wheeljo2

iTrader: (2)

I'm running twin 57mm HP turbo kit on my 99 C5 347 forged 9:1 compression motor with 317 heads. I'm getting an intermittent popping at speeds under 3,000 RPM, generally under a load where it is most noticeable and right at the point where the gauge starts to read boost.

My A/F gauge is reading generally in the 13-15 range and the throttle is probably around 20-35%. Nothing out of the ordinary is showing up on HP Tuners. Has anyone ever encountered anything like this before? I am running a SLP MAF and thought perhaps this might be a suspect.

Any help or advice you could provide would be greatly appreciated.

Josh@MASPORT

iTrader: (3)

sounds exactly like your going lean and misfiring, but the gauge says differently........ could be a problem with a single cylinder also, injector, spark plug or pcm issue etc

does your wideband always read right?

wheeljo2

iTrader: (2)

Going lean is exactly what I was thinking but there are no misfire codes showing up. My A/F gauge does not seem to transition at part throttle from 13-14 to 11-12 like I would think it would. A/F O/2 is plumbed into the left side bank cylinders 1,3,5,7 and once I get to 3K and over 50% throttle is drops down to 10.5 or so where is needs to be. Plugs are new NGK TR6 gapped at .028, injectors are 60 lb mototron.

wheeljo2

iTrader: (2)

Ok I have a new theory, I disconnected my Meth pump but the main line is still plumbed into my throttle body. Could perhaps the boost in the intake tract be igniting the methanol still in the line? Otherwise, I'm thinking maybe a plug wire could be breaking down as a few of them were slightly burned from touching the headers. My wires are MSD 8mnm and I hear those aren't the best. Is anyone running those 10.4MM Taylor Thundervolt wires?

frcefed98

iTrader: (16)

I agree with Josh, it sounds like a lean condition.

wheeljo2

iTrader: (2)

Assuming I'm going lean, what A/F ratios would you expect in this case? There was a Meth pump on the car when I bought it and the vacuum switch was pumping in the meth at full bore at the first sign of boost so I'm thinking I need to richen the fuel between 2-3K RPM to offset the fact that there is no longer Meth being injected. You agree? Would a plug wire breaking down show up on HP Tuners?

RW99

Are you hearing the pop from the motor (perhaps lean) or from the exhaust (perhaps rich)? In the first case, perhaps the setup was tuned to use methanol and you've now removed necessary fuel... Are you seeing any knock retard?

If you've burnt a wire or two, you may have unburnt fuel making its way into your exhaust and lighting off?

wheeljo2

iTrader: (2)

I put my stock Packard wires back on to try it out and the pop is generally gone for the most part the motor seems smoother, idles down quicker after getting out of the gas. My tune is very rich at the moment 10.0 but climbs to 12.0 at the higher RPM range. How do I determine if I need a boost a pump or merely richen up the top end? Should I be looking at the injector duty cycle % and see if it is over 80%?

calongo_SS

iTrader: (7)

You need to check your duty cycle, but more importanty you should check fuel pressure in the areas that are going lean.

jason02Z

iTrader: (10)

my car had similar problems. once it would get close to 3000 rpm's it would start poping and would fall on its face. my hp tuners read fine. but the turbo side would get real hot and melt some wires i would change them and would work a lil beter but still **** the bed the first time i would bring up the boost. so after i narowed it down to i had low fuel pressure becouse of my intank fuel line would start to come apart from i dont know what, maybe the ethinal in the gas now. but it would do the same as ur goin through. lean on fuel hot exhaust melted wires blown o2's and made it run like ****. fixed the fuel psi new custom wires also so it wouldnt come close to the turbo header and runs great. it seems with turbo cars especial if u try to fix things on ur oun u learn all the lil things that big problems work.

moehorsepower

iTrader: (3)

If the A/F is good and it is popping through the intake under load, you may need more timing in that area, Log and add conservatively and see if that helps..