Piston Slap: Bogging Saab Viggen Keeps Austin Weird

Sajeev Mehta
by Sajeev Mehta

Longtime TTAC Commentator KeepAustinWeird writes:

Hi Sajeev, I’ve got a 2000 SAAB Viggen with 113K miles. Recently, I’ve noticed that after I’ve been driving the car for about 20 minutes and the car is good and warmed up, the motor totally bogs until I can get to 3,000 RPM, at which point the car takes off. This is particularly annoying (unsafe) pulling away from full stop, where I either have to gun the motor or crawl thru 1st and part of 2nd before the RPMs rise enough for the boost to kick in. Wondering if this is a MAF (which I’ve cleaned) issue, a drive by wire sensor issue, or a dying turbo issue?

Sajeev answers:

That’s a tough one to armchair from the Internet, unless you spend hours on SAAB forums. That said, I suspect several trouble spots for late model turbocharged applications: fuel starvation, Engine Computer trouble code, exhaust/turbo leak or a vacuum leak. I don’t see a turbocharger failing this early, unless oil changes and abuse are a problem. Then again, abuse a Viggen mid-corner and you’ll be kissing a whole lot of Austin hill country. And have far more pressing issues than engine bog.

You cleaned the MAF (and I’ll assume you checked for trouble codes) so my money’s on a vacuum leak. Do the easy stuff first: a complete visual on the rubber/plastic/whatever lines, especially around the fuel pressure regulator, if applicable). Check every hose that starts from the intake and snakes every which way, and, if needed, get under the car to spot look for cracked, split or blown hoses specific to the turbo/intercooler. Most modern vacuum systems are more than just rubber hose, so if a forum doesn’t give enough diagnostic info, punt and go to a SAAB wrenchhead.

Another possible concern: the lack of fuel. When did you last change the fuel filter? If it’s been over 30,000 miles, that’s too long. If that doesn’t help, check fuel pressure while driving: rent a long-hose fuel pressure gauge from a parts store, connect at the testing location (usually the fuel rail) latch (but don’t close) the hood, drive and compare the gauge’s numbers to factory specs and DIY for free. If the pressure is below spec at idle or drops under full throttle, the pressure regulator or fuel pump need to be tested.

Good luck with all that.

[Send your queries to mehta@ttac.com]

Sajeev Mehta
Sajeev Mehta

More by Sajeev Mehta

Join the conversation
2 of 19 comments
  • Keepaustinweird Keepaustinweird on Mar 01, 2010

    AustinViggen - just seeing your post now so apologies for the delayed reply. I actually have a 2000 5-door Lightning Blue Viggen, not a '99. Supposedly it is the only 5-door LB in Texas. Seen your car at Swedish Auto.

  • Keepaustinweird Keepaustinweird on Jul 11, 2011

    Just in-case any other Viggen owners with a similar issue comes across this, I wanted to provide closure. The culprit? The ECU. Swapping the ECU made the difference. The original ECU got so sick it didn't even throw codes anymore. Now I have a wild beast of a Viggen. Couldn't be happier.

  • Kcflyer This is a joke right? Kevin James invented this in a movie years ago. As I recall queen latifa loved it. The movie was called "The Dilemma". It was even a dodge. Life imitates art indeed.
  • RHD This is the modern equivalent of the Horsey Horseless. (If you don't know what that was, look it up!)
  • Loser What’s next, simulation of the “Hemi tick”?
  • Ajla There's a melancholy to me about an EV with external speaker-generated "engine" noise and fake transmissions. It feels like an admission from the manufacturer that you're giving something up and they are trying to give back some facsimile of it. Like giving a cupcake scented candle to someone on a diet. If I was shopping for an EV I'd rather go to a company enthusiastic about it rather than apologetic.
  • EBFlex More proof of how much EVs suck. If you have to do this, that means you are trying to substitute what people want...and that's ICE.