The truck is a '93 Blazer with a CPI Vortec with 225k on it. I've been through the usual injector replacement, once at 110k, and again at 220 just this last June.

The last failure began as a bog at about 30mph after a normal takeoff from a stop. Anything more than around 20% throttle would result in a bog, even more throttle would produce a mild backfire. Less than 20% throttle, it would accelerate and shift normally. It idled perfect. After a week or so it also developed an occasional no start condition. It would eventually start after about a minute of off and on cranking.

Nothing significant showed up on the scanner and the only trouble codes that came up were probably caused by the bog and backfire. Fuel pressure was 54-61psi running and no leakdown with the engine off, a timing light showed spark even through the "bog". In neutral there was only a hint of a miss at around 2500rpm and up.
I keep some spare parts around so I started swapping. Module, MAP, TPS, IAC, coil, nothing. The only thing out of the ordinary was that the plugs had the extra white "lean running" look to them.
I ordered a Spider.
Pulling the plenum, there were no leaks. I replaced it. Ran perfect.

Until now, 4 months later.
The same exact problem even with the "no start" showing up a week or so later. I pulled the plenum and started checking the electrical connection at the injector. It's a brittle plastic piece that locks in place but looking into the contacts area it seemed as though they were spread a bit wide to be able to clamp tightly onto the electrical pins that come out of the injector. Using a miniature screwdriver I bent the clamping tabs inward to get a good connection when it snapped onto the pins. Put it back together and it's been running perfect ever since.

After going through this, I think there might be a simpler way to check for this condition. The "red and blue" wires for the injector exit through a 1" grommet at the front of the intake manifold about 5" below the MAP sensor. You can reach them with a pair of needle nose pliers without removing anything. Pulling on the wires will take up some of the slack inside the manifold. When you feel it tighten up give a light tug on one wire. This will give the connector some rotation and jam the connection enough to possibly see a change in running condition. Don't worry about pulling the wire out of the connector, I already tried that with full force when it was apart and it didn't budge.

I imagine this is more likely to happen on higher mileage vehicles but it makes me wonder, maybe the 92 to 95 CPI injectors aren't the only ones to get bad connections.

Hope this helps.

Great post, great information, great tip! One thing to note, GM factory spec for fuel pressure test on CMFI and CSFI is 60psi to 66psi, cold engine, pump running, engine off.

Thanks old master, I appreciate it.
As for the fuel pressure, I wanted to include the highest and lowest readings I saw for accuracy, but to elaborate, yes, the key on engine off pressure was 61psi. Engine idle in gear was 57 to 61psi with a bounce down to 54 on deceleration, if I remember correctly.

I can understand the accuracy thing. GM does not publish engine running fuel pressure. All fuel pressure readings are made with a cold engine, while the engine is off. The reason they specify cold engine is the same reason tire pressure is checked cold... no temperature influences other than ambient. Heat radiating from a warm engine will increase the temperature of the fuel which will increase the pressure. When checking for pressure leakdown, it's very important that fuel temperature stays constant so you can achieve an accurate reading for several minutes.

I understand,
In my post I wasn’t trying to show whether the fuel pump was within spec but rather the pressures were within poppet nozzle operation spec throughout the important part, the run and bog. Static pressure wouldn't have been conclusive in this case.
I tried to keep it Short and Sweet but I guess that can get confusing sometimes too, eh?

Chilton; Min.51psi
Chilton; 55 to 61psi
Haynes; Min.52psi
Haynes; 54 to 64psi

I imagine "Factory" has different numbers?

Not sure where Chilton and Haynes get their information, they're both wrong! GM factory shop manual specifies 60psi to 66psi. Anything less than 59psi can give hard/no starting and hesitation/stumble etc. Leakdown, 3 to 5 minutes after the pump shuts down, must remain above 55psi.

The numbers are poppet nozzle requirement not fuel pump.

I went through about 6 months of heartache on my '94 Astro CMPFI spider unit- with the electrical connectors not making good contact-(same engine as yours). The red and blue wires do get brittle- the wire into the plastic harness on top of the spider was holding on only by a thread- took me several times- and lots of "tow homes" to finally figure out what was going on- Dealer wanted $87 for the wiring harness- I made my own eventually- and finally curred the problem- I'll bet I had that upper plenum off and on a dozen times- I ran new wires all the way back to the connector outside the plenum- and fashioned new contacts on the spider-- there is really no good way to test for good electrical contact under that upper plenum-- just my thoughts....

$87, I figured they would want a lot for that harness.
You’re right, there is no good way to test it. I did do a continuity test on it but it would have tested good if it were hanging by one strand. Also, I put a big tie wrap around the injector and connector to help keep the vibration down, maybe that will help. I really don’t see having a problem with it anymore but I’ll still grab a spare next time I’m at the salvage yard.
At what mileage did your harness go out?

Good job on the 335,000

Wow this is just great ive, been haveing the same prob on my Blaze 93 CPI with bogs and idleing like crap,replaced nut kit because of leaks and FPR,all Ignition realted checks out. But those darn coneectors i never even though of them being the problem at all. Thanks ill be checking them ASAP

Autozone.com has the connector for $9.