Hi RPM miss

JagPlt1 · 06-13-2004, 09:18 AM

1985 Carerra, 3.2 motor, runs smoothly at idle and light load. Accelerating hard sluggish at 2500 - 3000 RPM, then at 5200 starts to back fire and the tach starts to fall off... if you stay in it, speed holds but tach continues to drop. If cold runs fine in tests to isolate the problem. Once on temp, problems.

Changed the plugs and plug ends with no change. Took out an aftermarket O2 system and replaced with an origional O2 sensors in the test pipe. Swapped out the coil, mass meter, speed sensors again with no change. Didn't have an ECU to swap, plan on checking fuel pressure when I get home from this trip.

Anyone had similar problems or know of some where to research this problem. Any suggestions will help.

Thanks,

Mike

vash · vash's Garage

talked to a mechanic yesterday about the same topic. he said miss shifts typically bend a valve just slightly to mess up your car holding idle. especially coming off the throttle.

yelcab1 · 06-13-2004, 10:11 AM

DId you change your spark plug WIRES ?

JagPlt1 · 06-13-2004, 10:20 AM

ok at idle and quick response.. sluggish at 2500 - 3000 then accells well through 5000 then breaks down. Put a scope on the wires, no miss in any particular wire...

JagPlt1 · 06-16-2004, 12:43 AM

wish this post got as many responses as my "disappointed in the forum" post.. it got a lot of hate mail! lol

k9handler · 06-16-2004, 01:07 AM

fuel issue? Check the fuel filter and pump just in case. I had a clogged up filter that would cause the car to miss and run sluggish, after I POR-15 treated the fuel tank and replaced the pump/filter it was all better. Just a suggestion.

JagPlt1 · 06-16-2004, 01:17 AM

HD.. what the miss a high speed or low speed on yours. the tank's pretty clean with a scope down it.. POR 15's some great stuff huh! fuel filter's new, the only thing fuel wise I hadn't checked yet is the line pressure. I'm going to do that when I get home this weekend, the test gauge should be at the shop by then... oh by the way.. just flew over a corner of iraq yesterday and didn't see a Porsche center.

JagPlt1 · 06-16-2004, 01:19 AM

HD.. if you've found POR 15 .. you know about PB Blaster right? Hadn't used an easy out since I found out about that stuff!~

k9handler · 06-16-2004, 01:36 AM

yes I used the POR-15 fuel tank treatment, and the POR-15 on my interior after I removed all the old sound material and carpet. It's great stuff and worth the hassle for sure.

As for the miss it was at 2300-3000 rpm and then once in awhile under acceleration above 5000 rpm...all caused by rust in the tank.

jluetjen · jluetjen's Garage

What's the condition of your alternator, battery and voltage regulator? It sounds like you're running out of spark at higher rev's when the current draw is greater.

I see that you've swapped stuff out, but have you taken the time to try to troubleshoot the systems? It seems like you have the know-how and access to equipment.

JackT · 06-16-2004, 04:34 AM

You also need to make sure your warm up regulator is working properly. I had the same problem and replaced the WUR and the problem went away. Unfortunately I replaced a lot of other things before the WUR.

stlrj · 06-19-2004, 11:55 AM

What's a 3.2 engine doing with a WUR?

Joe

raceman · 06-19-2004, 03:57 PM

l`ve got the factory test plan,both editions,for the 3.2.This is what the factory sent to the dealers for motronic diagnostics on the 3.2 .l`ll make you copies if you like,just pay the costs.Perhaps someone wants to post the complete test plans? The information is invaluable and really straightforward,good for all 3.2`s but applicable to any first gen. motronic system,Porsche or otherwise.

ed martin · 06-20-2004, 09:45 AM

I had a similar problem in one car. Basically it ran great cold, but when it reached operating temperature the car just wouldn't get up to speed with a lot of popping through the stacks (MFI). If I recall correctly, I don't think I had a problem with the tach though, it seemed to hold steadily. Turned out to be a bad fuel pump. But I did just recently have a problem with another car where the tach would not remain steady after 4000 rpms and the car would lose power and felt like it would stall. Adjusting the valves completely solved that problem, as they were very tight.

gsxrken · gsxrken's Garage

I changed my cap and rotor yesterday and a similar missing condition to what you described appears to be cured. I figured I start simple before I got into CIS fuel pressure stuff, and I had never changed it. Judging by the gnarly interior of it, the PO hadn't either...