stumble...dammit

toolmann

toolmann

Member
hey all...it was a loooong weekend of busted knuckles and foul language..i started the weekend by changing my cap/wires/rotor/plugs (Conrad,black beauty,stock @ .35) on my TY in hopes of getting rid of a stumble...
and while i was at it i changed nearly all the vac lines xept for a couple(cruise/trans) cause they looked ok-no breaks or holes...
put in my PTE afpr (set to 45psi)
covered my intercooler with heat relfective material and did the hard line delete to 3/4 hose...
BUT i still have a stumble at idle,dammit...misfire?...all the wires are secure and clear of exhaust mans.
i recently had the timing chain replaced by a local shop-BUT good mech.are hard to find (he charged me for some stuff he dident put in the truck,but thats another story) soo i checked the timing myself as a follow up and sure enought it was retarded by about 10 F'N DEGREES-totaly off the timing indicator thingy
soo i disco'd the brown wire in the pass.foot well and set it a 0 degrees.(I acutally did that during the week, before the tune-up)
i have a guy who has a Snap-on scanner soo i plan on pluggin in to see if there are any codes stored(no cel)
any particular values ya'll can suggest i should look for?? truck has 100k+ on it...bad sensor some were?
im hoping to catch up with a local Sy guy this weekend for a dm run,but iv been trying to do all the basics before i go see him.the truck seems to run well xept for the stumble...all the intake bolts are tight and no leaks were found....
is it too much to ask for a smooth idle??
any input is appreciated!!

T
 
turbodog

turbodog

Donating Member
A smooth idle is one of the most elusive things about these trucks. GMC must've gotten tons of complaints when they were new. There is actually a service bulletin that states "these trucks do not idle smoothly, due to lean idle to meet EPA requirements". There was a PROM issued to address rough idle, but it only applied to Sy's. All Ty's should have come with the 'improved' PROM.

You might try bumping the fuel pressure up a little. I run 48psi, and the last few psi seemed to smooth it out some.

Of course eventually the BLM will offset that change... unless you run a 160 degree thermostat. But, the 160 thermostat COULD have it's own negative effect on idle quality.

Another item that has been known to help: replacing the pickup coil in the distributor. We get a lot of corrosion in our distributors (my theory is that the rear edge hood seal is worthless, and water goes right down onto the distributor).

I'm not aware of a trans vacuum line, so you might want to double check where that one is going. Also don't rely in visual inspection. My mytyvac found small leaks in hose assemblies (at the 'tees' and where the hard tubing goes into the rubber elbows) that were not apparent to the eye.

HTH!
 
toolmann

toolmann

Member
thanks for the response t-dog
i am running a 160 but the issue was present before repalcement.
the truck will idle fine for 5-6 seconds and then it "bumps" like its gettin bumped from behind.then its fine agian for a 5-6 seconds...thats why i was thinking maybe a sensor is bad...considering the mileage
when i did the vac.line at the map,the clip broke(very brittle)but i secured it with a wire tie-same with the o2 sensor at the dp (had to unplug it for some reason).ALL the vac.Ts & elbows broke when i pulled them soo they are all new.i re-used some of the hard plastic lines that dident break or crack under stress...and they held vac. soo...
WOW what a p.i.t.a. that was..
i have noticed after its warmed up the exaust smells rich-but upon replacement,all the old plugs looked ok-maybe on the light side but no real carbon build up,oil or fuel stench..it had all stock stuff on it-Delco cap/rotor/wires/plugs-
i also noticed the K&N filter is pretty f'n dirty-gonna pull it-clean/oil it tonight

i could try to bump the pressure some.i plan to put the Walbro 255 in the next week or 2...gonna do it myself soo ill know it done right!!
i wreckon ill try the pick-up coil..is that dealer item?

hopefully if i have a bad sensor the scanner will pick it up-

we'll see

T
 
turbodog

turbodog

Donating Member
Well, if it smells rich after warm up, could be o2 sensor headed south. Scan tool will not tell you directly, but you should see BLM way off from 128 'nominal' value.
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: stumble...dammit

My Sy does the same thing at idle, it fine but opnce and a while ippear to stumble and drop 200 rpm. I have replaced lots of items (thought haven't rebuilt the distributor yet). For what ever reason my old 160K mile Ty with little previous maintance idled smooth.
 
toolmann

toolmann

Member
i will supersix.
my first plan is to put the scanner on it and check a few things.and go back & re-check all the vacs. i put in sat & make sure there is nothing loose-

the truck seems to run fine,i took it to Maine sat and it got nearly 270 mile to a tank with alittle less than an 1/4 tank left...seems like decent mileage compared to my s/c'd s-10 which runs out of gas around 225 miles...but i HAMMER that thing....

ill post if i come up with anything.

T
 
ed hess

ed hess

race or get outta the way
one other thing you might do. I learned this from myclone.
take an analog meter and connect to your iac. watch very closely for dead spot on iac as you slowly open the throttle while looking at the meter pointer.

you can do this on dm also if you have that.

do this with engine not running igniton on.

ed
 
ed hess

ed hess

race or get outta the way
oops

yeah i did mean tps. sorry about that...

little frustrating here today..... harwood is jackin me off, seems they cant find my lexan rear window order.... and my truck is in pieces since i have the headliner out for the bars to be welded into the back tonite.

but whats really worn me out was just getting the damn visors and rear light out. since the cage went in with the stuff still in place.... visors might get back in but the light never will.... and besides that atco tech can suck my dick if they dont like these bars out the back....

ok rant off for now.....sorry to get off topic but i gotta vent.

ed
 
toolmann

toolmann

Member
well..hooked up the scanner...i couldent print the info from the hook up but wrote down all i could see/remmember.....
it did go into closed loop with the 160 t-stat...
found the tps to be seemingly operatating ok-0-100 percent without any jumping around as the accel.was slowly pushed...
o2 sensor was jumping round quite a bit...from 750 to 2 then stumble-800 to 6 then stumble-825 to 2-stumble... kinda repetative...i knew it jumped around but dident think it would drop THAT low on the low side...
coolant temp was at 67c(the scanner was set up for celsius.,not degrees) i neglected to get the mats...i wanna say they were around 45c and boost was in some kinda units,not lbs....55(??) @ wot
the wastegate showed 100% till wot then went to 60% (i dont know what thats suposed to do)
no stored codes,no misfires noted-i did notice that when i disco'd the vac at the afpr (thats the easiest one to access) the idle came up slightly & the miss was gone-when reappling the vac. to the afpr the truck would stall....
the guy who hooked up the scanner thinks its an injector issue.he suggest putting a scope on each cyl.one at a time to locate which is misfiring....
fuel delivery issue?-
i dont know if any of this info helps....any ideas??
hoping this weekend to do a dm run,but it may be next week.

T
 
toolmann

toolmann

Member
yeah...iv seen them jump in the hundreds 200 to 800,back and forth, but never to single digs.like that.....and it would stumble just as the single digs appear....
could the sensor be faulty or is it just showing what its seein'

i was lookin for a blm setting but dident see it described as that...dont know what else it would be called-

T
 
dgoodhue

dgoodhue

BuSTeD 4.3
The disconnecting & connecting the AFPR form a vacuum source isn't that surpirsing, you changing the FP bu approx 10psi, so the ECM probably isn't compensating enough.

I doubt a scope is going to show anything, it should just show PW that ECM is commanding. The only thing you can do is check the resistance of each injector, to see if one is abnormally low (belowe 15-16 ohms. I had my stock injectors clean @ 47K miles and they reports back on them bascially said I wasted money :) I haven't really studied my O2 sensor volt to seeif they correspond with a stumble, the really numbers would indicate a lean condition.
 
S

Supersix

New member
How long have you been running that O2 sensor for???...Do you use the truck at the track with very high octaine fuels???
 
toolmann

toolmann

Member
i run 93 octane pump gas...havent been to the track yet,i wanted to do all the reccomended upgrades first as it was completey stock.still got a Walbro to put in & figure out this mis-
that o2 sensor has been in there since iv owned the truck(9/03).there has always been a mis but i had hoped that a good tune up and replacing all the vacs. would clear it up.the guy before me(2nd owner)had just had it tuned up with all AC Delco stuff soo i figured id upgade eveything when i pulled it out of storage.
can the o2 sensor cause a mis or does it just reporting what it sees??
every time i start the truck in the shop everyone says"running alittle rich,eh??"....you can smell the fuel

T
 
ed hess

ed hess

race or get outta the way
os sensor reports what it thinks it sees. then the ecm makes changes to fuel. now if the o2 doesnt tell the ecm the correct thing. ecm being stupid makes the change to the fuel.... and you have whatever....

just do like most around here and throw more money at it. i.e. new 02. or if you got someone close by swap their sensor into it.

ed
 
toolmann

toolmann

Member
throwing money at it seems to be the trend soo far....i have a sensor i took out of my 95 tbi s-10 that turned out to have nuthin'wrong with it....
think that would work?

T
 
ed hess

ed hess

race or get outta the way
toolmann said:
throwing money at it seems to be the trend soo far....i have a sensor i took out of my 95 tbi s-10 that turned out to have nuthin'wrong with it....
think that would work?

T
Click to expand...

call a local parts store and ask em if the part numbers are the same for both motors.

ed
 
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