94 850 Turbo Sedan - Runs Rough Until It's Restarted

[budoboy]

I would drive it for a bit and recheck codes.

Yeah, I agree. Who knows how long those codes have been in there.

[budoboy]

My apologies. It's been a while. I have been dealing with other issues and the Volvo is more of a project car so I haven't been in a tremendous rush to fix it. That being said, I did replace a couple vacuum lines that had holes in them. The car behaves about the same as before, maybe a little better.

However, I have another very strange thing happening. I noticed it tonight after checking the oil level. I started the car, and closed the hood. When I closed the hood, the engine died. I tried it several more times and each time, I would start the car with the hood open, close the hood, and the engine would die. After it would die, I could restart it every time. I have seen people with issues like the engine dying while driving or idling (which I experienced with my last 850...bad fuel pump), but I can't find anyone else talking about the engine dying as a result of closing the hood. I assume a wire or sensor connection is loose, but I can always restart it and then it drives like it has been driving.

Probably just another layer to the onion.

[abscate]

Either a bad battery connection or trouble st the main relays under the radiator cowl up top.

[budoboy]

Here is a follow up for a few things. I finally got around to doing a full PCV system replacement. I did that mainly because I wasn't sure if the previous owner had done it. Upon inspection, the PCV system looked almost brand new so I ended up not replacing much of it. While doing that, I replaced all the main vacuum lines and the thermostat and ECT sensor. I also replaced the vacuum tree o-ring. The original o-ring basically crumbled when I tried to remove it.

I got it all back together and it wouldn't start. It would crank, but not start. Gearing up for a long, lengthy troubleshooting process, I decided to try listening for the injectors to fire and they weren't. So I put my hands on the fuel relay above the radiator. I heard a clicking sound when I bumped the relay. I checked the connection and it was almost disconnected. The male female pins were just barely holding on. I pressed them together while holding the wires so that they could seat with a little more force. Then I turned the key and the car fired right up. Also, I figured that the loose relay was the reason for the weird "closing the hood causes the engine to die" problem since I am now able to slam the hood and it doesn't turn off like it did before.

Aside from discovering a massive crack in the upper radiator outlet, the car is running much better now. So, a new radiator is on order. Also, it doesn't seem to do that weird thing were it would run like garbage unless you turned it off and back on again.

All in all, I think the main issue was several vacuum leaks and possibly the thermostat/ECT sensor having a problem. I'll just keep chipping away at the issues and it will be a great car some day.

Thanks to everyone for the input.

[abscate]

Either a bad battery connection or trouble st the main relays under the radiator cowl up top.

I’ve warped the time/ space continuum on this one…

[budoboy]

Replacing the fuel system relay seems to have fixed the "engine dies when the hood is closed" problem and also some "fuel cutoff under acceleration" problems I was noticing. It also vastly improved the battery life of the car. Before, it would drain the battery almost completely if it sat for 2-3 days. Now, it can sit for several weeks and still be able to start. Must have been a short in the relay. I haven't been able to verify that the rough running problem is resolved yet, but I am hopeful that the new fuel system relay clears that up too. It does seem to run better overall now. Thanks for everyone's input on this.

[budoboy]

I don't know if this is the record for the oldest topic resurrection, but here goes.

It’s been several years since I’ve really driven my 1994 850 Turbo, but now that we have a couple of new drivers in the house, I’ve finally committed to making it roadworthy again. That means I can no longer ignore the strange warm-restart problem that has plagued this car for as long as I can remember. After a lot of troubleshooting, I think I’ve finally found the "smoking gun" that explains its bizarre behavior.

Because the car runs incredibly rough from a cold start and doesn’t clear up until the engine is fully warm and restarted, I spent a lot of time this past week looking into temperature-related components. I was leaning toward the old O2 sensors being past their prime, but then I remembered a friend who had an exhaust leak just ahead of his front O2 sensor that caused idle and drivability issues. I decided to take a closer look at the exhaust manifold, turbo, and downpipe connections, and I can’t believe I missed this before: the two bottom nuts holding the turbo flange to the exhaust manifold are completely MISSING!

I’m positive the car has been like this since before I bought it. This car is a total Frankenstein's monster with bits and pieces from other models, so it wouldn’t surprise me if a previous owner tried a turbo swap and either couldn't get the top nuts off or simply didn't tighten the bottom ones to spec.

My theory is that at a cold start, a small air gap at the flange is letting in enough outside air to give the front O2 sensor "garbage" readings. The ECU thinks the car is lean, dumps in extra fuel, and causes a massive rich condition. Once the car is warm, the steel expands enough to close the gap, allowing the O2 readings to return to something closer to normal after a restart.

My next step is to get two new flange nuts and try to cinch the flange down to close that gap. I have no idea if the gasket is even in one piece anymore, but I’m hoping it is and that the flange isn't so far out of whack that I can't bring it all back together.

[rolsen11]

I like that theory, I looked into that exact problem few years ago when my car was having surging idle problems making the car undriveable (the problem was the ETM, and I was in extreme denial about it because the ETM was new, lol). I ended up plugging a small gap in the bottom of the flange where the manifold meets the flex pipe because there was carbon residue there indicating a leak. This flange is right before the upstream O2 sensor so I had the same concern as you. Of course this didn't fix it for me because it wasn't the problem but the theory is solid as your friend proved. If you're gonna get in there and fix up that flange I would try to get a new gasket in there to make sure it's sealed up well. Looks like you can get an OE one for about 10 dollars (PN 8642450).

[abscate]

Well, I don’t like that theory because on cold start the car is open loop.

However, exhaust leaks out and air in are bad so that needs to be fixed anyway.

[rolsen11]

Well, I don’t like that theory because on cold start the car is open loop.

However, exhaust leaks out and air in are bad so that needs to be fixed anyway.

When you say that do you mean the signal for the oxygen sensor is open loop on cold start?