Gen V Swap tune needed

**wpbboy81** · 11-01-2011

I did research on the Gen V swap prior to doing it as far as what was needed to accomplish it. The day before i did it, i was told that i'll need a tune afterwards. i needed to tune my car anyways, as the only one i have is a ZZP pcm. but OMG, my gas mileage has dropped so bad since i did the swap. Im not the type to sit home long, so i'm always out, and it's like i'm at the gas station every 2-3 days ($25 a time). IDK if its because of the swap or not, but thats the only mod i've done recently. I have no vacuum leaks...only a slight coolant leak at the adaptor plate. Does anyone have any idea if the untuned swap is the culprit? Should i put my Gen 3 back on until i can get a tune?

**buck531** · 11-02-2011

What's your vacuum at idle? with a VS it should be around 17-20ish. If it's lower than that you have a vac leak. I know you don't have tuner but I'm going to bet your fuel trims are crazy pulling fuel.

You might want to invest in a tuner (DHP on other boards for $300 or so) or get an Aeroforce gauge to see what fuel trims you are seeing cruising.

**BillBoost37** · 11-02-2011

I've never really been able to see a vacuum leak with a gauge.

I doubt you have a leak though. YOu put on a go faster mod and are likely enjoying it. Therefore the uh...6-7 gallons you are burning every 2-3 days doesn't seem like all that much. Back off the throttle and you'll see it improve.

As for the tune. Keep in mind that yoru Gen 3 M90 pushed 90 cuibic inches of air per revolution into your motor and your Gen V M90 is also pushing 90 cubic inches of air into your motor.

The only difference is the Gen V is sending a cooler more dense charge in. There shouldn't be a large fueling difference. the biggest difference is usually in the driving style.

**wpbboy81** · 11-02-2011

i know there's no vacuum leak, just a coolant leak @ the throttle body gasket. which reminds me...i ported a throttle body also n im guessing thats the problem behind the fuel consumption. im gonna put my original TB back on and see if it makes a difference.

**BillBoost37** · 11-02-2011

by porting..you messed around with the maf readings. That's probably the issue.

**wpbboy81** · 11-02-2011

yea thats what i was thinking. i hope i still have my original TB (i tend to keep all my old parts just in case), but i did some cleaning up recently. if not, guess i'll pick another 1 up tomorrow at the yard. thanx for the input

**wpbboy81** · 11-04-2011

Well, i disconnectedt the battery and installed the stock TB and my fueling probs seem to have gotten better. i went from 14.3 mpg back up to around 20. i wish i woulda figured that out sooner....i spent so much in gas these past 2 months smh

**BillBoost37** · 11-04-2011

Mechanics..will often ask, what's the last things that heppened to a car. If you ask yourself that...you'll commonly find the problems much faster than 2 months.

**wpbboy81** · 11-04-2011

Thanx for the help. i honestly forgot i even ported the TB until i thought about that coolant leak at the gasket.

**coolone** · 01-23-2012

Just a Question... Porting the TB will allow more air (less restriction too) into the SC.

With the F/A mix not changed, the tendency would be for the mix to run leaner then am I correct?

So how would it be burning more gas then? Would the PCM be compensating for the lean condition?

I'm just curious and interested...

**Juanmiguel** · 01-23-2012

What it actually happens is that the PCM calculates the amount of fuel needed to achieve that A/F ratio using the O2 sensor, those calculations are called long term and short term fuel trims.

The PCM delivers fuel based initially on the MAF table and then adjusts it with the trims. The more accurate your MAF table, the lower your trims will be.

If you make any flow mods on your car, your MAF table will no longer be accurate and therefore your trims will increase. This normally leads to either rich or lean conditions and in reduced mileage. Which ultimatelly doesn't make much sense to me since the trims are designed to compensate these differences and are also "learned" over time, but I've seen it and tested it myself.

**SnowFlake** · 01-23-2012

Differences are learned and the car will be fine.

**coolone** · 01-23-2012

Interesting... lol Why couldn't the just leave the cars with simple carbs?
Holley Double Pumper anyone? hahahaha...

Thanks!

**buickman104** · 01-23-2012

after I did my Gen 5 swap my gas mileage took a really bad hit. I was getting about 32 MPG highway and after the swap it went down to 24 MPG. Then i did 2 changes. Originally I was running the EVAP off the gen 5, then switched to the gen 3 external EVAP and finally did a decent tune with the gen 5 and my MPG went back up to 32MPG.