Stutter power loss under full boost!
 

Having spent the winter installing an Asian intercooler with much help from this forum for which I am eternally grateful. I decided to throw some recent poker winnings on a revamp of interior and paint, pictures to follow. However I had not taken the car for a test run, due to all the wet weather we have had these past months. Finally took her out only to realise I had issues. Main issue is, under hard acceleration/full boost the engine stutters cuts out as if the over boost is cutting in. bypassed the over boost switch by sending to ground, that made no difference. Have checked rigorously for air leaks and I am 100% confident that there are none. Changed all the red relays. and eventually took to local Porsche specialist to have the fuel pressure checked. Pressure was fine under normal conditions. Whilst there they checked the warm up regulator and that was working correctly. They took the car for a test drive and without further investigation and £££'s they could not identify the problem. It is real strange, my first thoughts was a fuel issue, but if I accelerate smoothly she will go as fast as I wish but floor it and stutter/cutout but not stall. Am I missing something? waistegate issue maybe? Fogot to mention, the turbo now whistles constanly.

This sounds too simple but have you checked the battery? How old is the battery? Older, worn out batteries may not hold sufficient charge to generate a good spark which is needed especially when on boost. Though I don't own a 930, for years I had the same issue with my SC "turbo" until a fellow Pelican helped me out.....what a difference it made!

Cheers and all the best!

Alex

Battery is brand new, but thanks anyway.

I know you said you tried grounding the overboost sensor/switch, but were is it mounted? I ask, because the part it is mounted to needs to be well grounded. For example, when the switch is in the stock location, if you powdercoat the recirculation housing, like I did, then a wire has to be run from a bare spot on the housing to a good ground point (in order to ground the housing as it is now insulated by the powdercoat). If your overboost switch is now mounted in the intercooler, the intercooler might not be providing a good ground as it is isolated via the hoses . . .

Another possible problem is that one of the two fuel pumps might not be working at 100% and it shows up under sudden acceleration. You might start by flowtesting each one separately. I know there are some past threads detailing this process . . .

Your points are right-on for proper operation of the OB switch, but I think 930Guy unplugged the wire from the OB sensor and grounded the wire...thus taking the sensor out of the equation altogether. Probably wasn't necessary since the symptoms don't point to your typical overboost shutdown anyway, but one never knows for sure.

Thanks Ronnie, I am getting a good contact between the switch and intercooler, when I disconnect the wire feeding the switch the pumps switch off. and when i ground the wire they both switch back on. I will find out if the garage that it just came out of did a flow test and update.

I would check the vacuum hoses that go to and from the dizzy

I had a similar issue that turned out to be fuel starvation, even with a 1/2 tank and a foam-filled ATL fuel cell.

Sounds like a IC leak somewhere.

Flow test showed 1.4 litres per 30 seconds. Could there be a problem with one of the relays shutting off a pump under high boost? Will jump 87 and 30 pins on relays and try that, will update.

I just have the same problem exactly you have one week ago, I replaced the Over Boost Switch And Pressure Sending Unit For Turbo Boost Gauge.
Parts Number:-
930-606-101-00-M100
993-606-103-01-M100

you have to replace both of them in one time.

My car is working now perfectly .

Regards,


FALNAIM

sounds like fueling issue up top. any afr #s?

Have removed boost pressure sending unit as I have an aftermarket unit. As for over boost switch I sent cable to ground to override it.

Bypassed the relays so pumps on constant, took it for a drive no change, wasn't really surprised.
Warm idle AFR 14.1
Crusing AFR 14.4
Full Boost AFR low 9s
Heard the waistegate open so figure that is working ok.

Isn't the full boost AFR much too rich?

Exactly what I was thinking, will take it out for another run just to make sure, I live in a really build up area so not many opportunities to floor it for a bit. Could this be where the problem is?

I think you found the problem. What were the boost AFR's before changing out the IC? Any other changes?

from memory around 11.5.
I may spend an hour and put the old one back on and see what I then get.

Any quick solution to lean the fuel out underboost, just to test. Or do I need to spend the rest of my winnings. :rolleyes:

Spent more than an hour refitting my old intercooler to no avail still the same problem although under full boost was more Teeth in glass as apposed to jerking and loss the power. :confused: