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Hey guys,
I have a question for you:
I've noticed that my '84 900S has a bit of hesitation to it during warm-up, about the time the temp guage's needle reads at the top of the white zone at "L." A minute or two later, it's fine.
Here's my thoughts on why, and maybe how to "fix" it:
Background--My current '84 900S has the "red-tipped" temperature switch which is open until 110°F or so. When switch closes, "telling" the Lambda box to listen to the oxygen sensor. This is the SAAB Technical Service Bulletin retro-fit switch for 1984-5 8-valve 900s with CIS, simply screwed in place of black-tipped switch (closes at about 75°F), in thermostat housing, underneath the distributor. This was a factory standing change on 1986 900s. I did this switch swap myself, but did not change the location of the switch with the thermo-time switch on head between cylinder 2&3 as the service bulletin suggested--I didn't want the wiring headache and a SAAB mechanic told me it would work just fine.
This switch swap improved cold-start & cold drive-away of my 900S VERY much, don't get me wrong. Before, the car would balk at startup and cold idle was very iffy. After swap, it starts right up and idles fine, it's just that during the warmup period, it sometimes hesitates on throttle "tip-in", or acceleration from a standstill, as I've learned on a recent post.
I think what is happening during the hesitation is that the water/coolant temperature has reached that 100-110°F range, turning the red-tipped switch on, and the Lambda box has begun "listening" to the half-warmed O2 sensor's signal, but that signal is a bit intermittent as the engine has only been running for about 2 (maybe 3) minutes. Remember, back in these cars' day, the O2 sensor ISN'T electrically preheated, relying only on exhaust to warm it up.
In other words, the problem occurs immediately after the car switches from "open-loop" cold mode to "closed-loop" warm mode.
Testing--I suppose that I could get some hard data on this if I connect an ohmmeter (or, even better, an LED test light) to the red-tipped switch's terminals and see if the scenario is as I suppose. Or, I could also connect a voltmeter inline with the O2 sensor and see if it's signal is intermittent, as I suspect, when the problem occurs. (I'd need to run leads into cabin, whichever method is used, so I could do this while driving.)
A "Cure"--What I propose to "fix" this is a 60-second-or-so timed delay switch (or a simpler, but sloppier, dash switch) which will automatically (or manually) keep the Lambda box from "listening" to the O2 sensor signal a bit longer in order to have a reliable feedback signal to deal with. That bit of delay should make the open-loop to closed-loop transition perfect.
I'm not thinking myself smarter than SAAB or Bosch engineers here, but they are the ones who came up with the red-tip switch retrofit anyway. They didn't bank on the fact that some American locales were warmer than those in Sweden, making cold start temps too warm for their "listen-to-the-O2 sensor-at-70°F black-tipped switch. So, since they did a retrofit, I figure either my O2 sensor is on its way out or I need a retrofit of my own!
Any comments/ideas will be appreciated.
Micah in NC
'84 900S, 225K mi. (staying out of salt for now, using '76 Chevy K10 4X4)
posted by 216.77.23...
, Fri, 6 Jan 2012 09:27:55
, Fri, 6 Dec 2002 13:06:54, Fri, 6 Dec 2002 15:29:28
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