Hey guys and girls 8 recently noticed oil leaking from the lower intake manifold on my 99jimmy. Figured since the engine had been rebuilt prior to swapping it from my totaled blazer it had most likely been dealt with already but no i figured meh its a common blazer issue so ill just reseal and carry on. Once I removed the intake I noticed that the spider was the old style cpi and not the mpfi. Checked the ruined original 4.3 that i pulled from the jimmy to find a newer version injector and i installed it hoping id luck out however that's usually not the case for me. It seems to be filling the cylinders with fuel i dont have the distributor back in yet so im guessing the injectors arent being fired and they're leaking the prime pressure when i turn the key on. Anyone have experience repairing a leaky spider?

 

96 thru mid-02 were SCFI not CPI, but I digress.

Repair depends on what's leaking. You really should pull the upper plenum off and reinstall the lines again, then pressurize the system with the injectors all out of their respective ports to see where it is coming from. If it is just a single injector that is stuck open, then you can get replacements, but if two or more are stuck, then I would recommend a new MFI spider. The FPR can also be replaced if it is leaking, but on the SCFI/MFI spiders, the FPR is rarely at fault in these cases.

Until you get into it and determine the source of the leak, we can only guess as to what it is.

IMO, I would never put a used spider into one of these engines. Given the amount of time/effort needed to get down to it, it just isn't worth my time to do so. New, reputable parts only.

 

Appreciate the reply and pulling the upper back of isnt that big of a deal guess ill pull the plugs and evacuate the fuel then see what is leaking under pressure

 

In general, if You can imagine an electrovalve, that has a liquid input and its coil, that opens the valve when You apply the power and shuts when unpowered, then You know how to conduct testing/cleaning of a spider assembly. The only complexity lays within it's a set of six electrovalves in one box rather than one, separate unit.

 

Once re-assembled as recommended there is a test for the balance of fuel quantity from each injector using a fixed pulse box and fuel pressure gauge if you are so inclined.

George

 

Just so i dont go making assumptions about the operation of this fuel system the injectors are fire based on the cam position sensor in the distributor correct?

 

The crank position sensor is used for injector & spark timing.

One thing worth mentioning is that the injectors receive +12V at all times. The PCM sends a pulse-width modulated (PWM) ground signal to the injectors to get the desired amount of open time to meet the fuel demands of the engine at any given time.If somehow you have grounded one or more of the injectors out (damaged wiring harness, etc), it could cause fuel to flow whenever the system is pressurized.

 

Thanks thats what I needed to hear was really hoping th distributor sent the signalfr the injectors to fire since there is not currently a distributor installed

 

.. and the quantity of fuel based on the ground pulse width is first determined by a fixed pcm program based on sensor input when the engine is cold (open loop) but switches to fuel quantity based on the O2 sensors which try to keep the air fuel mixture ideal at 14:1 which keeps emissions at a minimum (closed loop) when the engine and sensors are warm.

George

 

Simplifying things in regards to the above, You may hardwire one side of the coils to the positive +12V battery line. Then, You may tie the other ends together and apply the negative power line to have them opened. If You direct the nozzles into a set of 6 glasses, then You may compare if they spray same amount over time. With this manner You don't need any source of PWM pulse generator....