Vortec 4.3L W CPI Injector Spider

I have a 92 S15 Jimmy that will not start - fuel problem. Before I go out and buy a brand new CPI Spider (or junk the Jimmy) I thought I would see if
any one could provide me with a method to actually check that the CPI itself is functioning. Right now I have the upper manifold off. I have a 60psi fuel pressure reading. Prior to actualling buying a pressue gauge, I tried to "shotgun" the problem (changed fuel pump and fuel filter). Tried to "hotwire" injector using a battery charger, saw no fuel coming out of poppet. Bought a used CPI on Ebay (came without the poppets - had to swap in old ones). Again tried to "hotwire" CPI, plenty of "clicking" but no spray.
Could I have fried CPIs by hotwiring? Do the poppets actually need to have intake vacuum to spray (i.e. do I really need to put everything back together and try to start it)? Has anyone actually seen the poppets spray either by "hotwiring" or by letting the ECM do it? Thanks
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Most certainly, yes.

Do you have a signal at the injector?
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So you are saying that I cannot manually fire the injector (and see the poppet spray gas) by only energizing the injector, that I actually need the engine vacuum to create a higher "effective" PSI in order for the poppets to open? Are you absolutely sure about this?

While I currently only have a Digital Voltmeter, it did have a fluctuating reading (implying a cycling of 12V?).
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110% sure. There has to be a pressure differential at the poppet for the poppet to open. The pressure differential from the individual intake valve opening is what makes this injector design -act- like a sequential injection system.

A 12 volt test light will work fine here.
Sounds like you have stuck poppets, you can either try flushing them with carb spray or replace the whole CPI with a remanufactured one from Linder Tech. http://www.lindertech.com/reconinj.htm
I'd recommend their part # CPI-200 which comes with a remanufactured CPI, upper plenum gasket, internal fuel lines (nut kit) and Kleen Screen EGR gasket.
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aarcuda69062 wrote:

DonW - As I am working on this problem, I have a pressure gauge always hooked up to the Schrader(?) valve on the fuel intake line. There is always 58 - 60 psi when I try to get the injector to fire. It goes up to about 62 when cranking and shows that I do not have a massive leak somewhere (although pressure goes down while sitting, it is on the order of many minutes not seconds).
aarcuda69062 - I am a bit confused by your response. First , only one poppet opening would reduce the pressure available to the other poppets. The injector would have to be energized every time one of the six intake valves was being opened. This seems to go against the general information that I have read that the injector fires once for all six cylinders. Second, "stuck poppets"? Like I said, I have replaced my original CPI with a used CPI body and my old poppets. One stuck poppet OK, but all 6? Like I said, I currently have the upper plenum off and would like to check this used / spliced CPI before I put everything back together. If like you originally said, the unit won't spray until everything is back together, fine. But, if you are just offering your honest opinion as to how the CPI "should" work, without actually having first hand knowledge, please let me know.
Thanks
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The poppet valves work using engine vacuum to signal which one opens. The injector itself triggers every time BUT without the vacuum on the poppet it will not open. Think about how the engine works, IF the injector fired fuel into every cylinder every time it triggered you would flood out the engine. Instead the injector fires, the poppet that is sensing a vacuum draw from the intake valve below it opens and the fuel gets sprayed into the bore. The others stay closed while this occurs. Then the cycle repeats in firing order.
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The info I have is for a 93 code W but should be the same. The CPI unit is "fired" through a grounding circuit controlled by the ECM. Constant ignition voltage is supplied to one side while the other is grounded through the ECM. Once the unit draws 4 amps the ECM will limit the current to 1 amp for the duration of the injector on time. The coil resistance was listed at 1.5 ohms. I don't know the process you used to hotwire the unit. My info also cautions NOT to try to start the engine with the upper manifold off. I didn't see anything suggesting manifold vacuum was needed for the injector to fire. HTH.
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DonW wrote:

My "hotwire" technique was to place a 6A, 12V battery charger across the injector and softly plugged the AC cord in/out of a 120V outlet. I could hear the CPI "click-click-click" as I quickly jiggled the AC cord to try to mimic rapid energizing and de-energizing of the CPI. I did not try to start the engine with the upper manifold off, but did go through several crankings (with the coil - distributor wire grounded) to see if I could get "spray" out of a couple of poppets that were not inserted into their manifold holes.
I really want to believe that just putting it back together (putting upper manifold back on) will allow my used / spliced CPI to function properly. But I would really like to see it spray first. I only have this one last crack at this vehicle. I have been dinking with it for a couple of months now and my wife wants her garage space back, plus it really has been a time / money hole. The original idea was to fix it and sell it for a few $$ instead of calling the bone yard, now I wish I had just had it towed away when it first died.
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What might be happening is without the engine running, the fuel pump only runs a couple seconds and shuts off. So you may not be maintaining pressure at the injector. Fuel will only flow thru the poppet nozzle until the pressure is 37-43 psi. Somewhere there should be a "fuel pump test connector". On my 95 it's a red lead located along the inside of the left fender and adjacent to the power brake booster. Has a single connector that doesn't go anywhere. You can energize the fuel pump by connecting this lead to a +12v source. You should hear the pump running. If it is putting out the 60psi as you say, I don't know why your test setup shouldn't work and spray fuel.
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DonW - Sorry for repeating myself, but this is my first time on a forum and I combined a reply to you with another reply thinking that it would show up at the end of chain of messages since it was the most recent post - it didn't.
DonW - As I am working on this problem, I have a pressure gauge always hooked up to the Schrader(?) valve on the fuel intake line. There is always 58 - 60 psi when I try to get the injector to fire. It goes up to about 62 when cranking and also shows that I do not have a massive leak somewhere (although pressure goes down while sitting, it is on the order of many minutes not seconds). I would tend to agree with you that if everything is OK, the poppets should spray when I energize the injector. Probably would have been better off buying a complete new CPI and not "testing" it. Thanks
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Finally fixed it - Bought another used CPI on Ebay and did not try to test it with a power supply or battery charger. Instead I installed it (hooked up fuel lines and electrical connector) and left all the poppets out (so that they were visible). With the coil - distributor cable grounded, I cranked the engine. First a couple of poppets sprayed. Next time, a couple more. Next time, all six poppets sprayed.
Lessons learned, don't believe everything you read on the web (too many EXPERTS) and don't "test" without knowing exactly what you are dealing with. I believe I screwed up the first injector that I bought by "testing" it.
Bottom line - the poppets will visibly spray (even without the upper plenum being put back on) if everything is working right. Thanks
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