Can't keep 5.3 running. RPM bounces up and down and then dies. (log file incl.)

[bubba68ss]

I have a 5.3 on engine stand in my garage and it will start and run pretty good until it warms up. It seems to be about before it enters closed loop so i don't think it's O2's. It will all of a sudden drop about 100 rpm, try to catch up and jump about 200 then repeat like that for 10 seconds or so in an oscillating pattern. Then it will eventually shut itself off after the last gasp.

[bubba68ss]

Which PID's can I monitor to figure out what is causing engine to die at idle once its warmed up?

[joecar]

Sparkadv, ltft1/2, map, maf, ect, iat, rpm, dynair, ftc.

[bubba68ss]

I logged those and everything looks good except ltfts are pegged at 25 and spark advance is bouncing around between 5 and 30. Map is steady, maf flows good... Manifold vacuum at idle is 10psi but don't know if that's good. Fuel pressure is 48psi with vacuum hooked up and 55 without. Have tried flat injector rates and sloped. No real difference.

When I snap the throttle it has a slight delay, revs and then boys and sometimes dies.

[bubba68ss]

would appreciate it if someone could take a look at this short log and tel me if they can see the culprit.

Running a stock 2002 silverado 5.3 tune

17662

[bubba68ss]

To save some time running log, here is a screenshot. WTH is going on here?

17664

[bubba68ss]

Engine is misfiring on all cylinders, spark is falling because of it, LTFT's are super high because there is either fuel starvation or huge vacuum leak. Does this sound right?

[joecar]

If you rail pressure is correct, I suspect a vacuum leak.

[joecar]

I logged those and everything looks good except ltfts are pegged at 25 and spark advance is bouncing around between 5 and 30. Map is steady, maf flows good... Manifold vacuum at idle is 10psi but don't know if that's good. Fuel pressure is 48psi with vacuum hooked up and 55 without. Have tried flat injector rates and sloped. No real difference.

When I snap the throttle it has a slight delay, revs and then boys and sometimes dies.Vacuum is about right at 10 psi (VAC 66 kPa, MAP 33 kPA).

Rail pressure at 55 psi is close (should be 58 psi +/- 1 psi... but 55 psi should be ok).

[bubba68ss]

How big of a leak would it have to be to produce max LTFT's? I would think i would hear it, right?

Would running my wideband during open loop tell me anything? Closed loop?

[joecar]

Not vary big... you won't necessary hear the airleak...

if you spray some volatile substance (carb cleaner, starter fluid, propane) anywhere near the intake manifold you will see/hear engine speed up;

also check exhaust manifold/header, if it leaks, it sucks in air and puffs out soot (and makes a noise).

The PCM keeps seeing a lean condition so it keeps increasing the trim until the LTFT's peg... wideband will show you what the NBO2 sees.

[bubba68ss]

So I hooked up the MTX-L wideband today on each bank while engine was cold and I am showing 16-17 AFR on both banks.

One other thing, I am getting a 'beep' when I am in diode mode on my volt meter and I test between coil pink (harness side) and engine ground. Is that normal?

I am fresh out of ideas, so can anyone offer some more ideas up by looking at a short snap shot of my log? Am I not getting the commanded fuel? Or am I getting way too much air leaking in? I put new intake gaskets and new caps and hoses all over the intake. Leakdown shows 8-10% on all cyls. New NGK plugs gapped at .060. Each injector showing 11.7ohms, O2's (although used) are showing 3-4ohms across heater, everything seems solid.

Based on my log where would you look next?17676

[5.7ute]

How much pipe have you got after the o2 sensors?

[bubba68ss]

I have a full y pipe hooked up. Probably one meter long after O2.

[bubba68ss]

Not vary big... you won't necessary hear the airleak...

if you spray some volatile substance (carb cleaner, starter fluid, propane) anywhere near the intake manifold you will see/hear engine speed up;

also check exhaust manifold/header, if it leaks, it sucks in air and puffs out soot (and makes a noise).

The PCM keeps seeing a lean condition so it keeps increasing the trim until the LTFT's peg... wideband will show you what the NBO2 sees.


Would this show in the injector duty cycle reading? What is a normal range for this at idle?

[400ss]

Fuel System Status Pid???

[bubba68ss]

OL and CL are happening at the right times. Idling in fuel trim cell #20 in OL and CL

[bubba68ss]

I reprogrammed with the original '99 OS and maxed out the misfire tables and it seems to run great now. The Spark no longer jumps all around but remains withing 4-5* at idle. it used to bounce between 4 and 30, Not sure what to take from this...