Stumbling issue
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From: Havelock, NC
Stumbling issue Hey guys. I have a 2000 SS M6. It has an LS6 intake, Pacesetter lt's, ory, asp 25% u/d pulley, lm1, msd wired, and tr5 plugs. Nothing out of the ordinary but lately the car stumbles and shutters some around 5k rpms and drops off bad. I haven't had a tune but I did have it dyno'd and saw that the AFR was around 14.2 at wot. It looks likes it's pulling time up top on the graph too. I'm going to try changing the plugs and seeing if it helps but I've heard that ASP pulleys can cause false knock making it pull timing like that. I hope it can just be tuned with new plugs and work out fine. The mods have been on for seven months and it's only been stumbling for a few weeks. Anyone else heard of this?
Hey guys. I have a 2000 SS M6. It has an LS6 intake, Pacesetter lt's, ory, asp 25% u/d pulley, lm1, msd wired, and tr5 plugs. Nothing out of the ordinary but lately the car stumbles and shutters some around 5k rpms and drops off bad. I haven't had a tune but I did have it dyno'd and saw that the AFR was around 14.2 at wot. It looks likes it's pulling time up top on the graph too. I'm going to try changing the plugs and seeing if it helps but I've heard that ASP pulleys can cause false knock making it pull timing like that. I hope it can just be tuned with new plugs and work out fine. The mods have been on for seven months and it's only been stumbling for a few weeks. Anyone else heard of this?
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From: Havelock, NC
I cleaned the MAF and the TB today and the problem is no different. Jamie and I are going to check the plugs since they've been in there for about 20K miles and 10K has been way too lean. If that's not the problem we'll check the fuel psi.
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From: Havelock, NC
Bump for more ideas. We changed the plugs and the problem still exists. I won't be able to check the fuel psi until Monday or Tuesday. Anybody else have any insight on it?
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From: Havelock, NC
We installed a Walbro 255 kit today because I was told that the reason it was stumbling was because it was starved for fuel at WOT and they also said that the reason it was lean on the dyno (mid-14's afr) was probably due to the fuel pump being weak. At first it did great but on the second time I did a first through third pull it started to stumble@ 5k rpms again. Any more suggestions?
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From: Havelock, NC
I guess that would be the best time to do a cam swap. *sigh* Thanks Steve. Jamie said his was acting very similar just before the valvespring broke. For over a year now I've had a lifter tapping intermittently and I was worried it'd be in the valvetrain. I'll be calling Tony @ Speed Inc. this week or next.
I wouldn't jump to conclusions, you can get the valve covers off pretty quick and have a look at what's going on. You might not see anything, or there might be something that sticks out like a sore thumb.
Any single cylinder misfiring will whack the wideband
reading on the dyno. At 10 years old, it's not unlikely
to have developed an injector imbalance from silt
accumulation (I've had cars do it in 5, and then
be fine for another 10 with no touching; go figure).
Did you look at the plugs when you changed them?
See any cylinder-cylinder differences in appearance?
reading on the dyno. At 10 years old, it's not unlikely
to have developed an injector imbalance from silt
accumulation (I've had cars do it in 5, and then
be fine for another 10 with no touching; go figure).
Did you look at the plugs when you changed them?
See any cylinder-cylinder differences in appearance?
you should have put a fuel pressure gauge on it before you wasted your money on a fuel pump. Here's a stupid question but whens the last time you changed your fuel filter? Maybe you have a vacuum leak.....Have you checked your vacuum at idle? I'm not surprised your getting KR and big time power loss running a 14.0:1 a/f ratio.
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From: Havelock, NC
When I changed the plugs they all looked the same. My buddy checked the fuel pressure and it was 56psi @ idle. We talked to Mayhem Motorsports and told them what was going on and told them that we had changed the plugs, O2's, and fuel filter within the last few weeks and they said it was definitely fuel-related. They said they had tested cars with great fuel pressure at idle that fell off on the top-end and they suggested changing the pump and filter. I have not checked the injectors though, or the regulator for that matter. Thanks for the replies guys.
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From: Havelock, NC
The appointment went awesome but we couldn't figure it out. Jeff (the tuner) worked for 6 hours messing with the tune, data-logging, changing plugs and wires and switching coilpacks, and taking off the valve covers for visual inspection of the springs. Nothing fixed it but he did suggest that it could still be a weak valve spring or something else with the valvetrain so my best friends and I are doing a cam swap in the next few weeks.
