Fully Built LQ9 Missfiring/Stalling/Sputtering/Backfiring At Any TP when warm
09-26-2017, 04:25 AM
#1
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Fully Built LQ9 Missfiring/Stalling/Sputtering/Backfiring At Any TP when warm Sorry if this doesnt belong here....i couldnt find where to post this.
Ok so a little history if you don't already know. 2 year project of mine, lq9 iron block fully built, by fully built I mean .30 over, sleeved, pistons, rods, heads, intake, ARP yada yada yada. Built by me to support well over 1500whp. Sent it to the same state that I bought the shell from to have it and the trans installed this year, tuned by a shop out there (it's a SD "speed density" tune so no maf guys) flew out, drove it back, lots of issues on the way back....none of which had to do with the engine...in fact I still think my work is good as I don't think my problem has anything to do with my engine and so far all the other problems haven't either, o2's, plugs, wires, thermostat, MAP, crank sensor, iat sensor, TPS sensor, alternator, battery, basically all the stuff I paid them to do/install/check before they let the tuner do his work then check before I drove it back which was 1800 miles. Anyways, after all that it seemed to be fine...not even 3000 miles on it yet. Today driving to LA all seemed well, on the way back it all of a sudden started backfiring...and we're not talking like 1 or 2 every once in awhile, I mean like anytime I went anywhere near part throttle or 25% throttle and got way worse as I progressively got further in the throttle until WOT. So I stopped gave it a break and looked stuff over, didn't see anything out of ordinary so after it cooled I started up and it took off fine and cruised fine until it warmed up again then all hell broke loose again....literally, fire ***** as if I had my 2 step turned on and was using it....or dat naawwwsss. Anyways, so I got it home and now she sits because I'm stumped, not much that can go wrong with speed density and my AFR are normal at 12-14 cruising and 11-12 on it (I'm boosted making nearly 1000whp on pump gas so that's normal for me especially with the compression ratio I built the engine for) and not a single speck of smoke or oil in the plugs.....I'm in the engine alone $30k not including the shell and everything else so im kinda broke at the moment so be gentle.....thank you in advance for help.
Ok so a little history if you don't already know. 2 year project of mine, lq9 iron block fully built, by fully built I mean .30 over, sleeved, pistons, rods, heads, intake, ARP yada yada yada. Built by me to support well over 1500whp. Sent it to the same state that I bought the shell from to have it and the trans installed this year, tuned by a shop out there (it's a SD "speed density" tune so no maf guys) flew out, drove it back, lots of issues on the way back....none of which had to do with the engine...in fact I still think my work is good as I don't think my problem has anything to do with my engine and so far all the other problems haven't either, o2's, plugs, wires, thermostat, MAP, crank sensor, iat sensor, TPS sensor, alternator, battery, basically all the stuff I paid them to do/install/check before they let the tuner do his work then check before I drove it back which was 1800 miles. Anyways, after all that it seemed to be fine...not even 3000 miles on it yet. Today driving to LA all seemed well, on the way back it all of a sudden started backfiring...and we're not talking like 1 or 2 every once in awhile, I mean like anytime I went anywhere near part throttle or 25% throttle and got way worse as I progressively got further in the throttle until WOT. So I stopped gave it a break and looked stuff over, didn't see anything out of ordinary so after it cooled I started up and it took off fine and cruised fine until it warmed up again then all hell broke loose again....literally, fire ***** as if I had my 2 step turned on and was using it....or dat naawwwsss. Anyways, so I got it home and now she sits because I'm stumped, not much that can go wrong with speed density and my AFR are normal at 12-14 cruising and 11-12 on it (I'm boosted making nearly 1000whp on pump gas so that's normal for me especially with the compression ratio I built the engine for) and not a single speck of smoke or oil in the plugs.....I'm in the engine alone $30k not including the shell and everything else so im kinda broke at the moment so be gentle.....thank you in advance for help.
02-07-2018, 04:39 AM
#2
Is it a 1998 PCM.....?
When Coolant Temp Sensors start to fail on a 1998 PCM and wiring harness....you will get your exact symptoms.
----and if its misfiring, backfiring and hesitating....do not ever go WOT. Even a fully built engine can grenade if you do.
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When Coolant Temp Sensors start to fail on a 1998 PCM and wiring harness....you will get your exact symptoms.
----and if its misfiring, backfiring and hesitating....do not ever go WOT. Even a fully built engine can grenade if you do.
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02-07-2018, 04:42 AM
#3
Also, 02 sensors.....when it goes to closed loop after it warms up can cause these wacky issues.....IF one or both 02 sensors are failing.
No, you will not necessarily get a SES code until the 02 sensor is 100% dead. My PCM will not give me an SES code until an 02 sensor is completely dead.
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No, you will not necessarily get a SES code until the 02 sensor is 100% dead. My PCM will not give me an SES code until an 02 sensor is completely dead.
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