We aren't going to get anywhere if we keep on going over the same things. I ALREADY did this in Post #1 & Post #9.

That static pressure is good. This problem occurs during driving. I'm giving you live data on the engine while it is in use and the fuel pressure is making problems.

 

As already stated, there are is no fuel pressure numbers with the engine running.

So what is being asked is what is the fuel pressure at initial key ON...you have done this...but what is the pressure 10 minutes later...is this the number listed for "at start up?"

If so, seems fuel pump is good.

Now...when the engine was replaced, the distributor/rotor/cap were replaced....what brand of parts were used? Was the distributor a used plastic shaft or a new aluminum one? Was cam retard checked and set?

Is the fuel tank venting working? If you leave the tank cap loose and drive, do you get an error code?

Lastly just because parts are new, does not mean they are good....not anymore.

Stick with us...the forum will help get this figured-out.

 

We have asked you to do the fuel pressure test again because you are doing it wrong. The test must be done with the engine OFF.
Also there is no data of what your leak down test did. Was it at or above 55 psi after 10 minutes??

Do not worry about running the tank low on gas. These are bucket style fuel pumps, they have a constant supply of fuel to cool them.

 

I got it now. What I am saying then is that those numbers while the engine is running are "readings" for the fuel pressure. I can see the pressures as they are going into the injectors. When the gas tank hits "LOW FUEL" I can see the readings of the fuel pressure go crazy and when the motor starts to stumble, hesitate, and stall, I can see the pressures dropping. I have the fuel pressure gauge taped to my windshield.

Fuel Test #4:
- 65 psi at ignition on, engine off, fuel pump primes
- 55 psi at ignition off, engine off
- 53 psi, after 10 min

I think the pump is good but, I question if the sending unit part of it is causing a problem. NOTE: With the engine running, I think I can hear air in the injector lines around the Schrader valve. It sounds like BBs in a BB gun. That's the best way to describe it. I think that is air in the lines. The fuel filter is new.

Idk, the brand of the distributor. Whatever O'Reilly's sells. I can tell you right now I'm not too keen on getting an OEM distributor OR fuel pump. Those things are pricey. I don't think this is a distributor/ignition issue since I've been able to replicate this problem by getting the gas to run low.

I don't know how to test this venting. I do NOT get an error code when the cap is loose. I've tried this already to see if there was pressure building up inside the tank to see if it fixed it. And NO error codes.

Oh I know this, it drives me insane to change out new parts because they are bad! Telling me a part has a lifetime warranty does me no good when those new parts have to be changed again. I always ask, "So are you going to change it for me next time it if this "lifetime" warranty part needs to be changed again?"

I'm not going anywhere, WE ARE going to solve this!

 

You can have a parts store test your ICM or you can aim a blow dryer at it to simulate hot driving conditions. Or wait till it stalls and then test for spark.

 

I have been doing it this way. I know this, I've been following Chiltons. What I'm also adding here is live "readings" for the pressures. I'll go back and edit my previous Posts so that it is clearer. Sorry bout the confusion.

I just did it again in Post #14.

Fuel Test #4: Never started engine.
- 65 psi at ignition on, engine off, fuel pump primes
- 55 psi at ignition off, engine off
- 53 psi, after 10 min

 

Ok wait, let's think this through.

I can see the fuel pressure readings drop when the motor starts to stall and hesitate. The key is still on so that means power is still going to the fuel pump. There is no reason for that fuel pressure readings to drop/fluctuate if the fuel pump is operating properly. Or are you staying that the ICM may be loosing signal and causing the fuel pump to lose power?

NOTE: ICM is new and I did put all that thermal grease on it. I'm an Mechanical Engineer and I know all about cooling. Its a PITA!

If the fuel pressure readings stayed constant during the engine stalling and hesitating then I would agree with you that the problem might be ignition.

Please help me understand your point.

 

Your fuel pump is fine if those are your readings.

The ICM controls the coil. It tells it when to fire after it gets the signal from the PCM and the crank sensor. Is it an AC Delco ICM?

When your truck stalls you need to test if its getting spark.

 

Looks like it was the ICM. I had it tested 3 times at different Autozones and O'Reilly's and it failed all 3 times. I changed it to the one in the original engine (OEM part) that I also had tested (it passed) and I cannot get the engine to stall, hesitate or stumble. In addition, the fuel pressure readings do NOT go down under hard acceleration as in Post #9. It's 100 degrees outside and still no rain.

I still had the tank low on gas just to make sure it wasn't a "LOW FUEL" issue and it wasn't. Could not get the fuel pressure readings to drop as in Post #9 after I changed to the good ICM. By the way, use OEM GM parts for electrical. I know this but I tried the O'Reilly part when I swapped the engine and it failed less than 3 months later.

Interestingly, the ICM tests at Autozone check LOW RPMs & HIGH RPMs. When I changed the ICM, I could tell that that engine ran smoother at low rpms and obviously with my stomping the gas pedal, and the fuel pressure readings staying up around 65 psi, the higher rpms were also smoother.

Thanks to all you guys. @burned, good call!!!!

I'm going to drive this around a few weeks before I call this thread [SOLVED]. Keep you posted.

 

BINGO! Found this tidbit on why the fuel pressure readings kept on going down and I kept thinking it was something to do with the fuel system. I know it is for a 3.8L but I figure logic is the same for the 4.3 since they are both GM. Looks like the ICM failing to send signals back to the PCM tells the PCM to not activate the fuel injectors. No injector activating = no fuel demand = no pressure readings

CLICK LINK=> Part 1 -GM 3.8L Ignition Control Module and Crank (3X, 18X) Sensor Test

"Here is a little background information to help you diagnose this no spark condition. In a nutshell, when the system is working properly, at crank-up and below 400 RPM's the ignition control module controls spark (by activating the three ignition coils that sit on top of it) without help from the Fuel Injection Computer.


More specifically:

1. When you turn the Key to start the engine, the ignition control module gets power (12 Volts) and Ground.
2. Once the ICM gets power, it in turn supplies power to:
   1. The crank sensor.
   2. The cam sensor (if equipped).
   3. The 3 ignition coil packs sitting on top of it.
3. As the engine cranks, the ignition module receives the crank sensor signal.
   1. The crank sensor signal is an On/Off type of signal that can be measured with a multimeter or an LED Light.
   2. The crank sensor signal is also called the ‘triggering signal’ in this article.
4. As soon as the ICM gets the crank sensor signal, it starts activating the ignition coils sitting atop of it.
   1. The ignition control module does this by switching the ignition coils' primary current On and Off in a base timing mode so that they'll start sparking away.
   2. This On/Off signal is referred to as the switching signal thru' out the article.
5. The ICM also sends a Fuel Control signal to the PCM (Powertrain Control Module = Fuel Injection Computer).
   1. The PCM uses this signal to start activating the fuel injectors.
6. Once the engine starts and/or above 400 RPM's (anything above this and the Computer considers the engine as having started), the ECM takes over spark Timing and the activation of the ignition coils (thru' the ignition control module of course)."