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Old 12-25-2010, 05:22 PM   #1
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Default engine acting wierd over 5psi.....Fuel or spark?

lets start off Im on my way home from St Augustine thursday afternoon, after driving for a bout 3 1/2 hrs of perfect smooth sailing, I go to pass a semi and out of no where it starts acting wierd it builds the boost after a slow period of time sounds like misses almost, now my first thought was Maybe something got unplugged, cut etc. etc. so I drive the rest of the way home because the car drives fine with a good AFR and no misses/issues, mean while during this rapid missing deal the AFR's are normal around 10:7-11:8 in boost.

when I got home I checked to see if there where any hoses popped, wires snipped etc, and nothing... I did notice my #4 coil had risen up from its mount a little, after tightening that back down I took it for another test drive same situation. I parked for the night and started hunting around

Fri morning I started to consider all the possibilities, spark/fuel, so I checked the plugs again and they were fine, I reflashed my tune checked all the perimeters and everything was the same. I then checked my fuel pump filter and it is a little rough looking, So tomorrow I'll be buying a new one. And attempt to discover what's going on.... Also tomorrow I'll be picking up a fuel pressure tester and see what's going on there, I'm at a loss for explanations..

help me out guys, BTW the car idles fine no misses perfect AFR's the only time it starts doing its **** is above 5psi.....

I'm running Ms1 v 12q or something along those lines...plugs are gapped at .040, I have cops. I'm runnig NGK iridium ix's heat range of 6 I believe? walbro 190 non HV version, they are new plugs and a new filter.

once I hit 5 psi the engine sounds like a machine gun, more or less...
help a brother out here people!!!!!
I've also verified that the MS is reading the KPA's correctly and I checked the MS loom for any loose or cut wires and there is nothing.....

THanks for all the help people I will provide as much info as I can just ask me!!
Thanks
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Old 12-25-2010, 05:48 PM   #2
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Boost leak test? If it's not building pressure and missing like a bitch its a possibility you have a leak in the charge piping.
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Old 12-25-2010, 06:33 PM   #3
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it builds the boost, just slower through out the boost increase how would you check for a boost leak
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Old 12-25-2010, 08:19 PM   #4
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Quote:
Originally Posted by p51hellfire View Post
it builds the boost, just slower through out the boost increase how would you check for a boost leak
By pressurizing the charge piping and listening for a leak? Go make a boost leak tester at home depot. It can leak all of the time (ie, vacuum leak) or it can leak above a certain point (1/2/5/10/50) psi. Check the couplers and make sure they're tight, and then attach the boost leak tester to the turbo compressor inlet and run ~10psi through your charge piping and listen carefully. Soapy water in a spray bottle around the couplers can help you see air escaping as well.

Also: you're on MS, but are you using the MAF for airflow?
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Old 12-25-2010, 09:16 PM   #5
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I'm having a hard time believing that a boost leak would cause these issues? What is your reasoning behind it? I'm not pushing the suggestion to the side I'm just interested in how exactly it would cause misses
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Old 12-25-2010, 09:36 PM   #6
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Yah well if its missing it aint a boost leak assuming you are MAP not MAF.

how do your plugs look? Really, I would say you have a coil, plug, or wiring issue.
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Old 12-25-2010, 09:55 PM   #7
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Plugs look ok they look a tad white cuse I cruise at around 15-15:8 doing about 70-80.. Other than that I'm thinking maybe your right however I just replaced the number one coil due to a wiring issue, so technically it might be that again? My spare is in st Augustine and I'm not paying 70 at my job .... But, when I did replace that coil I redid the entire harness new wire and all...
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Old 12-25-2010, 10:28 PM   #8
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Quote:
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Yah well if its missing it aint a boost leak assuming you are MAP not MAF.
Exactly, but if he was using MAF this would be my #1 diagnosis. That's why I asked.
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Old 12-26-2010, 12:10 PM   #9
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Well I'm about to replace the strainer, I hope thats the issue however I'm not getting to optimistic... I'll let ya know if anything changes, on another note keep giving me your ideas?
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Old 12-26-2010, 09:50 PM   #10
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What. the. ****. is the STRAINER 0_o
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Old 12-26-2010, 09:58 PM   #11
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I had a bad plug or two once. They went out like a swtich...one min. fine...the other they were causing a massive misfire. My car sounded like I was bounching off 2-step/launch control when I went into a few psi of boost. The plugs looked fine upon inspection so I wrote them off at first. Chased it for a few days and replaced the plugs and all was fine. YRMV.
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Old 12-26-2010, 10:46 PM   #12
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Old 12-27-2010, 12:21 AM   #13
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Dude fuel strainer..... You know the one on the end of your pump? Commonly know as a fuel pump filter/strainer.... On another note thanks dopple that sounds exactly like the problem I'm having... I will replace them in the morning!!
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Old 12-27-2010, 10:20 AM   #14
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I had that issue once when I forgot to plug in my iat sensor. Baking run fine but backfire like mad when I got on it.
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Old 12-27-2010, 12:13 PM   #15
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I've had bad plugs wires act similar to that too.
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Old 12-29-2010, 12:10 AM   #16
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So After changing the plugs and switching back to .040 gap, it has become worse.... so it's ignition related for sure, I'm going to redo my entire cops harness this time what does everyone run for plugs?? I have to check fuel pump pressure still...
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