Hesitation just off idle (and only in gear)

[ckuske]

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 testIdle 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.

[Gary Lewis]

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.

[grumpin]

Have you checked the adjustment of the TV cable?

I’ve never dealt with one, but heard and read they can give you trouble.

[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.

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.

[grumpin]

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.

[mat in tn]

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.

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?

[ckuske]

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.

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!

[ckuske]

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?

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?

[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?

divide and conquer! cap the port feeding the hvac and test. and then reconnect and move on to the next circuit

[ckuske]

divide and conquer! cap the port feeding the hvac and test. and then reconnect and move on to the next circuit

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