TwitchZ28

iTrader: (3)

So here is the back story. Nearly a year ago I had a 228/228 .588/.588 112 cam installed with the supporting 255 walbro pump in my 2002 z28. The car has full bolt on's and long tubes, and a 3200 converter.

After the cam install I had it tuned, and all was well...for about 10 miles.

The car surged at low speeds especially in reverse. The rpms would flucuate and the car would stall out. The problem started small and got increasingly worse as the miles increased.

I went back to my tuner and he met me to adjust it. The car was at full temp the entire time he did the re-adjusting. When I left it was perfect.....for about another 15 miles.

The same issues have returned and are worse than ever. Low speed stalling, acting differently at different engine temps.

Things that make it better:
Resetting the tps
Pulling the battery cables and resetting the ecu.

Things that make it worse:
Reverse upon cold start
being in the temp range between cold and almost full operating temp
stop and go traffic(getting on the gas, then off and on the brake quickly.)
re-starts after being driven and then shut off for less than 10 mins. It will fire and instantly stall. Turn it over again and it starts and does not stall.


Things I have replaced:
TPS(Local auto parts store had a scanner that did live data and the tps was reading 14 at hot idle.) I don't know if that's volts or percent...but either is wrong so I replaced it.

Coolant temp sensor(no change, but I got it for free so no big deal



I am really at a loss. The car runs rich, stalls out at low speed after the rpms surge and fluctuate. It acts better or worse depending on the temp range it's in. I just can't figure out the issue. The tuner has seen it twice and it's been perfect when I left both times. It's re-learning something incorrectly...I just don't know what. This cam on a stock throttle body shouldn't be an issue. Any ideas guys?

TwitchZ28

iTrader: (3)

100 views and nothing?

SSellers

Possibly the O2's are getting fooled due to the cam overlap even with the 112 LSA. The exhaust gas can fool it into thinking it's lean and add more fuel so you chase your tail. Then you get a rich misfire which can further be read as lean and so on. I've got a 108 LSA in a SBC with an archaic EFI system along with a regular dizzy with vacuum advance and it was hell to get dialed in right off throttle and when clutching in coming to a stop.

Here's what I finally did to fix mine although it may not be exactly what yours needs. I set my low speed low load targets fairly lean and moved my vacuum advance to full manifold which pulled in 10 degrees extra timing. I was running ported advance before that and found that the hole wasn't drilled correctly in the TB so I wasn't actually pulling vacuum at very low throttle angles like it was supposed to. The leaner the mix, the more timing it needs to fire off correctly for full burn.

Anyway, that was my fix for low speed.... lean it out (which your tuner is probably doing) and add in more low load timing to help the lean mix burn better. Also after this I was able to greatly decrease my low throttle angle acceleration fuel enrichments (extra fuel when applying the throttle). It was previously too rich once I added in the extra timing and would start bucking when touching the gas at low speed.

Old Geezer

iTrader: (3)

Try posting the thread in the correct forum???
Tune/diagnostics may just be a source for more hits.....

TwitchZ28

iTrader: (3)

Will do. Mods if you want to delete this one go ahead.