Hesitation at high RPM's
 

My 98 Boxster seems to hesitate after 5,500 rpm's. It doesn't always do it, but at full throttle it sometimes feels like it stumbles. The air filter is new. I had my indy change the spark plugs. He inspected the coil packs and said they were fine. Any ideas?

Fuel filter or fuel pump.

I forgot to add the the fuel filter is new also.

O2 sensors getting tired?

Well i bought the car last summer. It did the same thing before i put it away for the winter. Since then i have replaced the plugs, air filter, fuel filter, clutch, IMS bearing, flushed break fluid, replaced belt and replaced AOS. If it could be the coil packs, that would seem like an easy fix. The fuel pump seems like a pain. I believe it's in the tank, i hope i'm wrong about that. My Indy has a fair labor rate, but i'd rather try to do more myself before the wife kills me.

MAF??? My hesitation cleared up after I changed the MAF. At first there was no CEL but as symptoms got worse I got a CEL, and O2 sensor codes that pointed to a bad MAF.

MAF? Maybe, but so far I have never had a CEL. Then again I have never hooked up a reader just to make sure. But the CEL light does come on when I switch on the the key, just like all the other lights under the gauges. So I would think that it does work and no one has disabled it.

Did you retrieve any codes? Bad spark can cause the same, maybe one of the coils how old are the plugs? A can of techron couldn't hurt.

That is the first step in diagnosing these cars. Get it hooked up to a scanner and see what is going on.

The plugs are around a month old. The tech at the shop said that the coils looked fine when he changed the plugs. But one or more of them could have cracks he didn't see i'm sure. I'm thinking that even though i have never had a CEL i should have it hooked up to a scanner. Does it have to be a Durametric or will any professional scanner that a shop would have work?

Changing the fuel pump is not a pain. Just pay attention. After you do it once , You will say how easy it was to do. Good luck !!

I also forgot to mention that I have a chirping sound upon hitting the gas. It happens more when i let out the clutch ( under load ). If i just hit the gas in neutral ( wife helping ) then it's just a quick chirp, instead of a few chirps. I'm thinking after replacing the belt, I'm putting more stress on a pulley or the water pump. Or after searching the threads maybe the tech didn't snug down one of the spark plugs when he replaced them. Could any of this ( Original Post ) loss of power at higher RPM's and Chirping be related?

Yes.
Failing AOS, loose spark plug, and badly worn chain tensioners have been known to make a chirping sound. Your car is a possible candidate for all three.

Well the AOS was replaced last fall. It didn't make the noise before the belt and plugs were replaced, but it did hesitate from time to time before that. So they probably aren't related now that i think about it. I'm just going to have to hook it up to a scanner and see what the issue really is before i just throw parts at it.

A new fuel pump is one of the best investments you can make for $ 200.00 bucks. Well worth it !!!

Unless the one in the car is still ok. ;) Changing out good parts is never really a good investment. Get a clear diagnosis first. Measure the fuel pressure and if the fuel pressure is low, change the fuel pump. If the fuel pressure is normal, changing out the fuel pump might be fun but it won't solve the hesitation at high rpm.

+1 I thought by now the codes would be on the thread, why take the circuitousness hard way when you can get some clues as to where to start looking?

will be spark plugs for sure

Well the codes are not on the thread yet because I haven't had the chance to take the car to the shop. The check engine light is not on, nor has it ever been on since i've owned the car. I don't think i can just swing by Auto Zone and have them see if there are any codes can i ? It has been pouring rain here the last few days. I hope to get it somewhere to see if there are any codes in the next day or two. Thanks for all the suggestions so far.

Read the first thread - plugs have already been changed out by his indy.....

Tommy, no dis intended, in fact you're right in the hood and yeah it's been Noah's Ark. I always heard AZ would do free code reads but I never had to run the test. The other poster might be right spark plugs could be a great guess. Let me know if you need something, I can't lift but I can guide you through a lot of jobs including the plug tubes and plugs if necessary and I have a great set of tools including many of the Porsche specialty items, a Bentley manual and hours of wrench time on 1998 986.

PS Whose wrenching on it? Avoid Cantech unless you like paying 125% more than any job should cost.

Ghost, no dis taken. I agree with you on Cantech. I went there once, never again. I have been taking it to Upstate Imports in B'ville. I might have to take you up on your offer to help one of these days.

George at Fehlman bros is pretty good on Porsche cars if you hit the wall at the other place, as for the simple stuff just let me know.

Well I think I have found out where the chirping sound is coming from. With Ghost Rider's help, as he did most of if not all of the work. One of the spark plugs was loose. Tightening this plug has reduced the noise by at least half. I hope when we get time to do the other side, the noise will be gone altogether. Thanks Ghost!

Tommy, I think i have a shorter allen in house for that job, that's why it was easier last time. All we have to do is check what plugs are left and that should do it.

Well I got around to tightening up the plugs on the passenger side. The front plug was about 1/4 loose. No more chirp! I'd like to thank Ghostrider for his help as well.

OK update. The chirping noise has been solved. It was a loose plug. The hesitation at RPM's over 5,500 is still there sometimes. I stopped by an Autozone on the way to work. There were no codes using the ODB II scanner. Now should I just buy a Durametric or would an Indy have a scanner that would work.
To refresh the situation the car has new plugs, fuel filter, air filter,AOS and belt. The indy that put in the plugs said the coil packs look good. I have never had a check engine light come on. I have run 5 or 6 tanks of gas since the car was taken out of storage. It did the same thing last year before i put it in storage.
From the input i have received from you guys so far i still need to check fuel pressure, MAF and maybe O2 sensors. Thanks

Considering what you have left to check and what's been replaced so far, it's a pretty safe bet that your hesitation issue is somewhere on the fuel end of things. But do check out your MAF and see if it's filthy, it could be that it's dirty enough to cause some issues without throwing a CEL, but I'm betting it's fuel delivery related.

Well on the ride home from work the car ran great. It's around six miles to the hi way on ramp. So the car was nice and warmed up before i got to it. I took her to 5 grand in first, 5,500 in 2nd and 6 grand in 3rd. No hesitation. 65 deg outside temp. Got on it in 1st and 2nd when i got off of the hi way. Still good. With a cooler outside temp i would think that it's not a fuel pressure issue. Cooler air is more dense, so i would need more fuel to have a good burn? I'm going to clean the MAF to see if that helps. I'd rather try that for the cost of the spray before I pay to get the codes read. Good idea? Maybe there is some oil in the intake from when my AOS failed?

Oil in the intake is possible, even very likely if you never actually went in there and cleaned up after the AOS failure (did the AOS full-on fail or was it on its way out?). I'd say get in there and check your throttle body and the intake plumbing for some oil, and give it a good cleaning if you find any.

No harm in cleaning the MAF before going with a replacement, but I'd recommend buying one anyways and having it on hand so that you can replace it when the time eventually comes. Pelican Parts is where I got mine from. Also, whether you clean the MAF or not, go get the car hooked up to a scanner anyways, might as well give it a good once over since you've yet to do so. It can't hurt, right? Small expense for a gain in knowledge, even if it ends up telling you everything's ok.

The AOS was on its way out so i changed it last fall. I never did clean the intake or the MAF. I think i will do both this weekend and see if it helps. If not i'll have to take it to the shop next week and put it on the scanner.

What ever came from this Tommy?

I found the carbon canister to be clogged solid. I ordered a used one from Woody. I blew out the lines with compressed air and installed the the new canister. Hesitation gone and no more CEL.