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Turbo stumbling under high boost 200 1983

Greetings all.

Been a while since I've been here, but I've got a couple of 'new' Volvos, one of which is giving me a hard time. Here's the skinny:

'83 244 Ti, when boost levels reach 2 o'clock on the stock boost gauge, car starts to stumble. No black smoke or anything, it just doesn't go. It's not *all* the time, either, sometimes getting into 2:30 or 3 before it'll start to give up.

Replaced plugs (NGK's), checked plugs today after driving for ~1 month - look clean, dist/rotor look good, cleaned out and checked intake path/intercooler for splits, replaced fuel filter. Still need to: replace plug wires, air filter.

I thought it might have been the fuel-cut off switch (@~11 psi?), but I disconnected that today before the short drive to work with no change in the car's running. Earlier I'd pulled out the dwell meter and DMM to see if I could determine if it was a lean condition or the O2 sensor is bad... With interesting results. I don't have my Bentley on-hand since prior to owning this car I'd been Volvoless for about a year, so it's been misplaced. I'll find it eventually, but until then, bear with me.

Duty cycle with O2 sensor attached and car running at idle, dwell + to red test lead, dwell - grounded was between 80-90. That didn't sound right, so I checked it with O2 sensor disconnected. Drops down to between 40-50. Did not ground green wire during any of these tests. Perhaps the O2 sensor was bad? DMM on sensor, fluctuating between .1 and 1v at idle. Give it some gas, runs up to .930v or so. So the O2 sensor is probably still good. Duty cycle reading bothers me though. T11 article says nominal reading is supposed to be between 71-75?

There's something wrong here, but I can't for the life of me figure out what it might be. I don't want to just start replacing things willy-nilly. I know I'll have to replace the plug wires and air filter here pretty soon regardless, so consider them on my list of things to do. But what else might it be? I'll do a compression test this weekend, but I'm pretty sure I won't have any *really* bad cylinders. The engine wiring harness has been replaced, but there are a few smaller harnesses along the left fender well that look like they could use some help.

What's really odd is that as long as I keep the boost under a certain level, it hauls like a raped ape. I suspected an intake leak before thinking that I'd popped the intercooler or something else in that area, but I pulled everything apart and found nothing obvious. Intake manifold is nice and snug, everything *looks* okay. Might be a vacuum hose leak somewhere as well - but then I'd be belching black smoke, wouldn't I? And the car just doesn't do that.

I just realized something. Since the '83 model year didn't come with an intercooler from the factory, this one had to have been dealer installed. (actually it's a late '82 car, '83 *model year*) I've been trying to determine at just what boost pressure it starts to give out, and checking Dave Barton's 52mm face pics (like this one), and I realized that the gauge there looks to be the non-intercooled gauge due to the position of the orange and red dividers. My gauge has the demarcation line at nearly 3:00. And looking at the old gauge, it seems to me that my boost problems start to occur right around the non-intercooled orange/red demarcation.

Since I've already ruled out the overboost switch by disconnecting it, I'm thinking now (and again) that this is an issue with the dealer intercooler addition. Or perhaps a part that was replaced by the former owner that was meant for an intercooled car but was purchased for a non-intercooled car...

What should I check now?
--

-- Richard - volvogeek --






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New Turbo stumbling under high boost [200][1983]
posted by  rlangis  on Fri Sep 24 22:05 CST 2004 >


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