ForcedTQ

iTrader: (1)

This has got me stumped a bit. I've been searching for an answer for this for the last 2 weeks as I've had time, but have not come up with an answer. 2001 5.3 with EGR and AIR. 95% of the time when I go to start the truck it will fire within 2-3 cranks, but will act lethargically to get up to speed (stumble/gurgle) for the first 2 seconds as it starts up then it will idle OK. At this point I have been getting missfires logged on my Flashscan V2, and it shows my EGR with a "duty cycle" of 14%, and a "voltage" of .756V, but a "postion" of 0 at idle. When I am taking off from a stop sign/light and slow/medium accelerating I get the same kind of stumble/hesitate/backfire? for the first 2 seconds (low rpm/low throttle). And the last instance of this weirdness rears it's ugly head right as I let off of a heavy acceleration, namely just as I let off I get a back fire or two? WTF?

List of things I've done: Checked for vacuum accessory/intake tract leaks, replaced intake manifold gaskets, cleaned the PCV, cleaned the MAF, verified no fuel coming out of the FPR, cleaned the EGR Valve pintle and seat, confirmed the IAC at idle is around 22-25 steps, and checked electrical connections for the injectors / spark plug wires.

I'm wondering if anyone could tell me what a "Good/New" EGR valve shows for a "closed state" voltage/duty cycle, as I'm suspecting this to possibly be the culprit.

I'll admit I haven't pulled plugs and replaced the wires yet, but this issue just doesn't seem to be ignition related. I'm waiting as a last resort to replace the O2 sensors, which look as though they could use a change out, sometimes not even switching once in 2 seconds, sometimes switching 2 times per second - dependent upon TP and load.

Any insights into this would be much appreciated, as I'm trying to get this issue fixed so I can commence with tuning my fuel and spark tables for my installed mods.

mhotrodscooter

iTrader: (13)

I got a low idle miss after my last dyno runs. Seems the headers got so hot it melted the core of the wire. The looked fine just looking @ them, till I went to remove them & they just broke in half. It would never miss under WOT, just around 1500 to 1800 rpms.

ForcedTQ

iTrader: (1)

Well, it seems I have got the "stumble" somewhat removed. I went through removing the throttle body and thoroughly cleaning it and the IACV/passage. I also went back through and Re-Torqued the intake manifold.

I am still getting Missfire counts when I BBL with my Flashscan, I also still have the Backfire issue on acceleration when it upshifts, or after 50-100% TPS acceleration while letting off of the accelerator pedal.

Running a set of PID's for all 8 cylinders shows all cylinders affected by missfires, although cylinder #1 seems to see the highest counts. My next step I think is to perform a Crank Relearn, pull the fuel rail/injectors, go through and remove each one and clean them. Then flush out the rails, install new o-rings, and re-install in the manifold. I've heard that missfires and weird issues like mine can crop up from water being "stuck" in the fuel rail. I'll also install a new fuel filter to rule that out, although the old one is only 15-20,000 miles old. Next up is to install the new TR5 spark plugs I bought last night, last result will be new plug wires.

I've included a couple logs for your viewing pleasure, any ideas are greatly appreciated.

Thought I'd add that what ever is causing the weirdness in the engine operation seems to be affecting my transmission shifting as well. Very irregular up-shift engagement when I get the backfiring, as well as when down shifting and applying moderate to heavy throttle 4>3 or 3>2 the engine revs up to where it should be, then momentarily revs ~500 rpm higher, then settles back down to the rpm range it should be in. ?????

ForcedTQ

iTrader: (1)

Allright, last night I removed the EGR Valve AND the gasket from the mounting base. I found that the gasket around the opening to the tube leading to the intake manifold had two areas (1/8") where it wasn't sealing. Vacuum Leak Found (Ithink)! I cleaned both surfaces and installed a new gasket, and like magic I all of a sudden have a "more firm" brake pedal, and better off idle throttle response. I also removed my NGK TR55's that had been in there for ~50,000 miles and replaced them with the TR5's I had bought late last week.

Reset the computer fuel trims, went for a drive, did a CASE relearn, and almost everything is better. The truck no longer "backfires" at the release of the throttle after a +50% throttle acceleration, nor does it seem to stumble off idle on light acceleration.

BUT... I still have missfires showing up on most cylinders!!! I'm thinking it's got to be either the plug wires being so old (156,000 miles) or there are some contaminants in the fuel lines/rail. I'll be changing out the filter tonight and removing & flushing the fuel rails/injector inlets tonight to rule out fueling issues. If that doesn't take care of it, I'm buying new plug wires.

ForcedTQ

iTrader: (1)

No Codes stored. No MIL save for a couple of times flashing while driving 4 months ago.

I can't get this figured out, and now it needs to be fixed for smog. Went for a pretest and at times I'm seeing as high as 320ppm HC at idle, 2500 rpm test is fine, while the other levels are all down around where they should be. Plugs were replaced in my thread above, and wires were done 50 miles there after. I just can't get a handle on this one.

Could it possibly be O2 sensors not switching enough?

Only other thing I haven't done is sent the injectors in for a sonic clean and balance. If the FPR in the rail doesn't have fuel leaking at the vacuum port does that necessarily mean it's working correctly, or is there something else to check (take it apart/replace it)?

I have included a log of cylinder misfires, and O2 readings below if you care to take a look. Any ideas are appreciated.

Bluehoonigan

I’m having a similar issue, I recently installed a new 3000 stall torque converter and a new 4l80e tranny, I’m running a stand alone ecu for it , but now the engine misfires really bad at low rpm and won’t even idle good , if I give it gas it will shut off, the weird part is the misfire goes away after 3,000 rpms and the truck pulls good , Im lost at this Point, any help would be appreciated

MikeGyver

iTrader: (5)

The guys with the answers are going to want to know more than what transmission and torque converter you have.

madmann26

iTrader: (7)

Sounds like the misfire tables in whatever standalone system you have need tuning.

1slow99

I had the same issue on my truck no codes, ended up being the tps sensor, it was reading low voltage. Ended up being the wire connection, got it replaced and problem solved.