rough idle vs cat vs performance decrease
#1
02-13-2011, 07:25 AM
rough idle vs cat vs performance decrease
Over the course of a year I had 4 or 5 times a rough idle. Mostly when I started it, once when I was accelerating from a red light. Different throttle positions didn't really change anything. Ignition off then followed quickly back on and problem resolved.
I've noticed a gasoline smell when it was idling. I don't make a habit of sniffin the tail pipe when the engine is running. However when I have my bad habit of letting it idle in the garage to warm up a bit I don't smell a gas smell.
I know it's a thirsty truck, however.....I was runnin 4x4 for a couple of days and my mpg tanked, so out of curiosity I was playin with the trip computer. One thing led to another and now I find myself on the highway 2 wheel drive all the time resetting the damn thing and checking to see what I am getting. 55mph 14mpg: 75mph 11mpg.
Now I'm thinking perhaps I'm noticing a performance decrease on the highway. On a very slight hill cruise on 55mpg it will downshift, perhaps odd that it would with the hemi, doesn't it have enough hp? I don't think it accelerates as good on the highway now.
I've searched this forum and internet and I find myself pondering over new cat, destroy the inside of the cat, 02 non fouler, and something about the egr (i lost my link to the info on the egr and I can't recall what that was all about)
Talkin to a friend he mentions a dyno test could tell me more information.
In conclusion: I'm heading down this path of a "tune up" at a professional shop. I believe this will be $$ just walking in their door. This seems crazy to me that a stock 2003 hemi would get any benefit of hooking it up to a computer and running it up full throttle. Would the technician give me the results that my cat is clogged and if I fix it and they will tune my truck's computer I will magically get better economy and more power?
Of course I don't have any dash lights on to indicate there is a problem.
I think it would be easier to head over to dodge and check out that used 2006 cummins mega cab....hmmmmm.....that's nice.....oh wait....no.....because then I will be pondering how to get that exotic 25mpg that EVERYONE ELSE is getting but me....haha!
(quote from hammerz71: Some days, I wish I never did that DIY, LOL...) This relates to me because maybe I should just change the computer to compass and temp and just forget about it. ha!
I've noticed a gasoline smell when it was idling. I don't make a habit of sniffin the tail pipe when the engine is running. However when I have my bad habit of letting it idle in the garage to warm up a bit I don't smell a gas smell.
I know it's a thirsty truck, however.....I was runnin 4x4 for a couple of days and my mpg tanked, so out of curiosity I was playin with the trip computer. One thing led to another and now I find myself on the highway 2 wheel drive all the time resetting the damn thing and checking to see what I am getting. 55mph 14mpg: 75mph 11mpg.
Now I'm thinking perhaps I'm noticing a performance decrease on the highway. On a very slight hill cruise on 55mpg it will downshift, perhaps odd that it would with the hemi, doesn't it have enough hp? I don't think it accelerates as good on the highway now.
I've searched this forum and internet and I find myself pondering over new cat, destroy the inside of the cat, 02 non fouler, and something about the egr (i lost my link to the info on the egr and I can't recall what that was all about)
Talkin to a friend he mentions a dyno test could tell me more information.
In conclusion: I'm heading down this path of a "tune up" at a professional shop. I believe this will be $$ just walking in their door. This seems crazy to me that a stock 2003 hemi would get any benefit of hooking it up to a computer and running it up full throttle. Would the technician give me the results that my cat is clogged and if I fix it and they will tune my truck's computer I will magically get better economy and more power?
Of course I don't have any dash lights on to indicate there is a problem.
I think it would be easier to head over to dodge and check out that used 2006 cummins mega cab....hmmmmm.....that's nice.....oh wait....no.....because then I will be pondering how to get that exotic 25mpg that EVERYONE ELSE is getting but me....haha!
(quote from hammerz71: Some days, I wish I never did that DIY, LOL...) This relates to me because maybe I should just change the computer to compass and temp and just forget about it. ha!
Last edited by jetjarv; 02-13-2011 at 07:35 AM.
#3
02-13-2011, 09:02 AM
I believe it would be similar to leaving your choke on your motorcycle. Turn the throttle and it is too rich. You are able to accelerate just not very fast and it runs rough.
Spark plugs are believed to have been replaced 13,000 miles ago. There was a service receipt in the truck when I first bought it. 55k miles on the truck. perhaps they were never changed.
#4
02-13-2011, 10:20 AM
First off, a Dyno is NOT for diagnosing a problematic vehicle and if you walk up and tell a dyno shop that your having trouble, they aren't going to strap you down.
You must have a healthy running vehicle to step on the dyno. it's their first requirement.
Also, You cannot "tune" a stock vehicle without the purchase of a custom handheld tuner that overwrites the factory data. Those handhelds are atleast $300 NOT inlcuding the dyno time itself which can run anywhere from $150-300 itself.
You need to get hooked up to a starscan or a Snap-on LIVE diagnostics handheld, the kind that do their diagnostics while the truck is runnng, not just a code puller. These will test the fuel trims, and verify and and all active DTC codes that arent present on the dash(if any at all?)
as some won't set off the CEL.
You also need to NOT use the overhead as a trusty MPG source. The accurate way is by hand calculation but based on those overhead numbers....My truck reads very similar numbers.
These trucks have 2 overdive gears...both 4th and 5th. If you have 3:55 gears I could clearly see why you would downshift on slight uphills because when my truck was on it's stock tune, it would do the same thing even with 3:92's.
You could be losing some performance though.
I would do a leakdown test and pressure test to see what shape the motor is in, but I would Definately stay away from a dyno shop and DO NOT blow out your cat. You'll be smelling worse fumes than gas! Which by the way, on a cold start-up isn't unusual to smell gas.
You must have a healthy running vehicle to step on the dyno. it's their first requirement.
Also, You cannot "tune" a stock vehicle without the purchase of a custom handheld tuner that overwrites the factory data. Those handhelds are atleast $300 NOT inlcuding the dyno time itself which can run anywhere from $150-300 itself.
You need to get hooked up to a starscan or a Snap-on LIVE diagnostics handheld, the kind that do their diagnostics while the truck is runnng, not just a code puller. These will test the fuel trims, and verify and and all active DTC codes that arent present on the dash(if any at all?)
as some won't set off the CEL.
You also need to NOT use the overhead as a trusty MPG source. The accurate way is by hand calculation but based on those overhead numbers....My truck reads very similar numbers.
These trucks have 2 overdive gears...both 4th and 5th. If you have 3:55 gears I could clearly see why you would downshift on slight uphills because when my truck was on it's stock tune, it would do the same thing even with 3:92's.
You could be losing some performance though.
I would do a leakdown test and pressure test to see what shape the motor is in, but I would Definately stay away from a dyno shop and DO NOT blow out your cat. You'll be smelling worse fumes than gas! Which by the way, on a cold start-up isn't unusual to smell gas.