1984 GMC truck: hesitation / shifting issue

[Clay]

This was my grandfathers truck that he purchased new and drove until he passed away 10+ years ago. Its a 1984 GMC w/ 305 automatic. My grandmother still has it, and still uses it occasionally. Its only got 47,000 miles on it, and my grandfather kept up the maint as it should have been (which wasnt much with so few miles).

anyway, Sunday I did the normal plugs/cap/wires/rotor/air filter maintenance on it because it was just time. It was beginning to show signs of needing it, in addition to a hesitation problem, so it was done.

afterwards it runs GREAT, but still has the hesitation problem. Seems worse when its cold, but it still does it after driving for 50 miles.

Basically its either a hesitation issue, or a shifting issue. Only seems to happen in the 1 -> 2 shift. Floor it, truck goes fine until it gets to the point where it should shift, then the engine just seems to fall on its face, and stay there. It will chug as long as its floored, and wont stop/shift until you lift off the pedal. Then its fine. Floor it while cruising (ie in 3rd gear), it down shifts and goes, and shifts with no problems.

Any ideas on what the problem could be? truck is completely and totally bone stock. I went through most of the vacuum lines and replaced what bad ones I found but that was no help. Trans fluid is nice bright red, and full.

thanks,
clay

[BadAssPerformance]

Quadrajunk?

[Clay]

I think it does. the carb is kind of my first choice for the problem.

that and all the fawkin vacuum lines/systems on these 80s vehicles.

[BadAssPerformance]

First, get a six pack, no wait, better get a 24.

second, rip off all that commie govenment airpump, egr and what not emmisions crap

third, you'll have a lot more problems than hesitation! LOL

[Clay]

so what your saying is I need to stick with the pieces of crap that are on the engine.... or it will run worse! ;)

[jre97]

Toss out the pos feedback qaudrajet, get a good dual plane intake, and a edelbrock/holley/etc... 4bbl. The only vacuum lines you need are brake booster, vacuum advance, vacuum modulater(if applicable), and a line for the heater stuff inside. Oh and invest in one of those distributor mechanical advance tuning kits made by Mr. Gasket it's the best $7.50 I ever spent.

May be all of that's a little over kill. Make sure your kick down cable is adjusted properly. Good clean fuel filter. Pull the top off the carb and make sure it's good and clean.

The feedback quadrajets are junk.

[roachjuice]

get a 2.5 turbo and drop that ------ in there.:thumb: problem solved

[Tony Hanna]

Toss out the pos feedback qaudrajet, get a good dual plane intake, and a edelbrock/holley/etc... 4bbl. The only vacuum lines you need are brake booster, vacuum advance, vacuum modulater(if applicable), and a line for the heater stuff inside. Oh and invest in one of those distributor mechanical advance tuning kits made by Mr. Gasket it's the best $7.50 I ever spent.

May be all of that's a little over kill. Make sure your kick down cable is adjusted properly. Good clean fuel filter. Pull the top off the carb and make sure it's good and clean.

The feedback quadrajets are junk.

+1 to the fuel filter. It really sounds to me like you're running out of fuel just below the shift point. Also, check to make sure the choke is opening all the way. A partially closed choke will cause the engine to run super rich when airflow is high (full throttle, higher rpm's) but may not be noticable at lower rpms/part throttle.

[turbovanman²]

Q-Jet's aren't junk, its the idiots that work on them that need help-its one of the best stock carbs ever made. Great power and wicked fuel economy.

Ok, what tranny? if its a turbo 400, the modulator-aka vacuum pot on the trans could be leaking or tired.

2nd, this is what I do to all older cars-make sure the EGR valve works, if the valve works, make sure the temp vacuum switch works-if not, keep going. Your going to redo the vac advance on the distributor-right now, its getting full manifold vacuum at idle-big no no. So, if the EGR system works, tee into the signal line after the vac switch and hook up to the dist. Reset base timing to 8-12 deg, you have to play as bad gas, carbon etc make this vary. If the temp switch or egr don't work, just use the carb signal line straight to the distributor.

Check the fuel filter, check the carb choke break and make sure the secondary doors can move with the truck shut off.

[jre97]

No the feedback qaudrajets used on computer controlled vehicles are junk which is most likely what he has being an 84. If you get a regular quadrajet that the throttle shaft isn't shot in, then yeah you couldn't ask for a better carb. It most likely is a 700r4 or a th350

[Tony Hanna]

No the feedback qaudrajets used on computer controlled vehicles are junk which is most likely what he has being an 84. If you get a regular quadrajet that the throttle shaft isn't shot in, then yeah you couldn't ask for a better carb. It most likely is a 700r4 or a th350

+1

I love an older (non-feedback) q-jet. The spread bore design makes for a great compromise between fuel economy and performance when tuned right, and the throttle response is really nice with the smaller primaries. I'm not a fan of the feedback models either though.

[turbovanman²]

No the feedback qaudrajets used on computer controlled vehicles are junk which is most likely what he has being an 84. If you get a regular quadrajet that the throttle shaft isn't shot in, then yeah you couldn't ask for a better carb. It most likely is a 700r4 or a th350

Agreed on the feedback but 84 should still be a regular one unless its a California one.

[Tony Hanna]

Agreed on the feedback but 84 should still be a regular one unless its a California one.

Might have been on a truck. I'm thinking they started with the feedback carbs somewhere around '82 on the cars though. The emissions regulations weren't quite as strict on the trucks back then...

[turbovanman²]

Come to think of it, I haven't seen a truck with a feedback carb, only cars. The only goofy thing they put on trucks was a ECU box for the dist, I just take out the dist and put a regular HEI one back in. :nod:

[jre97]

I have an 85 K10 that had the feedback carb. I don't what year they started but I have seen several cars 81-82 and newer with them on it. Most likely since his hasn't been driven much it's probably just gunked up from old gas and isn't getting the proper fuel delivery, holes dry rotted into the vacuum lines, electric choke malfunction, etc...