Greetings,

The car is a 91 with the LH3.1 fuel system and it keep running rich on me. So rich it bogs down and gets about 15mpg. I replaced the intank fuel pump, coolant temp sensor, cleaned throttle body and IAC motor, replaced the fuel pressure regulator. The car starts very good and does not have any trouble codes. I tested the AMM and it is working (car runs like crap with the wire harness removed).

I've owned about 5 volvo 240's and have NEVER had this problem. please help!!!

Two more, real easy: Air cleaner clean? Thermostat stuck open.

Was the FPR new or used?

1) Air cleaner is BRAND New.

2) FPR was used, but when I pulled the vacuum hose on my old one the rpm stayed the same. On the new (new to me) FPR, the idle does go up about 200rpm when the hose is pulled.

The car has no trouble codes, just the 1-1-1. Meaning, no codes.

I did disconnect the battery and pull the wire to the O2 sensor, and the computer gave me the trouble code for the o2 sensor. SO when I plugged it back in and ran the car, the code went away. That means its working right (I haven't tested it with a multimeter).

I did have to remove the cat converter because the old one was SEVERELY clogged. It was making excessive back pressure and blew some exhaust manifold gaskets.

Question: If there is a exhaust leak before the O2 sensor, can this cause the vehicle to run THIS rich? It is so rich the plugs look black and sooty after a 5 mile drive and the engine bogs because of so much fuel. You have to pump the gas to get it to rev up, but once it has revved up (say 3000rpm+) (and you can keep it there) it will run fine, but uses 2-3 times the amount of fuel it should be using (I havent figured it up but it will get about 12-15mpg in current state)

The car has new plugs, plug wires, distributor cap and rotor.

I could never make this mistake category: A friend’s car ran poorly after a tune up, kind of like yours. He had the plug wires crossed. Check the cap and rotor.

Question, how long after you did something to the car did this running rich problem start?

I cannot answer your question concerning an exhaust leak ahead of the o2 sensor. A poster below thinks this could be an issue and I have heard this before.

Tom

The plug wires are in the correct spot. I did all this double checking once before. The car orignially had a bad coolant temp sensor and I replaced the old exhaust while it was in the garage. It ran better, but still not "good". I did have to weld the "bung" for the O2 sensor in a new pipe when I removed the cat and I know my welds are good (nothing blowing past with motor running).

I've been fighting this darn car for about 6 months and would like to be driving it instead of it being an eyesore.

Thanks for the help!

That was the experience one of the regular contributors had about a year ago, and the problem turned out to be a crack or cracks in the exhaust upstream of the cat. Just due to funny gas dynamics it sucked in air rather then blowing exhaust out. This made the O2 sensor indicate lean running to the ECU, so the ECU responded by enriching the mixture. Definitely not intuitive, but fixing the exhaust leaks cured the problem.
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No one ever went broke underestimating the taste of the American public - H.L. Mencken

But I didn't think that the O2 sensor alone could tell the ECU to enrichen the mixture THIS much. This car will belch black smoke at times.

Still could be an exhaust leak??

Put a screw driver on the injectors when the engine is running, are they all clicking?
If it is as rich as you say you should be seeing ODB codes, I wonder if the ECU has failed?
Dan

I thought there should be a trouble code,too. But there isn't.

All the injectors are working, but I still have to see if any are leaking. I did disable the cold start injector because I thought it was leaking (had one do that on a 85 240 Turbo once.)

Read out the ECU codes and let us know what they are. Search the BB for the procedure, or read the Bentley manual. The code may provide a clue as to the problem. Beyond that, I'd suspect an O2 sensor but check the codes first.

jorrell
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92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

Here are my 2 cents .
2-3 more things come to mind which can cause rich runing
1. exhaust leaks before o2 sensor
2. leaking injectors (check by taking out fuel rail, grounding the wires and key in position II , to prime the fuel pump)
3. bad o2 sensor

Regards
Gopesh
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DD-1990 240 DL SW M47II FI 3.1 220 K miles Turbo Sways,Custom headlight circuit ,Insulated roof,Tinted Glass,