sd944s

Ok, here's the background:

I recently (two months ago) changed timing belt, balance belt, water pump, rollers, and seals on my '87 944S. I got the timing lined up and drove merrily away and performace felt fine. A week later, I noticed that I hadn't gotten quite as far on a tank of gas. I hit just under 400 miles of city & highway combined driving before the light came on. Before this, I usually got approx. 420 miles per tank (without "spirited" driving) before seeing the light. I chalked it up to a bad tank of gas or a fluke.

Then, about three weeks after the belt/pump change, the car started hesitating when I would accelerate. The exhaust started making a "fluttering" sound on acceleration. Each time I filled up the tank, I noticed my fuel economy getting worse and worse. Last week, I only got 335 miles before the light came on

Now, when I really give it gas, it feels like there's no additional power from the engine. Also, idle isn't quite as smooth but the symptoms only _really_ come when I accelerate under load. I push the pedal and it gets louder but there's nothing "there" to really move me forward. I'm trying to explain it the best I can but the power band just feels "hollow" and it sputters along.

This past weekend, I took the timing belt cover off and noticed that my timing marks weren't aligned perfectly. In fact, the crank was one tooth ahead of the cam. I thought I had found the problem! Instead, the car drove just about the same as before

So I've searched this board through and through and I think it might come down to something with the vacuum, fuel pressure regulator, or DME. I'm leaning away from the DME being the culprit but I'm not counting anything out. I'm also having a bit of dificulty troubleshooting the vacuum system. I have the schematic from clarks-garage.com but tracing it seems like a crapshoot.

Any thoughts? Maybe I dislodged something when I changed the water pump and belts? Why would it be increasingly worse?

If anyone has any insight, I would greatly appreciate it.

RMills944

Replace the O2 sensor - easy to do and it's probably time anyway.
Your hesitation may be due to that or you may have the AFM going out, but that's more money to fix - do the simple stuff first. It could also be a fuel pressure regulator too, but I'm not sure on the symptoms of that one.

I doubt it's a vaccuum leak, but you will want to find out anyway. Siply buy a can of starting fluid or carb cleaner and spray that around the intake joints (by the j boot, AFM and throttlebody) and see if the idle raises when you spray those areas - if it does, there's a leak there.

sd944s

Better late than never, but I'm following up on this to close the thread in case someone else searches for this problem.

So, what turned out to be the problem? A faulty fuel injector!

Once I had taken the injectors out and activated them with a battery and ran injector cleaner through them, it was clear one of them wouldn't actuate fully. When it was replaced with a new injector, performance and fuel economy were back, better than ever.

BTW, I've found that even if the injectors seem to be functioning well, pulling them out and giving them a good cleaning can make a performance and economy improvement because of deposit buildup. Of course, a good fuel filter can prevent a lot of these headaches in the first place