Caller says their 78 Volvo fails emissions testing, CO too high. Ray explains the main reason on Volvo’s (with late-70’s CIS fuel injection presumably) is the fuel injector o-rings get hard over time, and now aren’t sealing the opening properly. This allows unmetered air into the engine, causing a too-lean mixture. Ray explains they might experiment changing the air/fuel mixture screw (on the fuel distributor) in the shop, or spray carb cleaner looking for other vacuum leaks.
I expect my prior same vintage VW Rabbit had this same fuel injection system. Ray is correct about the o-rings, they were a frequent trouble spot on mine. Icing on the cake, when the o-rings got old and hard, they’d also split. What a joy! … lol …
My question however is why a too-lean mixture would cause an increase in CO ? As the normal byproduct from combustion is CO2, hard to understand why too much O2 would result in CO. Common sense says too little oxygen (rich mixture) would cause an increase in CO.
fyi, here’s a link to how the CIS mixture, later year models w/O2 sensors. No O2 sensors in 78.
The best thing you can do with some of the old Volvo fuel systems was to pull the engine and drop a small bock Chevy in it, they even had the motor mount kit years ago to do it… Back in the 90’s it was around $4000.00 in parts plus labor to replace the fuel system including the new pump… a SBC and kit was 1/2 that and ran better and had way more power… Just don’t remember what years they were, tried hard to forget about them… lol
But Volvo’s that looked showroom new were sitting in junk yards do to the fuel system…
Too lean for the catalytic converter to generate enough heat to work properly I’m guessing.
The computer controlled mixture alternates from lean and rich for proper catalyst operation. Or air is pumped in to the exhaust based on commands from the computer.
That SBC into Jag swap got done a lot, but it was actually all the other parts of the Jag that were even worse. The Jag 6 was a pretty reliable engine (the v12, no so much).
I rarely see any CIS K-Jetronic equipped VW’s of that vintage on the read these days either. They were fun to drive, the engines purred like a kitten when new, very responsive to the gas pedal; but it was definitely a challenge to keep the fuel injection system functioning consistently, and in full-tune.
Can’t speak to a 78 Volvo, but on my same-vintage VW Rabbit, there was a cat, but no computer or electronic control for the engine. No O2 sensors either. In any event I would have guessed too lean would make the exhaust hotter, not cooler. Too lean is like blowing air on a campfire.
Ok, so too-lean the exhaust might be hotter out of the engine, but without enough HC coming out of the engine, the exhaust stream might not be hot enough to heat up the cat to the needed operating temperature. Hence more CO. Makes sense.
