Newbie with a stutter

[sniffer]

Hi y all,

First post! This forum is a font of information and worlds best for 930's.

When getting on boost (about 2800 revs) the engine can stutter sometimes> The stutter can be quite violent. Over boost connection is grounded so dont think that is cause. Have new filters (fuel)> Have checked all the air connections I can (intercooler seals etc.) Had a CDI box failure last year and had that rebuilt so dont think its that either. Car has been to moon and back but had mcuh rebuild engine work. I am wondering if this problem can be caused by distributor cap or ignition wires (yes checked green wire from coil to distributor).

So my question is

1. Shuold I order clewlett stuff and bosch cap and rotor from our hosts.
2. Is it something else causing this like fuel starvation (or flooding)

Cheers Mark

[sniffer]

I should add some info about car to help with diagnosis of problem. The problem only started after I had the car serviced (big service). However the mechanic thought was overbost switch kicking in> Had a manual boost controler. So removedthat so as to see if that problem> well waste gate opens at 0.8 bar without the MBC but intermittent problem remained. Also noted that someone (overboost thingy) in past had removed the connection to the fuel pump cut out switch. The car has done 140000 miles and i guess the CIS system has had no input since it built. Car very smoky on start up with crap fuel economy so i think WUR is on last legs but I cant work out if that could be the cause of stuttering at boost onset.

I realize I need to get my AFR meter fitted so I can get some more information. However need new headers and muffler so will fit after they go on. By the way Rarly8 (hope spelt that correct) when you gonna start selling your headers coz would make neat package for me your headers muffler and a non standard turbo.......dreams

Sorry to go on and on

yours mark

[Hirevtuner]

Welcome Mark, you mentioned just having a major service done. Have you talked to the shop and told them how it's running poorly now? Also what happens sitting in the driveway and rev it to 3500rpm, is there still a stutter?

[Miguel Antonett]

Welcome to the forum!

If you post some pictures of the car you might get quicker answers....

Did I say pictures?

I would start with checking the overboost switch.

[RarlyL8]

Please describe the studder in detail.
Many things can cause a "misfire" on boost. Fuel starvation, WUR malfunction, O-ring blow-out, ignition malfunction, boost switch malfunction.
You just had the engine serviced which may or may not be a coincidence. Check the easy stuff first such as the boost signal line to the WUR. May be that hose is off or O-ring pinched.

[sniffer]

Many thanks to all who read my post. Will try and answer questions in order.

Will post pics when i can

Yes spoke with mechanic post service. They not of any help. They thought it was the fab speed air filter that was causing it. They fitted a new plenum chamber as the original cracked where the intercooler bolts on to it. Was not cheap but getting the old one welded was same price.

Have not tried stationary 3500 revs test, will do now.

The fuel cut out overboost switch is no longer in use (I know that beep beep would not approve of that!).

Many thanks Rarly8 for giving me some pointers. I will now try and describe the stuttering a bit better. It happens mostly in second gear if one stamps the throttle and can stutter at any revs post boost threshold (which seems to be at 2800). If you keep the throttle nailed to the floor the stuttering mild (feels a bit like car stalling when one hasn,t given the car enough gas when you pulling away from stand still). If you don't keep gas pedal nailed then you get a face in dash board moment (beep beep quote i think). Thinking it through as i write this i reckon it could be a fuel /WUR related problem. Have wifes parents stying for weekend so cant get out to car to check the things you mentioned. Cant wait to try suggestions out and see if it works.

Have to say owned loads of cars in my life. some really expensive ones to. This 930 thing (bug) has bitten me so hard. Best car in the whole world.

Yours Happily Mark

[h2oplr11]

Having a similar problem to Mark's here too.

Recent engine overhaul (last few hundred miles); complete disassembly and new exhaust valves on #s 4 and 6. Also had some recent electrical problems. Mechanic installed new fuel pump regulator and transmission ground strap which seemed to solve my electrical issues, but now having this problem.

My symptoms are similar, but not exactly the same as Mark's. I have the "dashboard in the face" moment usually at around 1.1 bar, however I have also noticed it a couple of times at around .5 to.6 bar. Before the overhaul I never had this issue. It would top out at 1.1 bar, but never got the dashboard in the face, just a smooth ride. I'm assuming this is the fuel pump regulator cutting off the fuel, but since I've also experienced it at .5 to .6 bar I really don't know. Usually happens in 3rd or 4th at higher RPMs than Mark (4-5k). I should also mention that I have an earlier ('77) 930 and that my turbocharger was upgraded somewhere along the line. I'm thinking maybe that the new "stock" fuel pump regulator doesn't take this into consideration and thus the issue???

Not sure what everyone else's experiences are; when you floor it in 4th and the turbo tops out, does it seem like the engine shuts off, kicks on, shuts off, kicks on . . . etc???