Fuel vapor smell after cam swap...

[STL_G8GT]

G8 guys/gals...

You all probably know I finished my cam swap two weekends ago. Its tuned, totally good to go.

Immediately after the swap I noticed what seemed to be an exhaust smell. I swapped for new exhaust gaskets thinking that would curb it, but no dice.

When I had my tuner work on the idle today, he told me it definitely is fuel vapor. I've never had an issue with fuel vapor prior to the swap.

When the car is sitting, cold, I don't notice the smell at all. Its only evident when running or after its just shut off.

Before getting it tuned, it turns out that the leads on the arh 02 extension were swapped so for a 150 drive the ecm was seeing zero volts from the driver front 02 so it was dumping fuel to attempt to compensate. Other than that, there were no issues/oddities with the install.

Ideas? Pointers?

[G8Smitty]

Any leaks where the fuel line mates to the fuel rails? Are all of the injectors seated properly?

Can you isolate where the smell is coming from?

Because it occurs when it is warm of shortly after the motor is off sounds like a fuel leak when it is under pressure.

I could be way off base, but that is where I would start.

[99-LS1-SS]

What are the cam specs?

[fiveoh]

And how do you like the pat g cam?

[Ktlplxm]

Depending on the CAM specs, the overlap will let unburned fuel into the exhaust possibly causing the smell. If its a loose line it should reek regardless of conditions, but its still somewhere to check. Don't forget to look at the Evap lines as well, vapor can come from them too

Sent from my Droid using Tapatalk

[Patrick G]

What kind of changes did your tuner make to the open loop & closed loop fueling tables? If they were not changed, then chances are good that you may be overly rich at lower rpm. Also, if you ran for a bunch of miles with your O2s hooked up wrong, they may be very fuel-fouled. I'd log O2 switching plus ST and LT fuel trims to know for sure.

[DSteck]

It's definitely raw fuel smell, and not exhaust gas smell. My personal car (C6 Z06) has a cam with 23º overlap, and doesn't smell anything like this. Unburned fuel in the exhaust has that distinct hydrocarbon smell, and not the sweet smell like at a gas pump. Given the negative overlap on this cam, I can't imagine that there is such an inefficient burn at idle that it'd smell like straight gasoline. It is only set to idle at 650 (it's stable and has good engine vacuum) because I didn't want to go higher and risk pushing through the converter. I've tuned enough cammed cars to differentiate the smell, and I am overly positive it is NOT exhaust. I noticed it was stronger when the AC was turned on, so I'd have to imagine something is venting vapor in the engine bay.

I checked all of his EVAP lines with three push-pull tests each, and all of them were secure. I tried to inspect for cracks in any of the EVAP lines, but didn't find any... although I wasn't able to fully inspect the section of the line that runs under the wiring harness on Bank 1 (engine bay was extremely hot). He did have a P0455 code for EVAP system leak when he dropped it off last night.

As far as changes made to fueling, I recalibated the air flow model to the point that trims are in the -2% to 0% range, and with my wideband in the car, showed a relatively steady 14.7 AFR during idle (this is when I tuned it originally). I say relatively steady due to the nature of low exhaust flow at idle. He is not overly rich at idle, I can assure you of that.

When he originally dropped the car off with me, I plugged my laptop in and found something amiss. The Bank 1 O2 sensor (front) was reading exactly 0mV, and the LTFT as well as STFT was maxed to +25% each, for a total of +50%. I forced the car into open loop, and it immediately idled better. I got it up in the air and crawled under to search for a wiring oddity, and sure enough, I found one. I know that when a sensor is disconnected, it reads 450mV (give or take a couple mV). When inspecting the O2 extension, I saw that pin A on the harness side had a blue wire and pin B had a green wire. On the sensor side, pin A was green and pin B was blue. I repinned the sensor side of the extension, plugged the sensor back in, and restarted the car. The sensor immediately started behaving like normal. I then went out and drove it around for a while to do some logging and make sure the idle was consistent and steady, and then came back later and put my wideband in. After dialing in WOT (I did probably 5 WOT passes in the car), I took my wideband back out and reinstalled the narrowband, then went back out with the car just to recheck everything. If the bank 1 plugs were fouled (which I'm sure they were), then the WOT runs should have cleaned them if the normal drivability stuff didn't. I've killed plugs before from over-fueling (like letting a fuel solenoid spray while the nitrous bottle is closed), and they clean up after some WOT pulls. While idling, there is definite noise in one of the O2 sensors, and although I don't have a log in front of me, I am pretty sure it's the bank 1 sensor. When I say noise, I mean it still cycles just like the bank 2 sensor at idle, but is constantly jagged.

The trims look good. Bank 1 and Bank 2 match each other pretty close, typically with 2% or less difference between sides (much better than most LSx engines I've seen... I typically see a spread of about 5% where Bank 1 is more positive). The only anomaly I see now is the jagged output from one of the sensors, and when I get home, I can verify if it was Bank 1 or Bank 2.

[99-LS1-SS]

Welcome to the forum DSteck! I'm the guy that bugs you on HP Tuners forum.

Did the injectors get removed? Any chance there's an o-ring messed up?

[STL_G8GT]

Ill post camspecs later today... yes injectors were removed... and my thinking was along those lines. Driving the wifes car to Florida currently, so I can't check them right now. That will be the first thing I look at when I get back though.

Thanks for all the replies and ideas!

Love the cam... need to get these little things knocked out and we'll be all good, but the car is a screamer now and a blast to drive. We kept very VERY good drivability a requirement, and the car meets that need remarkably well!

[DSteck]

Welcome to the forum DSteck! I'm the guy that bugs you on HP Tuners forum.

Did the injectors get removed? Any chance there's an o-ring messed up?
Nobody bugs me on that forum, really. I like discussing the stuff!

The cam is a 219/227 with 0.593"/0.596" lift on a 115+2 LSA.

Also, I checked the log, and it was the Bank 2 sensor that was reading with a lot of noise. Bank 1 was smooth.

[STL_G8GT]

Maybe some of you other guys that have done cam swaps can chime in... can you possibly bolt the fuel rail in place without having an injector seated? I was talking to Dave last night, I cleaned the orings, but to be honest wasn't super super careful when reinstalling the rail. When I say super super careful, I mean I didn't treat it as if it was "Fragile"... I reinstalled it the same way that I did when I removed the intake cover.

After running the car, I have felt around the fuel line fittings and didn't get any smell of gasoline on my fingers at all, so I'm guessing it's not the line, or at least not the line right there.

[Ktlplxm]

Sure you can. Its not a super rigid piece, and there could be some play in the injector

Sent from my Droid using Tapatalk

[c5racr1]

i had the same thing happen. the line above the fuel line at the rear of the intake but closer to the firewall. its is the fuel vent from the tank if the line is not snapped tight you will get the raw fuel smell through the a/c vent and such. it is a hard plastic black line that has two yellow prongs, if you trac it it goes to the front of the intake manifold on the selinoid on the front of the passenger side head.

[STL_G8GT]

Thanks c5... I'm driving back to st louis tomorrow and will be checking that before I pop the fuel rail! Ill keep the board updated.

[DSteck]

i had the same thing happen. the line above the fuel line at the rear of the intake but closer to the firewall. its is the fuel vent from the tank if the line is not snapped tight you will get the raw fuel smell through the a/c vent and such. it is a hard plastic black line that has two yellow prongs, if you trac it it goes to the front of the intake manifold on the selinoid on the front of the passenger side head.
I had checked to make sure that one was fully seated, and it seemed to be... however, I did not disconnect and reconnect it to make sure.

[STL_G8GT]

I looked around all the lines tonight and they seemed to be alright. I got closer to the rail and it looks like there may have been a leak at the cylinder front left. I definitely smelled fuel right above that injector. I looked at the oring and it looked alright. We'll see at this point... I have to drive to jeff city tomorrow so ill check for the leak sometime during the trip... thanks again for the help!

[99-LS1-SS]

Good luck.

[STL_G8GT]

I have messed with it a bit, but haven't found the source.

The next step will be devoting an afternoon to removing the evap lines and reseating all of them and then removing the fuel rail and swapping orings.

Its definitely stronger at startup, and Dave is spot on with the AC thing, it blows right in...

[c5racr1]

If it is stronger at start then it is something to do with the evap, the evap sends fuel vapor into the intake on startup. Question, do you have a noticeable vacume leak? if you do then i would say an o-ring if not then check your evap conectors.

[Ktlplxm]

once the vapor has passed through the cabin filter its hard to get that residual smell out too. while searching for the cause you may want to remove the filter so you can accurately gauge whther the smell is stronger, weaker, etc. Then buy a new filter

[STL_G8GT]

I messed with it a bit this afternoon but broke the damn first rule of troubleshooting, I changed more than one thing at a time. I tightened the fittings on the catch can, wrapped and sealed an evap fitting and removed the air filter. Air filter in or out doesn't matter, smell is the same. Wrapping the evap fitting above the back of the block seemed to make a difference, but I did it at the same time I tightened my catch can fittings.

I called GM parts and they said there are two different part numbers for the evap line that goes to the back above the engine block. I am going to get my VIN over to them and have them order a new set. Is there any sort of oring in the evap fitting? I simply took the fitting off and then reinstalled it for the cam swap... what in the world could I possibly have done to damage it? What exactly does that / should that look like on the inside of the fitting... nothing is visibly broken or bent. The whole set will run about $30 and will replace both evap lines. If the evap line was leaking to that extent, why doesn't it throw a code?

If after I replace the evap lines, the smell is still there, I'm swapping orings on my injectors. Whereas before I could smell fuel above one specific injector area, now I don't, but I still get the smell through the vents on a cold start specifically.

[STL_G8GT]

If it is stronger at start then it is something to do with the evap, the evap sends fuel vapor into the intake on startup. Question, do you have a noticeable vacume leak? if you do then i would say an o-ring if not then check your evap conectors.

I dont know how to diagnose a vacuum leak... how would I know if I did? I get a CEL for the gascap, but no other cels.

[Ktlplxm]

Leave the filter out until you get it remedied. otherwise, you'll continue to smell the vapor from the filter. I had a line rupture in the engine bay and it took months to get it out of the filter

[STL_G8GT]

I think any and all under the hood issues have been resolved, but with the car up on ramps, I absolutely smell exhaust at the knuckle joints by the xpipe on the ARH system. I also smelled a bit at the junction before the axleback flanges, but think I have resolved that by refitting the slip fittings with the pipes inserted as far as they will go. When I was inspecting the system, I could see "soot" marks on the pipes where gas had escaped.

I have spoken with Charlie on this, but was wondering if there are any additional steps I can take to eradicate this odor/leak - specifically at the knuckle joints. I have tightened the bolts with a breaker bar...

[norm8332]

I recommend new clamps if you have the "Torca" Style band clamps, They stretch and become loose with repeated adjustments, over tightening or use of an impact gun. . I fixed some leaks this way.

[c5racr1]

were your exhaust leaks before the cats? if so that will give you a fuel vapor smell also. since you have the evap line off pressure it and see if it leaks. put your finger over one end and blow into the other. BTW the way i check for vac leaks is to get a can of quick stat starting fluid in a arsol can and spray a little on the suspect part. If the engine rpm goes up its a vac leak.

[vic2186]

totally off topic but how much power you made??i just want to know i like you cam specs!!

[STL_G8GT]

No dyno yet... but enough to slaughter a '10 camaro ss from a 50 roll and again from a dig... when I get it dyno'd I'll post it!

[G8-4-Speed]

I had a bad raw fuel smell and it was a broken vapor fitting on top of the tank(had to get the tank replaced). Since you have or are tuning it, there may not have been enough time to set a code. Blow compressed air through the fill tube with a rag covering the gap. You'll need a extra hand under ther car listening and sniffing.