Hey everybody.

i'm newto this forum and this is my first post. i just bought a 94 blazer for my girlfriend's nieces' mom... long story lol. But anyway, this Blazer has the vortec 4.3 that is hard to start, runs rough at idle and if you snap the throttle wide open it falls flat on its face... butif you gradually rev it its fine or if you spray carb cleaner in the throttle body it revs fine. The following parts have been replaced before i got the truck the other day: Plugs, wires, EGR, fuel filter, and MAP sensor. In a little bit im going to run to auto zone to get a fuel pressure tester. i think i have narrowed it down to either the fuel pressure regulator, the fuel pump, or the spider injector. I got such a good deal on the truck i just couldn't pass it up and it would be perfect for the girl and her kids. Any thoughts? any help would be appreciated.

 

[sm=welcomesign.gif]to the Forum, and I agree that a fuel pressure test is in order.

 

Yeah fuel pressure test. Keep us posted on this as well I'm curious on fixes your issue.

 

Ok so i went out and got a fuel pressure gauge and hooked it up as the service manual says, turned the key to the on position and i get 55psi... just as the manual says. So i start it up and let it run for a bit and the rough idle goes away and it seems to be running pretty good. i give it gas and it revs to about 3000 rpm where it seems to run out of fuel. it holds pretty steady at 3000 at wide open throttle while popping and spitting through the intake. Then something else pretty interesting happened, it randomly died, 3 times. so then i start it back up and look at the fuel pressure gauge and it reads around 40-45 and when you hold it at wide open throttle and sometimes bounces up to 60. Another thing that happened as i was backing out of the garage was that it cut out a couple seconds after i put it in gear. Any ideas?

 

How many miles are on it? Mine was doing the same thing and it ended up being a leaky internal return line. Take the upper manifold off (it's easy) and check for leaks inside there and pools of fuel. If you need to replace something in there here's the place to go...

http://www.lindertech.com/reconinj.htm

If you have the extra coin it might be a good idea to get the entire kit and replace it all at once. Also, that inverted torx screw that holds the plate for the fuel lines was seized on mine. So prepare for battle and soak that f*cker down with PB blaster first.

Hope this helps and good luck!

 

The fuel pressure needs to be over 52psi for proper operation.

What does the fuel pressure do after you turn the truck off?

 

The truck has 190K miles on it. When the truck shuts off the fuel pressure drops off quickly, as if the injectorsare dumping fuel.I actually have another identical 94 with 50K at a friends house,I am going to go grab it and compare fuel pressures while running.

 

fuel pressure while running isnt the cause for concern from what i see the quick bleed down with the key off is. In your original post you said it runs fine if you spray carb cleaner in the throttle body (used in less than 1% of these trucks in 94) but you also mentioned the spider injectors so without knowing for sure which you have im going to assume its the cpi engine since its the common one pop off the upper plenum and look for clean areas this will tell you which is leaking for sure fpr or spider and just in case im right in assuming its a cpi engine check out this link for more detailed info (including pics) of the repair, hope it helps! http://www.automotiveforums.com/vbul...d.php?t=473110

 

ok i messed with it more today and for ****s and giggles i replaced the fuel pressure regulator. that seemed to clear up thehard starting and the little miss i had. while i had the upper plenum off i popped all of the injectors out to see if any of them were bleeding down when the key was on. nothing. not a drop. so then i decided to compare fuel pressures when i got it all back together. my friendsjimmy with the key on but not running has 60psi and does not bleed down. Then when its running fuel pressure is at about 52-54 at idle and jumps to about 60-62 when you rev it compared to the 56 psi when the key is onand48 when its running on my blazer. another thing i noticed was that when i had the battery charger hooked to it it seemed to be fine, which led me to believe that maybe the alternator wasn't putting out enough amperage under a load. so i went and picked up an alternator and checked and cleaned the cables and even replaced the ground cable with the one that is on my s10. still doing the same thing... we even went a step further and took the coil off the other 94 jimmy and swapped them just to check another thing off the list. so now i think i narrowed it down to the fuel system bleeding down after the pump cuts off. what could be causing this? could the fuel pump be bad?

 

generally its the fuel pressure regulator or the spider itself leaking that causes it to bleed down with the key off, you said you just replaced the fpr so thats likely not the cause, any clean areas on driver side that you noticed when you had the upper plenum off? Other than that i'd say take a real hard look at your fuel lines just to eliminate the possibility of a leak even a small one, pay special attention to the nut kit a bad o-ring at that connection can cause a leak too. Good luck.