99horsey

Background: I installed a Department of Boost GT500 blower a couple weeks ago. Got it dyno tuned last Friday. On the dyno, we discovered that the clutch is slipping. The car ran great on Friday but between heading to the dyno and the last time I drove it, it never got cold. Saturday morning I drove it and it kept going lean and falling on its face. Later Saturday I drove it and it was bad until it got warm, then it drove ok. I talked to the tuner and he thinks that it's not running on the correct fuel table when the engine is cold. He sent me a new tune Monday and I loaded it and it was pretty much the same. He had me datalog last night and it still behaved the same (I talked to him this afternoon and he hadn't had a chance to look at the log file), when cold, it would fall on its face with more than 10% or so throttle, after it was warm, it was ok. I drove it to work this morning to see how it did in colder weather (30s). Same deal, stumbled until the engine got warm, then it did ok.

Tonight I went to go home and the car won't start. It cranks and starts to run on it's own and immediately dies. After several tries like this, I gave it a little gas when it was "sort of" running and couldn't get it to stay running. It seems like it's getting gas - when I replaced the fuel pump, I cranked it with the fuel pump fuse out and in that case it just cranks and cranks. Now it "tries" to run but craps out. So I think it's getting fuel based on that difference. It's not throwing any codes. I tried reloading the tune - same deal. Loaded the original tune from Friday - same deal. So I don't think it's tune related. Even when I had a startup tune before the dyno, it started up and idled just fine.

The only things I can think of are MAF problem or throttle body problem. On the way home (the car is still stuck at my office), I thought about the bypass valve - if it had a problem or if the vacuum line to it leaked, it might not open which would cause too much load on the belt and/or not enough air flow at idle and could choke out the engine?

Anybody have any other ideas to look at? I have to assume that whatever the problem is has something to do with the blower install even though it ran ok up through this morning. Or maybe it's a complete coincidence, but then it's anybody's guess...

Simon1

It's your cold based timing and fuel table most likely. Call your tuner and explain it's not fixed. It's pretty common for this to happen. The only fix is in the tuning.

If the weather is warm where you are you can park your car outside and let it get warm so it can start so you can drive it to get fixed.

99horsey

Thanks for the response. Yes, that is definitely at least part of the issue, if not the whole issue. The tuner confirmed with my datalog that it's using the normal fuel table on startup instead of the one that it should use up to 170 degrees ECT. He's trying to figure that out. It seems possible that is also what is not allowing the car to start. I definitely suspect the tune at this point. This tuner does Mustangs all the time and should know what he is doing but has never run into this before. So either he sucks or it's just my luck that something very unusual and goofy is going on with my car.

The next problem is somehow my stock tune is corrupt. I loaded it and the car won't turn over. The screen on the dash that shows odometer, trip, etc. just shows dashes and the tuner won't read the strategy or anything. If I flash back to one of the custom tunes I have, it all looks ok and cranks but immediately dies.

I do have an old Bama tune (pre blower) that I might flash just to see if I can get it started and confirm it is the tune.

Simon1

I would make sure your battery is fully charged too.

If your tuner has never ran into this, I would be suspicious. It's a fairly common tuning issue to have on FI cars when they are first getting retuned.

99horsey

I flashed my old Bama NA tune and the car started right up. No hesitation at all. After it got warm, I went to the dyno tune and it also started. I am now very suspicious of my tuner. I would have completely written them off by now if they were not a Mustang only shop that has done countless S197 FI tunes. They had to drive a 2010 GT500 off the dyno that made 918 to the wheels to do my car. My car should be cake for them. I don't know what to think...