I't has nothing to do with air temps, because talking strictly about mid days in florida,and it's hot. I have a automatic and maybe that's the problem. Some days it's faster then ever,then other days it's nothing impressive, to me atleast. Do any other automatics experience this.

 

Do you have a boost gauge? It sounds like you're having boost problems.

 

I would worry about hte boost as well

 

mine can do that, and its auto too. I know that I'm not getting full boost from turbo #2, I figure its a vacuum leak somewhere, got a Hose Techniques kit in, now I have to find the time to put the damn thing in. But yeah, find out if you're getting full boost patterns.

 

My 5-speed does the same thing, and boost does not seem to be the issue... I have a boost gauge, and I've checked. Like the first post said, temperature also seems to be irrelevant.

It seems like I've been hunting this problem down for the 4 years I've owned the car. I've had the hose job done, replaced the leading coil, upgraded IC hoses and couplers, etc.

The fact of the matter is that some days the a$$ end is all over the place, while others it's not. Don't get me wrong, the car is still fast. But somedays it feel like it'd run low 13's, others it'd be low 14's.

I have heard the heat soak argument thrown around out there, but I don't necessarily buy into it. For example, I could be driving around with the car running OK, shut it down for 15 minutes, get back in, and the car seems much faster. Shouldn't heat soak work the other way around? Just curious.

Here is the only other thing I can come up with... my main cat is partially clogged. I just installed a RB catback, and noticed that the exhaust smell is more potent than with the stock exhaust... maybe this is common?? I'm not sure how to check if the airpump is working, but I am not hearing any of the tell-tale noises of a failing pump.

Here is the other thing, bumps on the road can also kick the car out of OK mode into kicka$$ mode. So, is crap getting rattled around in the cat, freeing up backpressure from time to time? My car can also run on the warm side from time-to-time, but I have no temp. problems if I run with the parking lamps on.

Let's hear some thoughts. Does variable performance seem to be commonplace, or should I be checking something else to fix this gremlin?

Cheers,
Jeff

94 VR PEP
Boost Gauge
M2 Downpipe
RB Catback
RB Intake Duct
SR Radiator
Pettit AST
Greddy Elbow & IC Ducts

 

same thing happens to me. It seems to be unrelated to boost. I have a PFC, I'm going to start looking at other variables like inj timing. Here are my observations so far:
when it is having a good run:
1. much stronger off idle to 2500rpms.
2. much strong under boost, particularly when the second turbo comes on.
3. accelerator pedal resistance "Stiffer" ?!?
4. sometimes when I shut it off and restart the power changes dramatically(always for the worse).
5. seems unrelated to heat soak. I do notice the power decrease as the car heats up, but it still doesn't drop to "normal/weak" for lack of a better word.
6.I noticed it before and after doing the hose job, ECU upgrade.

I'm baffled, but would guess it has something to do with timing-mainly b/c I know nothing about it and therefore assume it is the cause of all my unsolved problems
The change in the accelerator pedal feel seems strange-is that a clue?

 

Amen on all of the above points. You are dead on about the intial response, pedal feel, and especially the difference in the transition to the secondary turbo.

 

SilverFlash, You say you are sure that it is not air temps, but what are you basing that on? The weather outside? Or are you actually measuring the air temps inside the intake?

The reason I ask is that I used to notice the same thing about my car. One day, it's 70 degrees outside, and the car is really fast. The next day, it's also 70 degrees outside, but the car is slow. I was thinking WTF?

Then I got my Power FC, which among other things lets you read the air temps from the intake. Then it all became clear as day why sometimes it's fast, while other times it's not. Just because the outside air is the same temp doesn't mean that your intake temps are the same. Things like heat soak really seem to play a big role in how hot the intake air is.

Now I never have to wonder why it feels faster on a particular day. I've gotten so used to how my car feels with different air temps that I can typically guess what they are by how my car feels. I go for a drive, and say "Wow, it feels fast today, I bet air temps are around 20C"...sure enough they are. Or "Damn, the car feels slow, I bet my air temps are up around 50 or 60C."

Anyway, I don't know if that is what you are experiencing, but that was what turned out to be the difference with my car.

 

Red Rotary Rocket, thanks for the insight on the intake temps! Did you also experience any of the symptoms the CCarlisi and I pointed out?

 

Itradem, No, you guys' experience seems a little different from mine. In your case, if you know the cat is clogged, then I think you have probably already solved your problem. Having the power change after going over bumps is just wierd ...but it seems logical if there is loose junk in the cat that is bouncing around causing better flow one minute, then blocking the flow the next. Though I have no direct experience with a clogged cat, it sounds reasonable.

In CCarlisi's case, I am really intrigued by the stiff gas pedal. Man, your car has a mind of it's own Perhaps something is binding the cable or throttle plates? Waaaayyy back when, I used to own a Datsun 510. It was never as fast as I thought it should be. Then one day I was poking around and I discovered that pushing the gas pedal to the floor did not open the carb butterflies all the way. After some bending and adjusting the accelerator linkage, I made it so that the butterflies would open up all the way, and the power increase was noticeable....before the adjustment, my top speed was a lousy 75 miles per hour. After the adjustment, I could go a blistering 105 MPH I'd check to make sure your actually getting full opening of the butterflies when you put the pedal to the floor, and that there is no interferance.

Since you have a PFC, I'm guessing that you have already tried to make the correlation between good days and air temps. The only comment I can make is that to me heat soak doesn't always make sense. Surely, after turning the car off, then back on, some amount of heat soak occurs and the car is slower. But on some hot days after a hard drive, I expect the air temps to skyrocket...but they don't. Other days, when it's cooler outside and I haven't been driving hard, I get a lot more heat soak....weird.

 

I have DP MP and CB intake and fuel/boost computer. I have always hade a spoiled princes of a car that makes it's own mind up about how strong it wants to run that day. I did the mods in stages from bone stock and they made little impact. On thing that I have found is that the car likes to be beat up some times. Go out and run the hell out of it boost the bastard and run it like crazy. (safely) not around the block at 100mph. I think this helps to clear out some of the crud like oil in the intake and intercooler pipes and cleans some carbon off the walls of the rotor housing etc. seems to work for me except when something breaks

 

my observations:

1) rotaries do not seem to like sitting for extended period of time....after a week in the garage, my car feels pretty weak, then it starts to "perk up" after a few hours of running

2) ambient temps do seem to have a big impact....the engine absolutely craves cool air...on a clear (dry), cold, night, the car absolutely rips, it feels like it has another 50 hp, no problem, even though I'm only boosting about 1 psi more

 

Are you also comparing the feel when you're on the same tank and the car is fully warmed up? Old tank of gas can make the car weaker.

Also, it could be a LIM leak. Any of you have high idle? When there is any vac leak, the car behaves inconsistently bc the computer is trying to adjust bc can't.