Go Back   986 Forum - The Community for Porsche Boxster & Cayman Owners > Porsche Boxster & Cayman Forums > Boxster General Discussions

Post Reply
 
LinkBack Thread Tools Display Modes
Old 10-19-2009, 04:57 PM   #1
Registered User
 
Join Date: Oct 2008
Location: Canyon Lake, Texas
Posts: 801
this all started within about a month.
tonight on the way home from work, i threw another code (only 1 this time)
p1128 which looks like a rich threshold on banks 1-3

i'm suspecting some kind of vacuum leak at this point but will have to dive in tomorrow morning. how does a "driveway mechanic" spot a vacuum leak? any tricks?

i was all ready to just have my air changeover valve and ECO valve replaced, but this code might indicate something different. I scoured the net, but haven't found too many people with just the ONE code, many had the accompanying 1130 code. What does having one code indicate?

*thanks for all the help and suggestions, hopefully i'll get her running top notch again soon*
stateofidleness is offline   Reply With Quote
Old 10-20-2009, 08:49 AM   #2
Registered User
 
Join Date: Jan 2009
Location: Arvada, CO
Posts: 229
Quote:
Originally Posted by stateofidleness
this all started within about a month.
tonight on the way home from work, i threw another code (only 1 this time)
p1128 which looks like a rich threshold on banks 1-3
I believe if you look for a vacuum leak, you will be looking in the wrong direction.
I believe that this code is going to point more in the direction of the two O2 sensors on that bank of the exhaust going bad.

When the exhaust passes through the headers and past the O2 sensors, the computer receives a signal that tells it if there is or isn't alot of Oxygen in the exhaust. If there's too much Oxygen, then the computer richens up the mixture. If there's too little, then the computer leans out the mixture.

Right now, the O2 sensors are saying that the one bank is running too lean, and the computer can't richen up the mixture for that bank any more than it already has, hence the CEL being lit.

If you replace those two O2 sensors, that will most likely resolve the issue.

Some recommend just replacing all 4 at the same time for the best results.

BC.
__________________
Its not how fast you go, or how expensive your toys are.
Its all about how big your smile is at the end of the day that truly matters.

'98 Silver Boxster, '08 Ducati 848, '89 Honda Hawk GT, '89 Honda Pacific Coast
Bladecutter is offline   Reply With Quote
Old 10-20-2009, 08:56 AM   #3
Registered User
 
Join Date: Oct 2008
Location: Canyon Lake, Texas
Posts: 801
consensus seems to be that it is the O2 sensors that are REPORTING the problem, but are NOT the problem. They don't really affect the mixture, they just report it.
stateofidleness is offline   Reply With Quote
Old 10-20-2009, 09:02 AM   #4
Registered User
 
Join Date: Jan 2009
Location: Arvada, CO
Posts: 229
Quote:
Originally Posted by stateofidleness
consensus seems to be that it is the O2 sensors that are REPORTING the problem, but are NOT the problem. They don't really affect the mixture, they just report it.
You're most likely going to find out that your impression is incorrect.

If the sensors are faulty, then they will send the wrong signal to the computer, which causes the computer to richen the mixture.

Here, try this:

Switch the O2 sensors from the left exhaust to the right exhaust, and vice-versa.
If the problem follows the O2 sensors, then my suggestion is correct.

If the problem stays with the bank, then you are on the correct path.

It won't cost you anything more than about an hour's time to swap the sensors, and a day to drive the car around.

BC.
__________________
Its not how fast you go, or how expensive your toys are.
Its all about how big your smile is at the end of the day that truly matters.

'98 Silver Boxster, '08 Ducati 848, '89 Honda Hawk GT, '89 Honda Pacific Coast
Bladecutter is offline   Reply With Quote
Old 10-20-2009, 09:22 AM   #5
Registered User
 
Join Date: Oct 2008
Location: Canyon Lake, Texas
Posts: 801
sounds logical. i'll give that a try! googling some more and I keep coming across people stating the MAF.. yada yada... When I looked at mine, it looked BRAND NEW! Does a failed/failing MAF have any visible signs of failure or do they just "not work" after some point? also, during reinstall of it, could that have introduced a vacuum leak where it connects? I've read that if you get BOTH codes, it is most likely the MAF, one code and it means something is wrong on that side... (might go along with the 02 sensor theory, but i haven't had ANY indicators up to this point that an O2 was on the way out)

Also, and this may be far-fetched, but I have been using 92 octane (Valero) gas for the past few weeks only because my Shell (only 93 octane in town) is not on my daily route. Could this cause some kind of lean issue as well?

Would filling up with 93 and maybe some additive do anything for me?
stateofidleness is offline   Reply With Quote
Old 10-20-2009, 11:39 AM   #6
Registered User
 
Join Date: Jan 2009
Location: Arvada, CO
Posts: 229
Quote:
Originally Posted by stateofidleness
sounds logical. i'll give that a try! googling some more and I keep coming across people stating the MAF.. yada yada... When I looked at mine, it looked BRAND NEW! Does a failed/failing MAF have any visible signs of failure or do they just "not work" after some point? also, during reinstall of it, could that have introduced a vacuum leak where it connects? I've read that if you get BOTH codes, it is most likely the MAF, one code and it means something is wrong on that side... (might go along with the 02 sensor theory, but i haven't had ANY indicators up to this point that an O2 was on the way out)

Also, and this may be far-fetched, but I have been using 92 octane (Valero) gas for the past few weeks only because my Shell (only 93 octane in town) is not on my daily route. Could this cause some kind of lean issue as well?

Would filling up with 93 and maybe some additive do anything for me?
Well, I just changed my MAF on Friday.
The old one was just as clean as the new one I put on.

In fact, when using the Durametrics program, I was getting the same Air Flow readings and Air temp readings with the new sensor as the old sensor. The only difference was in the Voltage reading, which was 1 volt constantly across the rpm range, while the new sensor increases as the rpms rise.

As for the gas, it would affect both banks, not just one.

If you wanted to get technical, we could break down the different fuel systems piece by piece:

MAF sensor - tells computer amount of air being ingested by the entire engine (doesn't differentiate between cylinder banks)

Air temp sensor (in MAF) - Tells computer temp of air being ingested by the entire engine (doesn't differentiate between cylinder banks)

Throttle body - Controls amount of air ingested by entire engine (doesn't differentiate between cylinder banks)

Vario-cam valve timing - Adjusts opening and closing of valves in relation to crankshaft position and engine speed. Both banks are activated at the same time at certain rpm points, but controls just an individual cylinder head. Should not affect fuel mixture in any way.

Fuel injectors - Each one is assigned to a cylinder. If one was sticking open, could cause a bank of O2 sensors to report an error, but would also be associated with a cylinder misfire, and bad engine performance. (opposite of what you are experiencing)

Spark plugs and Ignition coil sticks - One per cylinder. If one is failed, cylinder misfire, bad engine performance, and too rich of a mixture would be reported on that bank of cylinders. (opposite of what you are experiencing)

Cat converters - Two per bank - the second set of O2 sensors will be able to point out if the primary cat converter is not scrubbing the exhaust optimally.

O2 sensors - Two per bank. First set of O2 sensors controls the mixture as the computer uses its signal to determine the Oxygen content of the exhaust stream. Second set is primarily used to check the efficiency of the cat convertor, and determine if it has fully warmed up, based on the differences between the two sensors in that bank.

The O2 sensor swap is probably your best bet for quick and easy, with no cost involved.

BC.
__________________
Its not how fast you go, or how expensive your toys are.
Its all about how big your smile is at the end of the day that truly matters.

'98 Silver Boxster, '08 Ducati 848, '89 Honda Hawk GT, '89 Honda Pacific Coast
Bladecutter is offline   Reply With Quote
Old 10-20-2009, 12:01 PM   #7
Registered User
 
Join Date: Oct 2008
Location: Canyon Lake, Texas
Posts: 801
wow great info!

ill try to swap them when i get home tonight.

any thoughts on what the "thunking" sound is on cold starts? like hitting the side of an empty 50 gallon drum with a hammer.. or a low steel drum.. i hear it randomly about 3 times on cold (not driven in 10+ hrs) starts, if i turn car off and then restart, it's fine, but idles at 1k steady. When i put it in R, it goes down to 500 like normal.
stateofidleness is offline   Reply With Quote
Post Reply



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -8. The time now is 07:06 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2025, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0
Copyright 2025 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page