Need Help!

As some of you know my Jeep has been backfiring for awhile now. It has been getting worse as of late. I am running the Chev SB found in 96-98 p/u's and Suburbans. It is a 5.7L (or 350cc) vortec motor and I believe its model is L-31. It is throwing NO DTC's per OBD 11 scanner. I have checked many things..it is not fuel pressure regulator, not fuel filter or pump, not wires/cap/rotors, and the list goes on and on. PSI at fuel rail is normal (60 psi) w/ key on and jumps up +5 with rev'ing of engine (normal). Idling fuel rail pressure is about 55 (also normal). Reading online/talking to the boyz at Olympic 4x4 it sounds like timing, 02 sensors, fuel injector "poppets" stuck open, or mass flow air sensor (cleaned with special cleaning spray)! My OBD 11 scanner gives me "live data" but I don't have any parameters to compare it to....for example...volts to front 02 sensors vs back, normal timing advance for this engine at idle, how much air is supposed to go thru the mass air flow sensor, ect, ect...... PLEASE HELP if you know where I can get a list of these spec's. Maybe online? Shop Manual? It's time to get technical!!!!!!!

Let me think about this one. Does the exhaust smell rich?

rubicons4 wrote:Let me think about this one. Does the exhaust smell rich?

Yes it does! I think raw fuel is in exhaust system....btw it happens when I let off the gas pedal (deccelaration) only!!!!

I'm no expert, but how do you have rich condition in the exhaust with no code? I can see how your scanner won't find anything, no code no problem. Will your live scanner pick up what your on board computer won't? This all started after the roll over, I would start with basics. Grap every electrical connection with your hand, don't just look at it.(ground wires too) Check all vacuum lines, I had a BB chev that didn't throw any codes and only ran bad under load. It had a loose vacuum line. Good luck

No, it was missing before the roll! Now it's growing worse (and only w/ deccelaration)....I checked all electrical connections and vaccum lines (good thoughts). The scanner is reading data given to it by the computer...so that is way I need to know timimg spec's ect.....might have skipped a timimg gear tooth along the way, or electronic distributor moved (advancing or retarding timing) currently at idle the timing is advanced20-23 degrees (seems high to me) per computers output. I would expect maybe 8ish max? (But I need to know for sure before I just adjust the distributor.) Also, the computer has a crank sensor and distributor sensor and the computer can correct up to +2/-2 degrees!

Run it for a little, shut it off, and then look down the throttle body. There should be no fuel sitting at the bottom.

Is it injected directly into the cylinder or through throttle body?

Done yesterday.....nothing! I may have a bad fuel injector that leaks fuel thru the "poppet" (in ather words leaks fuel continuouisly into cylinder)! The computer will not put up an open poppet, but only a stuck closed one (no gas that causes miss). Also will pick up if a plug is fouled but not if gas is being expelled via exhaust (and not fouling plug). Just throwing out what I have learned.

I was just going to say poppet valve. Did you make sure the vacuum is good? Think it runs on vacuum.

Here ya go.

http://www.johnstonauto.com/news/TechBulletins/MFI_Kit.pdf

Those kits run $300 plus (for all 8 injectors).....I have looked at them already but want to make sure that will fix my problem!

Poop!

Yesterday I cleaned out Mass Air Flow sensor.....I took it for a run today 95% better (after cleaning solution completely dried)!!! It would only backfire once or twice and NOT 6-10 times. Today I took off air cleaner and it was soaked with motor oil, dirt, and Moad red dust. Now I am cleaning that! Maybe I just needed more air to mix with gas??? Time will tell! I know that my MASS AIR FLOW sensor was getting .966 LB's/minute of air thru it (per scanner)! Can't find online or in manaul normal LB's/minute! Anyone know if that's the right amount of air flow or were I can find that info????

This is why I need EFI live! Oh, Elaina probably won't see this.

Try running with the MAF unplugged. See if it's better or worse.

Last run after air filter serviced and re-oiled -- no backfiring noted! Problem solved??? Time will tell..thanks for everyones ideas!!

Ah! Running K&N filter? You should switch to a dry filter.

Yep...I read all about wet vs dry filters! Dry sounds like the way to go!!!! My was really "wet" with 10/40w motor oil.

Nice, "extra" lube!

Wow, glad to hear you found the problem!