Momentary power loss at specific RPMs only when cold
Momentary power loss at specific RPMs
I've been reading posts all over the site, but none (that I've found at this time) match my current issue exactly (some have pointed me in interesting directions). If you want to flame me for asking for inputs, or have off topic comments, I'd ask that you do it in a PM or elsewhere.
When my car is not yet up to running temp, if I start out in 1st gear it will stumble at 2700 RPM, with or without traction control turned on. It has occurred once or twice in 2nd gear at the same RPM when accelerating gently and manually shifting. It will not occur again unless the car is allowed to sit at idle for a while. It just started alternating between 2700 and 1400 RPM. It may be engine or it may be transmission, I do not see the tach acting oddly, it smoothly moves up, but you can feel the loss of power and the exhaust note changes (if anything it sounds more aggressive). I'm thinking the tach may have some smoothing in it's circuitry, so not sure that counts. I suppose the odd part is that it happens only when the engine/trans are cool, which lends credence to the vacuum leak theory (as the engine warms the leak goes away? I'm also thinking it could be the trans, but I'd expect the problem to be more persistent, this is just a <1 second drop in power. I have a new S/C IC pump, and have been looking for vacuum leaks for a while. I've also noticed that even at idle, the s/c is still turning. I've no ideas what others have done before me (other than a few posts from ChopsSRT6).
Engine mods to date: K&N's, high flow cats on a NeedsWings exhaust, ASP178mm crank and PSK kit, EuroCharged tune. The problem began to occur recently, but before the pulley mods, and I've tried running with the stock exhaust (even though it ran fine for 6 months with the new exhaust).
Update: it's starting to happen when warm now, so maybe I'll be able to pin it down before long.
When my car is not yet up to running temp, if I start out in 1st gear it will stumble at 2700 RPM, with or without traction control turned on. It has occurred once or twice in 2nd gear at the same RPM when accelerating gently and manually shifting. It will not occur again unless the car is allowed to sit at idle for a while. It just started alternating between 2700 and 1400 RPM. It may be engine or it may be transmission, I do not see the tach acting oddly, it smoothly moves up, but you can feel the loss of power and the exhaust note changes (if anything it sounds more aggressive). I'm thinking the tach may have some smoothing in it's circuitry, so not sure that counts. I suppose the odd part is that it happens only when the engine/trans are cool, which lends credence to the vacuum leak theory (as the engine warms the leak goes away? I'm also thinking it could be the trans, but I'd expect the problem to be more persistent, this is just a <1 second drop in power. I have a new S/C IC pump, and have been looking for vacuum leaks for a while. I've also noticed that even at idle, the s/c is still turning. I've no ideas what others have done before me (other than a few posts from ChopsSRT6).
Engine mods to date: K&N's, high flow cats on a NeedsWings exhaust, ASP178mm crank and PSK kit, EuroCharged tune. The problem began to occur recently, but before the pulley mods, and I've tried running with the stock exhaust (even though it ran fine for 6 months with the new exhaust).
Update: it's starting to happen when warm now, so maybe I'll be able to pin it down before long.
Last edited by JimB; 11-13-2017 at 05:42 PM.
Re: Momentary power loss at specific RPMs only when cold
Ha... It's stopped doing it. My engine finally died the other day while driving to a memorial cruise for a local car guy who was basically killed because he had a bad *** car. Anyhow, the codes led me to the CPS and after I swapped it out for a new Bosch unit all us good. So this may be an early indicator along with occasional codes for misfires for a Crank Position Sensor going bad.