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Registered User
Join Date: Jan 2017
Posts: 1
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Massive "Hiccup" @ 1300 RPM - Variocam Plus?
Hello All! Long time lurker, newly registered member. I've put Many hours into researching the forums for my specific issue and could never really find another issue quite like mine, so here i am. Before I get into it, I want to say that I appreciate all the info that the Pelican Parts community has brought to the table, many of my past questions have been answered with a quick search here on the boards, thank you for that. Now for my 996 issue....
Car "mechanical background": My car is a 2002 911 4S 6 speed with a factory installed replacement motor ( replaced in 2006 and chassis had 20K miles at the time). Chassis now has 97K miles on it and I bought the car when the odometer was reading 75K miles. Car has no computer mods, engine is stock with the exception of the Cat bypass pipes. The front diff was taken out of the vehicle around 85K miles as the carrier bearing was going out and I just didn't reinstall the diff after replacing the bearing. Vehicle sitting on 19" aftermarket wheels. My issue: One night I was out driving the car thru a long windy road. I was alone and decided to run thru some RPM and some gears like any responsible Porsche owner would! I kept the car in its upper power band thru 2nd, 3rd, and 4th gears, 3000 rpm and above, but never red lining. I jumped on it from a rolling start, so this was not a "dump the clutch and go" kind of approach. Once I got done with my run thru the hills, I came to a stop and proceeded to make a U turn. As I did this, I let off the clutch, began to accelerate regularly, and as soon as the vehicle hit 1300 rpm, it had a "massive hiccup". For my old school mechanics, it felt similar to a carburated muscle car that has the accelerator squirters plugged. As you romp the throttle, the car falls on its face hard and then recovers when the fuel catches up. This is as close as I can describe my Porsches problem, but it is a Much more violent drop out and accel. It falls on its face at 1300 and then almost bangs when it catches up. The vehicle is my daily driver and it has been like this for some time now. I have learned to feather off the clutch and into the throttle when accelerating from a stop, creating a gentle acceleration thru 1300 and the hiccup is not present or detectable. There is no check engine light, and no codes. The vehicle idles fine, accelerators thru its power band normally (passed 1300 RPM), doesn't make any strange noises, no ticking, no clunking, etc. You would think that nothing is wrong until you hit 1300 RPM on moderate to heavy acceleration. For testing purposes, I've confirmed that it does this hiccup regardless of what gear you are in. The car ran fine with my mods (pipe, wheels, etc) for several thousands of miles prior to my run thru the hills. I do still feel and notice the very common 3200ish RPM "kick" and always have, that part hasn't changed. I recently pulled the number 1 cylinder side Variocam Timing Solenoid wire and created a check engine light (as I would expect) for testing purposes, and the strange thing is, I drove the car with the timing solenoid unplugged and the "hiccup" was all but gone even when I tried to produce it. Once I plugged the solenoid back in, i was able to easily create the hiccup again. I pulled the timing solenoid and screen, visually inspected and things "look ok". I manually energized the solenoid and it has movement. I only have a basic understanding from my internet research on variocam plus system function. My best guess, its seeming to me like something is either hanging up (sticking), or damaged with the variocam timing actuator or slack in the chain or something. It just gets me that I have no check engine light and the vehicle runs like a champ all the time, otherwise. I wasnt thinking to condemn the solenoid since it functions when I bench tested it, and was thinking that its engagement was causing my hiccup, but I dont know. What do the Rennlist pros think?? I'm sorry for my long windedness, its just in my nature, haha. I'm just trying to cover all details of my problem. Thanks in advance for any help I may receive! |
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