87 s4 bogs right before 7k rpm
09-06-12, 07:34 PM
#1
87 s4 bogs right before 7k rpm
hey guys im getting my car all together for a car show this weekend. i havnt driven it only started it hasnt had a filterbox/filter on it just the afm the last couple of months and started it yesterday, it ran good turned it off, then i put the oem filter box and ducting on today and gave it wot and the rpm went up slower then normal and wouldnt touch 7k rpm... any ideas?
havnt driven it for a while and its been started in a clean environment never sucked dirt or sand... the original engine only has 62k miles so its not a compression issue it starts easy idk what it could be....
its N/A
havnt driven it for a while and its been started in a clean environment never sucked dirt or sand... the original engine only has 62k miles so its not a compression issue it starts easy idk what it could be....
its N/A
09-06-12, 09:17 PM
#3
Rotary Enthusiast
Does it feel low on power above 3800 RPM or brief periods of jerking up to redline? If you're not able to exceed 7000 RPM under load, then the engine may not be getting the air it's supposed to get at high RPM; in other words, the 5th/6th port/auxiliary port valves are not opening.
Make sure they open/close by hand, that the hose to the split air pipe is connected and in good condition, and test whether they open or close by doing the following:
Warm up engine to operating temperature.
Disconnect boost pressure sensor vacuum line.
Start engine (keep throttle open to prevent stalling) and increase RPM to 3800+. The actuators should move and open the auxiliary ports.
If they move by hand but don't open when the engine is running, disconnect the air line and run a little pressurized air through it (even your breath should move the actuators). If they don't move, check for leaks. If the actuators were removed and reinstalled with sealant, too much sealant might have clogged the air passages (that happened to me, after thinking it was a different problem with the fuel injection system). If that's the case, clean out the sealnt, get new gaskets, (optional) spray the gaskets with gasket sealer (just a coat or two), and reinstall the actuators.
If you can't rotate the valves by hand, then there may be carbon buildup preventing the valves from moving. In which case, you'll need to remove the upper and lower intake manifolds, remove the auxiliary port valves, clean them, clean the passages the valves slide into, then reassemble (per the FSM's procedure) and test. One of the passages on my block had some carbon that needed to cleaned out before the valve could move freely. I also coated them with some motor oil.
Make sure they open/close by hand, that the hose to the split air pipe is connected and in good condition, and test whether they open or close by doing the following:
Warm up engine to operating temperature.
Disconnect boost pressure sensor vacuum line.
Start engine (keep throttle open to prevent stalling) and increase RPM to 3800+. The actuators should move and open the auxiliary ports.
If they move by hand but don't open when the engine is running, disconnect the air line and run a little pressurized air through it (even your breath should move the actuators). If they don't move, check for leaks. If the actuators were removed and reinstalled with sealant, too much sealant might have clogged the air passages (that happened to me, after thinking it was a different problem with the fuel injection system). If that's the case, clean out the sealnt, get new gaskets, (optional) spray the gaskets with gasket sealer (just a coat or two), and reinstall the actuators.
If you can't rotate the valves by hand, then there may be carbon buildup preventing the valves from moving. In which case, you'll need to remove the upper and lower intake manifolds, remove the auxiliary port valves, clean them, clean the passages the valves slide into, then reassemble (per the FSM's procedure) and test. One of the passages on my block had some carbon that needed to cleaned out before the valve could move freely. I also coated them with some motor oil.
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