mike_c

iTrader: (13)

The car idles rougher than normal and there is a low rpm miss/stumble below about 2000 rpms. This started after my MSD distributor took a dump on me. It would barely turn over with the MSD in it and it ran terribly at all rpms. I put in a new GM Performance distributor that fixed the barely starting and driving problem, but that's when the idle and low rpm stumble problems started. The weird thing is that the car runs better with the ESC module unplugged. I put a new ESC in it and the problem remains. Here's what's been replaced: Distributor, knock sensor, ESC, and plugs. I've swapped out the cap, rotor, and ICM on the GM dizzy with known good units as well. The base timing is set a 6* and fuel pressure is good at 43 psi. I should also add that this isn't a stock engine. It has an SR intake, AFR heads, and Comp 280XFI. I've been running with this combo all summer and haven't had any issues until now. Any suggestions on what could be going on here?

rusty vango

any codes? cel on ? hows your MAF? hows your MAF relays?

mike_c

iTrader: (13)

Forgot to mention that, no stored codes and no cel. Maf is older, but was replaced a few years ago. I'll swap out the maf relays with some spares and see what happens. Now that you mention it I remember getting a maf burnoff circuit code about a month ago but it hasn't come back since and only showed up that one time.

rusty vango

they are VERY sensitive . make sure you have the correct relays in the correct places. (and NO they don't use the same relays for both burn off and power) a common mistake. also don't forget that the fuel pump relay plays a part in the MAF power circuit.you can call up your favourite GM dealer and have them give you the GM relay part #s for the correct relays. then you can be sure to have the correct ones. also a factory service manual is your best friend. NO a Haynes or chiltons wont do. just a heads up from a member who has been there and done that.

mike_c

iTrader: (13)

Thanks for the tip. I'll give the relays a try tomorrow if I can track some down locally. The maf and related relays being the issue makes sense because iirc, the ecm takes inputs from the maf up until only a certain point and then the ecm ignores it, correct? That would explain why it runs OK with more throttle input and at higher rpms. Forgive me if I got that totally wrong.

rusty vango

nah, the ECM has total control, UNTILL the MAF and/or relays are not within spec. then it all goes to hell. the key is proper ,quality components and wiring. any one of these not up to snuff can, and WILL drive you stupid. (ask me how I found THAT out)

maks10

Was the msd in there while it was running well? Was your final tune around this time the dizzy was failing? I'm thinking tune since it runs ok when esc unplugged ....hook it up and try adjusting tables...or if you have tuning done, if you haven't already try to datalog and see what's going on at idle and 2k

TylerSteez

iTrader: (3)

the maf was the first thing I thought of, If you have a friend with a tpi with a maf sensor try his maf on your car and see if it fixes the problem

mike_c

iTrader: (13)

Finally got it figured out! I datalogged it the other day and compared it to some old logs that I had. MAF values all seemed normal and nothing else really seemed out of whack. So on a hunch, I went ahead and checked the TDC mark on the dampener against the actual TDC and go figure, it was off quite a bit. So when I thought I was setting the base timing at 6* I was actually setting it at a lot more than that. I'm estimating it was at about 12-14*. It was strange that it wasn't audibly pinging and I got zero knock counts. This also would seem to explain why it ran better with the ESC module disconnected because with ESC unplugged, the ECM would pull timing, right? I'm kinda ticked that the dampener slipped because it's only a few thousand miles old and was a brand new GM part. But at least it's running like it should be again. With that, does anyone have any suggestions for a replacement dampener?

maks10

Nice you figured it out!!!! Not for sure on timing pull with esc unplugged but it obviously goes into a default mode (maybe someone can explain)

but great news on fixing it!!!

I just have a stock replacement jegs brand dampner and does fine