Fuel smell / valve overlap?
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
Fuel smell / valve overlap?
This post is for you experienced tuning and cam guys,
My latest Hyd-Roller cam, 238/242 - 293/300 @ .592 lift,,,really pepped up the engine and I love the drive-ability but the occasional fuel smell while idling/sitting in traffic is becoming pretty annoying.
I had my 86-89 Stock ECM tuned by a local tuner that did an awesome tune, (www.prodynotech.com) the tune is 100% drive-able in all conditions, no bucking, sputtering hesitation etc.
Do you guys with aggressive Hyd-Roller cams have this same issue?
If this cant be tuned out, as my tuner says it cant, then I will change my cam and maybe downsize my heads from AFR 210CC to 195 CC as well if I do a cam downsize. The tuner said , " this cam is on the ragged edge of tune-ability for the street"
I am still considering building a new engine with more cubes and or forced induction but that is a year away for me right now
My latest Hyd-Roller cam, 238/242 - 293/300 @ .592 lift,,,really pepped up the engine and I love the drive-ability but the occasional fuel smell while idling/sitting in traffic is becoming pretty annoying.
I had my 86-89 Stock ECM tuned by a local tuner that did an awesome tune, (www.prodynotech.com) the tune is 100% drive-able in all conditions, no bucking, sputtering hesitation etc.
Do you guys with aggressive Hyd-Roller cams have this same issue?
If this cant be tuned out, as my tuner says it cant, then I will change my cam and maybe downsize my heads from AFR 210CC to 195 CC as well if I do a cam downsize. The tuner said , " this cam is on the ragged edge of tune-ability for the street"
I am still considering building a new engine with more cubes and or forced induction but that is a year away for me right now
Race Director
Joined: May 2003
Posts: 10,749
Likes: 41
Our cams are very similar. I havent noticed any fuel smells, but I typically dont sit in traffic too long and therefore dont idle for long. But I certainly will let you know as I start to drive the car more. Those heads certainly arent big for your 406, but I know when we chatted on the phone you mentioned that I did it right by going with the 195's.
What is your cam lift and lobe seperation. You are running a sligtly more duration then I do. I have a 236/242 stuffed in the 421, but I have a tad more lift.
Maybe some cats to clean up the smell a bit? Or maybe you have those....
Jim Barth and Paul Thompson are probably one of the two most knowledgeable guys on the forum, however Paul isnt on much so you can pm or email him this thread because he has alot of tuning experience.
What is your cam lift and lobe seperation. You are running a sligtly more duration then I do. I have a 236/242 stuffed in the 421, but I have a tad more lift.
Maybe some cats to clean up the smell a bit? Or maybe you have those....
Jim Barth and Paul Thompson are probably one of the two most knowledgeable guys on the forum, however Paul isnt on much so you can pm or email him this thread because he has alot of tuning experience.
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
I would dearly love it, if in fact, this is strictly a tuning issue, I can not find any air leaks, nor could my tuner find any air leaks, which is the typical culprit,,
If I need a FAST, then that's what I'll do, I'm sure it will help with a 421, or a 434 or a Supercharger build etc.
If I need a FAST, then that's what I'll do, I'm sure it will help with a 421, or a 434 or a Supercharger build etc.
Melting Slicks
Joined: Aug 2003
Posts: 3,401
Likes: 397
From: Lakeville MI
Does it idle in closed loop? If so, is the INT and/or BLM rising and adding fuel due to the extra oxygen (and unburned fuel) in the exhaust?
It may be necessary to limit the INT and/or BLM or even to prevent closed loop operation or BLM updates below x rpm via special programming.
Otherwise, you can try and run it as lean as possible at idle and retard the ignition timing a bit to put more heat into the exhaust.
If its rich in an open loop idle, then maybe too much injector offset, a too rich MAF cal or a too rich target AFR.
Gotta determine the cause of the richness first.
It may be necessary to limit the INT and/or BLM or even to prevent closed loop operation or BLM updates below x rpm via special programming.
Otherwise, you can try and run it as lean as possible at idle and retard the ignition timing a bit to put more heat into the exhaust.
If its rich in an open loop idle, then maybe too much injector offset, a too rich MAF cal or a too rich target AFR.
Gotta determine the cause of the richness first.
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
Does it idle in closed loop? If so, is the INT and/or BLM rising and adding fuel due to the extra oxygen (and unburned fuel) in the exhaust?
It may be necessary to limit the INT and/or BLM or even to prevent closed loop operation or BLM updates below x rpm via special programming.
Otherwise, you can try and run it as lean as possible at idle and retard the ignition timing a bit to put more heat into the exhaust.
If its rich in an open loop idle, then maybe too much injector offset, a too rich MAF cal or a too rich target AFR.
Gotta determine the cause of the richness first.
It may be necessary to limit the INT and/or BLM or even to prevent closed loop operation or BLM updates below x rpm via special programming.
Otherwise, you can try and run it as lean as possible at idle and retard the ignition timing a bit to put more heat into the exhaust.
If its rich in an open loop idle, then maybe too much injector offset, a too rich MAF cal or a too rich target AFR.
Gotta determine the cause of the richness first.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
My cam is slightly smaller, 230-240 with more lift (.600). I don't notice any raw fuel smell at idle. A wideband will show you if you are running possibly too rich which would explain the fuel smell. If you know anyone in a gas station with a smog machine, maybe you can pay them a couple of bucks just to sniff your motor at idle and see what the afr is.
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
Yeah, I guess I am going to have to dig into this, I will take it over to a local dyno shop and get a wide band and get some datalog's at idle.
I certainly thought the tuner was going to get this ironed out but evidently not,,, I just don't have the time or desire to learn the GM 86-89 ecm tuning system
I certainly thought the tuner was going to get this ironed out but evidently not,,, I just don't have the time or desire to learn the GM 86-89 ecm tuning system
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
I left the car at his shop for 3-weeks and he tuned it on his dyno and drove it, so I figured he would be able to zero in on it, but he said that this was the best he could do because of the cam.
Le Mans Master
Joined: Feb 2005
Posts: 6,482
Likes: 566
From: Clearwater Florida
................ Do you get a lot of vapor out of the tank when re-fueling ? It might be that the CCP can't keep up with the warm fuel return and it starts venting out of the cap ... I have this problem when in stop and go traffic at relatively low speeds ..............
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
My tuner says:
"The rolling misfire from overlap increases the Hydrocarbon output and the only cure is to add cat converters....... if you go leaner than 14.7 with an aftrmarket engine management you will stall. Might try a higher desired idle rpm "
anybody think a Hi - Flow cat will take the smell away?
"The rolling misfire from overlap increases the Hydrocarbon output and the only cure is to add cat converters....... if you go leaner than 14.7 with an aftrmarket engine management you will stall. Might try a higher desired idle rpm "
anybody think a Hi - Flow cat will take the smell away?
