Well, it is actually partially my fault for not following the manuals to the letter~

About a week or two ago I posted a thread about my 928 suddenly blowing blue and black smoke everywhere. I cleaned a few things, and it ran OK afterwards, but not perfect. The past few days it started doing the same thing again- running very rich, giving a hint of hesitation at throttle tip-in, and idling low/stalling at stoplights.

What causes LH injection system to run rich consistently? Three things that come to mind right away:

1. Failed LH box. Not; I have a spare LH, and the car ran the same with both boxes.

2. Failed MAF. I pulled the MAF and set the pot to 300 ohms. The range is 0-1000 ohms, and the lower the number the leaner the car is at idle. This can't be the culprit- it checks out fine and is set lean.

3. T2 sensor. In this case, when I tested it, it checked out at around 1800 ohms at 30 degrees C, which is right in the middle of the range. Both pins on the T2 tested at this value.

[My mistake: The book says to test at the LH box, not at the sensor.]

I discovered yesterday that I had NO signal at all at the LH box from my T2. The car is set lean enough and runs lean enough to make up for this for the most part. The background, now that I think about it, is that a few days before my blue smoke episode, I cleaned the top of the engine and apparently disturbed the odd wire that led to the T2. The day I bought this car, I noticed that the wire to this sensor had been spliced, and it looked like a blob of rubber had been glued onto it to prevent the splice from touching the side of the fuel damper. I never thought to investigate this odd splice....

Yesterday I did. And guess what I found when I took it apart? None other than a broken-off 500 ohm resister soldered into the wire to the LH! The higher the resistance the lower the temperature that the LH senses and supposedly the richer the mixture.

[To the PO that did this: "You dumb bastard! Never heard of an RRFPR?"]

THIS is likely the cause of my rich running situation all these years. What has me a little perplexed is that in the past, I had a definite improvement when I cleaned the MAF contacts. I suspect is that this points out the sensitivity of the S2 to tune; that is, a small problem creates a much larger performance deficit in these cars than it does on S4's and others. Then again I've never owned or worked on an S4, so maybe they are the same way....

In any case, this is a possible mod to AVOID. This DOESN'T work. It FOULS your plugs, and you wind up with a car that doesn't drive right at all. I'm sure I've put some extra wear on my clutch simply because I've had to slip the hell out of it during the past 8 years. The difference in how the car runs is VERY obvious; I only get black smoke when I really get on it, and then not more than any other car, and the clutch is totally different! It doesn't want to stall at lights anymore.

N!

Picture of some *******'s work:

 

So instead of just replacing the sensor the guy soldered in a resistor? You bought this car from redneck white trash didn't you?

 

Yes.

He definitely lived in a trailer, or deserved to. But he probably performed the modification not to try to replace a sensor [I did that three years ago], but to try to get the car to run richer = more performance. Moron. There's a right way and a wrong way to do everything.

N!

 

Good catch, Normy.

Let that be a lesson (again) to all of us...
check out abnormal/odd/different looking items:
"why is that wire routed there? Why is that plug a different color?
Why is that connector an odd shape? Why is that bolt not like the one over there?..."
usw ad nauseum


G'luck all.

 

Running your car rich is fine if you can get more air in too...that takes some common sense to do though.

This is just stupidity at its finest.

 

Nice job, Norm.

Hey, OT, but that is a nice picture. What camera model do you have?

 

I don't believe you said that about running rich=more performance. I was actually thinking that when I first responded.

 

Sony DSC-W100. 8.1 megapixel, set to auto focus. I had to take several pics to get one close that wasn't blurred. This thing does a nice job for an inexpensive camera.

JHowell- In theory, what he was trying to do makes sense, since the majority of 928's seem to have weak fueling curves, and adding this resistor will definitely richen the car up throughout the whole rev range. However, remembering what that guy was like in the short time I dealt with him, I bet there was some silly stupid problem like a plugged fuel filter, and instead of doing proper maintenance and/or diagnosing the problem in an organized fashion, he or the idiot he hired simply spliced in a resistor and drove on down the road fat, dumb, and happy.

Hmm. Interesting take on things; add a problem to fix a problem.

I've spent the past 8 years this way...

N!

 

Glad you found it -- must be annoying to think of all the time that's down the tubes because of this.

 

I thought that due to a lack of knock protection the '85 models tended to be set to run richer then the later S4s, hence our 24lb/hr injectors versus the 19lb units in the S4s.

 

Not so fast

Friend of mine who has been a Porsche mechanic for over 30 years has done this before in 928's. He has shared this story with me more than a few times.

Doctor shows up with an ill running (when cold), brand new 928 back in 1984 (at his shop, no longer working for any dealers). They tried everything to fix the running problems (wires, plugs, sensors etc...)

He then called a friend at the Porsche dealer. Their recomentation? Solder a resistor (cannot remember the value) to the temp sensor. The variation of temp sensors was so wide, even a new one (they tried 4) did not fix the problem.

I have three temp II sensors on my work bench, one in the car. I did multiple tests on these sensors, in the freezer, outside in july, room temp etc.... Each one "passed" the specs in the shop manuals. Each one made a noticable difference in how the car ran.

So chances are, the guy who did this may not have been some "redneck white trash" but an actual Porsche mechanic.

 

Some of us may take offense to the red neck white trash comments.

 

Truth hurts, don't it?

 

Isn't this essentially what Porken's EZ-F'er does? I think he's got it wired in at the other end, but that's the point of it.

I think the problem was more likely that it was broken and/or cooked than that it was a dumb thing to do.

Since you weren't expecting it and were metering the value from the terminals, you didn't see the problem.

True, if you had been given some record of this, or a note were placed somewhere by the relay panel showing this 'fix' it would have helped.

 

Mike,

There are two separate sensors in the LH Temp II, one for the LH, and one for the EZ-F. Normy's resistor is on the LH side.
...

My '81 had the same thing hiding near the Temp II, and I only found it by breaking the resistor, which makes for a no-start on a L-Jet car.

People do this instead of fixing all the broken hoses and vacuum leaks!