HI everyone,i've really only have one issue with my 93 s10 blazer 4x4 (4.3l vortec cpi) its running kinda bad i've changed tps,map,both knock sensors,o2 sensor,cleaned egr,and done all other routine maintance.the problem:when i start the truck it revs up and down and when i throttle it up in rpms it smoothes as soon as i let off revs up and down and only about once a week sputters pretty bad but give it gas smoothes out.and i do have quite a bit of black soot coming out of tail pipe.i checked codes shows 12,13-o2 sensor right.most of the time it runs pretty good.once in a while it smells like sulfur.i have pretty good exhuast flow.if anyone can help would be happy.thanks

 

I would start by testing your fuel pressure. Sounds like you are getting too much fuel into the engine which is typically caused by a faulty fuel pressure regulator on the CPI motors, but could also be caused by a leaking 'nut kit' (internal fuel lines).

Test the pressure via the fuel pressure test port on the back of the intake plenum near the wiper motor. You will be specifically monitoring the pressure after you shut the key off. If it drops more than 2-3psi initially and continues to drop, you have a fuel leak.

 

thanks,for reponse i will try these ideas and get back as soon as possible.by doing the presure test will i be able to tell if its regulator or 'nut kit'.thanks agian.

 

No, you won't be able to tell what part it is without atleast pulling off the MTV (manifold tuning valve) located under the trim cover on the top of the intake. Once you have that out, you should be able to look down into the passenger side of the intake and see if you have pools of fuel. Now if it isn't that bad of a leak, it may not have pools of fuel... But if you notice that the fuel pressure is bleeding down, there is a leak somewhere.

 

do you know how much the 'nut kit' costs roughly?and what the oeart number is off hand?and should i be prepared to replace the lines there also?thank you for all of the help i usauly can figure stuff out on my own.but sometimes i need pros help.thanks agian.

 

Check out Lindertech.com. They have a whole kit or just the parts that are necessary. If you remove the CPI unit either for repair or replacement, you should replace the 'nut kit'. These lines don't like to be reassembled once they are disassembled...

Before you buy any parts, you may want to clean the TB, specifically the IAC valve. It could be something completely unrelated like the idle air control valve in the throttle body being dirty...

However, the CPI motor is known for internal fuel leaks and testing the fuel pressure is a good way to know for sure if you have fuel issues.

 

hi again,sorry i could not get back sooner but i had a few problems getting a fuel presure tester ended up having to buy one.but i did test it and it sits about 55psi but when i shut the key off the psi contiuosly drops to 0psi.it only takes about a second or two to drop to 0psi.so its most likely a fuel leak in the intake plenum somewhere?

 

I would say it is a pretty safe bet that it is internal to the plenum. You can either pull off the MTV (black plastic piece under the trim cover) or just crack off the upper plenum and repressurize the system.

 

how do i depressurize the system? and do you know how long it should take to replace the injector,fpr,nut kit?and thank you vary much for the help you givin me with my problem.

 

Seems like your system depressurizes itself in a few seconds... Shouldn't be something you need to worry about at this juncture.

Check out the instructions on Lindertech.com for the CPI regulator kit. This kit replaces the stock FPR with the 96+ SCFI FPR which is a much better design. I am betting that you have a faulty FPR, but it could also be the internal fuel lines ('nut kit'). Lindertech has a kit that has everything you need if you would rather replace the whole CPI spider. Regardless of which repair method you choose, you should replace the internal fuel lines whenever you do work on the injection system as they are known to become brittle and leak if moved during repair work to the CPI spider.

Hope this helps.