Hot start fuel issue

[the_merv]

PCM: 2002 GM 0411
Engine: Cammed 6.0l
Trans: T56 6spd Manual

I have everything dialed in on the car except for this one issue. When you leave it parked for about 10 min or so, enough to where it's still warm, you get in, start the car up, and then if you move it, it will sputter and about die unless you sit still and let it recover itself.

This is the best way I can explain what goes on:

1. Start the car, go to move, and it will sputter and run very lean until it recovers itself or stalls, re-start, and it's fine.

2. Start the car, wait 15 sec and the engine will flutter and run lean for about 2 sec, then straighten up and be fine. I watch it on the wideband. I have messed with the after-start enrichment to get it to where it will run this long without going rich or lean, but for some reason that 15 sec time seems to be a critical time, I can't figure out why the engine wants to run that long before it goes into closed loop and then idles fine.

Short term fuel trims on or off, doesn't matter. This is a non-AC T56 Manual car so Adaptive Idle has been disabled. Most of it is Auto trans assist stuff and AC tip-in.

This car has been doing this for years, basically if you go to move it while it's within that 15 sec time, it'll lean out and want to stall. You let it idle on it's own and flutter and work itself out. No issues.

Anyone have any insight I would appreciate it.

[IARLLC]

I wonder if the injectors are dripping when shut off. Seen it a few times. It only affected hot start. By the time it cooled off the fuel had evaporated. Unburnt fuel/wet plugs would show lean. Maybe?

[the_merv]

Doubt it

[DGS]

What fuel do you run? Is your fuel pressure high enough to prevent vapor lock? Does your lift pump turn on at key up? Pressure regulator leak? Fuel return or return less? Year , make , model , tune, log?

[kingtal0n]

1. watch fuel pressure during the time
2. disable closed loop
3. watch injector pulse in scanner during the time

if it holds pressure and the pulse is there it shouldnt run lean right. If it still runs lean you got only a few other items left it could be.

[the_merv]

I'm thinking afterstart enrichment.. fuel pressure stays at 60psi constant, regulator is fine.

"Year , make , model , tune, log?"

Literally at the top of my post.... why I don't even care for forums anymore because people can't read.

[5FDP]

My favorite part is when people don't post logs or tunes with their problems.

Yes you detailed your issue clearly but seeing it happen through a log file and maybe seeing the tune file is really helpful when it comes to the little things. Maybe someone would see something that could help.

[the_merv]

I would have to post a vid of this happening because my wideband is setup to my scanner, if I emailed the log, no one would see the wideband. The commanded AFR does not change the whole time when this happens. It goes lean if I move the car and then I have to let it recover by coming to a stop. If I let it idle it is fine then goes lean for about 2 sec before steady state idle kicks in. Then it's fine.

I detailed it because can't really show it on the log because of the above mentioned.

[the_merv]

6.0l Cammed T56.hpt

This is the tune file here.

[02statesman]

Only happens on hot restarts after a 10 min sit time.... I'm guessing your IAT sensor is getting heat-soaked and that's causing you to run lean on restart. The 15 seconds is how long it takes for the O2 sensors to get 'ready' to read properly. Once you go into closed loop, the trims correct the lean condition and then the engine runs nicely.

[DGS]

02statesman

- So then would one modify the Afterstart Enrichment Initial Adder Modifier vs. Soaktime on the table at 600 seconds (10 minutes) and longer to add fuel. His table in the tune is set to not provide any from 600 (10 minutes) and longer? Also, the Rich/Lean vs. Airflow is set at 420 most of table. Does this only come into play after it goes to closed loop? Closed loop readiness is reached when switching reaches min and max levels/ cross-counts. Poor performing o2 heaters and proper placement in exhaust determine how fast they would reach closed loop operation? We have no information on this. The rolling idle is set to 1000 rpm.

[the_merv]

https://forum.hptuners.com/showthrea...tart-IAC-issue

Here is a more accurate post of this issue, I am thinking startup and friction air flow

[the_merv]

I'm going to update this, yup it's from a long time ago. The car would have a surge idle warming up and as mentioned above, when you went to move it after starting it the car would idle really lean and want to die shortly after starting it.

Afterstart enrichment and friction/startup airflow tables are from my stock 2001 2500HD, I adjusted them slightly for the Cam in this 6.0l setup and they seem to work very well. Cold and warm start initial is about 1400rpm, then drops down nicely into an idle rpm around 760 when fully warmed up. Fuel would come in a little rich then level out to 14.3-14.4 idle. I spent some time in the Open Loop EQ Table, Closed Loop set to come in at ECT 131*.

Sounds all perfect, still had a surge and still had the afterstart problem, then I found it.

The damn timing. Never thought to look at it because I thought it was stock, I had bought this PCM used years ago.

Base Timing was set to never go below 20* advance, and the Overspeed/Underspeed tables were set about half as much as the stock parameters.

I set the Base Timing table to 10* Advance up to 1600 RPM, 15* at 2000 RPM, and 20* from 2400 RPM-up. Overspeed/Underspeed tables I set to the stock ones in my 2001 2500HD.

Car starts and goes into stable idle damn near instantly. Warm start after parking for 15 min the car starts, comes down to set RPM and idles perfectly. IAC counts start at their high point depending on IAC and come down to 70 Steps or so, pretty much stay in that area. Haven't ran my wideband on it to see where the AFR is after the enrichments time out, I don't feel the need because the car starts and drives spot on. There is no stall, no surge, not even a hiccup.

Literally was that timing change. Posting that all here because it's closing out the thread and I had a PM on it asking if I figured it out. I got into it earlier today because I had the time and got tired of dealing with it. Base Running Air Flow was dialed in, AFR was dialed in, I was hung up on dialing in them two to the T then it popped in my head the timing was the only remaning thing. Air Temp outside here is 90 with a real feel of 100+, so the hot temps of the tables are dialed in. Have to see what it does when it's cold out around November or so.

If anyone here knows my screen name from LS1Tech you know the car. For those that don't, this is what the Cammed 6.0l & Built T56 setup is crammed into..

[blindsquirrel]

^^^ What HVAC box is that?

[bk2life]

I'm going to update this....

If anyone here knows my screen name from LS1Tech you know the car.

Thank you for the update. It is really great when these get 'closed out' because someone else probably needs this info.
And yes, i thought that screen name looked familiar...

[the_merv]

That is why I came back here to this old thread to post up what I found. Yea someone else may have known that was the answer but given no one responded saying to check Timing I figured I'd mention it as a major factor to look at. It's a healthy setup, 2006 LQ4 with LS2 243 Heads, LS6 Intake, TR 230/236 Cam. Literally drives like it's stock I drove it for an hour earlier just enjoying the fact it was running amazing. Sweat my ass off the whole time didn't even care...

^^^ What HVAC box is that?

Factory Gbody Non-AC Heat Only HVAC Box.

[1BadSlug]

That car is amazing! And it's nice to see people come back and update their posts.
NEVER let forums die!!