RPM and boost drop at 3k in high gears?

[sumenlo]

So this just started happening recently. At WOT in 4th and 5th gear ONLY, my car will drop RPM's and Boost simultaneously. It almost feels like the clutch starts to slip. The drop isn't that drastic - maybe about 500-600 RPM's. It will drop for a couple of seconds, then start to climb again at full boost. The weirdest thing about this, is that it will not do it in 1st, 2nd, or 3rd gear. My car will pull very hard (like normal) through my first 3 gears.

I was moving more away from thinking it's a turbo problem and more toward something like a TPS problem or something. I figure that if my turbo is having issues, my RPM's wouldn't drop with the boost. On the other hand, if it's a throttle problem, the boost would obviously drop with the RPM's. Am I correct in assuming this? What do you guys think?

 

[DSM90AWD]

Fuel cut
That or you are getting some knock accompanied by pulled timing.

Do you have a datalogger?

 

[sumenlo]

I'm pretty sure it's not fuel cut. It's not that drastic of a drop in power. I've felt fuel cut before and this is in no way as violent. My buddy does have a code reader for our cars. It has the ability to show the counts of knock in the engine. I guess we can hook that up and see if it's doing anything weird. Should I maybe check the timing as well to make sure it's not off?

 

[Froyd79]

That was my first thought was that you may be pulling crazy timing due to knock. I would just log a run and see what the results are. IIRC for every 3 counts of knock it pulls 1 degree of timing.

 

[oldman]

How much boost are you running on that 14b? I don't see a boost gauge in your profile.

 

[DSM90AWD]

I'm pretty sure it's not fuel cut. It's not that drastic of a drop in power. I've felt fuel cut before and this is in no way as violent.

Yea, once you've felt fuelcut firsthand, forever the expert you will be (why do I sound like Yoda ) And with the altitude in Tucson (2600ft) and the warm temps 74F (*jealous*) would keep the onset of fuel cut to >18psi boost.

Should I maybe check the timing as well to make sure it's not off?

If base timing is more advanced than 5*BTDC (maybe bump the CAS during valvecover gasket change), you will be more prone to knock > retarded timing since you will have more timing advance at all airflow conditions.

BTW, a slipped clutch would show as RPMs increasing faster than the actual car. What you describe is very likely knock or a boost leak (BOV leaking/fluttering?)

 

[sumenlo]

How much boost are you running on that 14b? I don't see a boost gauge in your profile.

At WOT, my car is peaking at about a bar of boost. maybe a pound or so higher in the higher gears.

Yea, once you've felt fuelcut firsthand, forever the expert you will be (why do I sound like Yoda ) And with the altitude in Tucson (2600ft) and the warm temps 74F (*jealous*) would keep the onset of fuel cut to >18psi boost.

I wasn't saying that I was an expert at all. But I have felt fuel cut many times and this was in no way, comparable.

 

[oldman]

At WOT, my car is peaking at about a bar of boost. maybe a pound or so higher in the higher gears.

1bar=?psi.

I wasn't saying that I was an expert at all. But I have felt fuel cut many times and this was in no way, comparable.

John wasn't being a smartass (for a change ) when he said that, no one ever forget what a fuel cut feels like.

 

[sumenlo]

1bar=?psi.

well, from everythin I've read, 1 bar=atmospheric pressure, which is 14.7psi.

John wasn't being a smartass (for a change ) when he said that, no one ever forget what a fuel cut feels like.

ah, gotcha. I know what you mean

 

[Defiant]

Plugs (NGK BPR6ES, .028") and wires.

 

[DSMvroom]

1) hop on the highway
2) cruise in 5th at roughly 60mph
3) floor that pedal
4) watch the tach

If RPMs rise, then hold or fall before rising again . . . time to start looking for a new clutch before you stab yourself

I haven't the faintest idea what's going on with your car, but if you suspect the clutch then try what I've suggested

 

[sumenlo]

Plugs (NGK BPR6ES, .028") and wires.

but if it was plugs and wires, wouldn't i see the same symptoms in all gears? Not just 4th and 5th?

I'm starting to lean more toward a boost leak. Here's why:

When we installed my Gredy type S not too long ago, we ran into a problem. The set screw on the BOV was stripped out, so we couldn't adjust it either way. What we wound up doing is tapping out the stripped out hole to the next bigger size. We also replaced the set screw with the next bigger size. It wasn't a perfect fix. Meaning, the set screw was a little wobbly in the threads. It had enough bite on the threads to not pull out, but who knows what it's trying to do at 14psi or higher. Not to mention, when I was driving today, I glanced down at my boost gauge at WOT in 2nd, and I'm only hitting 11psi. My car has never boosted that low. I think maybe my BOV is starting to leak.