can anyone help?? i have a 95 z 383 a/i headed car. a/i cam, a/i intake. holley 58mm. trick flow 36# injectors, msd coil, msd opti (adjustable one), msd 6al, racetronix fuel pump sys. valve timing is dot to dot....used a degree wheel and it was right on. 12.25:1 cr running 93 octane right now. car was tuned by bluecat up in ky. elevation is way different from where i am (i'm a lot higher). car seemed to do good up there. the only thing i have changed is the spark plugs since the tune. went from delco to ngk 8s (requested by my tuner due to application). i have a intake pop. @ night u can see fire coming out of the maf. earlier today i had the cut outs open and removed the screen from my maf (very carefully removing the retaining ring...did not damage maf sensors) and i couldn't get it to backfire. i capped the exhaust tonight and changed the oil and ran it for a bit and it is popping again. it does it from idle when you snap the throttle and sometimes on a pull under load. CANNOT be good on the engine. if anyone knows what can cause this or has been through this plz help!! thanks

 

Fuel pressure is good (under load and idling), i've replaced my intake runner gaskets for good measure, sprayed brake clean on all vacuum areas and hoses and got nothing, i'm kinda at a loss for what to try next! (these few things are not the only things i've tried)

 

Please do NOT "bump" a post until 24-hours have elapsed. To expect someone to answer in 30 minutes at midnight is not a reasonable expectation.

Might not have gotten a response to this point because you are on the wrong forum. You are asking about an LT1 engine, so I'll move this to LT1 Based Engine Tech, where it belongs.

 

i have found similar problems to mine on other forums but it seems like every time you get close to what may be a solution they just quit talking about it ??!! thanks anyone for any help at all

 

I had a similar problem to this before. It sounds like it would be a intake valve issue, but if you say your valve adjustments are good then I'm not sure what would be the next step. Maybe double check to see if an intake valve isn't tight?

 

i'm more than willing to check it again....the other day i had a friend come over and lay under the car and turn the engine over so i could dedicate my comlete attention to adjusting the valves. i'm positive they are done right though. i'm actually a mechanic for caterpillar and i know anybody can make a mistake but i went over the valves very good haha. i was hoping it would be something that simple but not my luck

 

maybe retard the timing a bit? I mean there is only a few ways to get fire going the wrong way in an engine right?

 

Is it possible you have cross-firing on the wires, or in the Opti cap, and a couple cylinders are firing with the intake valve open?

You mention an elevation issue, but don't provide any hard numbers? What was the elevation where it was "tuned"? What is the elevation where you are at now? Shouldn't make a lot of difference, unless the MAP sensor is bad or unless they put a lot of advance into the low load/lowMAP area.

 

catlettsburg ky is 553 ft. abingdon va (where i am) is 2200 ft. i'm pretty sure the wires arent' cross firing. as far as the opti......it's practically new msd (adjustible timing -/+5) i know that doesn't mean much that its new.. i do know bluecat put a lot of timing into it and said i may end up having to run race fuel in it due to cr and timing.

 

could a bad icm cause it to fire @ the wrong time?

 

i retarted the timing as much as my opti would let me and no change but i haven't hooked up my laptop with cats and messed with anything there.

 

No, not the ICM. The PCM tells it when to fire, based on the cam position signal from the Opti, and the value pulled off the timing table showing RPM vs. MAP (plus a few other offset adjustments).

One of the problems with the MSD's adjustable timing feature is the fact that there is no "0" reference, so you have no idea where its actually set. Try retarding the timing with the screw and see if the "fire" in the MAF sensor goes away (which it appears you may have already tried).

You seem to dismiss the idea of cross-firing very easilly. Have you observed the wires in the dark?

 

yeah last night i was watchin it very close i didn't see anything on the wire side. and when bluecat tuned it he turned the timing screw all the way in before he started tuning and told me i wouldn't need to mess with it but last night i did retard it all the way and it didn't seem to help

 

bump

 

Pull the opti and check the rotor and optical sensor. It is worth a try. My car acted the same way right before my rotor destroyed the opti.