RedCarrot

Some background:
I had the A&A supercharger installed by a shop some 350 miles away from me. On my way home, I noticed gas fume from the vents whenever I came to a stop at toll booth. Initially I thought it was from cars in front of me so I kept on going. I should have know better because it smells like pure, un-combusted fuel rather than exhaust.

Now, nearly 2 months later, the gas fume is occurring much more frequently, pretty much every time I turn on the fan. Even without the fan on, I smell a hint of it but not nearly as strong.

This could very well be not related to the SC - that it just so happened to start after the SC install or perhaps it exacerbated it. The shop has no idea what the cause may be. A&A suggested it could be from the BOV or catch can, but I put my nose an inch from them and smelled nothing. In fact, I don't smell any hint of gas from any part under the hood. Wherever the gas fume is coming from, it's right near where the car draws air into the cabin.

FWIW, there is not a single drop of oil in the catch can after 2,000 miles. There's barely enough oil in there to coat the interior wall. (yes, I did check the connections and made sure they didn't install a check valve in the inlet) Just thought I throw it out there.

At the same time, I notice the engine response is not smooth under 40mph at light throttle. It feels like it has continuous mini pulses even though I kept the throttle as stable as humanly possible. At first, I thought it was just me not used to the additional power but I longer believe that is the case.

If you put the two together, doesn't it sound like a bad injector is the culprit? There is at least one such case posted on the forum. I have already brought it to the dealer once, and of course the tech did not smell it after running it for 15 minutes at idle. I will have to take the tech for a ride next time.

So until I get a chance to take it the dealer next week, I like to gather as much info as I could and not just rely on them to solve it. Helpful input would be very much appreciated.

Edit: I took my car to MacMulkin where I bought my C7. As many Corvettes as they sell, I figure they probably have the best Corvette techs.

Motohead279

Car may be running rich. Who did the tune on it? You might wast to have a different shop look at the tune, preferably one who has DI experience.

wv8090

FWIW

I got a supercharger and full exhaust and after I got it back the fumes were BAD BAD BAD... I mean give you a migraine while driving it bad. Than after about 1-2 weeks they went away? Completely disappeared, the best I can figure is that it was residue on the new exhaust burning off or something.

RedCarrot

Moto, a/f on the dyno sheet is nearly a flat line at 12.5:1 so it doesn't appear to be it. I will hold off on naming the installer in case someone reads this but doesn't return for the conclusion and turns out it's not related to the installer.

But, holy crap, get this:
I went to check the hose connections again and found the catch can is NOT hosed between the intake manifold and the valley cover, but between the passenger side valve cover (inlet) and passenger side SC piping instead. (The hoses are tucked underneath the throttle body so I took it for granted). Yikes, that explains the lack of oil collection, and possibly the pulses.

The U-shape connector is still in place with a hose from the BOV T'ed in. I am going to correct this tomorrow but I am not sure this has anything to do with the gas fume. I also don't understand the reasoning behind routing air from the BOV back to the intake manifold after the MAF. Won't that make the air flow reading inaccurate?

BLKTA

The WOT AFR doesn't mean anything when you're driving around part throttle. Do you have headers with no cats? That along with the a rich part-throttle/idle tune is usually the culprit. Wouldn't hurt to check all of the fuel connections for a leak. You should also get a wideband oxygen sensor hooked up to monitor AFR at all times.

RedCarrot

Excellent point on WOT AFR vs. part throttle AFR - I didn't think of that! That might also explain the 10% mpg drop that I had attributed to parasitic loss.

I have stock exhaust pipings through and through. Good advice on AFR gauge... in the short term, I am going to find a shop to do an AFR reading for me.

Thank you

Higgs Boson

part throttle will always run at stoich for the fuel in your tank with a closed loop system.

unless your tuner disabled the O2 sensors and is running open loop (which i doubt) or you have mechanical issue (which will hopefully turn on the CEL) then you aren't having rich/lean issues at part throttle. the only other things can cause fuel smell is no cats, big injectors with bad low speed tuning, or a big cam, which it sounds like none of these apply.

your loss in MPG is called boost, lol.

RedCarrot

Thanks Higgs, that makes sense too. I have never heard anyone has to tune for partial throttle. That's brings me back to square one. I have no other engine mods other than the SC and custom tune. No CEL.

One thing for certain is that it's getting much worse than when the SC was first installed. It used to be that the smell occurs when coming to a stop after cruising on the highway for a stretch over 15 miles. Now it's happening as soon as the car is driven. (Dealer had it in idle for 15 min and fan on with no smell) The engine pulses / mini surges are stronger and more noticeable as well.

Could be a bad injector(s) as originally thought. I wouldn't be the first one:
http://forums.corvetteforum.com/c7-g...uel-smell.html

RedCarrot

Engine is now not idling smoothly bouncing within a 100rpm range. Between that, the surges under light load, gas smell, poor gas mileage, and excessive soot on pipe connectors and exhaust tips, all signs pointing to an injector stuck open and dumping more fuel than the engine would use.

If that turns out to be the case, is it reasonable to expect it be covered under warranty. I know that power train warranty is 90 percent gone with aftermarket FI, but it's upon them to prove the failed part is caused by the mod.

carlrx7

can you post a video?

BLKTA

You need to hook up a scan tool to monitor the various engine sensor outputs. It could be a few different issues, but it's hard to say reading over the internet without solid data. I would start with the basics; any DTC trouble codes, check the plugs for fuel fouling, check the plug wires, check O2 sensor voltage, etc. Did you contact the shop about the problems?

BTW - I doubt the dealer will honor the powertrain warranty at this point because the car has been modified.

RedCarrot

Carl, video wouldn't be able to show much other than idle rpm fluctuating within 100rpm. The surges can be felt easily but not so strong that could be captured on video. I'll try to get a video that captures the idling sound.

BLKTA, I contacted the shop a month ago to help me diagnose possible causes of the gas smell. They haven't provided much help other than saying the fuel system was not touched in the install and they have no idea that may be causing it.

I don't have tools with me. My game plan is to bring the car to a meineke shop half mile from me Monday morning to do the most basic diagnosis: spark plug, wire, fuel injector, etc. if it turns out to be something as simple as cleaning an injector, I will let them do it and see if the problems go away. Beyond that, I will bring it do a dealer 3 miles away. The dealer sells small volume Corvette but I had rather not drive 25 miles in this condition to MacMulkin.

RedCarrot

Just want to report back to close the loop.

After I corrected the hose routing from the valley cover to the catch can last weekend, the fume smell went away after 15 miles of driving, presumably after it burnt off the oil already there. The engine roughness seems to all but disappear as well. Took the car to a local dealer (Lannan) for diagnostic anyway and all they found was couple MAF related codes which I think is normal for aftermarket FI cars. They didn't write down the codes but they were awesome to not charge me so I didn't want to press them for it.

Super glad the car is running well again. I am pretty amazed the excess oil from FI can cause that much problems. Anyway, just wanted to post the result in case it helps someone down the road.

Frans96ss

Hooking a catch can up between the valley and the Valve cover wouldnt do much. It needs a source to PULL out of the valley or valve cover.

RedCarrot

This is true for for NA application. For FI, isn't it true that boost - even at low throttle - provides enough crankcase pressure to push the vapor from the valley? The results certainly support that. 1) Ten days after I rerouted the catch can between the valley and intake manifold, a table spoon full of oily gunk was collected in the catch can. 2) The vapor smell was 90% gone after 20 miles of driving (presumably after the residual oil in intake manifold was burned off). 3) Engine hunting has partially subsided as unmetered air from valley has to go through the catch can. At idle, rpm bounce reduced from 100 rpm range to 50 rpm range. Engine output got noticeably smoother in low throttle operation.

Some engine hunting remained nonetheless. A shop confirmed the car was running very lean at idle, which prompted the engine to add fuel intermittently, hence the hunting. It remained lean at low throttle operation but not nearly as bad as at idle.

Then this week, I removed the routing from the catch can to intake manifold altogether to vent it to the atmosphere. RPM bounce at idle reduced from 50 rpm range to 25 rpm range - it can no longer be felt or audible, only showing on rpm needle movement. Low rpm throttle response is back to what to what a SC'ed 6.2L should be where as before it felt a little bit like a 90's turbo'ed car. Vapor smell may have returned a little bit via this method. If this is confirmed, I will T the catch can outlet with the driver side valve cover to the SC pipe inlet.

Frans96ss

The valley and inside the valve cover are the same area. So if it "pushes" it out of the valley all its going to do it push it into the valve cover.. The way it was originally hooked up is the correct way to hook it up.

Higgs Boson

The valve covers and the valley are all pressure exits.

The intake manifold (behind the TB) is an entrance (vacuum source).

The intake tube in front of the TB is not a vacuum source. It is designed as a passive fresh air draw to compensate for the vacuum pull of the intake manifold for the stock system.

With FI, the valley and valve covers can be vented to an LMR style can and the intake manifold and intake tube ports (may no longer exist) can be sealed.

sirjames_CO

I have the same problem as RedCarrot with the MAJOR fumes. I have the Z51 dry sump and a ProCharger. The catch can is "after" the dry sump. I do not see the verdict on this problem in this thread...

Jim

Higgs Boson

If the catch can is vented, like with a filter open to the atmosphere, that is where your fumes are coming from. Doesn't matter if it is FI or not....

That's the whole point of the PCV system in cars in the first place. To keep the fumes contained.

Gadfly

Yep... you nailed it.