My wifes '94 Blazer S10(4.3L V6 CPI motor, 4X4 auto trans) stopped running while I was driving it. After I got it to the shop I tested it for spark, fuel, pulse at the injector etc...

Everything seemed to be working fine. This car has the CPI or CFI? Central fuel injection system with one injector under the intake that has a built in regulator and six spider arms that go one to each cylinder.

I pulled the upper intake off to check the CPI injector.

I used a 'noid lite' that shows pulse at the electrical connector on the injector, and I have excellent spark.

Fuel pressure is steady at 38-40 PSI. Fuel is coming into the injector but not getting to any of the nozzles at the end of the spider arms.

I pulled the return line from the CPI injector and left the fuel inlet line connected but I have noi fuel comming through the injector and back out to the return side. Also as stated before no fuel is reaching the nozzle end on any of the six spider arms.

After removing one of the spider arms from the CPI injector I turned on the key and had fuel coming out of that hole where the arm used to be.

After doing some research on this CPI system I found the fuel pump pressure should be between 54-64 PSI. If that is the correct pressure for the '94 CPI fuel injection system then my problem could be a bad fuel pump.

From my understanding, the built in regulator on the CPI unit uses a spring diaphram to regulate a constant fuel pressure of 54-64 PSI regardless of engine load. I also understood that the nozzle on each one of the spider arms has a spring or a ball valve in the end that must have adequate fuel pressure or it will not spray into the combustion chamber.

My question(s) are if my fuel pressure is only a constant 40 PSI then will the CPI system work or does it require 54-64 PSI. I would like to verify the fuel pressure for this vehicle. I may be incorrect about the 54-64 PSI.

I think she needs a new fuel pump but Is it strange that my fuel pressure stays a constant 40 psi? Can it be because of the rubber in the tank between the pump and line is cracked or rotted.

Thanks in advance, I'm on to work now will check later.

We had the CPI unit replaced in our '92 Jimmy for $800+.
It still runs like shit, but that's because it's 3/4 of a Chevy small-block V-8 with all the attendant valvestem oil leakage into the cylinders...

The only motor I've ever blown-up was a Chevy small-block and I wasn't the least bit sad to walk home!
I hate Chevy small-blocks.

You didn't replace any parts, correct?  reason I am asking, is 40lb is the rating for a 2.8 engine.   The 4.3(with cpi) should be 60-65.  (source s10forums.com)

You got those injectors out without cracking the plastic clips that hold them in??? that is quite impressive  generally they get so brittle that looking at the the wrong way will crack them

Also, when you pulled off the upper plenum, was there puddles of fuel in the bottom half?  This is a very common problem with this engine, causes many drivability problems.  What happens is the regulator (built into the cpi) leaks and dumps too much fuel into the air intake portion of the plenum.   If this was leaking, it could also cause your low fuel pressure, but I would think that it would be fairly noticable..   Look for shiny gold colored spots inside the plenum, this is a good indication of a leak as well.  

Wifes vehicle and YOU driving it?  why are you looking for a reason.  It's your fault, you were abusing it  instead of treating it like a Ladies car and it decided to mess with you.  They conspire against husbands.  

"I don't know, Mom, it ran fine for me and then he took it out and broke it."  "No, he's out there in the garage trying to fix it. " "Well he can fix things sometimes."  "No, Mom, I'm not going to bet how much it's going to cost at the dealership to get fixed."

Quoted: You didn't replace any parts, correct?  reason I am asking, is 40lb is the rating for a 2.8 engine.   The 4.3(with cpi) should be 60-65.  (source s10forums.com) You got those injectors out without cracking the plastic clips that hold them in??? that is quite impressive  generally they get so brittle that looking at the the wrong way will crack them Also, when you pulled off the upper plenum, was there puddles of fuel in the bottom half?  This is a very common problem with this engine, causes many drivability problems.  What happens is the regulator (built into the cpi) leaks and dumps too much fuel into the air intake portion of the plenum.   If this was leaking, it could also cause your low fuel pressure, but I would think that it would be fairly noticable..   Look for shiny gold colored spots inside the plenum, this is a good indication of a leak as well.

Thanks alot for the help, my apology for not responding sooner. I had to run out to work before I was late.

The only thing I changed was the CPI injector itself. I didn't put back the plenum yet because I still don't have any fuel spraying from the nozzle end of the spider arms. After reading your reply I am certain that the fuel pump must be going bad because it should be reading ~60PSI. The fuel filter is new and there are no restrictions in the line so I will probably drop the tank tonight after work and check the pump and the hose inside. I have seen that small hose split many times before resulting in low pressure, stalling, hard starting, and no starts.

Originally I suspected that the CPI injector went bad because I thought I had good fuel pressure coming into the CPI at 40PSI.  Now I see that it was not enough pressure. Luckily there was no sign of any fuel leak inside the manifold, it was dry. About a year ago I changed the two lines going into the CPI, through the back of the manifold. The car was flooding out like crazy, I had so much fuel in the crankcase and when I opened the plenum it was full of fuel! One of the fuel lines to the CPI had a small hole under the plenum. I should have changed the CPI injector back then, but it is rather expensive.

BTW, I did break off the tabs on at least one of the spider arms while removing the old CPI!

I'm glad you brought this up.  I have been having problems with my 94 Jimmy.  I paid $900 to get the injector replaced two years ago.  I have been haveing problems starting the truck.  My mechanic says it may need a new injector.  Thhe key word here is may.  I don't mind paying for the repair if the problem gets fixed but I am pissed that the work needs to be done again.  I think I am just going to trade the truck in.

Quoted: I'm glad you brought this up.  I have been having problems with my 94 Jimmy.  I paid $900 to get the injector replaced two years ago.  I have been haveing problems starting the truck.  My mechanic says it may need a new injector.  Thhe key word here is may.  I don't mind paying for the repair if the problem gets fixed but I am pissed that the work needs to be done again.  I think I am just going to trade the truck in.

There is a somewhat easy way to tell... (at least to tell if you have to take the top off the plenum to identify the leak)  If you take off the plastic "vortec" badge off the top of the plenum ( 2 torx screws) you will see a round black thing held in by 2 torx screws and a wiring harness attached (I am fairly sure this is an electric choke of some sort) Remove it, and use a flexible light (like a bore light) to look inside the plenum.  If you see any puddles, or if one side is ALOT cleaner than the other side, it is a good indication that you have to replace CPI or the Hose kit.

Quoted: Quoted: You didn't replace any parts, correct?  reason I am asking, is 40lb is the rating for a 2.8 engine.   The 4.3(with cpi) should be 60-65.  (source s10forums.com) You got those injectors out without cracking the plastic clips that hold them in??? that is quite impressive  generally they get so brittle that looking at the the wrong way will crack them Also, when you pulled off the upper plenum, was there puddles of fuel in the bottom half?  This is a very common problem with this engine, causes many drivability problems.  What happens is the regulator (built into the cpi) leaks and dumps too much fuel into the air intake portion of the plenum.   If this was leaking, it could also cause your low fuel pressure, but I would think that it would be fairly noticable..   Look for shiny gold colored spots inside the plenum, this is a good indication of a leak as well.   Thanks alot for the help, my apology for not responding sooner. I had to run out to work before I was late. The only thing I changed was the CPI injector itself. I didn't put back the plenum yet because I still don't have any fuel spraying from the nozzle end of the spider arms. After reading your reply I am certain that the fuel pump must be going bad because it should be reading ~60PSI. The fuel filter is new and there are no restrictions in the line so I will probably drop the tank tonight after work and check the pump and the hose inside. I have seen that small hose split many times before resulting in low pressure, stalling, hard starting, and no starts. Originally I suspected that the CPI injector went bad because I thought I had good fuel pressure coming into the CPI at 40PSI.  Now I see that it was not enough pressure. Luckily there was no sign of any fuel leak inside the manifold, it was dry. About a year ago I changed the two lines going into the CPI, through the back of the manifold. The car was flooding out like crazy, I had so much fuel in the crankcase and when I opened the plenum it was full of fuel! One of the fuel lines to the CPI had a small hole under the plenum. I should have changed the CPI injector back then, but it is rather expensive. BTW, I did break off the tabs on at least one of the spider arms while removing the old CPI! albums.photo.epson.com/j/View?u=4187335&a=31093200&p=68015110&Sequence=0

Let us know how you make out.

UPDATE There appears to be a dupe topic that accidentally got posted. I just found it today while looking to update this one. Thanks to all who replied to both threads, great answers!

The truck is running! I finally got time to change the fuel pump. The sending unit was also changed because it had rotted lines that would not seperate. I have a lot of experience breaking free rotted out lines, but there was no way these were coming off so I finally just cut them after a little while.

The old pump was severley shorted out, I haven't seen one like that in a long time. I had to take a few pics for this thread, you really have to see this one!. I am surprised it was able to maintain a constant 38-40PSI in it's condition, it kept running but iot just didn't have enough pressure to work with the CPI unit.

After  swapped the pump and sending unit, I put the plenum back on without even testing the CPI unit to see if the nozzles were going to spray. The fuel pump was so bad(Visually) that I had no question anymore that the trruck would run when I finished assembling it. I also did a L.O.F. change to clear the fuel out of the crankcase.

When everything was done, I  cranked her up. She started as soon as she had fuel pressure coming in, but quickly stalled. I forgot to set the timing, so I did that and she fired right up again, only this time she was running great. I let it run for about 30 minutes to clear out all the crap from cleaning the intake etc...

Total cost was just over $500, and I did all the labor myself and the parts were at our cost in the shop. The CPI unit alone was $310, Fuel Pump $65, Plenum gasket $8, Valve cover gaskets $12, and the Sending unit was around $125. I can't imagine the cost of doing this in another shop.

Thanks for all the replies and great information.(in both threads).

Pics:

dont ya just hate the fuel pump wiring looking like it want to catch on fire.

 
LOL MickeyMouse!

My wife would never get back in her truck if she ever saw those pics of the fuel pump.