice by the local expert. He seems knowledgeable, but I have mentioned this issue to him twice and it is still lingering. He says that the mixture is lean on these trucks anyway (especially CA trucks) and when the EGR opens, it makes it worse. Basically, he is saying there is nothing to be done.

I know this truck didn't always have this issue - it certainly didn't when it was new, or even 20 years ago.

So, now to what I've done so far:
  • Gotten the carb rebuilt (twice)
  • Adjusted accelerator pump throw from Hole 2 to Hole 3 (no Hole 4 present)


  • Other theories on the list of things to try include:
  • Check for vacuum leaks via smoke test
  • Idle is a little low after warmed up - ~500 RPM. Curb idle is supposed to be 575. Would that difference in vacuum cause something to not actuate somewhere?
  • ???
  • Just to lay all the cards on the table, there is another issue I feel is unrelated, but... When you first start the truck, for the first 30/45 seconds, it seems to miss while in high idle (~1800 RPM). It will be idling, you'll hear a pause in the exhaust and the tach will dip. It will then recover. If you kick the idle down, it goes away. If you let it warm up and then try to go at the same RPM, it's fine. I figured I would confess all my sins in one shot... This one is hard to describe. Maybe I'll do a video and post it.

    If you're still reading this, thanks for reading this novella. I've wanted to write about it for awhile, but was hoping it would go away... it hasn't.
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    Gary Lewis
    Administrator
    I agree that the mixture is lean, but I don't believe it is supposed to be nor that there's nothing that can be done.

    And I also agree that the smoke test is a good idea as a vacuum leak could cause the problem.  If that doesn't turn up something I'd plug the vacuum line to the EGR valve for a test.  If that doesn't make a difference I'd pull the EGR valve to see if it might be leaking.  Or I'd block the EGR valve off with a plate to see if that makes a difference.

    Basically you are looking for anything that can allow air or exhaust gas into the system when it shouldn't be there.
    Gary, AKA "Gary fellow": Profile

    Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
    Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
    Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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    Re: Hesitation just off idle (and only in gear)

    grumpin
    In reply to this post by ckuske
    Have you checked the adjustment of the TV cable?

    I’ve never dealt with one, but heard and read they can give you trouble.
    Dane
    1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
    1992 Bronco XLT 4x4 351W E4OD
    1998 GMC Sierra SLE K1500 350 4L60E
    Arizona
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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    Thanks Gary for confirming vacuum as one path.

    Dane, in my limited knowledge, I thought the TV rod only affected the shift points. How would it cause this issue? (I am not arguing, I’m asking because I’m curious!)

    I did happen to buy a pressure gauge, because if I bumped the idle up more than 50 RPM, you have to check the trans pressure. So, add that to the list!

    Also I forgot to note, no codes in the ECU. Codes are clean in KOEO and Continuous. I haven’t done the KOER test yet.
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    grumpin
    ckuske wrote
    Thanks Gary for confirming vacuum as one path.

    Dane, in my limited knowledge, I thought the TV rod only affected the shift points. How would it cause this issue? (I am not arguing, I’m asking because I’m curious!)

    I did happen to buy a pressure gauge, because if I bumped the idle up more than 50 RPM, you have to check the trans pressure. So, add that to the list!

    Also I forgot to note, no codes in the ECU. Codes are clean in KOEO and Continuous. I haven’t done the KOER test yet.
    I don’t know, I’m under the impression it does strange stuff. And it sounds like you’re on top of things, so I was trying to think of something that wasn’t checked.

    First thing I do on this era of vehicles is check for vacuum leaks. And with what it’s doing, the accelerator pump.

    Bill was mentioning a hairline crack in a carb he had in another thread.
    Dane
    1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
    1992 Bronco XLT 4x4 351W E4OD
    1998 GMC Sierra SLE K1500 350 4L60E
    Arizona
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    Re: Hesitation just off idle (and only in gear)

    mat in tn
    one of the odd means of a vacuum leak is the chassis vacuum circuit. the brake booster if leaking will be a vacuum leak. any part of the hvac or defrost control circuit also. are there any quirks in how either of these systems are working?
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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    In reply to this post by grumpin
    Thanks Dane, I appreciate the ideas!  Keep ‘em coming!

    You never know what could be related to changing one thing. A truck is a system of systems with dependencies, knock on effects etc. like all “good” or “fun” problems, it’s typically not one thing that goes wrong. (Like in aviation)

    I’ll add these to the list, and just go by process of elimination. Thanks again!
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    This post was updated on .
    In reply to this post by mat in tn
    Brakes were just worked on and checked out, and they are working well.

    I think I really need to have a full vacuum check done.

    Now that you mention it, I’ve been hearing some noise coming from the HVAC system. When I turned the fan off, the noise went away. I assumed it was wind noise in the ducts. But maybe not? Maybe I can plus the hose under the hood to try and isolate it?
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    mat in tn
    divide and conquer! cap the port feeding the hvac and test. and then reconnect and move on to the next circuit
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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    I've been running more tests before blocking vacuum things off.

    KOEO is still clean, but have Continuous code of 22 (can't seem to get rid of this one, replaced MAP sensor, line, and redid wiring)?

    Just ran the KOER.  Got one code (35).  Looks like I'm back to looking at the EGR...

    I replaced the EGR and its position sensor already a few years back.  (But very little usage)

    I will start with backprobing the EGR sensor voltage I think.  I need to run out for a bit, but any other insight?

    If the EGR is acting wonky, I *think* it could explain my symptoms
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    Gary Lewis
    Administrator
    Yes, if the EGR is coming in while you accelerate gently the AFR will be very lean.  And a stuck EGR valve would do that.
    Gary, AKA "Gary fellow": Profile

    Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
    Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
    Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    This post was updated on .
    Thanks, I'll dive into that this weekend.  I guess I should just pull the EGR off in general and see if it moves freely etc.  Or should I leave it in place, ensure it is closed, and plug its vacuum line first to see if things improve?

    I also disconnected the HVAC vacuum line that comes off the tree on the firewall.  At fast idle, the vacuum is at around 22".  At normal idle, about 20".  The missing at fast idle causes the vacuum to dip to 20" when you hear a "blip" in the exhaust.

    Hopefully this is all related!
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    Gary Lewis
    Administrator
    I hadn't thought of the vacuum test, but that is telling.  As the idle RPM goes up so should the vacuum.  But yours goes down which says that something is killing the vacuum.  EGR would certainly do that.

    But the fact that you don't have a problem at normal idle suggests that the EGR valve isn't leaking or it would do it at normal idle also.  So that implies that the valve is being told to open.

    Pull the vacuum line off the EGR and see what happens?  That's how it is controlled, so...
    Gary, AKA "Gary fellow": Profile

    Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
    Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
    Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    I just realized that I got it backwards!  I just edited the text above.  Vacuum dips on the miss, it doesn't increase.

    I have never seen a gauge where 0 is on the right hand side of the dial!  But, now I have. (That's how I got confused, just looked at the big number and counted the small hash marks from there, in the wrong direction!)
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    Here is my vacuum diagram.  It's always a joy to read, but looks like the only vacuum is to one of the solenoids mounted on the driver's side valve cover?

    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    Gary Lewis
    Administrator
    I see EGR?

    Gary, AKA "Gary fellow": Profile

    Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
    Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
    Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    Yep, sorry I didn’t phrase my question well. At all.

    It looks like the only vacuum going into the EGR is from the solenoid on the valve cover. The line is smaller that I thought it would be, but I’m no expert. I just wanted to ensure that was the only line.

    I’ve pulled that line, will cap it, and drive the truck again.

    Also regarding the vacuum test, should the vacuum reading be steady?  Or reasonably steady?  It was jumping about 2” on either side of the 20” reading while running.
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    Gary Lewis
    Administrator
    Vacuum that jumps back and forth can mean valves that aren't sealing, but not always.  In any event that's probably something you can check out later as I don't think it is the issue you are chasing now.

    I'll be anxious to see what the drive with the EGR valve disconnected finds.
    Gary, AKA "Gary fellow": Profile

    Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
    Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
    Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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    Re: Hesitation just off idle (and only in gear)

    ckuske
    Administrator
    I'll hopefully get to that tomorrow!

    In the meantime, I took a video to show the vacuum and you can see/hear the stumbling at fast idle.  This isn't the main problem, but it may be adjacent.  This video doesn't have the EGR disconnected (that's tomorrows job)

    https://drive.google.com/file/d/1MZygufOC7WSG52hxLHgggvVgT7gncPex/view?usp=sharing

    The audio is a little different in person, but hopefully this adds a little more color to what I'm trying to describe at fast idle.  But, this item is secondary (but annoying).  It's odd, but driving, this isn't noticed in performance, the tach, or in listening to the engine.  Driving, it's all good, or when you kick the idle down.
    Chris

    '84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread
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    Re: Hesitation just off idle (and only in gear)

    grumpin
    EGR, hopefully that is the problem.

    Wish I could remember better, , had an EGR give me a stumble on a Suburban we used to own. Checked everything, all good, finally disconnected the EGR and found the problem.
    Dane
    1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
    1992 Bronco XLT 4x4 351W E4OD
    1998 GMC Sierra SLE K1500 350 4L60E
    Arizona
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