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imtermittent stutter under boost

First off, not my car. It is a 92 talon, b16g, 550's, gm maft, keydiver chip, 1G dejon IC and piping, ngk bpr7es at .028" gap, napa beldon plug wires.

It was running awesome on 18 lbs, just a tiny bit of boost creep, that's it. A couple of days ago it started stuttering under boost, like it is misfiring. It is more pronounced at WOT. The stuttering starts at varying boost pressures.

He was thinking boost leak, I said ignition, but we tested for leaks anyway. The only leak we found was at the J-pipe to turbo flange, but his gm maf is set up as blow through, so I still think ignition.

We are going to warranty his wires and get new plugs, fix the j-pipe leak, and clean his maf. I am thinking that I'm forgetting something though, any suggestions?
 

Adorsey

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I dont know if you need a mafT with a keydiver, but was its raining out when he was driving?
Almost everyone running a gm with a mafT will get some sputter while driving in the dense moist air, aka rain.
 

No it's blue skies and about 90 degrees today. The keydiver chip was installed after the maft was installed. Neither us like the of trying to tune with the maft, so when he got the 550's, he got the keydiver too.
 

Well none of that made it right, only better. I went to get my datalogger from home, we drove his car plugged in for like 20 minutes, the O2 voltage stayed under .019 v the whole time and every one of his fuel trims was at 139%. The computer has a stored dtc of 11, which is the O2 sensor. We're going to change that, in hopes that the sensor is actually bad, tricking the ecu into thinking he is lean. Otherwise, he really is lean. Sad face!
 

Ok new O2 sensor and it is switching rich to lean to rich etc., but it seems a little slow, but it is working. I don't think we drove it enough to have the ecu relearn its fuel trims (we did reset the ecu), but this also didn't fix the original stutter either. I'm officially stumped.
 

Slap a known good maf on and rewire your fuel pump(cheap) if not already done.
 

We've been talking about re-wiring that pump for months now. I did forget to mention that the pump is SUPPOSED to be a 255. Sorry, I guess I ass-u-me that everyone just automatically upgrades. I like the idea of swapping in a different maf. It might be next weekend before we get back to it, but I'll repost once we've tried these.

.
 

The rewire should be performed with any fuelpump your running IMO. Keep us posted after you've tried these.
 
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Well sometimes it's the stupid shyza that kicks your arse. He just called me and said that he was checking his oil today and he decided that he'd go ahead and just double check his electrical connections. He said he found an injector clip that was "barely hanging on" and once he plugged it back in the car was back to normal. I guess we'll be cutting all of those off and replacing them, as the PO had broken them all. We'll still rewire the pump, as I agree with you Dbossman, but it's one thing at a time when you buy someone else's project. When he first got the car, it had a brand new rebuild on the motor, and we had to perform "surgery" three times in the first 200 miles to make it right. The first time was replace the reused lifters that shouldn't have been reused. The second time was to replace the rods and mains because the re builder never plugged the b/s oil feeds after performing a b/s elimination. The crank was just barely scored(we caught it early) so we robbed one from a builder motor that we had and polished it up. The third go around was because the arp heads weren't ever retorqued and they used a crap gasket. So since both the head and block had been decked, and the head was still flat, we grabbed up a mitsu MLS and the motor has been super solid ever since.
 

Wow! Sounds like you've been through an adventure with this one. Definitely was a halfassed build when you got it. Good luck with all.
 

Yeah, the car was very hacked together when he got it. But its coming along nicely now. His galant has been JSB since '07 so he picked this up to feed the 4G63 need.
 
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