I am attempting to run down a rich running condition on a 1991 245 and I need some advice before I condemn the ECU enrichment circuit. I have done a battery of tests and replacements on this car which I will spare you the deatils of. My question is if a faulty O2 sensor can cause an excessively rich condition(soaked plugs, no power, excessive fuel consumption, backfiring, etc). I suspect that the engine is not running full rich due to disabling the AMM which made it run even richer. This is the last thing I can do before sending off the ECU for a rebuild. As a last note, I checked the O2 sensor but it seemed to dwell around .9v which I believe is at the top of the spec. It is my understanding that there should be a cycling action with changing fuel/air mixture. Lastly, any tips on a suitable tool for removal of the sensor?As usual, thanks for the input...
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1991 245 130k-(Volvo number 4)

Most parts stores carry a special socket for o2 sensors for $17-25. it has a slot in the side of it as a relief for the wire. Buy it if you need to remove the o2 sensor, you don't want to round off the fitting. jack it up and soak the threads with Aero Kroil or similar overnight at least before trying to remove it.
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '82 Mercedes 300SD

Having recently read some information on the fuel regulator, it comes to my mind that the symptoms you describe might be related to a failed or failing fuel regulator. Just a thought.

If in deed you need a rebuild on the ECU, I'd be willing to go pull one from the current batch of 240's here at the pull-it-yourself junk yard. These ECU's can be purchased with a warranty and are relatively inexpensive compared to a rebuild. Let me know if I can help. Lord knows, I've been well served on this board.

Sincerly,

JBeechcraft

Thank you very much.I replaced the fuel pressure regulator a few weeks ago to no avail. As I mentioned in my post, I have done a battery of tests and replacements before arriving at my present conclusion (if that's what you can call it) I have decided to try a new Bosch (OE) O2 sensor (I am unsure of the present sensors age and if it doesn't need it now...it will soon). If this doesn't fix the problem I will definitely contact you. Many thanks.
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1991 245 130k-(Volvo number 4)

" As a last note, I checked the O2 sensor but it seemed to dwell around .9v which I believe is at the top of the spec. It is my understanding that there should be a cycling action with changing fuel/air mixture."

The O2 sensor may well stay at .9V if it sees a steady over-rich condition. I would try the following the following O2 sensor — ECU exercise...

A test of O2 sensor/ECU interaction is to "force" Full Lean and Full Rich signals to the ECU, and watch for appropriate response from the O2 sensor. This is done "Open Loop", (i.e., with the O2 sensor unplugged), and with Voltmeter on the O2 sensor lead.

Full Rich Test: Apply a + voltage potential to the ECU Green wire. Use the + terminal of a grounded 1.5 volt battery, or hold the ECU terminal with one hand and put the other hand on battery + (usually quite a stretch, but impresses onlookers). ECU sees a "Rich" signal and goes very lean mixture setting. Idle should worsen, and the O2 sensor should respond with a correspondingly low output (.1 to .2 volts).

Full Lean Test: Ground the Green wire going to the ECU, which sees this as a "Lean" signal and should go to a very rich setting. The RPMs should increase, and the O2 sensor output should rise to nearly 1.0 volt.

These tests are described in the the Bosch FI & Engine Management manual (p 6-22, "Rich stop" and "Lean Stop"), for Continuous Injection (CI) K-jet, but are equally applicable to LH injection.



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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

The high voltage means that all available oxygen is used in the exhaust gas, and therefore the dis-similar oxygen content from the exhaust side to the ambient air side generates the voltage - hence the engine is running rich. To test the O2 sensor, add air to the intake system, without causing a misfire. Remove the power brake hose and put your thumb over it. With the engine running, and while monitoring the O2, add a bit of air by lifting your thumb a small amount. If the sensor quickly shows a lower voltage, preferably below .200 volts, then it is probably OK, and you have confirmed that the fuel system is otherwise at fault. If the O2 won't respond, or get much below .300 volts, then it is faulty. It's a quick check, but it works. You may also find the engine smooths out.

Have you checked your fuel pressure regulator? Pull off the vacuum hose and smell for gas if it is there the diaphram is busted. The Fuel pressure regulator is about $35 mail order lots cheaper than an ECU. You should pick up a spare ECU for trouble shooting and piece of mind especially if you have a 561. The 561 is prone to failure but the failure is a no start condition not a rich running condition. Look for a 556 or 961 ECU on ebay or the bone yard for $50 - $100. My bet is the Fuel pressure regulator. Dan
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85 245 M46 195K, 92 245 A70 123K

Dan,

This ECU can cause a full ass rich problem as well. Basically they "generally" fail one of three ways, lost ground, full ass rich, or jacked up idle. The ground problem is the most prevalent, followed closely by the rich problem. Just an FYI from the trenches...

Chris

Chris
Thanks It's always nice to know the whole story.
Dan
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85 245 M46 195K, 92 245 A70 123K