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UPDATE NEW ISSUE,help me diagnose my truck,UPDATE NEW ISSUE

7

79 blazer

1/2 ton status
Joined
Dec 29, 2003
Posts
114
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Location
FORT COLLINS,CO
ok so i got it running pretty good now, not where i want it but pretty good, but now when i shift into drive and L2 it doesnt move :mad: , just revs up. but reverse and L1 work fine :confused:. so is my tranny fried or is there something i can do to fix this? im sure that letting it sit for over a month didnt help the th350 tranny.



so im going to work rebuilding my carb. i want to make sure this is my problem before i try to start the thing, so my truck was stumbling/cutting out at full throtle after about 8 seconds of having it mashed to the floor. then it progressivly got worse over about a month so that it would start doing it at less throttle, and then under any load at all like a slight hill or having the gas pushed more than feathering it, it would get up to speed as long as i let it get up there slowly and only pushing the gas slightly. then one day at the grocery store i come back out and have to have the pedal all the way down to even get it to start, it runs sketchy for a about 30 seconds then dies to never start again. when i try to start the truck it sputters but never comes close to starting. the fuel system looks fine, filters clean, hoses fresh and in good condition. im not sure how to tell if the fuel pump is good or not. i was told i needed to rebuild the carb, but i think the mecahnic just wanted the cash to do this, so im not sure if that was right, but im doing it myself anyway, so now that you've read my essay,lol, any help would be apreciated because i need this blazer going bye next week for school.
thanks with all the thanks there is in the world - mark
 
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I would change the fuel pump. It's pretty cheap and easy to do, and it sounds like the problem to me. When you change it, there is a push rod that comes down from the cam, that tends to be a pain, but if you take one of the fuel pump bolts and screw it in to the front of the block in the hole right around the corner from where you took it out, it will engage the fuel pump rod and if you push it up and tighten it up FINGER TIGHT it will stay up.
If you decide to use another bolt, make sure you take it out after you're done putting the pump on.
I dont know if all SBC's are drilled and tapped like this, but every one I have ever changed a fuel pump in has been.
 
thanks alot, for the tip and youre speedy reply, all people need to work on there own cars and save hundreds in labor is some help like this, i apreciate it greatly. i will replace the fuel pump asap. anyone else have 2 cents on the problem?
 
I would definetly check fuel press & volume.

Take off the airfilter and pump the throttle. Is there fuel quirting in? If not I would pour some gas down in the intake (not very much) and see if it cranks right up. If so I think is pretty clear that its a fuel system problem. Could be either fuel pump bad, Fuel filter clogged or could be the float in the carb. might be stuck closed.
 
Check the fuel lines too...

You could use a pressure gauge to test the fuel pump before deciding to change it..A cheap Vaccuum gauge/Fuel pump tester is about 15 bucks(but so is a mechanical fuel pump--so you might be better off to just put in a new one if yours is old)....

If any of the steel lines have pinholes in them,air can be sucked in instead of fuel(if the holes are on the top of a bend,it might not leak gas!)--or if the rubber hoses are old,they can collapse internally and restrict the flow of fuel..

One hose thats suspect is the one near the gas tank on the passenger side frame rail that joins 2 steel lines together,it looks like an inchworm!-most GM trucks have it...I drove myself batty on one truck that had symptoms like yours..I replaced the fuel pump,carburator,gas filters,even tried a new ignition module in despair!--I finally tried blowing out the fuel line with the air hose,and found it was not letting air get to the gas tank in any great quantity...

I replaced the steel lines that were rotten and ready to leak anyway--but when I took off that "inchworm" hose,I could not blow thru it!--the inner layers of rubber were all separated,and was blocking off the flow of gas to the fuel pump!--I spent 75 bucks on parts that did NOTHING to fix it!--the new hose was a buck fifty with tax! :doah: :mad: ----and it ran great after I put the hose on!.. :rolleyes: :crazy: ..pays to check EVERYTHING before throwing parts at something! :doah: :crazy:
 
I had similar problems with my 305... I got so sick of the problems that Im swapping it out for a 350.

When I had my problems, I found a few thing that helped it until something else broke...

1. Check the timing
2. Check Distributor
3. Spark plugs?
4. Definately rebuild your carb
5. Fuel Pump
6. Check for vacumm leaks


Each and everyone of those things fixed my engine. until something else broke of course... It was a cursed engine. :D
 
ok so i tried the gas in the intake thing, and started it right up first try but idle is insanely fast, also the fuel filter(it is the see through glass variety) was quickly filling up with fuel like when you look in at the filter element the gas was steadily rising inside the space between the glass and the element.... so does this mean that the filter is bad even though it looks clear, also could a clogged in carb filter be causing this? or is it normal for it to do that? what does this say about the fuel pump if anything? and what cmight this mean about a float being stuck? i checked all the lines and they apear to be ok, whoever i did not blow air through them except with my lungs caus i dont have a compresor. i was sure i wouldnt get it to start but i am now excited at having made prgoress, if it will start im sure i can work out the rest with all of youre help, thanks again this site has been a life saver and keep the help coming - mark
 
check the fuel hoses. if they are older, alcohol in todays gas will rot them quick
 
If its been a while since you changed the filter(s) then I would go ahead and do it anyway. Other than that it still might be a prob. inside the carb.

Might want to take off the fuel line and crank it over some. Get you a coffee can or something to let it drain into and see how much comes out. That will verify volume anyway.
 
When changing the pump loosen the 2 bolts holding the pump to the block until there is roughly a 1/2" of play between the pump and block......
now rotate the engine slowly until the fuel pump pushrod has the least amount of pressure on it form the cam lobe that actuates the pushrod.....
push down on the pump to drive pushrod up against the lobe and gently hand tighten the bolt you have selected to place in the hole for that purpose.....
do not overtighten the bolt as this will bend the pushrod, just enough to hold the rod in place.........replace the pump, replace the bolt with the short version to seal the hole and tighten everything up. :bow:
 
ok so it likes to sart now and run like its at half throttle, to fast to put it in gear or anything like that, and adjusting the screws seems to have no efect at all? :doah: so i want to try staring from scratch on the adjustments, where should i start the screws at, and what increments should i adjust them in and in wich order ect. i know how i should do it in theory :rolleyes: .......but like i said it didnt seem to have any affect. also i am replacing all the soft lines today to see if that does anything.
 
ok so i got it running pretty good now, not where i want it but pretty good, but now when i shift into drive and L2 it doesnt move :mad: , just revs up. but reverse and L1 work fine :confused:. so is my tranny fried or is there something i can do to fix this? im sure that letting it sit for over a month didnt help the th350 tranny.
 
Read another post...

Read the post on page 1 titled "Help Me Please!" by a poster named "Prime"--I told him about the govenor gear possibly being stripped in his tranny,which has the same symptoms yours has...might be your problem too.. :crazy:
 
ok, so i found out that when i was towing my k5 home from my fuel system problem my girlfriend unintentionally shifted the truck from N to park and then back right away :eek1: becuase it made " a silly noise " :doah: while coasting to a stop uphill at about 5- 10 miles per hour, i am going to try the governer gear replacement that you suggested. so the question is, is it screwed inlight of this new finding or could the nylon gear still be the culpret? :confused:
 
I am having the exact same problem you are - currently stranded in Utah. Mine is at a shop now - I'll post up what they find. Maybe it'll help.

For the record, the list of possible casues are:

Vacuum lines
accelerator pump
fuel filter
fuel pump
tranny governor (from post above - going to check that one myself - just had some tranny maintenance done, maybe they messed something up)
soft fuel lines
hard fuel lines
float
ignition system

Did I miss anything? (Maybe we could make this into a tech article for diagnosis)

BTW I've already replaced the fuel pump, fuel filters. No apparent vac leaks... and my truck is still messed up.
 
lol, tech article indeed. i readjusted the carb on mine and the floats and changed the fuel filter and pump and now it runs ALOT better i also changed the soft lines but that was just to keep ahead of the game. the carb was the issue for me, i think it had a stuck float.
 
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