runs rough after cap and rotor change
 

today i had some extra time sooooo.....

1990 928 S4

i changed the distributor rotor and cap because when its real humid out or after car wash or rain it would loose a lot of power. i noticed green corrosion on driver distributor cap end that goes to coil. i thought that may be holding moisture. i have replaced the coils recently. but when i replaced the distributor and cap and rotor, if feels like i have no power. all plug wire connections seem ok. bad wires? why a loss of power from changing cap and rotor? new cap and rotor bad?:confused:

Yes...bad wires would be my guess. In the process of bending them to install new caps and pulling on them to move to new cap...I would bet there is a break in more than just one.

BTW...old plug wires almost always LOOK fine.

I will order wires next. thank for the reply

I'd start with checking all the connections are well seated, but if the wires are old, more than 5 or 10 years old, they a new set removes doubt and potential problems.

+1

Sometimes the end pulls off; however, it usually is left behind on the spark plug. Try a wire from your DD to isolate the culprit.

well, i changed the wires today and it stil ran rough. so i tried looking at coils, have spark, after checking for spark, now it won't start. i made it worse. i smell fuel now. he thing is, it was running fine when dry out, thats why i was trying a tuneup. im going to try to put the original cap and rotors tomorrow and see what happens.

Do you have a hot post cover in place???

i verified firing order, hot post cover is on.

im going to look at tdc and verify the rotors are in the right position tomorrow. also going to try old caps and rotors. could i have broken a wire to something critical?

ok, got it. it was new rotors and caps.

i first verified tdc rotors at 3oclock. was good. then i put old rotors and caps in and VIOLA! all good. I will have to verify why my new parts dont work. Thanks for the replies.

IDK what that 4 cylinder fire order was for though....

With the corrosion issue I would clean the grounds for sure. The main motor ground too.

There are a few sensor connections that with age get brittle. Double check all those within the work area are still snug and in good shape.

Keep in mind this new running problem may be non related to what you did. Make sure you have spark and gas. Would not be the first time something like this has happened.

Compare the new rotor button to the old. Are they EXACTLY the same in height and projection?

Did you get the caps , rotors from one of the main 928 suppliers...or off ebay?

Glad to hear it was a simple fix. Also you may see a better running car , especially under load with the new wires.

I got rotors from pelican and caps from ebay, the rotors and caps were Bosch

I did compare caps and rotors. The caps had a black cover that did not fit, so I used old ones, but both parts looked the same to me and I have an eye for detail

Grounds all look new cable wise but the main one in the rear has a bit of white corrosion between the bolt and crimp end, I mean minimal. I will still clean it though

Woopsies. I quess I had my 924s on my mind--I just replaced the same stuff and couldn't help but think that your post was for the same. I see now that you were talking about a 928 which kinda makes sense given that this is a 928 forum after all. Heh, heh, heh--silly me.