Under boost, loud pop!

H

HRobertson1

Member
Joined
May 30, 2011
I have finally got my car back on the road with the help of Scott Atkinson. I snapped my stock crank in half last December and its been a whirlwind of parts and money since then. When I broke the crank it was under boost, between 10-15 pounds, and I heard a loud pop, the engine looses power for a sec, I let off the gas, and it just picks right back up. I was hoping since almost everything in the engine bay is new now, that issue would have dissappeared, but no. I took it out for its maiden journey around midnight last night, gave it about half throttle, and POP!, same thing again. I checked all of the IC hoses, all are still secure. Other than that one thing it seems to run awesome. I have a powerlogger I still need to install, but I have the scanmaster on and running, nothing looked funky. Is there anything that comes to mind that would cause that?
 
I am not an expert yet but I am sure everyone will ask you the running conditions first, Engine temp, Air temp, how much Alky, fuel pressure check, AFR and O2 volts etc?

I had a Pop recently through the intake, the engine was cold and the air at 75 deg. I believe the alky at low temp was my problem. I have not had the problem since I made sure the car was fully warmed up.
 
Maybe sounds like bad ignition coil,wires. Wrong spark plug wire on wrong plug. Check the basics.
 
I will try to install the powerlogger tonight to get some numbers. Everything on/in the engine is new except the coil and crank sensor
 
Some suggestions, maybe raw fuel or alchy getting into the exh. system, by a leaky inj. or siphoning of alchy. Loose reluctor ring, crank sensor, etc.
 
I had the same problem. It was my M.A.F. At least that what it sounds like. If you have a friend close that you could borrow M.a.f. Fixed my problem.
 
No wideband. I got the powerlogger in, just need to install on the laptop. I hope to have some numbers up soon. After doing some thinking, I need to check the MAF and the translator (horsepower in a box). It was one of the first things I switched when I got the car, I remember opening it and having to flip switches around. I wonder if I did it right?
 
HRobertson1 said:
No wideband. I got the powerlogger in, just need to install on the laptop. I hope to have some numbers up soon. After doing some thinking, I need to check the MAF and the translator (horsepower in a box). It was one of the first things I switched when I got the car, I remember opening it and having to flip switches around. I wonder if I did it right?
Click to expand...
Id check that first thing then
 
Ok, Finally got the PL in, heres the file. You can see where the pop is the rpm goes from 5k to 1250then back to 4k, any help is appreciated
 

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If I'm reading the log correctly:
Boost is 15psi
Rpm is 6025
tps is 2.44
Maf is 203 G/S

Looks fishy...
 
One of the worst backfires I ever had was because of a loose cam sensor. At wide open throttle, it moved and caused a back fire that sounded like a shot gun. Dented the up pipe and cracked the paint of the hood
 
No I havnt tried that yet Burt, I will try to hunt one down. Scott I can bring the laptop over to see the file, or I can email it to you. I dont know how to take a snapshot.
 
I got a new coil and module on its way. My chip was burned by Eric for 24lbs of boost, I am running about 12-15 until I can get this figured out. Would that have anything to do with anything? I have been doing a lot of reading but the PowerLogger is still confusing to me.
 
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