Porsche Technical Discussions Porsche related technical discussions and questions go here. |
|
Thread Tools | Display Modes |
#1
|
||||
|
||||
WOT dead spot
Something I’ve noticed since the HPDC this year is I have a dead spot at 5k in the 964. It basically feels like the engine dies for a moment then comes back full power. It only happens when I am WOT and always at the same RPM. It seems correlated to ambient air temp as the colder it is the “harder” the engine dies.
I have: 1) verified the resonator flap is working through a Durametric. 2) smoked the intake but found no leaks. 3) replaced plugs, wires, caps, and rotors. 4) replaced the full B&B exhaust with a stock exhaust, minus race cat and j pipe 5) I was getting fault codes for o2 sensor and right knock sensor. After 3 and 4, I am no longer getting codes. 6) gone through tanks of gas and just added fuel cleaner. Other than the dead spot, the car feels awesome. (And the new/stock exhaust is so much better. Awesome sound, no drone, no noticeable difference in power). My next steps seem to be to replace th fuel filter and maybe the coils, since they are still stock. Does anyone know how I can test if it is weak spark, fuel, or something else? Anyone seen something like this?
__________________
Aaron 1993 964 2004 GT3 2017 M3 |
#2
|
||||
|
||||
Quote:
It doesn't look like this engine has variable cam timing, but can you confirm? ed
__________________
ed 2016 GT4 2005 Lotus Elise 1994 RX-7 R2 |
#3
|
||||
|
||||
What about the chip? What fuel are you running? Air/oil cooled cars and their fuel/air ratios fall off right in that rpm range. My bet is natural behavior showing itself. Our cars HATE today's gas. Go see John Behe and have him adjust the air/fuel ratios it will make a world of difference and you will see exactly what your motor is doing. I did this for my car and the difference is quite impressive. Bad news is 100 octane is expensive (kinda like HoHos). Good news is a tune will even with 93 octane post air/fuel tuning will be very different. My HP/Tq numbers are closer to table top post 4k rpm versus the backside of a rollercoaster!
__________________
Ken 2023 Audi Q7 Daily Driver Considering next Porsche 1990 964, Red, Number 692 (Misty) sold 2010 Trailex (Dusty) sold 2003 996, (Speedy) Grey sold Life is short; just drive....... (boat, bike, etc.) |
#4
|
||||
|
||||
Is is 5k everytime, load or no load? Belt good in distributor? Also, airflow meter clean? Can also check the voltage to check operation.
__________________
78 SC, the 'Red Car' |
#5
|
||||
|
||||
Quote:
Quote:
I've also been curious what chip I'm running. I'm almost positive I have to be running one because it has a LWF but doesn't stall, and the throttle response is very good. How can I tell? Quote:
I'm not sure about the AFM or the intake. I know I should take the intake apart and check that and the flap, but I've been trying to avoid it. I'll look up how to check voltage.
__________________
Aaron 1993 964 2004 GT3 2017 M3 |
#6
|
||||
|
||||
Could be a dead spot on the AFM wiper board, very common. This happened to mine, same symptoms. If you unplug the harness from the meter and put a voltmeter on it then manually move the vane through its range of motion you will see a sudden drop in continuity at the affected spot, once past it it will pick back up close to where it left off. It can be corrected by moving the wiper arms into a new unworn area of the wiper surface. Easiest way to do it is to loosen the screws and shift the contact board slightly downward rather than mess with the actual wipers. There a few videos on YouTube showing the process.
__________________
Chris Robel Current: 1987 Carrera Targa 3.4 993SS cams, Smokey Silver Semi-Daily Driver 2006 Cayman S, Guards Red, #11 part time track addict (sometimes #12 or #22) X-Terra, Blue Sold: 1970 911 T coupe, Bali Blue 1982 911 SC Targa, Guards Red 1974 914 2.0, Champagne Gold 1982 BMW 528e, White and rusty.. Deceased but not forgotten: 1968 911 sunroof coupe, Black 1972 VW Super Beetle, White |
#7
|
||||
|
||||
^^This. If you don't have an analog ohm meter, find one to borrow. The old black Simpsons are the best. Watching the needle move, and then dip as you manually move the door will speak volumes as to the health of the carbon trace rheostat inside the AFM. a good cleaning and realignment of the wiper arm to a new spot can solve the issue.
__________________
Steve Potomac PCA Co-CI(retired) 89 944 Turbo Race car 85.5 944 NA son's 2015/2019/2020 944Cup and PCA Nat'l Champ racecar 94 968 1 of 11 Iris blue coupes 92 968 1 of 2 Tahoe Blue Cabriolets 98 993 C2S w/Aerokit II 77 911S Vintage race car project 70 Boss 302 86 Mustang SVO 08 F250 SD Diesel 15 Audi SQ5 "Noel spun! Noel spun! Don't do anything stupid, Dad." -the boy on the radio on the last lap of NASA race as the second place car spins behind me in T5 at Summit Point. |
#8
|
||||
|
||||
Re: dead spot on the AFM board - I thought the same thing too. Problem is, Aaron says this is happening at WOT. There are two switches on the throttle body - idle and WOT - that are enabled in those positions (pins 52 and 53 of the DME). At WOT the ECU ignores the variable signal from the AFM (pin 7) and switches to the WOT map based on the input from the WOT switch.
So... do you know if you're hitting and enabling the WOT switch? Unhook the DME and test that with a multimeter. Should be continuity to ground at WOT.
__________________
Chris M 1985 911 Carrera with a couple cosmetic only mods 2006 E90 330i 1999 E46 328i |
#9
|
||||
|
||||
Thanks, guys. I had a shop check the AFM voltage and they said it was good across the board, but I can test again.
I've checked the WOT switch by moving the throttle by hand, and I can see and hear it click, but I have not tested that A) the throttle pedal moves it that far and B) that the switch is working. My assumption is it is, because if I am just below the WOT threshold, I don't have the problem. It's only once I cross into it. I did find a mention on rennlist about an oddity at 5K in the stock fuel maps (See https://rennlist.com/forums/964-foru...l#post11493599), where it drops fuel to near idle levels for a moment, right where I am seeing the issue. This makes me lean towards Ken's thoughts that it needs a professional tune.
__________________
Aaron 1993 964 2004 GT3 2017 M3 |
#10
|
||||
|
||||
We can always test the theory quite easily, pull the chip out of my car and put it in yours and go for a drive. PM me if you want to try.
__________________
Ken 2023 Audi Q7 Daily Driver Considering next Porsche 1990 964, Red, Number 692 (Misty) sold 2010 Trailex (Dusty) sold 2003 996, (Speedy) Grey sold Life is short; just drive....... (boat, bike, etc.) |
|
|