100 octane unleaded == $4.13 in wayzata, minnesota (today)
Shell gas station

 

Well after dealing with a tire issue that arose and getting four new ps2's I finally got around to trying some 100 octane unleaded ($5.94/gallon). You can definitely feel the difference with the 100 octane, but unfortunatley my power loss issue remains. The car begins to pull really hard at 4000rpm in 4th and 5th only to begin cutting out somewhere around 5000rpm, only this time it picked back up and began pulling again. So it was on and off, then on again. I'm beginnning to think there's an overboost problem going on here. Any recommendations on where i should go from here? Should i look at adjusting the waste gates? If so, how is it done?

thanks

 

You said that you were going to check the boost pipes. Did you do that? Did you check the top and bottom of both pipes? I went throught he same missing issue. Checked and changed a bunch of stuff. I finally changed the spark plugs and thought the problem was fixed. The car ran great for several days. All of a sudden, the problem was back exactly as it was before the plug change. I found that one of the clamps had slipped up on turbo end of the hose. This was allowing a lot of metered air to leak during high boost, causing the mixture to become really rich, resulting in a bad miss at WOT. The hose was still on the turbo so not much air was leaking when there was no boost so the car ran fine under low boost conditions. I reseated the hose, positioned the clamp and tightened it good. The problem was gone.

I think that a loose boost hose was my problem all along. I think that when I removed and replace hoses to get to the sparkplugs, I temporarily fixed the loose hose and thought at the time that it was the plugs that fixed the problem.

I'm going to order some new orange ended hoses and good clamps. That should fix it for good.

 

Look at your O2 voltages. See if the car is going lean under boost. Lean misfires are a real problem with the weak stock ignation. Jegs sells a wide band kit that runs dual O2's and you can see both banks at once. Look for 12:5-1 and less under WOT

 

Car has been at the shop for about a week now for the 45k service and to deal with the power loss issue. I tried the 100 octane fuel a while back and there was no change. Also checked all the hoses. The shop checked it all over as well. They pulled a spark plug and said it looked pretty tired, so they changed all the plugs. Initially they thought the problem was solved but then they felt it again. The O2 sensors are working within specs and the voltages are good(0.8 volts) according to a test drive with the laptop plugged in. Apparently 1.5 volts or more for more than 5 seconds means they are bad. Can someone explain these numbers please. I'd appreciate the education here. Now they think it could be a bad coil or MAF even though there are no codes. I mentioned to check the knock sensors too. Fortunately they are working to find parts to test in the car to rule things out rather than just racking up the parts bill on me. I'm waiting to hear back......

 

They way to determin fuel ratio using the o2 voltages is to use the voltage number and multiply times 14.7 using this formula your ratio is 11.76 to 1

If you have a laptop with the obd2 program log the maf voltages. Also install a boost gauge.

Make sure the maf does not max out if/when you have a boost spike.

 

These cars are very sensitive to ignition. As Kevin mentioned, your might try changing the plugs. Also, check the cap, rotor and plug wires. Any issues with these can cause your problem. Especially as you get up towards 5000 RPM where ignition is most critical.

 

K24madness,
thanks for clarifying the numbers. so the O2's are OK. i will pass the info on to the shop re: voltages for the MAF, if they are still having difficulty finding the problem.

viperbob,
thanks for your input. i will pass this info on as well. the distibutor is new and they've already changed the plugs. They plan to swap the coil next then the MAF. If those don't fix it we'll go from there.

I will report back.......

 

Check 1)fuel filter
2)MAF meter
3)fuel pump

 

mpls, minnesota: shell 100 octane unleaded = $ 4.19/gallon (cheap insurance)

 

I had major problrms with my K&N filter, the media had shrunk and was restricting the air flow to the engine, the MAF sensor also needed to be replaced because the filter oil had damaged it.

 

In SoCal, 100 octane is $4.59. I mix about 1/3 100 to 2/3 91 to get the required 94 or octane. Our 993s, TT or NA are really designed with 94 octane in mind. Nothing bad will happen... you may see a tiny bit better performance in a NA 993.

 

$4.50 It won't mess anything up.

 

Well I finally got her back. Amazing how much I missed driving the car in just a week and a half. In the end the power loss was happening because a spark plug wire at the distributor was not down tight all the way and a vacuum line was off at the intake manifold. So many of you were right on track with the plugs and wires and someone once posted about vacuum lines being critical and to make sure they are all plugged up. It seems a few of you know a thing or two. Thanks everyone. Full boost all the way to redline sure is fun. Bye.