SaabCentral Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
2,584 Posts
Discussion Starter #1
I've noticed a funny engine feeling at idle, kinda feels like little ticks (little funny spots with extra vibration). Well I checked my data from the Carchip, and its interesting, baseline idle rpm sits at 880 rpm, but looking at one graph their were some spots where it went up to 920 on its own (no cooling fans turning on, no AC running). During the same time frame my timing advance bounces between 9.5 degrees and 11 degrees. Should the timing advance be moving around at idle?
A graph (black rpm, red timing advance):
 

·
Registered
Joined
·
6,596 Posts
I don't know, but I'll give the post a bump :D

I think the question is whether the change in timing is causing the idle to wander OR vice versa. It sort of looks like the shift in timing comes first, more or less.
 

·
Registered
Joined
·
2,584 Posts
Discussion Starter #3
Its funny that after a while the rpm's settle down while the timing advance keeps bouncing a few more times.
 

·
Registered
Joined
·
4,293 Posts
"hunting"

The sensing of the rpm and crank position is not that accurate, so some amount of hunting is normal with an electronic ignition control, no matter which ecu. As the sensors and other companonts age, it gets more noticable.

My warm idle does something similar. It drops a bit, then recovers immediately. Best explanation I found was the CPS (crank position sensor), and if it really bothered me, I could replace it now, before it fails... sometime in the next 50-100k miles... (NOT!) That makes sense, because I think the CPS is a Hall-effect sensor.

In theory the output from the sensor is a 5V square wave. In reality the signal is noisy. A clean waveform depends on an effect called "hysteresis", which filters out some of the noise but creates jitter in the waveform.

In other words, the sensor translates mechanical rotation into an electrical signal. Mechanical vibration in the shaft is converted to electrical noise by the sensor. That noise is filtered to obtain a clean signal. The filtering causes some inaccuracy called jitter. If that signal is used as one of the inputs to correct the timing, firing angle etc., you get some variation in rpm around the correct speed... a.k.a. "hunting". You can see it plainly on the graph...

Btw, thanks for posting that, I wish I had one of the cold idle on my car... :cheesy:
 

·
Registered
Joined
·
2,584 Posts
Discussion Starter #5
I gotcha on that PMI.

In an attempt to stabilize this stuff yesterday I did some work:
-Reglued the metal nipple back to the throttle body that connects to the AIC
-Glued a crack in the evap line that runs to throttle body
-Glued the metal nipple back to the coolant tank
-Cleaned AIC
-Cleaned TB
-Figured out how to get the serpentine belt off

But my so-thought prized project was the air intake. Eventually I will enlarge, but to study the available space I attached the end of a funnel to the air intake. Unfortunately I went from about 6.5 grams/second of air going by the AMM down to 6 g/s. I guess that funneling idea isn't going to fly. Guess I'll have to chop the box up.
 

·
Registered
Joined
·
21,583 Posts
The two of you should be working at Saab as design engineers !

Hopefully, in the future, electronics will continue to improve...Right now, the RPM adjusting circuit seems to be too sensitive, but how many drivers can detect this ???

Right now, under hood temperatures are, IMO, far too high and damage results....
 

·
Registered
Joined
·
4,293 Posts
What did you use to reglue the nipple seals? Looks like epoxy to me, but I am not really sure what it is.

Mine are solid so far, but some of the reddish color glue was cracking and coming off. Cleaning some of the crud did not help. I have a spare tb for another reason (the sticky throttle lever), but have not put it on yet and the seals are about the same. Did you take a look inside the two chambers on the underside of the tb? The one where the pcv line goes was coated with almost 1/8 inch of black oily crud, and the replacement was not much better when I first got it.

Speaking of the evap purge line, on the turbo that can cause some idle issues if not working correctly. Not sure on the n/a version. On the turbo, the ecu waits until the engine is warmed up, then it starts to cycle the purge valve (tapping sound you can hear at warm idle when you put your ear next to the fender). The reason for allowing only short pulses on the purge valve is to avoid screwing up the air/fuel mix with the fumes from the charcoal canister. If the purge valve does not work correctly, opening and closing when it is supposed to, you get idle problems and poor mileage at low speeds.

(A cracked evap purge hose does not help either.)
 

·
Registered
Joined
·
2,584 Posts
Discussion Starter #8
PMI said:
What did you use to reglue the nipple seals? Looks like epoxy to me, but I am not really sure what it is.
I used Devcon High Strength 5 Minute Epoxy. In my absentmindedness I didn't take note of the temp. range of it (-40F to 200F). I think the TB stays below 200F, I'll just monitor it carefully. Holding well thus far (over 200 miles on it already now). One thing I noted with the original epoxy was that none of the residue of the epoxy stayed on the throttle body portion.

One thing I found interesting about the evap purge lines was that, at least on mine, their were short (1.5"-2") length of pipe at the connecting points between the TB, purge valve out and purge valve in. I wonder why it was found to be necessary to add these sacrificial pieces. The main portions of the line appear to be of the same material (and theirs plenty of length to them that I have them looped). Another Saab mystery I guess.
 

·
Registered
Joined
·
2,584 Posts
Discussion Starter #10
The carchip graphs are done by the carchip software. Then you have the option of copying it, so did that and put it in MS Paint, then just overlayed the two.
 

·
Registered
Joined
·
4,293 Posts
Slaab4life said:
...I wonder why it was found to be necessary to add these sacrificial pieces. The main portions of the line appear to be of the same material (and theirs plenty of length to them that I have them looped). Another Saab mystery I guess.
I was told those hoses have to be treated the same as a fuel line, because they carry combustible vapors. If need be, they should be replaced with reinforced fuel line, not rubber hose. So, the reinforcing pieces may be there to keep the hose stiff enough so the ends can be clamped harder. Mine has some mutant crimped clamps.

I don't like that evap system very much. That hose had an encounter with a pulley during one of my unfortunate pulley and belt incidents. When the belt broke and knocked the hose loose from the plastic clip, the looped portion dropped down and made contact with the pulley. Not good for much anyway, the activated charcoal does not last more than a few years w/o being reprocessed.
 

·
Registered
Joined
·
4,293 Posts
tidewatersaab said:
the charcoal canister probably costs more than it's worth to replace,right?
p/n 4445821, $35 at saabsite.com, probably the cheapest part of the system, but I would say none of this is worth spending money on unless you need it to make the CEL go away and pass emissions.

Getting the engine to run well w/o fouled plugs or O2 sensors and improving the mpg would do a lot more for the environment in the long run. New plugs, injector cleaner, and cleaning the crud out of the IAC and TB usually improves my mileage about 10%. That 10% difference in mileage translates into a much larger difference in emissions, because fuel is burned more efficiently all the time. Compared to that, the evap system and SAI together are negligeable, and much more expensive to repair.

Imagine what would happen if everyone in the country did a tune up over Memorial Day... next week, nation-wide gas consumption would drop 10%, and so would the price of gas :cheesy: ... makes you think, doesn't it?
 

·
Registered
Joined
·
6,596 Posts
Imagine what would happen if everyone in the country did a tune up over Memorial Day... next week, nation-wide gas consumption would drop 10%, and so would the price of gas ... makes you think, doesn't it?
Commie!

Good thing we're all getting into our tricked out turnip trucks and driving out to the mall instead. Next thing you know you'll want us to stop dumping our used oil down the storm sewer! :D :lol:
 
1 - 14 of 14 Posts
Top