dcairns Posted November 11, 2004 Report Posted November 11, 2004 A few others have commented on this and I thought I would see if I could catch it in the act with EFILive running I can't tell what is cause and what is effect on this. You can see the RPM dip, centered on the vertical grey line. This occurs despite a constant throttle position (and actually increased TP a bit, in my foot's response to the stumble). The AF ratio is going rich about the same time. I see the MAF remaining flat while the MAP is making a bit of a peak. I also see the timing has been retarding slightly in advance of the event. Any takers on reading the "tea leaves"? Sorry about the size of the pic. You may need to scroll around a bit.
2nd Sierra Posted November 13, 2004 Report Posted November 13, 2004 good question because mine is doing the same thing. Let's hope someone can steer us in the right direction.
hank Posted November 14, 2004 Report Posted November 14, 2004 mine has been doing this since i got the radix 17000+ miles ago. i'd call it normal now.
deezel Posted November 14, 2004 Report Posted November 14, 2004 Was there a 1-2 gear shift going on there? My guess on the stumble is that the open loop AFR table is not properly adjusted.
dcairns Posted November 15, 2004 Author Report Posted November 15, 2004 It's not a big deal, just happens within the first min after startup. I just thought I would capture it, since others have mentioned the problem too. There is no shift involved.
hank Posted November 15, 2004 Report Posted November 15, 2004 mine only does it right after the 1-2 shift when it is cold and only for about the first minute after start up. by the way, I've gotten about 5 or 6 tunes from Allen. the same thing still happens.
SS--BLOWN Posted December 6, 2004 Report Posted December 6, 2004 Brand newbie here--just got my SS 2 weeks ago and the Radix installed on Friday, Dec. 3rd. I have had a couple of instances that are similar to what is described above and want to make sure it's the same thing. Two or three times now, between shifts 1-2 under full acceleration I have bogged down for almost 1/2-second. Feels like either the shift is taking too long or it is stalling. This has prompted me to wonder if there is a need for a TransGo reprogramming (not sure what this does to Radix tune--any help here would be appreciated), or if this is just cold-engine performance. I will try to note if it happens again on a warm engine. Thanks for any suggestions. Michael
vdrumright Posted December 6, 2004 Report Posted December 6, 2004 I have a split second stumble at 3000 rpm under hard acelleration.
BenKey Posted December 6, 2004 Report Posted December 6, 2004 Cold start stumbles have been a Radix problem for a while. Mine did it also. It got so bad in the past that they even issued an update to the tuning. I thought you already had that Dave? After I started tuning it myself it went away. Not sure why it did, it just did. It went away after just a few small changes in timing in the lower rpms. Not sure if that was it and forget what other changes that were made. It was some of the same things that you need to do for a bigger cam. After the PCM relearned the tune, it never did it again. Only reason why I say it's a tuning problem now, or in the past. Nothing against anyone's tuning or tunes. Maybe my truck was slightly different.
zippy Posted December 6, 2004 Report Posted December 6, 2004 good point ben.... dave, put a cam in there....
deezel Posted December 8, 2004 Report Posted December 8, 2004 Actually, Ben's point about low end timing makes sense. Assuming this issue occurs when the compressor begins to overpower the natural "suction" of the eninge... With the blower pushing a larger air/fuel charge into the cylinders, the engine will need more time to burn the mixture completely. Thus, more timing advance would provide smoother operation by allowing more complete combustion in this transition phase. Since its very slight "boost" conditions, it probably only needs slight timing adjustment.
yeary03SS Posted December 14, 2004 Report Posted December 14, 2004 The Radix on my old 01 5.3 engine did the same thing. Allen did a couple of tunes for me and it seemed to go away, but every once in a while would pop back up (mostly when it was really humid outside). Brian at magnacharger suggested to me it could be a fuel pressure problem. I rechecked the gaskets on the fuel pressure regulator and it ran great for a few weeks, but sure enough it came back, but it didn't stumble as much??????? I thought I was the only one who had this happen, but it sounds like it's common.
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