jebia

My boost sensor is acting erratic (slow to increase, max reading is .6). My car runs great. After completing an oil change yesterday, and spilling some oil during the refill (start car after tha 7th quart before it backs up), I removed the intercooler to make access for filling and clean up of spilt oil a bit easier.

Since I had the car jacked up for the oil change, and the inter-cooler off I decided to change out the boost sensor (I had bought it about six months ago, but had saved it for the next time the intercooler was off). Now I know the boost sensor is some where on the left side of the engine under (saw a diagram once, tried finding the picture in the shop manuals, including the turbo supplements but couldn't) all that HVAC plumbing.

I started to take the plumbing apart, taking a couple of bolts off the holding bracket in the rear, then removed one of the pieces of duct work, and then got stuck. I removed a long bolt holding another piece of duct work for the heater fan outlet, but couldn't get the screws holding the duct work to the heater fan (there way in the back, I can see a second, but the third seems almost impossible to get a screwdriver on it).

Am I on the right track or is there an easier way?

I check for a DYI for removal of the HVAC and heater stuff, but coudn't find anything for our cars, the non-turbo cars HVAC stuff looks a bit different than ours.

Thanks in advance.

Jon
Albuquerque

BABaracus

Jon,

Could you give me the part number for the boost sensor, mine is giving erratic numbers as well...often the guage sits on 0.2 bar even though I am not on boost.
I will watch with interest everyones input on the sensor replacement.

thxs


- james

jebia

The part number I purchased was 993-606-103-00, "Boost Press. Sensor (Druckgeber). It cost me $100 from my local dealer in Albuquerque. I think I found the part number from of the PET parts cd.

Jon

viperbob

The pressure sensor you purchased has nothing to do with boost. The gauges on our cars interpret the boost pressure. There is no mechanical sensor. The sensor you purchased goes into the aluminum intake before the turbos, so there could be no way for it to even see the boost pressure. Sorry..

jebia

Thanks Bob, You saved me removing all that HVAC stuff. I still have my reciept, so I can probably get my money back.

If it is not the sender causing the eratic reading, then what is the fix for an eratic boost gauge reading. Again my car runs great, so I don't think I actually have a boost issue (leak, etc.)?

Thanks again.

Jon

DougB

Actually that is the boost sensor. Even though it mounts on the plumbing before the turbo it actually gets its signal from the intake manifold via a seperate hose.

The wiring for the boost sensor goes to the central informer. The central informer sends the boost signal to the OBC.

-doug

jebia

Thanks Doug, back to the original question. Is there a trick to removing all that duct work on the let side of the engine?

DougB

Jon,

A couple of bolts, a couple of clamps and some electrical plugs is all it takes. The fan motor attaches from the side with a couple of long bolts with 10mm heads.

The duct that connects to the engine fan shroud is a little tricky to re-install.

-doug

jebia

Thanks Doug,
I'll give it another shot this week end.

Jon

BABaracus

Jebia,

Let me know how the sensor replacement goes, I plan to do the change next weekend...any tips would be greatly appreciated.

Regards

- james

Rob 97 993c2

my boost guage reading also now sits at 0.2bar no matter what (even when im at a stop light). It seems to climb when i accelerate, but doesnt fall back to 0.0. Yet, when i got the car 2 weeks ago, it did go down to zero. Car seems to drive nicely though.
Anything i should worry about?
Any other fix that isnt a huge project.
Also, there is a chance that the ECU has been chipped/reprogrammed (see earlier post) - the jury is still out on this question.

Carrera GT

I saw this 0.1 or 0.2 reading with key-on (before starting the engine) and sometimes at idle on one car. It went away before I could track it down.

If the ECU has been flashed, there's no way of knowing what mess someone put in there. I'd put a reflash from a credible shop (say Protomotive) on your shopping list when you decide on engine upgrades. If the thing is running nicely, I'd spend $100 on a dyno run (find a good, local AWD dyno shop that's done 993s) and see if the engine is developing decent power and torque curves.

The sensor could be at fault but I haven't seen that happen.

The ECU uses the intake air pressure and the MAF reading -- along with knowing the state of the boost cycle valve -- to determine the turbocharging effect and along the way it interpolates those values to put an approximate, steady number in the digital display. The ECU then happily ignores overboost (a normal process for the ECU) which I guess is done so the driver doesn't see the gauge jumping around.

I recommend a mechanical boost gauge for anyone that wants to know what the engine is doing as distinct from what the ECU senses.

Also, for all I know the ECU might also check the TPS to compensate. I've noticed the fuel maps are more likely to make mistakes at WOT.

Very tricky little bugger that boost gauge ... only the Germans would go to all that trouble instead of snaking a boost line along with the vacuum lines into the dash ...

Cheers,

Carrera GT

You might remove the power to the ECU for 250seconds -- this will restart the adaptation process and it's your quickest remedy. Just take the negative terminal off the battery post. Be sure to resecure and tighten both terminals afterwards -- if you drive down the street and the terminal jumps off the post, the alternator/generator might not survive the experience.

BABaracus

Jebia,

How did the sensor replacement work go ?
Also, did it resolve the boost display issue.

- james

jebia

I did replace the boost pressure unit saturday (hard to get a normal wrench on the sensor and be able to turn it, but was able to use a short cresent wrench to loosen it) but have not started the car yet.

I noticed my hood struts were weak and decided this was perfect time to replace them. It won't ever be easier (Now that I had the duct work, intercooler, and the air cleaner cover out.) I had the air cleaner off because I'm putting ina BMC aircleaner and a motorsound type cover (I want to see if I can hear the intake and turbo wine a bit more, the turbo intake as quite as it is, makes me miss the NA car's beautiful noise).

Taking the HVAC duct work was easy after a member mentioned the two 10mm bolts holding the fan on. The second bolt holding the fan is hard to see, you kind of have to feel for it about 5 o'clock near the bottom of the fan (I was confused at first since the PET parts diagram only shows one bolt near the top of the fan). Once this hidden bolt is removed its just a matter of removing connecters , ductwork and a couple of hose clamps.

I'm stopping after work to pick up the hood struts form the dealer ($16 each). I'll put everything back tomorrow and let you know if my boost readings are more linear (my problem was that even though I could see 0 to .8 bar, the reading jumped a lot and sometimes didn't go back t zero, but stayed at .2 bar at idle).

Jon