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1999 Silverado 1500 5.3L hard to start/dies immediately


lucas.a.bradshaw

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Hey ya'll,

A Little back round: 1999 Chevy Silverado 1500 LS ExtCab 5.3L V8 Vortec 4WD 160K/Miles. P0171/P0174 DTC's (Bank 1 & 2 TOO LEAN) w/ Check Engine Light

 

I've **replaced/*checked the Following:

**Fuel Pump

**Spark Plugs & Wires

**Coil Packs

**MAF sensor

**Intake Manifold Gasket

*Throttle Position Sensor

*Idle Air Control

*Throttle Body

*No fuel leaking after disconnecting fuel pressure reguator

*No Vacuum Leaks

*Good Fuel Pressure

 

So here's my issue, whenever I go to start up my truck it cranks and turns over just fine. but maybe 2-5seconds later idles low and dies. turn the key again and it might just sound like it's starved for fuel needing another crank but other times it cranks right up like nothing is wrong. I do not have the security light after start up or while driving(I have done the relearning processes). I have recurring P0171-174 DTC's. I may need to give it some gas to keep it going. Once I get on the road I'm layin rubber just fine.

 

hooked up my OTC 3109 scan tool and this is what I see:

MIL Status: off(I cleared it)

ABSLT TPS% 0.0

ENG SPEED RPM 571(this is once it's running fine)

CALC LOAD 2.0

MAF (LB/M) 0.71(is this right at idle on a cold day?)

COOLANT 212 Deg/F

IAT 75Deg/F

IGN ADV 15.5Deg

SECOND AIR ATMOS???

VEH SPEED 0(parked)

FUEL SYS1 CLSD

FUEL SYS2 CLSD

 

---Could someone explain what the following readings are and what they should be? All of them are constantly varrying, but not by much. I guess that FTRM is fuel trim, but what is ST/LT?

ST FTRM1 10.2%

LT FTRM1 25.0%

ST FTRM2 -1.6%

LT FTRM2 25.0%

O2S11(V)what are these? 0.500

ST FTRM11 11.7%

O2S12(V) 0.080

O2S21(V) 0.865

ST FTRM 21 -1.6%

O2S22(V) 0.265

 

Sorry for the huge post but I like to give as much info as possible. Iv'e work on fighter jets for 6 years, so troubleshooting is what I do.

 

Although this problem is very minor, aside from getting crappy fuel mileage, I would like to get it figured out. any help is much appreciated.

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UPDATE:

so I changed the fuel filter... it was disgusting how dirty it was. thanks dad! :idiot: still have low fuel pressure at the rail (slow creep up to 30psi). I pulled my injectors out and inspected them. little bit dirty but nothing major. I used the syringe and 9volt battery test (will attach directions) and they all work great.

 

I also changed out my valve cover gaskets. Bank 1 side was leaking pretty bad, but still changed both.

 

fixed my exhaust leak. apparently a nut came off one of the studs on the bank 1 manifold to pipe union.

 

cleared my codes and took it for a drive. came back with P0171 bank 1 lean, P0174 bank 2 lean, P0137 bank 1 O2 sensor 2 low voltage, P0157 bank 2 O2 sensor 2 low voltage. both O2 codes cleared but still having 171 & 174.

 

beings how I just bought a new fuel pump in October I'm having carparts.com send me a new one. hope fully that will fix my low fuel pressure issue. and by the grace of God fix my 171 & 174 :fingersx:

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These trucks don't like running even a couple PSI shy of the spec, let alone 25 under. Sounds like it'll need a pump and filter.

 

That should get the truck running pretty well. Don't worry about the MIL until you get the fuel pressure up to where it needs to be.

 

If after repairing the fuel system you still have a lean code, I'd suggest replacing those intake manifold gaskets. It's sketchy business reusing those gaskets.

 

Even if the truck is happy after the fuel system repair, I'd drop the $40 on a new set of gaskets and throw them in. Doing so will eliminate any concerns of gasket deterioration preventing a lack of a perfect seal.

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FOUND THE FIX TO MY P0171/P0174!!!!!!!!

so, after watching an 8 video mini series on youtube by "Schrodinger's Box" called test your knowledge on Fuel Trim and LOTS of note taking I came up with my plan of attack. (I HIGHLY RECOMEND EVERYONE WATCH HIS VIDEOS. SIMPLE, EASY TO UNDERSTAND, PRICE WISE AND GREAT KNOWLEDGE)

Once I found the issue I felt like a total dumb ass :banghead: ...

I started inspecting the exhaust manifold for possible leaks using my homemade mason jar smoke machine. when I got it going I looked around the engine bay and feeling around the head-to-manifold area. wouldn't you know, when I touched the forward most bolt on the bank 1 manifold, it wiggled. I tried to hand tighten it but the damn thing sheared off in my hand. inspecting the other 5 bolts, they were solid. then smoke started to come from around where I removed the head of the bolt. Following on to bank 2 side (although I haven't set a P0174 in a while, my trims were still high) checking the same bolts. on Bank 2 side the furthest aft bolt was sheared of like the other one.

after soaking the hole/bolt in PB BLASTER, inside and out, I drilled through the bolt and used an easy out. I then replaced all 12 bolts with new ones.

NO EXHAUST LEAK = NO P0171 OR P0174

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Fuel trims are your PCM adjusting the amount of fuel it delivers to the engine. In closed loop operation, the PCM monitors the amount of oxygen in the exhaust, using o2 sensors, to determine the proper A/F ratio on the fly. LT and ST is long term and short term as mentioned.

 

Both your long term fuel trims are maxed out at +25%. Your short term is approximately +8%. +25% and +8% means that your PCM is commanding the injectors to spray 33% more fuel than is ideal. Normal tolerance is about +10%.

 

Knowing the long term trims are at their maximum value means a) that the PCM still is not happy and would add more fuel if it was able and b) this problem has been going on for a while.

 

This could be caused by many things. A couple honorable mentions are:

-unmetered air entering the engine. This is any air being sucked in after the MAF sensor.

-fuel system restriction. Pressure is ok (spec is 55-62 PSI key on, engine off), but volume may not be.

 

Check to make sure both front o2 sensors (B1S1 and B2S1) are cycling from about .2 to .8V regularly. The rear sensors (B1S2 and B2S2) should be fairly stagnant.

 

Start by spraying the engine down with brake cleaner, especially where a mating surface is present (e.g. intake manifold gasket, throttle body etc.) Any rise in RPM when brake cleaner is introduced means you've found a vacuum leak.

 

I'd also look around to see if you can find the specs for a fuel volume test. It would be the best way to rule out a fuel system problem. Since this issue is affecting both banks, chances are the problem, if fuel system related, would be located somewhere between the fuel rail and the pump.

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---

 

Thanks for you input. I really don't mean to come off like a dick or anything. I appreciate any input anyone throws out there

but like I said in my post...lol

I've change the fuel pump and intake manifold gasket already. and I also stated that I've been under the false info that the fuel filter has been changed. I went back and re torqued the intake manifold and got rid of my P0174

yeah, I was thinking the same thing. address the fuel pressure issue first

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Thanks for your input. I think I was dumb to say fuel pressure was good... it's not. I was relying solely on what my father (the guy who sold me the truck...) said, and he also said he changed the fuel filter. which come to find out he hadn't... long story to be added to the "rants" forum...

*as soon as I posted this I realized what ST/LT FTRM and O2 11/12/21/22 are. DUHHH

My fuel pressure is 30-32PSI KOEO. which would indicate that i'm not getting proper pressure to the rails. beings how I don't know the status of the fuel filter I will be changing that soon.

 

***NOTE: while having some time this weekend I rigged a small smoke machine to check for any other leaks but I don't think it was putting out enough smoke or pressure. I didn't find anything tho. I also went ahead and un bolted my intake manifold and re torqued it using the proper torque and sequence. the P0174 has since gone away but my trims are still bad and SES light with the 171 is still there.

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