95 Jimmy 4.3 Vortec starting problems - weird

[batkoach]

as far as durability goes a CPI has only one injector and a cmpi has 6 micro injectors. either way if the cpi injector goes bad or just one of the micro injectors goes bad you still have to change the CPi or CMPI as the micro injectors and not replacable sperately. once you solve your concern you will be happy with your CPI again.

[rlith]

The nice thing about using the newer style MPFI kit on the 96+ though is that you can replace individual injectors.

[wb8yjf]

So what I "think" I'm hearing, the CPI has one injector, and the spider assy. is delivering the fuel to the cylinders...all at once? Is that right? I replaced the regulator on the injector...now I'm all confused... Damn, I miss the old style engines....

[rlith]

Originally Posted by wb8yjf

So what I "think" I'm hearing, the CPI has one injector, and the spider assy. is delivering the fuel to the cylinders...all at once? Is that right? I replaced the regulator on the injector...now I'm all confused... Damn, I miss the old style engines....

Correct,the CPI (92-95) Is a batch fired system...

[Megs1082]

Originally Posted by batkoach

yes from your pix this is a CPI unit. if it was starting with a jump but not on its own with a new battery there is a possibility you are drawing to much current and the voltage is dropping down to around 10 to 9 volts during cranking and the computer will not function when voltage drops this low there for no fuel injection however you may still get spark because it starts with the ignition module then switches to bypass for computed timing once the truck starts. check with a vat-40 tester if possible or two meters to check amp draw and how low voltage goes when cranking and if it is dropping to the voltages above ( around 9 to 10 volts0 then your starter is drawing to much current . a normal starter should draw between 125 and 175 amps. if more and volts dropping then this would explain why is starts with a jump as it is getting the additional ampsand voltage from your wifes truck.at this point replace the starter. if this checks ok then the test for the cpi is as follows . check fuel pressure if between 55 to 60 psi with key on engine off this is normal then you will need to do a fuel volume test . most quality gauges have this. there will be a small dia. hose with a valve coming off the gauge. get a 1 QT motor oil bottle with the see through edge and place hose in bottle and disconnect primary connector at ignition coil and have someone crank engine. with a watch time the fuel going into the bottle for 30 seconds . in 30 sec's normal volume should always be 1 pint or 1/2 a qt. if this is what you have replace your CPI . if you have the pressure but insufficent volume then your regulator is working and you will need to replace your fuel filter and if that does not work your fuel pump is done. thanks for listening, john harrier 20 year master machanic in michigan.

Guys,

My problem on the 1993 Jimmy isn't fixed. I replaced the regulator and it still won't start. I tried a couple more things I need to report on.

Batkoach- I appreciate your advice so far - read what I've tested here and see if you can offer any further direction.

I took a voltmeter and checked the voltage at the battery when the car is trying to start. It never drops below 11 volts and the battery sits normally at 12.4ish. The reason I checked this is that one guy said when the starters begin wearing out they suck up a lot more amperage - if they suck up too much amperage they will drop the voltage on the battery. If the battery voltage drops to less than 9 or 10 volts sometimes the computer won't function right and so it won't start because the computer is not acting correctly - This would explain why the car runs good when it actually is running because the battery is at 14.4 volts and so supplying enough juice to let the computer run perfectly. ALAS, this is not my problem nor a fix because my voltage never drops below 11 volts.

I checked a couple other things. Someone suggest a fuel pump volume test. They said the fuel pump here should put out about 1 quart of gas in 30 seconds. I'm not sure how scientific my test of this was because I'm not sure that the schrader valve/pressure fuel gauge release button allows full flow, but I tried this and let the car try to start with the fuel pressure gauge attached to the schrader valve and the bypass hose hooked up. I only gathered 10 ounces in 30 seconds. LIke I said, I'm not sure this is accurate because I don't know if the bleed valve on the fuel pressure gauge is of a diameter to let full flow out, BUT that 10 ounces is low compared to the 32 ounces it should have????.

3rd test -- Someone else said that I should find a point along the fuel lines with rubber hose. Turn the key to the ignition point (1 click shy of starting to where the pressure builds, and then turn off the key. Then pinch the hose and have another person check the fuel pressure at the shcrader valve. If the pressure remains the same at the valve you aren't leaking on the engine/injector side, and if it drops you are. Likewise, after a couple minutes, when you release the pinch, if the fuel pressure at the guage drops really low it means the pump isn't holding pressure in the tank. This is what happened. I pinched the line when the pressure guage read 57. I held for two minutes. The line pressure dropped to about 56.5. I released the pinch after about 2 minutes and the pressure dropped to 30ish PSI. That seems to point to a bad/dying fuel pump???

Do you guys agree? Any other tests I can preform to verify it is a pump before I drop the tank? What else should I replace besides the fuel pump while I've got the tank dropped?

[ZR2Stepside]

I have had several of the CPI systems, and even though they have one common injector that pressures the poppet valves, vacuum from the intake cycle is required to open each poppet valve. Thus, it is a effectively a simply smart sequential system.
I learned this while trying to clean and test a CPI (spider) poppet valve. I had a mock up of a pressurized system using air pressure regulator and sea foam in the poppet tube. I could not get fuel through any nozzle until I applied air pressure through a venturi creating a vacuum to the exit of the poppet valve. Also sea foam had to be diluted with fuel to exit the nozzle.

[maxwedge]

Welcome to AF. Good info but look at the date of the last post, this is dead for 4 years.

[savannaz34]

This is the exact same thing that my 94 4.3w is doing. When I saw this thread I got excited, because I was hoping someone found a remedy to the no start issue. Then to see it wasn't,is quite sad. 2006 lol. Does anyone know this guy personally? To maybe ask him what the prob was. And let the rest of the mechanics out there know. Thanks