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Discussion Starter · #1 ·
i have a 1992 4.3 cpi(w) in a 4 door blazer.the problem:hard to start sometimes,rough/drop in idle,misfire when increased rpm but smooths out past 3k rpm(guess) and when driving i have the occasional misfire and what sounds like a valve rattle.plus idle will drop sometimes when put into gear.what i have done to try to fix:replaced fuel filter,dropped and cleaned fuel tank,replaced fuel pump sock(prefilter or whatever you want to call it),drained and replaced gas,also ran fuel injector cleaner threw it before dropping tank,new dist. cap and rotor button,new spark plugs and wires,changed out distributer with a used one i had the looked like it was in better shape,cleaned up a used egr valve and put it on(one off the motor didnt look bad),reset timing and adjusted timing and this whole time no codes are being thrown. the motor is out of a junk yard.had to replace it and money only allowed a used motor.came out of a 93 blazer.ran like a top and passed emissions with flying colors.when i swapped motors i kept the old intake and distributer.so i have spare sensors on the old intake.but my old (blown) motor had over 200k mile on it. i know this is a lot.if you made it this far i thank you alot.i need all the help i can get.money is a big problem for me.so i need to properly fix the problem with out spending money i dont really have.thank again for any help!
 

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i saw what you did there!
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fire it up when dark out

look for any arc anywhere around wire boots at plugs or at distrib towers

sounds liek spark leak to me

exactly like it

been through this one before


always smooths out higher rpm dont notice it so much
 

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CPI Motor:

Check the fuel pressure. If it's too low, it can cause the problems you are experiencing.
 

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Start with grounds and fuel pressure, those CPI motors have a lot of fuel related driveability issues.
Side note:
Since you dropped the tank, did you remove the pulsator and replace it with a piece of rubber fuel hose? These are notorious for causing fuel issues.
 

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Discussion Starter · #5 ·
no i didnt replace the pulsator.i knew nothing about it until last night from searching the forum.i did check the vacuum with a compound meter last night.it stayed in the green thats 43-56cm hg vac.i dont know exactly which hoses to test it on.can i use the same meter to test fuel pressure?it does have readings for fuel pump pressure.if i can how do i?i have never use meters/tester like this before. and i can disconnect the pcv valve line or brake buster line and it seems to run a little better.thanks for all the help.this is my first time owning and doing major work on a obd 1 vehicle.
 

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How high does the meter read in PSI? it will need to at least be able to read to 70psi.
 

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Discussion Starter · #7 ·
it goes up to 10 psig dont know what the g stands for im new to this vacuum meter.and thanks to everyone that has posted.every little things helps and i greatly appreciated!
 

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It needs to read in pressure not vacuum. Unless you gage reads both, which I have never seen, but it's possible.

You can rent a fuel pressure gage from Autozone or Pep Boys for free. You just have to put down a deposit.
 

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Discussion Starter · #9 ·
i rented one.idle reading of 51-52 psi,eased on gas it would go up to 54-56 psi and drop back down to 51-52 psi.getting on the gas real good would make it spike to 58-60 psi then drop back down to 51-52.all while keeping on the gas.if i gave it gas and let off i would peak up then drop to 49 psi before returning to idle then back to 51-52 psi.when the engine would start to sputter and misfire it would rise up to the 58-60 psi range.
 

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Spec is 54-64 PSI(KOEO), so I'm gonna say your gauge is +/- 2 PSI. So I would not throw a fuel pump at it for sure.
You would kinda have a hard time diagnosing the regulator without another special tool, except pulling it out and looking to see if it has fuel inside the body on the wrong side.
But the regulator on that set up is not the same regular vacuum style, it uses pressure in the intake manifold to regulate the PSI. I am not sure if you could even check it. But the PSI is going up and down with engine speed so I would say the regulator is fine.
Did you observe the holding pressure?
You could also do a quick fuel pump volume test, just so you were sure. The pump should be capable of 1ltr. for 30 seconds of on time.
But I would probably go down the injector route, again, observe holding pressure for five minutes or so roughly.

Another thing to check is the resistance of that single injector.
Ohm spec is 1.3 ohms.
 

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Discussion Starter · #13 ·
holding pressure was in the 51-52 psi range.the gauge looked pretty new.i did rent it from autozone.it did hold that psi very steady and only changed with acceleration/decel.how would i check the injector on the cpi spider?and thanks for all the help!a lot!!
 

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Pull the "Vortec" cover off, and remove IMTV (intake manifold tuning valve) It's a round plug right in the center of the plenum. It's retained with 2 T-30 screws.


Then look down the hole into the plenum for pooling fuel or a clean washed looking intake. It should be all black and carboned up, if it's shiny and clean on one side or the other, the spider is leaking/spraying fuel inside the plenum. That would (usually) require replacing the spider assembly.

Search for "Spider Assembly" or "Nut Kit" Yes a nut kit. I'm not being funny :haha:
 
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