I've come to the realization that I need expert help with this stumble on acceleration. So this morning, I dropped the car off with the experts at Intersport Performance.
The techs were able to observe/replicate the hesitation, and they're working on diagnosing the cause(s). I can't wait to find out what the problem was. Hopefully this afternoon I'll drive home in a car that pulls hard at ALL rpm's, and at ALL operating temperatures.
Good luck! Hope its an easy fix.
It may not be an easy fix, but I don't think it's a really bad one either.
I just got off the phone with Charlie, one of the owners/principals at Intersport. He drove it this afternoon and he believes it is a broken valve spring. This makes a lot of sense because what's happening is a loss of compression while the oil pressure is high enough to restrict the valve from closure.
When it returns to idle, it takes a few seconds for the oil pressure behind the valve to subside, and then it purrs.
It makes sense to me, and it sounds like a straightforward job to fix, as long as one can confirm that the valve guides don't have excessive play/wear when you get in there to replace the springs.
Charlie recommended that I have a pro do it, since there are things that can be done to extract more power from the car while you're in there... Turbo springs? other adjustments?
I'm overjoyed that I have a diagnosis that makes sense. And props to Charlie for having that expert ear I needed. Now I need to research the repair and determine if I want to attempt it myself, or just have Charlie go in and do it. I just feel like I wouldn't learn anything if I had him do the work.
What do you think?
That does sound like it could be the issue. Quite the interesting diagnosis!
As far as DIY/Pro, if your going to do all of them, id say pro, they will be faster/better lapping, getting everything right etc.
If you dont care about how fast its done, I think its straightforward, as long as the head is in good shape once opened up. If machine work needs to be done anyway, pro job IMO
The thing with the 944 engine is that the cam is encased in a cam tower bolted to the top of the cylinder head and serves as the valve cover. Makes things a little more difficult.
So ideally, you'd have to change the timing belt, and the top end gaskets to repair that issue. Given the expense of just those parts alone, I'd be hesitant to pay for labor to R&R the cylinder head and related components.
Personally, if you've done the timing belt recently, I'd swap a good valve spring in place, toss a new cam tower and intake manifold gasket set on it and get back to driving.
If you want to play with a motor, get a good running spare engine for cheap, refresh the seals, belts, bearings and then you can play with the old motor, but there isn't too much to be had from the motor in NA form. This is why Porsche bumped up the displacement and added an extra set of cams, etc.
I've made the decision to go forward with the repair myself. The guys at Intersport were anticipating doing the repair, though, and ordered the parts the day I took the car home. Which is admirably proactive, but unfortunately I had also already ordered the springs. Mine, however are taking their time on a slow UPS truck across the country. So I'd rather have them now.
I bought the whole lot of parts from Intersport primarily so they wouldn't have to eat their restocking fees, but also because they got theirs cheaper, because I know they're the right parts, because they're genuine, and because it was one-stop shopping for the parts in a hurry. So I think it worked out for everyone. The guys at Intersport are really racer-friendly, and they understand my desire to do as much work as I possibly can for myself. I can't say enough about how understanding and agreeable they are.
Even though the timing belt was changed only about 6K miles or so ago (actually unknown since the odo was broken since then), I'm going to change it again because that was in 2009, and I have the new belt in hand. And some have said time can be as bad for these belts as the miles.
The only parts I'm missing (and I'm pretty nervous about this), are the valve spring retainer rings (the ones at the top which wedge the little keepers onto the valve stem). I've been driving this car like this for three track events. They might be a little beat up.
So the plan is this:
1) Remove the cam tower and assess the damage.
2) Clean it up and replace all the springs.
3) Replace the cam tower-to-head gasket, and the gaskets on both ends of the cam tower.
4) Replace two other little parts... one's a clear thin plastic ring about an inch in diameter, the other is a little short tube or bushing of some sort. I'll figure those out when I get there.
5) Replace the timing belt as I put it all back together.
6) Pray that I don't have to wait for more parts or tools before I can re-assemble it.
7) Drive at Summit Point next weekend!
Wish me luck!
Ambitious! Good luck!!
Over the weekend I got just about everything I aimed for, and then some!
I visited the dump and recycled 10 gallons of used oil and about a gallon of used brake fluid. That made room for... more oil!
Then I changed the oil on the Fiesta, replaced the front rotors and pads, and bled the brakes, and rotated the tires. Although it has been so warm, I should've put on my summers.
I also retrieved and tested a large compressor that a friend gave me when he moved away. It's been in my mom's garage for three years at least. It's a big 20-gallon unit which should easily do the job of retaining the valves as I press the springs onto them. And my compression tester gauge's adapter hose plugs right into it.
Finally, on Sunday, I jacked up the 944 to have it all ready for surgery, which I began on Monday.
The steel table also came from my mom's garage. It's really going to come in handy.
On Monday evening, I took off the cam tower, exposing the valve springs. Overall it went pretty smoothly, since there were a LOT of things that could have gone really wrong.
It took me a couple hours to do it once I got going on it. The scariest part was using the 3mm hex key to remove the distributor rotor, I thought for sure that I would strip it out.
Second scariest was the loud "TINK" sound it made every time I broke one of the internal cam tower bolts loose. They're 6mm hex socket head bolts, and I was afraid every time that the hex key I was using had broken off in side that enclosure.
The good news is that all of the valve spring retainer rings look like they're in good shape.
The bad news is that all of the valve springs look like they're in good shape.
Each valve stem has two coaxial springs, one inside the other. It's possible the inside one is the broken one, I guess. It's dark in there.
Bummer deal! Could you inspect with a bright flashlight before disassembling?
On Tuesday afternoon I hooked my compressor up to my compression tester's adapter hose. I had to remove the Schrader valve from the end to make it work. In essence, it was a leakdown tester. If I wanted to be scientific about it, I could have timed the intervals in which my compressor kicked on. But I didn't. Ain't nobody got time for that!
And that damn compressor would kick on at the most annoying times and it would make me jump every time. It was sitting right next to me and it's a loud one.
Anyway, the tool I bought worked beautifully. I never did send a part flying. It never slipped. And the handle was just right. So all in all, a good buy.
So anyway, I only had time (and energy) to do the valves of cylinders 1 and 4. The springs were all in good shape except for a little broken off tail, which wouldn't affect anything. Here's a picture of it, with the old springs above and the new ones below. The new springs seemed beefier, but I imagine the overall rates are the same. Maybe a refined design?
After I removed each spring, I wrapped a pipe cleaner around the valve stem to keep it from falling into the engine, de-pressurized the cylinder, and felt the way the valve moved in the guide. Did it wiggle side to side? Did it spin and move up and down freely? Did it meet with its valve seat with the same "tap" sound in any rotated position? Did it feel smooth when rotated against the valve seat?
All of them felt pretty good and solid except: Cylinder 4's exhaust valve seemed like it wiggled side to side a bit more than the others. It also felt like it had a less positive "tap" as it hit the valve seat... more of a "t-tap" feel to it. That was unnerving. So I thought maybe I had a burnt out valve seat, a chipped valve, etc. That cylinder also seemed to leak down a little faster than the other one, out the exhaust if I had to guess.
At about 9pm I decided it would be unwise to continue with the other two cylinders, or else I'd break something, lose something, or worse, hurt myself.
Wednesday was a beautiful, record warm day. I had scheduled the day off to finish this job, but I was feeling a little less enthusiastic because it seemed at this point that the problem was going to be deeper in the engine, and that I'd be taking the head off. Therefore, I wouldn't be driving the Porsche this Saturday. So I slept in a bit, and got to work around 9.
I started by removing exhaust valve spring #2, and... WHAT?!?
Yep, that Charlie from Intersport is indeed The Porsche Whisperer. Sure enough, a broken spring. The inner spring's two pieces were just sort of screwed into each other, taking up half the height of an intact spring. I was overjoyed, because here was my smoking gun. Time to finish up, put this back together, pronounce that valve on #4 as "marginal" as opposed to "unacceptable", and see how it runs!
But wait... rut-roh. The washer that the spring was sitting on was pretty beat up. That really shouldn't go back in. There needs to be a lip there to locate the new spring...
I didn't have one of those. I had also tested all the hydraulic lifters in the cam tower, and one of them seemed pretty soft. So I needed one of those before I could close up. With some calling around and searching online, I found a guy near Hagerstown who sells used 944 parts. I called him and he quoted a used lifter for ten bucks, and he'd throw in the washer for free. I said I'd take two and I'd be there in an hour. (Turned out he was an hour and a half away, but I was soooo happy to be able to rescue the rest of the day from a total letdown.)
When I got home I put everything back together. I got the cam tower back on. I got the fuel rail back on. I got the balancer belt off, and the old timing belt off, with a lot of effort. In fact, I spent the next 4 hours trying to put the new belt on without damaging it. Unfortunately, I didn't get that done last night. I was just frustrated about it and again I was getting to the point where I was about to break something or hurt myself. See a pattern forming here? If I were 25, I'd certainly work until I broke something or hurt myself. At 45, I have a bit more wisdom and patience than that, I don't mind saying.
So tonight I will work on it again with a fresh attitude. I'll put that belt back on, and I'll get the engine running again. Because I'm good enough, I'm smart enough, and, gosh darn it, people like me!
In reply to java230:
You know, I had always assumed it would be one of the outer springs that broke. I don't know why I was thinking that, but it was hard to tell right up to the moment of actually removing them.
Charlie is the best. He helped me out a lot with my 924 when I lived in MD.
Awesome! Glad that was actually the issue! Hope to see it back on the tack shortly.
This might help some folks visualize some of the fun you get to have with the front of engine service:
http://www.924board.org/viewtopic.php?p=379651
Also note the water pump impeller diameter issue he noted.
Good news, everyone!
The car is running again, this time with FOUR cylinders! And it feels like a new car. I mean, it seriously feels like it introduces zero to 60 way faster than it ever did. I can't wait to see what it'll do on the track.
Fortunately I don't have to wait long for that. My first track weekend starts Saturday!
So tomorrow afternoon I'll be changing the oil and filter, and flushing the brake fluid with fresh Motul 600.
Then it's off to Summit Point Main Circuit, where the weather is looking good at least through Saturday. Sunday we might get some scattered showers.
I hope you guys don't feel slighted or anything, but the detailed play-by-play on how this whole thing went down is over on Rennlist.com, where there is a large 944 community that has also been a huge help.
I hope that thread can be of help to others who have these symptoms. This issue doesn't happen every day, but it's not terribly uncommon either.
Car Prep for SCCA PDX at Summit Point Circuit
Well, it was a mixed bag of a weekend, and entirely exhausting for me. I was so tired at times that I questioned whether it was worth it or not, certainly on Sunday afternoon when it had started raining before our third of four sessions.
On Friday night I got the oil changed, brake fluid flushed, car loaded with wheels, tools, helmet, jack, chairs, fluids, and cameras. By then it was about 9:30, and I'd be leaving for the track at 5:30am. I was tired already, but I actually got some sleep.
Overheating due to more cylinders in play?
At the track, we had dry sessions on Saturday, and the car was running well, but after the first session I noticed a puddle of coolant forming under the car. It had spilled out of the overflow tank's vent hose. This had never happened before, but when I parked it after the session, I guess latent heat in the block boiled the coolant to push a bunch of fluid out. From then on I made sure to do a couple laps around the paddock to cool it down sufficiently before parking it.
Near the end of my second session on Saturday, I heard my engine suddenly sound REALLY loud, coupled with a clanking, grinding noise. I was just past pit-in, so I had to drag something all the way around the track again before I could pit in and investigate.
To orient you to what happened, my car's exhaust goes like this:
engine -> header -> welded flanges with gasket -> test pipe -> flared flanges with ring -> resonator/tailpipe/muffler assembly
The test pipe had broken at its connection with the flared flange, and the rubber hanger that might have held it up broke as well, allowing the resonator to drop to the track and drag for two miles. What you see is the broken end of the test pipe and the beating that the resonator took on its trip around the track.
Fixing the Exhaust
I could have driven without a muffler, but I was afraid the test pipe or something else would fall off too. So I threw the muffler in the back and headed home to try to do something about it.
I was under the impression that the exhaust was 2.5" forward of the muffler. But the test pipe is actually 3" until the very back end, and it reduces to 2.5 where it connects to the resonator. So the 2.5" extensions I bought on the way home from the track weren't ideal. What WAS ideal was all the 3" tubing I had at home, and the two flanges and a gasket I had purchased for my muffler project but didn't use.
So Saturday evening I quickly fabricated a replacement test pipe that bolted right in where the old one was, and it was perfect. I'm even getting better at TIG welding, and when I get my foot pedal wired up, I hope to get good enough that I don't need to pour so much heat into the work.
Exhaust Hanger Fix
Another thing that worked out nicely was that when I returned my unused exhaust pieces to the parts store that evening, I picked up a universal hanger isolator which I modified for my use.
After cutting the rubber between the upper slot and the two holes, it made the perfect replacement for $5, rather than waiting a week for a $20 OEM one.
Terrible Noise?!?!
I got all this done and bolted in by about 10:30 pm. When I fired up the car to hear it, I also noticed a horrible flapping noise coming from the distributor area. I decided I'd address that in the morning after some sleep, albeit an hour less of it due to daylight saving time.
Besides that, the exhaust still sounds like poo. I feel like there's something in that resonator that's rattling around, and/or the header has holes in it as well. I'll have to do a thorough assessment of the header's integrity, and I will soon replace the remaining old resonator+tailpipe portion with all-3" stainless tubing.
Sunday - Fixing the Serious-Sounding Noise
Sunday morning I got up at 5:30 and started looking for that noise near the distributor. I took off the cap, and finding nothing wrong, I went into the area of the timing belt cover, since that was what I had last messed with.
Then I took off the belly pan, and looking up, I found the problem, and it was what I had LAST LAST messed with: while changing my oil, I had jammed a piece of plastic jug under the oil filter to divert spilled oil away from the power steering unit and pulley. It worked like a dream. But I had simply forgotten to remove it, and it had ridden there all day Saturday. I just couldn't hear it over the noisy exhaust, I guess. It was flapping against the power steering pulley, making a racket. I pulled that out of there. Problem Solved.
I also re-tensioned the timing belt while I had that cover off, and headed to the track.
Sunday - On the Track
I joined the first session just a minute or so in, and I was just feeling better because a lot of these little bugs had been worked out. It was also good to get some decent dry laps in. Advanced group is nice because everyone is fairly predictable, and there weren't many trains to deal with because passing is allowed anywhere with a point-by. Intermediate group could be annoying that way.
The car is about 2 seconds faster around the track (1:32's vs 1:34's) that it was before the valve spring fix. It's still slow. But it's nice to know I'm getting all the power it has to give.
Don't Drive Tired
It rained starting the third session on Sunday. It was wet, it took all my concentration, and it just felt like work. Not thrilling, just taxing. I put down too much power coming through Turn 2 and got completely sideways. I actually ended up touching the inside tire wall with my bumper after sliding sideways across the wet grass for what seemed like a hundred yards.
Fortunately there was no damage, and nobody saw me do it. There were so few cars left that nobody even passed me while I restarted the car and rejoined the track. I dutifully came in to talk to the marshall, and went back out for three more laps before coming in and calling it a day.
I honestly think that if I weren't so tired, I would have been able to make the necessary corrections much earlier, avoiding any close calls at all. So I skipped the last session and mustered enough energy to pack the car, drive home, and unpack the car.
So, all in all, I gained lots of experience this weekend, but I really want to spend more time driving and thinking about driving, and less time wrenching and worrying about the car. That'll certainly have to happen before June, when this car is going to have to take me through competition school (NASA @ the new Dominion Raceway).
Glad you didn't wad it in your education session this weekend.
Me too... it could have gone poorly.
Fantastic, glad you didn't nose into that wall harder! Good lesson learned it sounds like.
Here's some video of a better performance earlier in the day... My friend and instructor Joe chases me down in his capable BMW 135i...
https://www.youtube.com/embed/n0eLNRy-MQk
I'm pretty sure he was giving me the thumbs up and not an obscene gesture. :-)
Yeah that was a very lazy spin, I agree if you would have been more alert you would have caught that.
That was an easy rub too. Any damage at all to the corner?
The bumperette should have taken most of the rub. which is nice.
Glad to hear you got it going again. Watching the video I thought the first part of the turn was where you'd spin, not where you did. (there was a big puddle at turn in.) Pretty amazed it spun at all to be honest.
In reply to Flight Service and Mad_Ratel:
I couldn't even find any abrasions anywhere on the bumperette, the bumper, or the fascia. So yeah, I'm very lucky, and quite fortunate that I'm not pricing out body panels and turn signals.
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