I did a cam and head swap, along with injectors. Went from 28's to 42's from John at FIC. BTW very nice guy to deal with. But here is by problem, I can get the car to run and idle, but it takes huge LTFT's to do it, they max out at 25 on both banks. If I shut off the LTFT's or clear them out it dies. I've tried using a couple different VE tables, as a starting point, with the same result. One was my stock table, another was a VE table from another car which has the same cam and heads I do, which was professionally tuned and right on the money in that car. Theoretically it should use less fuel at idle than a stock cam because of lower VE than the stock table calls for right?

I used the RussK method to set up my idle. I have set hot idle to 850, and added a couple g/s of idle airflow, and stuck in more timing, about 10 degrees, until vaccum improved. Pulling about 57-59 kPa on the MAP at idle. It is actually starting and idling decently, but I can't really even start to tune the VE table, because I am so lean with the fuel trims turned off.

I actually thought of multiplying my whole VE table by 1.25 but this makes many of the numbers rediculously high. I did multiply the numbers in both the primary VE and 2ndary VE, 800 and 1200 columns by 1.10 to try to give it more fuel, but this didn't seem to make any difference?

I have my my injector flow rates set at 42 at 0 through 46 at 80 kPa vacuum, as calculated by a spread sheet I found on the net? I think this should be correct for 42 lb injectors.

I do have an LC 1 hooked up, and I did take the car for a little drive. A couple miles at light throttle. It goes way lean for a little when it enters a new fuel trim cell, then when the trims come in, it gets itself back to stioch. It is drivable, but barely.

Any ideas about what is going on here? I have thought of fuel pressure, but the car was running fine before the swap. Possibly wrong injectors? I was thinking of putting the 28's back in and setting the computer back to those?
Any ideas would be helpful.

 

Whats your afr at idle? and if your tuning the car why are ltft enabled? Are you running a maf or sd? Also did you input the correct offsets voltage? I doubt its the injectors,more than likely the tune.if your using hp tuners open the scanner while idling and use the diagnostic section and try adding timing or removing air. That way you can easily see if something makes a significant differance

 

Thanks for the response. I really hadn't started tuning the car per se yet. I just wanted to get it to run enough to start data logging, and get a heat cycle into the new valve springs. Before the fuel trims kicked in was bouncing around in the 17ish range, and stalling. I am running a maf. I did not change the voltage offsets, it sounds like this may be my problem. I am using stock injectors that have been rebuild/reflowed to the 42, I did not realize they would have different offsets? I'm looking into that now. thanks again for the response.

 

"I have thought of fuel pressure, but"...........You haven't checked it??

 

What are your injector numbers?
Are you sure they are right? Did you check advertised pressure vs GM pressure?
Most are 3 bar, but GM is 4 bar rail etc.
Id be looking at injector values first.

 

I believed this was his problem as well the first time I read it. But, he said his IFR starts at 42. If the injector flow rate is lower than what the injectors flow, that would make the car run rich (because the PCM thinks it needs to keep the injectors open longer). Then again, it sounds like he's using re-drilled injectors. So, it could be that their flow is less than what was claimed. I've always been hesitant to try those...



OP - Maybe you should post up your tune and a list of your mods for someone to take a look at and see what's been done so far. I see what's in your sig - is that up to date? Any idea on what your compression ratio is with those heads? Also, I'd start checking for leaks (vacuum leaks, exhaust leaks, etc.) and find a way to see what your fuel pressure looks like (at idle, under throttle, etc).

For the short term, it might be worth it to switch back in the 28lb injectors and work on the normal driving part of the tune to at least get things close.

 

injector o-rings sealing correctly ?

 

Is it the stock/original MAF? Try unplugging the MAF and see if it is the cause. Those injectors should use the stock voltage offsets. Also, put a fuel pressure gage on it to verify pressure.

 

Thanks for all the input on this one. I have spent considerable time looking for a vacuum leak to no avail. I don't think thats it, but not 100% sure. I have not yet put a fuel pressure gauge on it yet, I'm not sure about the easiest eay to plumb that into the stock rails? Prior to the swap fueling was fine, so I'm doubtful it is fuel pressure, but I know it needs to be verified. The mods in the sig are correct, the heads have been milled alot, 0.060, so static compression should be a little over 11:1.

I have attached a tune and a log, for some reason the config didn't attach?

Thanks again for any help.
98 Camaro HC start up tune.hpt

went to gas.hpl

 

Your tune is not edited correctly for 42lbs injectors. If they are the green tops / green giants then everything dealing with the injectors in your tune is way off.

Your fuel trims will never come in right with bad injector information.

 

He said above that he's running factory injectors that were re-drilled to flow 42lbs/hr...

 

It looks like BLK02WS6 hit the nail on the head. I think the MAF was the problem, it is the stock one, now it seems to be giving bad data. The car did seem to run well before I changed out the heads/cam. I never did take the MAF out of the lid, but now it seem to be a problem? Maybe it had problems before and they were hid by fuel trims? Unplugging it made the car go extremely rich 10.5 ish, and the fuel trims actually go negative in closed loop. I'm going to go ahead and leave it unplugged, and shut off the fuel trims, and start getting the VE table dialed in. Hopefully that is the end of the troubles. I'll update the thread when I work it abit more. Thanks everyone who has contributed.

 

Glad you found it! Was probably being hid by the trims like you said... as the F-cars get older, stuff like that happens more and more. I always go to simplest setup (open loop speed density) so you have the least variables contributing to a problem - then as you add things back in, you will find the problem...

 

Yep, an untuned MAF will make the trims go haywire. It's best to go straight SD and start tuning immediately.

 

Just some thoughts here....you said that after adding .10 to the 800/1200 columns, it does ok....but then goes way lean at a certain point? If I'm understanding you correctly, drive the car in SD mode with PE disabled and ect scalar set to 1.0 in the 140*-230* range. Drive GENTLY/CONSERVATIVELY with the fans commanded to "on", while paying close attention to IAT numbers....I'm thinking that you want them less than 90*, and the ECT's at 190*-200*.....then log the FIRST column that starts to go lean....I'm guessing from what you wrote earlier that it starts going lean in the 1600 column? If so, try to log that entire column (foot on brake, foot on gas to try to mimic steady state/steady RPM...shooting for at least 30 cell hits each). Take the average percentage that you're lean in that column, and apply the same percentage of correction required in that column (ideally whatever will get you to 10% to 15% RICH) to the rest of the table from 1600 on up. At least that way, you should have a decent "starting point" to continue logging from and making VE corrections and not have to worry so much about going lean. Just make sure you have a quiet back-road somewhere to log the data.

Someone correct me if I'm wrong here, as I'm still learning....but that's what seems the best approach (as a starting point) to me.

Just my $.02

EDIT...Just noticed your car is an auto. If you find a nice quiet back road to do this, you'll want to command the trans into 3rd gear as well to keep it from wanting to down-shift. Probably better to have a friend help you too.