96 Blazer 1/2 Spark Plugs Dry

My 1996 Blazer has been sitting for several months. The only way I could get it to start was to pour a little fuel down the intake. After changing the fuel filter, it will idle but doesnt have any power.

After running for a few minutes notice the exhaust manifold on the driver side gets hot (good) the pasanger side is still cold (not good). Pulled 2 of the 3 spark plugs on the passanger side and they are dry.

I'm Getting P0300 - Random/Multiple Cylinder Misfire Detected

The fuel pump kicks in and gives pressure (measured 60+ but can't get the fitting on the pressure gauge from HF to fit tight enough to not leak. Makes testing the leak down pressure kinda tough).

What would starve 1/2 the cylinders of fuel?
Is this a symptom of a failed spider assembly?

P0300 is almost always caused by secondary ignition faults: Spark plugs, spark plug wires, distributor cap & rotor and the ignition coil. I would start with an AC Delco distributor cap and rotor, (don't waste your time or money on other brands). Put a dab of silicone dielectric grease on each terminal, inside and out, of the cap.

As for the fuel leak, try gently tightening the fitting to the test port with pliers. Sounds like the rubber seal in the tester isn't sealing all the way.

Got back to this POS after a few weeks, tried a new cap and rotor, no go. Put the originals back in, no go. Won't start at all unless I pour gas directly in the intake, then it runs untill the gas burns off and then stops. I'll check fuel pressure again, it was 60+ which is enough to start or so I have heard. Are we talking fuel pump, fuel regulator, spider, injectors all 6? I understand the spider is for drivability problems and not for starting problems?

If it starts with a shot of fuel, the ignition system is ok. Next step: Fuel pressure must remain above 60psi while the starter is engaged. Install your tester and double check it. If pressure remains above 60psi, remove the black plastic cover over the injectors to expose the back of the electrical connector. With the ignition in the RUN position, engine off, make sure all of the pink wires have battery voltage. Post your results.

old master, cudo's to your 4,360 posts.

After scouring this forum, I've read how important you say fuel pressure is. I've pasted some of your advice from other threads.

Other threads state that a '96 CSFI system requires 60 to 66 psi ... that's quite a range.

Then for a cold start, the system needs 63-64 lbs of fuel pressure to fire. They will not squirt fuel through the poppet valves if the system is 2-3 lbs low ... so 61 psi + is required to start.

I fixed the leak in my HF fuel injector pressure gauge (put a rubber O-Ring in the fitting).

It was about 35 F when I re-tested the fuel pressure.

Immediately
First turn after Pump Leak Down
Of the key stops Priming 5 min 10 min
1st Try 55 PSI 50 45 45
2nd Try 55 PSI 50 45 45
3rd Try 55 PSI 50 45 45

4th Try 59 PSI 52 48 48
5th Try 59 PSI 52 48 48
6th Try 59 PSI 52 48 48

Note: I watched the gauge as my sister turned key for the first 3 tries.
My sister read the gauge as I turned the key for the last 3 tries.

I didn't pinch off the return line at the rubber part to check full pressure. (Does this require removing the upper manifold)?
Later V6 GM engines should have 60-66 fuel pressure. (Is this pressure required to keep running)?
Cold start should be 64-65 lbs of pressure. (Is this for a 96 CSFI system)?
If you do not have full fuel pressure on a cold start (eg 2 psi low) the injectors will not squirt fuel (through the poppets)?
Do not (won't) leave home without it.
I did not have a fast leak down after shut off.

old master, do you advise replacing the fuel pump, sources, $200 ?

Well that didnt format very well
Fuel Pressure Results:
Leak Down
First turn Pump stops 5 min 10 min
1 55 PSI 50 45 45
2 55 PSI 50 45 45
3 55 PSI 50 45 45

4 59 PSI 52 48 48
5 59 PSI 52 48 48
6 59 PSI 52 48 48

Note: I watched gauge as sister turned key for the first 3 tries.
Sister read gauge as I turned the key for the next 3 tries

....Then for a cold start, the system needs 63-64 lbs of fuel pressure to fire. They will not squirt fuel through the poppet valves if the system is 2-3 lbs low ... so 61 psi + is required to start.

The factory spec for 1996 and newer 4.3L CSFI engines is 60psi to 66psi, anywhere in that range is acceptable. The fuel pressure regulator does exactly what the name implies... it regulates fuel pressure. Whatever the regulated pressure is set for, (at the factory) is the maximum pressure it will always regulate at, (it is not adjustable). For example: If key ON, engine OFF, pump running fuel pressure is 62psi, that is the maximum pressure it will ever achieve! Hot start, cold start or wide open throttle, doesn't matter, 62psi is it! There is a port on the regulator that is exposed to manifold vacuum. At idle, fuel demand is relatively low and manifold vacuum is high. Manifold vacuum pulls against spring pressure inside the regulator and causes operating pressure to drop to around 56psi, but it can vary significantly, that's why GM doesn't publish any "engine running" specs for the 4.3L.

The injectors are centrally located just behind the throttle body. The poppets are located at the intake ports and squirt fuel onto the back side of the intake valves. The poppet valve is spring loaded in the closed position and requires around 40psi of fuel pressure to overcome the spring pressure and squirt fuel.

Your fuel pressure at 55psi is too low. Leakdown appears to be OK taking into consideration the low fuel pressure.

...I didn't pinch off the return line at the rubber part to check full pressure. (Does this require removing the upper manifold)?



No, in fact, restricting the return line will rupture the diaphragm inside the fuel pressure regulator if pressure is allowed to rise above 75psi.


....Later V6 GM engines should have 60-66 fuel pressure. (Is this pressure required to keep running)?

60psi to 66psi is what is required to start and run properly. If it drops lower, a shot of carb spray helps get it running, but there will be driveability issues. Theoretically it will run if the poppets open and squirt fuel, but again, with driveability issues.

...old master, do you advise replacing the fuel pump, sources, $200 ?

If the pump is getting proper voltage and ground, and maximum pump output pressure is not within specs, (78pai to 108psi) the pump needs replacement. If that's the case, don't waste your time or money on anything other than AC Delco or Delphi.

New cap 'n rotor, new fuel pump, primes to 61psi, new spider, still no start unless you dump gas down the intake. Took back off electrical connector to fuel injectors, probing all wires measures 12v with a DVM, is that normal? Bought a logic tester at HF, (they didn't have any noid lights) they say it only draws 7 millamps of current so shouldn't damage injector drivers. Couldn't really tell if it was receiving pulces, seemed to indicate one side went to ground and stayed there ie didn't see any pulses, need a noid light - going to AZ. How do you use a noid light on this? Is it OK to unplug the connector and insert the noid light into the connector or do you need to penetrate the insulation on the wires while it is connected? It fires when you prime it and another post says the CPS generates timing signals for both spark and fuel injectors so the CPS shouldn't be the problem. Is there an underhood fuse box? Where might it be located? From another post "Old school - if computer is getting power and ground and signals and no injector pulse = bad computer." Starting to lean in this direction. Oh, the Blazer only has 15,000 miles on it :)

Oh, and BTW - Connected the old Spider to the wiring harness and cranked it while holding the Spider in my hand. I couldnt hear any injector noise (usually can hear them clicking on a running engine). I didnt feel anything clicking noise either. Bad PCM, fuse?

.....It fires when you prime it....

Check fuel pressure AND leakdown. When the ignition is initially turned to the "run" position, the fuel pump should run for approx 2 seconds and then shut off. Fuel pressure must be checked while the pump is running and the engine is off. Pressure must be 60psi to 66psi. After the pump shuts off, pressure must remain above 55psi for at least 10 minutes. Post your results.

Done that, tested fuel pressure at 60+ with first key on - runs 3 seconds. Leak down is fast bacause of cheap leaking HF tester. Have two testers and my luck was that I picked up the junk one. The fuel pump is new, spider is new (with new fuel pressure regulator). I can only get to this truck on weekends and its 50 miles away. 60+ should be good enough to start and sputter a little?

Shouldn't I hear or feel the injectors pulsing / ticking when I'm holding the old Spider in my hands next to my ear, electrical connected and then engine cranking?

Would a short from battery to the alternator body caused when disconnecting the battery cause something bad?

If you pour fuel in the throttle body, the air inlet tube must be re-connected so all of the air that the engine consumes passes through the mass air flow sensor. If it's not connected, the engine might start, but it will immediately stall.

With 60psi it should start, however, fuel pressure alone is not enough. The engine also requires a certain amount of fuel volume to run properly. When leakdown increases, fuel volume decreases.

If you hold the old injector assembly while it's plugged in, you should be able to feel the injectors clicking only when the starter is engaged.

Checked fuel pressure again, with a 2nd pressure gage from HF, it leaks too. Measured 61+ during the 3 sec prime. Leaked down fast due to the leaking HF gage.
Checked injector pulses with a noid light ... 3 injectors show pulses, and 3 dont! Am I missing something? Is the pinout pretty straight forward?

Code scanner didnt show anything. Engine still fires only when dumping gas directly in the intake. Are the injector drivers on the computer module ... PCM, ECM ...

Might have to return the pressure tester and get a good one somewhere else.

All of the injectors are fed battery voltage through the pink wire when the ignition is in the START and RUN position, (fuse #10 20 amp). The ECM sends a ground pulse to open the injectors through the following wires:
#1 Black
#2 Light green with black trace
#3 Pink with black trace
#4 Light blue with black trace
#5 Black with white trace
#6 Yellow with black trace

Swapped the ECM / PCM / ECU Computer and the #$% thing started, had to prime it once though. Reconnected the air-intake so the Mass Airflow Sensor can count all the air and it idles oh so smoooothe.