truck running poorly under load

[COCHEV]

my truck has been running great until my last trip over the pass it started running a bit sputtery and doggy up the grade. every sense then its the same. runs fine otherwise on flat ground etc. starts great every morning and motors down the road. but go up a hill or put my work trailer behind it and it dogs down and sputters a bit with any kind of load/ grade.

pulled the cap and didn't see excesive wear.

pulled a few plugs and they are all light brown and look good

made sure the choke was releasing and allowing the secondaries to open up, yep

i have one of those clear inline fuel filters and that all looks clean

so i'm stumped. unless i somehow got some crap clogging up a jet. i'm out of town and haven't been able to pop the top of the carb off

any ideas?

truck is the 82 in my sig- 350 with edelbrock 1406, th400

 

[4X4HIGH]

Are you sure the timing is set properly and not too far advanced or retarded? Could also be running lean under a load and then detonating. Make damn sure it is not detonating unless you like pulling engines.

 

[mr250twostroke]

Mine did the same exact thing on the way home over Chinook Pass last weekend. Had battery issues and picked a new one up yesterday, problems gone... not sure how that works .

 

[COCHEV]

well, i haven't touched my timing in months. i just drove the rig 500 miles through washington last weekend and no problems. then on the last grade over the pass to bend it started acting up.

i went to napa tonight to get a fuel pressure gage, but it was the same price as a new fuel pump, so just put a new one in-20 bucks- cheap insurance. well that didn't fix it.

i'm going to borrow a buddy's torks bits so i can pop the top off the carb this weekend and see what i see...

my oil pressure gage is acting up too. pretty much always pegged... don't think its related, but you never know so i'm throwin it out there.

 

[4X4HIGH]

Timing chain could have jumped some teeth and that will make for some bad issues. This actually just happened to me on my Ford T-bird about 6 weeks ago.

 

[COCHEV]

i'm still leaning towards a fuel problem. it starts great. idles nice. i can rev it out to redline, no hickups or bogs. and can rev it out manually shifting it on flat ground too.

put when you add a load to it- trailer, hill etc. thats where it bogs down.... i'm hoping i just have a clogged jet or something. altho i can't say that in all my years i have ever had a clogged jet even in the rattiest neglected beaters i've owned.

just love these fun little issues with old rigs. maybe i have crappy ass gas in there

 

[diesel4me]

I'd try another ignition coil,or if you have HEI,the module or pick up coil can cause weak spark that'll only fire the plugs under no or light loads,and "blow out" when you put it under a heavier load..plug wires can do it too..

Might be bad gas too,its difficult to see any water in todays ethanol gas,it acts like dry gas and disperses it..usually bad gas will cause poor idling or stalling even under no load though..

 

[COCHEV]

is there a way to test the pickup coil so don't just keep throwing parts at it?

last time i had a pickup coil go bad, it flat out wouldn't start or run at all...

 

[diesel4me]

There might be some kind of "tester",but none I know of the average guy will have..
I have seen many modules and pick up coils crap out intermittently,or run perfect for days,then make it run crappy or die outright..

Easiest way to replace one is to drop in another distributor,a boneyard one--its a pain to have to tale the distibutor shaft out and unpin the drive gear,etc..its quite unlikely two distributors would show the same symptoms..I usually kept a "spare" behind my seat in my gas powered trucks!..

They do have ignition coil testers that measure output voltage,but sometimes coils only crap out after being in operation for several miles when they heat up,so substitition is the best "test"..dont overlook the distributor rotor,I've seen many burn through where the "spring" thing is ,and lets the spark ground out on the distributor shaft.,under a load--.I once got stranded in my dads Chevelle wagon (one like my avatar) when the rotor did that,it was a 307 with points--it started right up,but putting it in drive would snuff it right out!..luckily after walking 1/2 mile,I found a
K-mart store,and they had one!..2.99 and I was back on the road again..

Another thing,if you swapped in an HEI to a truck that had points,you MUST run a 12 gauge wire to the fuse box or thru the ignition and NOT use the original "hot" wire to the coil--HEI needs a full 12V to run right,and an old points coil had a resistance wire,that limits it to 9V or so..enough to make the HEI work,put poorly,and spark will crap out under a load.

 

[COCHEV]

well, i have carb off and apart on the tailgate. there was a good amount of fine silty crap in the bottom of both flaot bowls. i sprayed out the jets and cleaned up the bowls with carb cleaner and i'm going to put it back together and go from there...

 

[COCHEV]

so, to update, its running better...ish

still flat on top/full throttle under load. so i guess i'll have to look deeper into the destrib, recheck timing and check out the mech advance and all that crap-o-la

don't you just love it when its not running horribel, but its just not right either...ah the joys of our old trucks.

 

[COCHEV]

so, to update, the truck ran good going home over the pass- even had a 1/2 cord of wood in the back. back in portland at lower elevations the truck runs much better.

i think i will lean up the main jet one step and see how that does...