1984 C10 305 stall at low speeds, loss of power during accel

[BucketofBoltsBob]

Hi, This is my first post so please bear with me. Title pretty much explains the gist but I have 1984 c10 305 automatic has quadrajet carburetor with HEI distributor. This turned out pretty long but feel free to skip the paragraphs and jump to tldr; tag at the issues breakdown toward the middle.

A little background on the truck: I received it a little over a year ago. On its ride home ripped some drive belts and blew a coolant hose (truck didnt overheat). Since then it sat for about a year and a month or so until I was recently able to work on it. When I had originally received it it started up fine with a jump as it had been sitting for a little before that but otherwise was in driveable condition. I was able to take it immediately to the gas station and drive it about 90 miles on the freeway at freeway speeds until the belts and coolant hoses busted. Fast forward to now, I've replaced the initially needed components and got it started. It had trouble starting and after idling for a bit so I replaced some basic ignition-related components and was able to get it to idle on its own without me having to worry about it. Was even able to drive it around the block real quick with no issue. Ok all good till then.
So now the other day I go for its first real drive to replace the tires which had some dry rot. I start up the vehicle fine get driving (engine still relatively cold tire shop maybe a 15min drive) and when i get to a normal road for a moment I notice that while I'm accelerating the car at first accelerates normally but then the power and pressure in the pedal kind of falls off (similar to if you were stepping on the gas pedal at idle.) It happened a couple of times each time power came back after a few seconds and it didnt seem to matter if I let off the pedal or stayed on the pedal while the issue was occuring each time acceleration power was restored in a few seconds. I kind of just shrugged it off as getting used to moving again its not gonna be perfect.
Moving to the second issue as I'm pulling into the tire shop low speed driving under 10mph I hit a speed bump and the truck stalls. Ok kind of weird but not the end of the world. Then as I go to park the truck stalls as I put myself in position to back in, then stalls again when put from drive into reverse. Got tires installed maybe an hour passes, pull truck out again truck stalls this time changing gear from reverse to drive. Ok keep going again for a bit then it stalls during a low speed maneuver when i go to press the gas and accelerate to get over the speed bump. After that nothing, was able to drive home just fine and although I do feel like the engine might have lost power again slightly it wasn't enough to call it the same thing.



tldr; start here

So my current issues are: (I'm hoping both a related and have the same fault cause)
- Loss of engine power during acceleration
- When pressing on pedal car initially accelerates normally, then abruptly loses power at the 15-20mph range (acceleration feels sluggish), if the pedal is released and gas pedal pumped or if gas pedal is held down engine feels like it is responding but will usually take a few seconds before acceleration power is returned. Truck is still able to reach highway speeds and while slowing down or sitting at stoplight idling it appears to be fine.
- Stalling during low speed manuevers
- During low speed movements <10mph engine such as 3 point turns, or changing gear from drive to reverse or vice versa engine cuts outs and stalls. It happens fast so the engine doesn't appear to have time to fight it to stay on. It also does not back fire or make any weird sounds from the exhaust or engine when it occurs. It simply dies. It does start back up reliably immediately after (within seconds) and will drive after.

Recent Repairs:
- Distributor Cap and Rotor replaced, Ignition Coil replaced, Spark Plugs replaced, Spark Plug replaced, Spark Plug Wires replaced, In-line Fuel filter (in carburetor) replaced. Air filter replaced.

Here are items that I have not yet done that might be related
- No oil change, Havent actually gotten it warm at the same time it has been drivable so the oil change is high on my list and I wanted to do it after I changed the fuel pump
-Fuel pump, I initially assumed this was my culprit and so I intended to change it till a friend cast some doubt demons my way and now im unsure this is the proper route to go.
- Gas, the gas is for at least a year and change old, I was hoping I could just burn the old gas and slowly mix it with newer gas and I would be alright.

I've checked the search form on this and and other forums but found these similar (but not the same) problems other memebers seem to be having. These are the threads:
- https://www.gmsquarebody.com/threads/i-need-help-diagnosing-1987-chevy.39096/
- https://www.gmsquarebody.com/threads/transmission-is-causing-engine-to-stall.39251/
- https://www.gmsquarebody.com/threads/truck-idles-fine-dies-when-put-in-gear.38079/page-2#post-799713

This has lead me to a few possible suspects:
- Fuel pump- my current top suspect. Just from what I've read and how unpredictable the acceleration is under load.
- Bad Gas- Maybe the gas is so bad its just not doing the job even if it seems like it is under idle
- Timing- The engine is old and doesn't look like anyone has messed with the timing in ages so this one seems less likely to me
- Vacuum Leak- maybe theres a clogged or ripped vacuum line that is causing the issue, i have no clue how
- Carburetor dirty or faulty component- from what I've read theres a lot of possible adjustment components within the carburetor that can cause these issues
- Personal Error- Could any of the components I have replaced be the cause of this issue as I made the rookie error of not test driving before replacing the earlier mentioned ignition components

ok now my questions:
1. What is the likelihood my issue is caused by one of my suspects?
2. Am I even on the right path with my suspects as far as the troubleshooting process goes (I do understand I am at the beginning guess and check phase)?
3. Is there anything I should look at first or instead of my suspects?

I can do further condition testing if needed. I was given a chilton manual and that has lead me to about 30 potential causes some of them rather intensive so if there's anyway to avoid going down that list 1 by 1 I am all for it.





Thank yall for taking the time to help me. This is my first time working with a carbureted engine and first time working on an older american car. I do have experience working on newer foreign cars but this is a whole new ball game for me. I might not have all the tools you mention or know exactly what you're talking about but I'm good at doing my research and can get my hands on almost any tool if needed. Any and all help or input is appreciated.

 

[BRetty]

Hi friend,

I am having similar problems so I will be watching this thread. My '81 350 SBC was running great, then yesterday 4:30pm suddenly started what you described:

Starts and runs OK
Get on fwy or mash accelarator, bogs, slows, surge/stumble, then dies.
Wondered if a fuel line had burst, looked for catastrophic fuel leak, nothing to see.

I wish you luck, I'm gonna climb in my truck tomorrow (Sunday), I'll report back if I learn something.

BRetty

 

[BRetty]

Also: Don't feel bad about writing too much! More information is always good! Even if only 20% is relevant, you don't know which 20% -- that's the whole reason you are asking for advice.

Best,
BR

 

[Ricko1966]

I do not suspect the fuel pump,I do suspect a carburetor problem,the floats sinking the float kevel is too high,the needle and seat is leaking. Here's why I suspect carb. You have 2 problems,no power and dying when you hit bumps or turn fuel spilling over will cause both of your conditions,I don't see anyway possible that a bump can cause a carbuerated car to die when it hits a bump.

 

[305_Square_Body]

Identical description for my 1987 R10. God help us!

 

[Hugomartin]

Lets start with vacuum lines, where are they located. I know of a vacuum line on the charcoal canister. Is pcv valve considerd one? Egr a vacuum? How does a vacum line stall a vehicle

 

[Ricko1966]

I do not suspect the fuel pump,I do suspect a carburetor problem,the floats sinking the float kevel is too high,the needle and seat is leaking. Here's why I suspect carb. You have 2 problems,no power and dying when you hit bumps or turn fuel spilling over will cause both of your conditions,I don't see anyway possible that a bump can cause a carbuerated car to die when it hits a bump.

Well I certainly didn't word this right,don't know what happened ,tired,spell check IDK. What I meant was I don't see any other way possible for a carbureated car to die when it is turned or hits bumps,other than too high of float level. Hits bumps singularly,a couple things I could think of would cause it,same with turns but bumps or turns,sounds like float level.

 

[Rusty Nail]

I had the same thought as Ricko.
Died over a speed bump? Bad float/ needle seat / carburetor parts

But! Before that I was thinking about bad gas = "ethanol" rotting stuff up and out sitting in the fuel system too long and this is very likely, I believe. Would it kill your fuel pump and cause the issues you describe? Not likely or it wouldn't run. Also want to verify the fuel filter was installed correctly and isn't backwards. The gasket ON THE FILTER goes towards the carburetor not the fuel line.

AND THEN!
I was thinking about the catalytic converter and the longer I think about it the higher on the list of culprits it moves but only to a point - again or it wouldn't run? Back to ethanol rotting it out while the truck sits. And rots.

AND THEN!!!! I got to the connector at the distributor coming loose and dropping spark which I believe is VERY likely because it would die and restart easy. At least it is a great place to look.

 

[Trucksareforwork]

Did the 1984 305’s have electronic spark control? Some of what you describe reminds me of my 305 with the ESC working (poorly!). Do you happen to know if you have an intact ESC distributor? It’s the one with the extra (grey) four wire connector out the side of the distributor. I might try bypassing the esc to see what that does if it’s still intact. Bypass it by cutting the green and black wires and connecting the distributor side cut wires together.

I would check vacuum lines, clean fuel, carb, etc, but it sure sounds like a spark issue to me at first read (and that’s of course because I have seen this type of behavior).

 

[ChuckN]

FWIW, I did have a fuel filter on it’s way out that would do that as well. Had enough flow that it would run, but couldn’t keep up when accelerating. If all of the other suggestions don’t work, maybe take a look at that.

 

[Rusty Nail]

I like how bob never showed back up and told us his HEI connector was half broken too and I was right.
*insert your favorite derogatory here*

 

[BucketofBoltsBob]

Ok coming back to this thread...

Hi, This is my first post so please bear with me. Title pretty much explains the gist but I have 1984 c10 305 automatic has quadrajet carburetor with HEI distributor. This turned out pretty long but feel free to skip the paragraphs and jump to tldr; tag at the issues breakdown toward the middle.

A little background on the truck: I received it a little over a year ago. On its ride home ripped some drive belts and blew a coolant hose (truck didnt overheat). Since then it sat for about a year and a month or so until I was recently able to work on it. When I had originally received it it started up fine with a jump as it had been sitting for a little before that but otherwise was in driveable condition. I was able to take it immediately to the gas station and drive it about 90 miles on the freeway at freeway speeds until the belts and coolant hoses busted. Fast forward to now, I've replaced the initially needed components and got it started. It had trouble starting and after idling for a bit so I replaced some basic ignition-related components and was able to get it to idle on its own without me having to worry about it. Was even able to drive it around the block real quick with no issue. Ok all good till then.
So now the other day I go for its first real drive to replace the tires which had some dry rot. I start up the vehicle fine get driving (engine still relatively cold tire shop maybe a 15min drive) and when i get to a normal road for a moment I notice that while I'm accelerating the car at first accelerates normally but then the power and pressure in the pedal kind of falls off (similar to if you were stepping on the gas pedal at idle.) It happened a couple of times each time power came back after a few seconds and it didnt seem to matter if I let off the pedal or stayed on the pedal while the issue was occuring each time acceleration power was restored in a few seconds. I kind of just shrugged it off as getting used to moving again its not gonna be perfect.
Moving to the second issue as I'm pulling into the tire shop low speed driving under 10mph I hit a speed bump and the truck stalls. Ok kind of weird but not the end of the world. Then as I go to park the truck stalls as I put myself in position to back in, then stalls again when put from drive into reverse. Got tires installed maybe an hour passes, pull truck out again truck stalls this time changing gear from reverse to drive. Ok keep going again for a bit then it stalls during a low speed maneuver when i go to press the gas and accelerate to get over the speed bump. After that nothing, was able to drive home just fine and although I do feel like the engine might have lost power again slightly it wasn't enough to call it the same thing.



tldr; start here

So my current issues are: (I'm hoping both a related and have the same fault cause)
- Loss of engine power during acceleration
- When pressing on pedal car initially accelerates normally, then abruptly loses power at the 15-20mph range (acceleration feels sluggish), if the pedal is released and gas pedal pumped or if gas pedal is held down engine feels like it is responding but will usually take a few seconds before acceleration power is returned. Truck is still able to reach highway speeds and while slowing down or sitting at stoplight idling it appears to be fine.
- Stalling during low speed manuevers
- During low speed movements <10mph engine such as 3 point turns, or changing gear from drive to reverse or vice versa engine cuts outs and stalls. It happens fast so the engine doesn't appear to have time to fight it to stay on. It also does not back fire or make any weird sounds from the exhaust or engine when it occurs. It simply dies. It does start back up reliably immediately after (within seconds) and will drive after.

Recent Repairs:
- Distributor Cap and Rotor replaced, Ignition Coil replaced, Spark Plugs replaced, Spark Plug replaced, Spark Plug Wires replaced, In-line Fuel filter (in carburetor) replaced. Air filter replaced.

Here are items that I have not yet done that might be related
- No oil change, Havent actually gotten it warm at the same time it has been drivable so the oil change is high on my list and I wanted to do it after I changed the fuel pump
-Fuel pump, I initially assumed this was my culprit and so I intended to change it till a friend cast some doubt demons my way and now im unsure this is the proper route to go.
- Gas, the gas is for at least a year and change old, I was hoping I could just burn the old gas and slowly mix it with newer gas and I would be alright.

I've checked the search form on this and and other forums but found these similar (but not the same) problems other memebers seem to be having. These are the threads:
- https://www.gmsquarebody.com/threads/i-need-help-diagnosing-1987-chevy.39096/
- https://www.gmsquarebody.com/threads/transmission-is-causing-engine-to-stall.39251/
- https://www.gmsquarebody.com/threads/truck-idles-fine-dies-when-put-in-gear.38079/page-2#post-799713

This has lead me to a few possible suspects:
- Fuel pump- my current top suspect. Just from what I've read and how unpredictable the acceleration is under load.
- Bad Gas- Maybe the gas is so bad its just not doing the job even if it seems like it is under idle
- Timing- The engine is old and doesn't look like anyone has messed with the timing in ages so this one seems less likely to me
- Vacuum Leak- maybe theres a clogged or ripped vacuum line that is causing the issue, i have no clue how
- Carburetor dirty or faulty component- from what I've read theres a lot of possible adjustment components within the carburetor that can cause these issues
- Personal Error- Could any of the components I have replaced be the cause of this issue as I made the rookie error of not test driving before replacing the earlier mentioned ignition components

ok now my questions:
1. What is the likelihood my issue is caused by one of my suspects?
2. Am I even on the right path with my suspects as far as the troubleshooting process goes (I do understand I am at the beginning guess and check phase)?
3. Is there anything I should look at first or instead of my suspects?

I can do further condition testing if needed. I was given a chilton manual and that has lead me to about 30 potential causes some of them rather intensive so if there's anyway to avoid going down that list 1 by 1 I am all for it.





Thank yall for taking the time to help me. This is my first time working with a carbureted engine and first time working on an older american car. I do have experience working on newer foreign cars but this is a whole new ball game for me. I might not have all the tools you mention or know exactly what you're talking about but I'm good at doing my research and can get my hands on almost any tool if needed. Any and all help or input is appreciated.

Ok so coming back to this thread again because I moved forward but still not exactly where I need to be. Thank you all for the replies I didn't check it out too much because I am impatient and went to go see if I knew anyone who had experience with this engine and carb to give me some advice as well.

So a little more information it is a 305 4bbl with an em4e (ill include a picture of what it looks like) quadrajet.

Here's what I've done in the past month since I started this thread.
- I moved away from the fuel pump just because I know when I got it running for the little bit it did run that it seemed fine at idle and mostly while driving. Plus from what I've heard and read its also not as common for the mechanical fuel pump to go bad on these. I may be wrong there
- I rebuilt the carburetor which took me forever and was a fun albeit tedious experience and if you go this route and don't already rebuild carbs take way more pictures from way more angles than you'll ever think you need because if you don't youll have fun guessing where everything goes back and how it goes back.
- I found and fixed a vacuum leak in some small vacuum lines. I've been looking for a diagram that tells me which lines are which I found one on day two of the carb rebuild online and made the mistake of not saving it and couldnt find it again.

Here's how it went:
After reinstalling the carb the engine had a very high idle that was around the 1100-1600rpm range that I could not figure out for the life of me. The tuning video I watched just used the idle screws not the mixture screws so I had no clue about the mixture screws and that you have to tune them with a vacuum gauge. Figured out that I needed to do that so after using the vacuum gauge and mixture screws to tune the carb my idle was still high 1000-1300 range but the vacuum was steady 16-18inhg (side issue that I didn't attempt to fix that just went away was that the idle would eventually drop from the 1000 rpm to <500rpm till it stalled). So I was inclined to believe I had a small vacuum leak. Took a hose and some butane went searching for the hole in the small vacuum lines. Once found and the vac lines were replaced I was able to retry tuning again.

Now here's where I am at currently, I went to retune the carb the mixture screws didn't need much adjustment which surprised me since I would assume the engine would be running very rich without the extra air coming through the vacuum leak. My idle is still high at 950+ rpm and there was only a very slight difference between the high (cold idle) and normal (warmed up idle). I was able to back off the normal idle screw all the way and could not get the engine to idle lower than 850rpms once warmed up. The vacuum is steady 18-20inhg and the engine starts and idles beautifully besides it being a little high and no longer drops 100+rpm after it is revved. I have gone back over it with a hose and the butane can again and could not identify any leaks

My question now is does anyone have an idea of what could be the current issue? Possibly another small vacuum leak or maybe I just haven't tuned the mixture screws properly? Could the pcv be bad and cause this? I will continue doing research but it would be great to hear your opinions.

Oh and if anyone has any tips for tuning the mixture screws cause on mine they have no screw head just flatend on 2 sides that look like it can be gripped with pliers (ive been using very small angled needle nose pliers) but the area where they are located on the carb is the most inconvenient spots.

Here are the pictures they are from before the rebuild just to show the components im referring to. If having better or new pictures would be more helpful let me know and I can take more.

The red arrows are the mixture screws (also shown in the last picture), the blue is the high idle screw, the orange is the low idle screw (if i named them wrong please let me know), and the green arrows are the vacuum lines i replaced due to leak.

If there's any questions I can answer or pictures I can provide to give a better understanding, please feel free to ask. Thanks

 

[BucketofBoltsBob]

I do not suspect the fuel pump,I do suspect a carburetor problem,the floats sinking the float kevel is too high,the needle and seat is leaking. Here's why I suspect carb. You have 2 problems,no power and dying when you hit bumps or turn fuel spilling over will cause both of your conditions,I don't see anyway possible that a bump can cause a carbuerated car to die when it hits a bump.

Yea I still don't know what caused it and I thought it was very weird that after that first bump the truck then had low speed stalling issues. Still don't know what caused that but as for now the vehicle no longer bogs down at idle and can be smoothly rev-ed without issues. I have yet to take it on a test drive over some bumps yet so I'll let yall know how it goes I have no idea what exactly fixed the carburetor during the rebuild but afterward it definitely runs alot smoother.

 

[BucketofBoltsBob]

I had the same thought as Ricko.
Died over a speed bump? Bad float/ needle seat / carburetor parts

But! Before that I was thinking about bad gas = "ethanol" rotting stuff up and out sitting in the fuel system too long and this is very likely, I believe. Would it kill your fuel pump and cause the issues you describe? Not likely or it wouldn't run. Also want to verify the fuel filter was installed correctly and isn't backwards. The gasket ON THE FILTER goes towards the carburetor not the fuel line.

AND THEN!
I was thinking about the catalytic converter and the longer I think about it the higher on the list of culprits it moves but only to a point - again or it wouldn't run? Back to ethanol rotting it out while the truck sits. And rots.

AND THEN!!!! I got to the connector at the distributor coming loose and dropping spark which I believe is VERY likely because it would die and restart easy. At least it is a great place to look.

Your and my thought process was very similar on this and I did go back check through the distributor, plugs, wires, and connectors, I couldn't find the vacuum leak originally with the carb cleaner but I'm sure that would've probably helped a little. The carb rebuild ended up showing the most improvement although as I have almost no experience with carbs and heavily relied on youtube tutorials I could not tell you what exactly I thought was the culprit. It still amazes me how little the amount of changes I did to it felt vs the result I got once it was back on. As far as the ethanol bad gas issue goes. I still need to replace the gas and I am less and less inclined to believe that it was the issue just cause as of right now it starts and no longer has a stall issue (havent taken it over any bumps yet tho) and runs smoothly. I hope I don't have any issue with the cats or fuel pump but I do at least have the replacement pump on hand if that does become an issue.

 

[BucketofBoltsBob]

I like how bob never showed back up and told us his HEI connector was half broken too and I was right.
*insert your favorite derogatory here*

Yea it took me forever to go through the carb rebuild myself I definitely give credit to the guys that do it cause i do not have the patience for that. Had to piece through 3 different sets of tutorials and the provided instructions on the rebuild kit and still felt uneasy with fingers crossed when reinstalling the carb but it seems to have turned out well.