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Struggling with a miss what type fuel delivery system do I have ?


scholzee
11-14-2007, 05:02 AM
1996 2 dr 4x4 Blazer 4.3L build date 5/96 VIN 1GNCT18W9TK209871. I do not see injectors, is it CPI ? could I ahve a leaking spider assembly. AC delco plugs, wires, cap and rotor 6 months old. I get code P0300 random multiple cylinder misfire. All help appreciated.

old_master
11-14-2007, 06:51 AM
Your engine has CPI. The system uses the "spider" assembly. There is a fuel pressure regulator, one fuel pressure line to the injector and one return line from the fuel pressure regulator called a "nut kit", and the injector assembly. All are located under the plenum. A fuel pressure test will tell you if the fuel delivery system is working properly. If there is a leak in the system, it can cause the P0300 to be set. It can also cause poor fuel mileage, possibly a fuel odor, hesitation, stalling, hard starting, and generally poor performance.

blazes9395
11-14-2007, 12:53 PM
OM, Scholzee, the '96's had CSFI, not CPI. The last year was '95 for CPI. The injectors are located in the middle, with tubes going to each cylinder. There is an update for this system that, gets rid of the nozzles that clog, causing a misfire, assuming of course, the mozzle is the problem in this case.

As what OM said, fuel pressure test is a must to start diagnosing this.

scholzee
11-14-2007, 02:10 PM
I have an accurate $50 pressure gauge with adapters specifically for fuel pressure testeing. My problem is seeing all kinds of specs from 50 PSI to 65 PSI and running not running etc. Anyone have definite specs for my vehicle, I am assumimng 60-65 psi, the pump is a NAPA model installed 6 months ago because the old ones connector to plug eclectrical connection failed. The new pump was installed and a new electrical connector soldered and shrinkwrapped to the harness. Thanks for the Help. If psi is low regulator, fuel filter ?

old_master
11-14-2007, 03:17 PM
GM light truck "W" code engines are all CPI. There are variations such as CMFI and CSFI, but all are CPI systems. http://service.gm.com/dealerworld/vincards/

There is a GM TSB, (00-06-04-003B) that deals with retro fitting a CSFI system back to a CMFI system.


Fuel pressure specs for all "W" engines: cold engine, pump running, engine off: 60 to 66psi.
Leakdown: Not to drop below 55psi after 3 to 5 minutes.

scholzee
11-19-2007, 05:40 AM
What do you make of these fuel pressure readings, pump is 6 months old from napa. Old pump quit because connector pin melted top of unit, a new pigtail connector was installed with the new pump. Key on prime jumps to 62 psi quickly to 58 psi and settles at 60 psi all in a second or so. At idle 52 psi 45mph 1700 rpm 57.5 psi, 70 mph 2000 rpm 59 psi. Truck always starts easy at first turn of key and idles smooth, miss occurs at acceleration and even sometimes at steady 70 mph. Miss comes and goes and is not always there, plugs cap roto wires done with ac delco 1 year ago.

old_master
11-19-2007, 03:42 PM
The only spec GM publishes in the "dealer issue" shop manual is with a cold engine, key on, engine off, 60 to 66psi, you're fine there, as long as leakdown is not excessive. It must remain above 55psi for 3 to 5 minutes. Does the SES light blink or stay on?

scholzee
11-19-2007, 05:03 PM
SES light has been steady and I feel the miss, it is getting worse and now sometimes blinks which I understand is a bad misfire and can damage converter. This is the latest dat non flashing ses.

P0300 Random/Multiple Cylinder Misfire Detected
Module: Igniton System Misfire
Status Stored
Freeze Frame
Air flow rate from mass air flow sensor 5.84 lb/min
Calculated load 22%
Coolant Temp 167 F
Engine RPM 2268
Fuel System status bank one Closed loop
Fuel system staus bank two Closed loop
Intake manifold absolute pressure 19.5 in.hg.
Long Term fuel trim bank one -1.56%
Long Term fuel trim bank two 3.12%
Short term fuel trim bank one -1.56%
Short term fule trim bank two 0.78%
Vehicle speed 70 MPH

I certianly appreciate your help and comments old master

old_master
11-19-2007, 07:03 PM
The right bank was rich when the DTC was set. It could have been from an ignition missfire, or it could have been fuel related (rich).

1) Check the fuel pressure again, just to clarify something for me. Cycle the fuel pump a few times and allow the fuel system to pressurize. Check pressure while the pump is running, engine off. Then check for leakdown: Must remain above 55psi for 3 to 5 minutes after the pump shuts down. Make sure the engine is cold so heat radiating from the engine does not affect the pressure.

2) Engine coolant temperature was at 167 degrees. If that's what the thermostat regulates the system at, it's too low. After checking fuel leakdown, start the engine and allow it to reach operating temperature. Connect the scan tool and check coolant temperature, (on the scan tool) while the engine is running.

Post your results.

scholzee
11-20-2007, 01:09 PM
Ok Old Master will do and post results, not sure if I will get to it before Thanksgiving but will continue to post. Enjoy the Holiday and Thank You for the advice.

scholzee
12-28-2007, 09:34 AM
Finally spent some serious time on my truck, truns out the rotor in my distributor cap was contacting 2 of the electrodes on the cap. The cap and rotor are AC Delco I put on about 1 year ago. Not sure what moved or changed since then. The truck has 240K on it, the distributor shaft is good with no obvious play or slop in it. the caps do not seem to fit on the housing all that well, seems like the slid around some, I centered it well and torqued it down good. I know the first place I will look if my miss comes back.

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