Augusto

I am having some trouble with my car.

The car accelerates in second gear until the red line with no problems, but when I try in third the engine cuts just above 4.000 rpm mark. Same in fourth gear.

The car has the stock wastegate with 0.7 spring. Has cat bypass with a FVD diverter valve.

It seems I have a overboost issue. I did change the overboost switch with no improvement. I did rebuid the wastegate with new diaphragm.

I really don´t know where to start...any inputs?

Thanks in advance!

Metal Guru

What is the condition of the valve guide in the wastegate? When it wears out and leaks the wastegate might not open at all. Take the wastegate off and bench test it.

Augusto

The did check the valve seal and guide, must be work ok.
However I will remove it and check; no many things left to check

Saw good reviews on the 46 Tial...is it worth the upgrade?

DA VINCI

Firstly, having a boost gauge on this cars is a must. I recommend you to install one of them ( I have a zeitronix system with boost, EGT and AFR) just for piece of mind and to keep this important parameter monitored.

Perhaps you have a leak on the pipe that feeds the wastegate resulting on a a higuer than normal boost level.

Augusto

I did a full engine rebuild, the exhaust is recently installed with new seals, flanges etc so must be no issues. However I will double check for exhaust and wastegate leaks.

I am interested on the boost gauge with AFR display.
Do you have more information about this display?

Thank you

DA VINCI

I mean the pipe that feeds the WG with presurized air. The one that comes from the intercooler. You can have a damaged/blocked pipe or perhaps the banjo that connects this pipe to the WG is not properly tightened.

Zeitronix info:

http://www.zeitronix.com/Products/zt2/zt2.shtml

I have the ZT-2 + EGT sensor + boost sensor + LCD display. I also fitted the "alarm" system (ZAVT-1) to detect high pressure/low AFR situations. These cars dont have detonation sensors and ignition retarding systems so It's advisable to introduce additional security elements.

Augusto

Great! I will check the Zeitronic web site.

Yes, I guess it´s a must to know the boost pressure before doing anything else.

Thanks for the help.
Augusto

Augusto

Ok, I put a mechanical boost gauge and went for a spin. I found out that tge stock digital boost gauge is extremely reliable, matching the mechanical gauge readings.
The maximum reading was 0,7 bars, wich is 10 psi, so I assume the wastegate is working properly.

I was able to reach 6.000 rpm in second gear, but at 3rd and fourth (I did not check in fifth the engine cuts at 4.000 rpm.

Seems an overboost limiter switch issue...at 0.7 bars?

Metal Guru

Try replacing the switch now.

cobalt

For your records this is the info from the TSB for the boost gauge which reads lower than max boost.

Found the TSB. Number 9032 9307.

Reads:

Concern: The boost gauge in 1994 911 Turbos will only read 0.7 bar at max boost

General Information The boost pressure for 1994 3.6 liter 911 turbos is .79 to .85 bar. 1994 911 Turbos are equipped with a boost gauge that is only capable of registering 0.7 bar. For technical reasons, the software for the boost pressure gauge was taken from the 3.3 liter 911 Turbo.

Should a 1994 3.6 Liter 911 Turbo have a customer complaint or "car will only reach 0.7 bar boost," the complaint must be verified and boost pressure must be checked before repairs are performed.

If boost pressure is within specifications, no repairs are necessary.

Repair Information: 1994 3.6 Liter Turbo Max boost 0.79 to 0.85 bar 1992 3.3 Liter Turbo Max boost 0.75 to 0.81 bar

Damage code 903210 0002

rstarga

I had a similar problem when my coil was going bad.

Augusto

Yes, this is the second switch I put on the car...

Augusto

Yes, the point is the mechanical gauge (pressure checked) reads 0,7 bars at full boost, so there is no overboosting issues.

fritz k.

seems not to be the - obvious- fuel cut caused by the pressure switch. could be an fuel pump relais or rpm sensor (located at the flywheel) issue.

cobalt

So you are not reaching full boost according to the mechanical gauge and the fuel pumps are still cutting out??

I know you say everything is new but usually that leads to a long mess of looking at other things that aren't the issue. I would start at square one and retrace your steps.