98/99 vortec 5.7 engine data needed

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Dustin Murry

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I'm having some weird driveability issues with my 99 suburban. What I am requesting is for anyone of you who have access to a scan tool or the such to provide me with your ECM data. I need ltft stft MAF g/s etc. Of your engine at idle. I have a fresh engine with excellent compression. A new Delphi pump, Delco mpfi injector conversion. Fresh tune-up etc. My engine hesitates out of the hole for about 150-200 feet then clears up. And doesn't act up again until I shut it off and start it again. also the exhaust smells of gas and will burn your eyes. any given time if I check my fuel trims the lt is about -18% and the st is about -3% at idle. The maf reading is 6 to 7 g/s. My fuel pressure is kind of low at 52-54 psi. I used a bore scope and inside of the intake is dry and so are the tops of the Pistons. I'm at a loss here. I don't understand why I have low pressure, but a rich condition.

Thanks in advance for any input.
 

885speed

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I'm having some weird driveability issues with my 99 suburban.

My fuel pressure is kind of low at 52-54 psi.

Since fuel pressure is a known issue, that should be the first item to attack. Gotta start with what you know for sure and take it from there.
More issues=more variables=more headaches. I think we all could agree with that.

Also, to my understanding of how they work(and someone more knowledgeable may jump in to correct me if I'm wrong..)
if a fuel injector isn't getting correct pressure, that can screw up not only the spray pattern, but how the injector actually opens and closes.
Meaning, instead of a nice atomized cone of fuel, the injectors could be doing more of a spitting spray where little droplets are coming out rather than a fine mist. Leading to your rich condition.
Just my theory on it.
 

L31MaxExpress

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Explain the theory of the lean misfire please.

Low fuel pressure means less fuel delivered for a given injector pulsewidth, aka injector on time. When the engine is running cold it will be in open loop. Open loop is not using the oxygen sensors for feedback on the air/fuel ratio. If the engine is drawing in X amount of air the computer injects Y amount of gasoline. In normal operation it is programmed with the assumed flow rate of the injector at a specified pressure. If the pressure is low the volume will be too. That would make the air/fuel ratio lean. Lean mixtures often do not fully combust especially in a cold engine. The fuel that did not combust is then forced into the exhaust with the other combustion gases. If the catalyst are not up to operating temperature the unburned fuel is not oxidized by the cat which combusts the unburned fuel and you will smell the unburned fuel.

One other possibility. I have also seen the linear EGR valves fail in a manner that the internal return spring gets weak. The computer will command the valve to say 10% opening and the valve will open say 50%. When the excess EGR flow is pumped into the intake manifold you get a massive stumble. The computer recieves feedback from the valves position and adjusts it closed which brings it back to normal operation. Until the valve is cycled and the same event happens again.
 

CW73

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Two things come to mind with the symptoms you described.. I had new outta the box injection conversion assemblies with a hung injector dumping fuel all the time. Does fuel pressure drop after the engine is turned off? Also I've seen injectors swapped and installed in the wrong holes. Your fuel trim, hesitation at low speed and fuel smell sounds more like a hung injector . You can pull the upper intake, pull injectors up so you can see them, install the fuel lines back on the injection assembly then power the pump with the connector near the fuse block or have someone cycle the key.. but not crank it. There should be no fuel coming out of the injectors.
 

Dustin Murry

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Two things come to mind with the symptoms you described.. I had new outta the box injection conversion assemblies with a hung injector dumping fuel all the time. Does fuel pressure drop after the engine is turned off? Also I've seen injectors swapped and installed in the wrong holes. Your fuel trim, hesitation at low speed and fuel smell sounds more like a hung injector . You can pull the upper intake, pull injectors up so you can see them, install the fuel lines back on the injection assembly then power the pump with the connector near the fuse block or have someone cycle the key.. but not crank it. There should be no fuel coming out of the injectors.

Thanks. I was afraid someone was going to say something like this.... Harsh realities. I've ran a camera into the intake and there are no visible leaks inside the plenum area. So I replaced my fuel pressure gauge and key on engine off it spikes to 60 psi levels to 58 then slowly falls back down to 50 psi over 10 minutes or so. However over roughly 24 hours it's still at 38 psi. I have a newborn and this is my weekend cruiser so my time working on it is hit and miss.
 
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L31MaxExpress

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Thanks. I was afraid someone was going to say something like this.... Harsh realities. I've ran a camera into the intake and there are no visible leaks inside the plenum area. So I replaced my fuel pressure gauge and key on engine off it spikes to 60 psi levels to 58 then slowly falls back down to 50 psi over 10 minutes or so. However over roughly 24 hours it's still at 38 psi. I have a newborn and this is my weekend cruiser so my time working on it is hit and miss.

Unplug your EGR valve and see if the symptoms go away.
 

Dustin Murry

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So I've checked all of my grounds. Every circuit nearly 0.01 ohms including the ecm grounds. I pulled the plenum and there are zero fuel leaks in there, no regulator or injectors are leaking. When I hold the test jumper near the fuse box pressure reads at 60 psi. The second I undo the jumper it immediately drops to 55 psi and over five minutes it will be at 48 psi. Throughout this I unplugged the ICM and heard something cycle under the engine along with the fuel injector. My question is when I unplug and replug the ICM the injector and the front axle actuator cycle... Why is that? Also what role does the ICM play in the fuel injectors?
 

Dustin Murry

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One other possibility. I have also seen the linear EGR valves fail in a manner that the internal return spring gets weak. The computer will command the valve to say 10% opening and the valve will open say 50%. When the excess EGR flow is pumped into the intake manifold you get a massive stumble. The computer recieves feedback from the valves position and adjusts it closed which brings it back to normal operation. Until the valve is cycled and the same event happens again.

Once I get the intake back together I will look into this... Should I key on engine off then unplug, then start it?
 
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