After testing cylinder compression (all still at 170 psi after 150k miles) completely dismantling the intake system (all the way to the head) and replacing all gaskets, injectors and o-rings, FPR, fuel filter, ECT, spark plugs, wires, cap, rotor, and the O2 sensor - my 1990 240 wagon still ran rich, smoked, stumbled, and set codes 1-1-3, 2-1-3, and others refering to rich mixture. However, during disassembly I discovered the female connector for the ECT was damaged by one of the sensors spade pins when someone pressed the connector on incorrectly. The pin "missed" one of the female clips and mashed it.

Called Don Beyer Volvo in Sterling, VA. The parts manager has been very helpful (I needed one part I couldn't get online). I described the ECT connector problem and he put me on hold for a few minutes....he came back with a connector he clipped off an old wiring harnass. He gave it to me with a couple of insulated pinch connectors and his tips for how to make the splice....no charge. I've never had a better experience with a dearler parts department. The guy took a clear interest in helping me solve the problem. However, he did say if this splice didn't fix it he thought it was a failed ground in the ECU (ECM) for the fuel injection. He said the bad connector could also cause a bad ground problem at the ECU (I was hoping this was the problem obviously).

So, I completely reversed all the work I did yesterday...but this time I left the injectors and fuel rail and lines still connected to the manifold. I suspect the damaged ECT connector probably occurred while someone replaced a previous ECT with the manifold in place. Because I'd removed it all before it took me less than 30 minutes to have the manifold off again and set aside with the fuel lines still attached (no swearing and no bloody knuckles). Now with open access to the ECT I could do a very careful splice and be sure the connector went on correctly. Then I put the intake and throttle linkage all back together....and took a deep breath.

So far (fingers crossed) it appears to be cured. No codes, no stumble, no smoke, and running great (but posting this message is sure to set off codes again!) I never suspected the problem was a damaged ECT connector - but I've learned my lesson the hard way ALWAYS check the connections first. The upside is that I learned a lot (first time I've ever worked on the car) can break down the intake really fast, know everything is new or very clean. I encourage everyone who hasn't tried to remove the intake and injectors to Just Do It. It's not hard and any high mileage intake needs a thorough cleaning (not just the TB) and FI O-rings will be hard. The cold start injector O-ring was the worst (and leaking).

Why did the guy at Don Beyer think it might be the ECU? Because I told him that after resetting the codes the check engine light and the codes would come back almost immediately. However, if I disconnected the battery the ECU settings in memory would clear and the engine would start off running great, but within 50 miles it would be running rich, smoky, stumbly, and the light and codes were back. This is a common symptom of a bad internal ground on the ECU. But the same ground fault can happen with a bad sensor connection...so check for these first. The bad connection was causing increased resistance...a signal to the ECU that the engine is running cold...and that the engine needs more fuel (gas was pooling in three of the intake ports on the head when I pulled the manifold tonight....a second oil change in 5 days tomorrow!)

Had I checked and fixed the ECT connector before buying parts (I didn't even know what an ECT was when I started) this fix would have cost me nothing! (though I'm sure it wouldn't be running as well as it does with a sparkling intake and new injectors...made a big difference in hill climbing power).

Jon