Hi, I have a 1995 W-code Blazer with the CMFI (CPI?) setup. I'm replacing the lower intake manifold gasket in the hopes that it will fix a really bad bouncing cold idle. It fluctuates a bit when warm too, but nowhere close to what it does when first starting up. I've pulled off the plenum, and everything is covered with carbon except for a small area on the rear passenger's side; there is some pooled gas there as well. Since I have everything pulled apart, I was thinking about replacing the spider assembly since the engine has 190k on it and somebody was mentioning that maybe a leaky regulator or spider assembly could be causing my problems.

What I want to know is if the MFI conversion is available for the CMFI/CPI system or if that is only available for the CSFI system.

 

The MFI upgrade is for the newer SCFI system only.

 

1995 GMC Jimmy 4wd 4.3L cmfi

Suspect CMFI spider unit has totally died. I can monitor 12v pulses at the wiring connector of the spider unit during crank. The unit's resistance measurement is ok according to Haynes. I do not get any fuel out if the injectors.

Do you have any suggestions. ?
Is this unit really bad. ?

Cferr7

 

As was said above, the MFI upgrade does not apply to 1995 and earlier CPI engines. You do not have CMFI (central multi-port fuel injection), rather CPI (central port injection). CPI uses a single maxi-injector to feed six individual pressure activated poppet nozzles in a batch fire configuration. As such, there is only one power and one ground wire to the injection system.

The later SCFI engines (1996 thru mid-2002) have six individual electronic injectors feeding six pressure activated poppet nozzles. Since there are six injectors, there are also six individual power and ground wires. This is where the upgrade to the Vin X MFI spider comes in. The later spider moves the injectors down to the intake runners, replacing/removing the often problematic pressure activated poppet nozzles.

With a CPI engine, your only option is to replace the CPI spider and the 'nut kit' (internal fuel lines) with new quality replacement parts.

As to your problem, have you verified fuel pressure is >55psi with the key-on, engine-off? If it is not >55psi, the pressure activated poppet nozzles will not open when the maxi-injector opens.