hesitation in acceleration

[hikersteve]

On my 84 t4wd i am gettin a intermittent hesitation during acceleration and an occasional hiccup and die or close to die in idol (maybe once every couple days)

It feels like a fuel filter issue to me, however the filter is new and clear so i can see it working and still clean. All other tune up parts are new (1200 miles)
It is timed at 5 btdc, i have checked for vacuum leaks, cleaned and tightened battery terminals, i use mid to premium gas always and passed CA emissions with flying colors.

i was under the assumption that with fuel pump being mechanical and simple it would be a work or fail situation with that, but have since learned thats not the case, so i will check that out (still its intermittent so i dont see how the mechanics of fuel pump could do that).

Any ideas for diagnosing fuel pump or overall problem?
thanks steve

[irowiki]

Does this happen when the car is cold or warm? Exact same spot during acceleration?

Might be a vacuum leak, or some bits on your carb need rebuilding (accelerator pump)

[durecell]

the hiccup and die at idle could be the tvsv if it only does it at a certain temp. mine would warm up enough to drive away then at a stop light or stop sign if the temp was right it would try to die or actually die. then start up just fine. it only did it sometimes depending on the situation. I replaced it with a good one I pulled at the wrecking yard. I did the fsm test on it first then installed it. the problem went away after that.

as far as the acceleration issue it could be carb related. accelerator pump. check the aap valve if it leaks intermittently it can mess with idle and acceleration. also I noticed mine had better response on acceleration after I moved my timing to 10* advanced instead of the 5* factory. just an idea.

[Petros]

my guess it that it is vacuum related such as the AAP or TVSV. It also could be a dirty carb with some crud stuck in the accelrator pump and/or low speed/idle jets.

Check all of the vac operated equipment per the FSM procedures, starting with the AAP and TVSV. If all is good than likely internal to the carb.

Also, the almost dying at idle may be unrelated. that is usually caused by the throttle stop being being out of adjustment. I do not remember what it is called, but there is a vacuum diaphragm on the front side of the carb on the throttle shaft (on the side opposite the throttle cable bell crank). it is supposed to hold the throttle open for a few seconds when you back off the throttle rapidly to prevent it from slamming shut, it is a simple adjustment screw on it. If the throttle closes too rapidly it could cause the idle to drop down and stall or nearly stall. there is a simple FSM procedure for the adjustment, but turning it in so it stays open a bit longer should tell you if that is why the idle speed dips when you come to a stop.

your fuel pump and fuel filter are fine. when those are marginal you usually start and run fine at idle and low speed and it cuts out under higher demand like high speed or accelerating up a hill.

[hikersteve]

thanks everyone for your input. will be working on it this weekend. let you know how it goes.
steve

[hikersteve]

so i tested the tvsv, checked out, went through the troubleshooting for hesitation in FSM. Couldn't find any info or details on testing the AAP. checked repair forum to and had about ten threads come up for accelerator pump but nothing detailed ????
However i was taking the dist cap of to recheck timing and noticed a substantial groove in the contact for plug 3. I know that rotor can wear a groove in contacts, but this was deep enough to cast a shadow under light (probly 16th of an inch). This groove was through plastic and metal, all other contacts were fine.
So i swapped out dist cap and rotor from my back up distributor i pulled from junk yard, now its runnin great. so bad dizzy cap. This also got rid of lazy idol i had since i got car. Put all new tune up parts on it before i drove it back from WA, so it must have just been a poorly manufactured cap. There was i tiny bit of play in rotor ( 1/8 to1/4 inch) so it could be dizzy shaft worn? It seems as tight as back up one though.

I am interested on how to check AAP, and cant find in FSM (only removal) so if any y'all got pics or info please share.
thanks steve

[irowiki]

It should be in the FSM. Will look for you in the morning!

[Petros]

the test for the AAP is to pull the vac line off of it after you were running it. If it is wet with fuel than the diaphram is ruptured and allows fuel to leak past it into the intake manfold through the vac system. it should be check soon after it was running because if it sits for long the fuel evaporates out of it. Smell the end of the vac line too, it should not have a gasoline smell to it.

There should be no wiggle in the distributor shaft in the side to side direction, any detectable movement there means the bearing are shot. Do not confuse this with rotational movement, this will be there for the mechanical advance which returns with spring force. So you should be able to rotate the rotor a few degrees (perhaps a 1/4" and it should spring back), but it should not have any movement perpendicular to the axis of the shaft.

[irowiki]

Page EC-54, EC-55

Bookmarks, Emission Control System, Auxiliary Systems, Auxiliary Acceleration Pump

It is worth reading the entire emission control system front to back.

[hikersteve]

do you have to completely rebuild dizzy to fix bearings? Can you get bearings seperately?are new ones still available? if so whats the damage?
thanks steve

[Petros]

you do have to remove it and take it apart. If the other parts are good likely you can reuse them. I seem to recall there is a thread on rebuilding the distributor, including replacing the bearings. It listed the parts, usually comes in a kit but you likely can order the bearings alone if necessary. There is a seal or o-ring that goes inside the shaft as well that should be replaced with the bearings.

Personally I would just replace the whole distributor with a good used one, they are very durable and wrecking yard distributors are good bets.

[hikersteve]

ya i have one that is in good shape, think i will do that.
it is play in the shaft, not the rotor rotation that i was talking about.
i will probably swap and then rebuild the one i have for learning purposes.
thanks