5.3L Swap Idle Problem

[C10_ustacould]

So, I have been driving my recently "completed" 5.3L swap and it is giving me an issue. When it gets warmed up it wants to die when I come to a stop. It also dies or the idle drops very low after revving it. The mixture seems a little rich also. Has anyone had this issue?

[ls1nova71]

Do you have a VSS hooked up?

[C10_ustacould]

Originally Posted by ls1nova71

Do you have a VSS hooked up?

I do, but I noticed tonight that the speedo wasn't working. I wonder if it came unplugged... How does it affect idle?
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[ls1nova71]

It let's the PCM know when you're slowing down, without it it will take a.second for the PCM to adjust and will cause a stalling problem. Usually more noticeable on rapid decel. If this is a new problem, not int that has always been there, and your speedo used to work then it probably is your problem.

I didn't see the part where you said it will stall after revving it. Could be an IAC problem. Is it DBC or DBW? Have you checked your fuel pressure?
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[C10_ustacould]

I was planning to check the fuel pressure after work today, what should the fuel pressure be with and without vacuum? I will check the VSS pigtail also. Thanks for the info!

[ls1nova71]

Should be somewhere around 58psi . Unhooking the vacuum line from the rail mounted pressure regulator will make it go up but not sure how much.
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[C10_ustacould]

Read a write up this morning that said the 99-02 5.3L with a return style fuel system should be 50-55 psi and around 60 psi with vacuum romoved. You are saying 58 psi... I guess I will see what mine is and go from there, I appreciate your help.

[68GMCCustom]

if its dbw.....seen dirty throttle bodies cause this on dbw systems.

[C10_ustacould]

Mine is DBC.
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[C10_ustacould]

Well, fuel pressure is 55psi with vacuum and 61psi without vacuum. The VSS is functioning correctly, but the reading on the electronic speedometer is very low. It reads 10 mph when the truck is going 40mph per a GPS. I suspect that is due to differences in my gear/tire configuration vs the original truck. I also cleaned the throttle body to eliminate that as a potential problem. I have a hand held scanner and it only gives the code P0650 for the Malfunction Indicator Light, which I new was not hooked up correctly. I have an appointment with a friend of Hart_Rod's who is an experienced LSx tuner, maybe he can fix it with a new tune. I don't know what else to do...

[1BADLS1tuner]

do you have the IAT and temp sensors hooked up? 02 sensors?

are you runing SD or MAF tune, OL or CL?

is it 100% stock? If not what mods have you done to the setup? are the pcm and motor from same donor vehicle?

So many things it could be lol, your friend that is a tuner should be able to nail it out!

GL man!

[C10_ustacould]

Yes the IAT, Temp, and O2 sensors are hooked up. It uses a MAF and has O2 sensors so it is OL... (when warm I assume). It has the GM "hot" cam upgrade and that is all. PCM and engine are from the same truck.

I get what you are saying, I am in research mode collecting info (final drive ratio etc) about the truck so I am ready for the tune on Sunday. Sunday! Sunday! Sunday! Be there!

[1BADLS1tuner]

Originally Posted by BucksSS

Yes the IAT, Temp, and O2 sensors are hooked up. It uses a MAF and has O2 sensors so it is OL... (when warm I assume). It has the GM "hot" cam upgrade and that is all. PCM and engine are from the same truck.

I get what you are saying, I am in research mode collecting info (final drive ratio etc) about the truck so I am ready for the tune on Sunday. Sunday! Sunday! Sunday! Be there!

Sunday wont come soon enough for you lol... An experienced tuner will normally catch something overlooked or a bad sensor, ect, pretty fast after hookng up and giving the setup/tune a lookover....

Youll get it figured out!

[BR3W CITY]

I didn't see which trans you were running, but assuming its an o/d trans, its possible the bog on deceleration could be related to lockup.

I had a misfire count issue causing the lock and unlcock to screw up on the overdrive. If it doesn't unlock properly on decel, the truck kind of stumbles and trips over itself, sometimes causing it to bog or die if it doesn't unlock fast enough to "catch" itself on the way down.

Tuner fixed it as part of a misfire count issue in the pcm.

[74project]

Had the same problem...if its running rich then it will run 25% richer to account for whatever the problem or code the ecm is having. I went to have a complete scan and my fuel pressure was 10% lower than what it was supposed to be in order to match what the current programmed specs were on the ecm. Runs like a dream now..no more stalls or? wasted fuel....also if it is running a code and dumping the extra fuel at it its fowling up ur plugs and 02 sensors....
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[Ranger6202]

Had this same problem when i first fired my conversion up. Turned out being the o2 sensors. My problem was that i didn't have them fully in the exhaust stream since i didn't have my exhaust hooked up (just dangling on the exit of the collector). I'd start the truck up, it'd idle just fine, and then slowly loose rpm as it got warm, and then go extremely rich. It'd sound perfect if i gave it a little pedal but would die when i'd let off. I know you have your o2's hooked up into the exhaust stream, but based on what i saw with mine and comparing symptoms, i'd guess you've got something going on with your o2's. Not to mention i've had a few fuel regulators go out, one went low pressure and the other went high, and i never had idling when warm problems, i would just notice the acceleration would lag when it went low pressure and it smelled rich when it went high pressure. So once again, i'd guess o2's.

[vannatta20]

My combo with a T56 did this as well. I didnt have VSS hooked up. After I hooked it up and calibrated it to read correctly the problem went away.

[C10_ustacould]

My VSS has been hooked up the whole time. How did you calibrate it?