Hey all,
I recently (this morning) built (and installed) my kit A/F meter. Basically i am trying to diagnose some problems with my car, when the car is "mid warm up" it splutters really badly (for something like 1/2 to 1 second...)when floored. According to my "test light" (LED installed using the test point for the Oxygen sensor in the engine bay) my car is running rich at idle the whole time, yet, my newly installed a/f meter goes from 14.7 (perfect) to about 15.5 (lean) at idle.... what gives? The A/F meter is hooked up right, i know that, 'cause it works! (And it's accurate at idle with a reference of a DMM). Now, when i floor it mid-warm-up, it goes LEAN, i mean the A/F guage is updated slowish (well, the bar graph is quick, rest is not) completely lean, as in off the scale, till it stops "spluttering" and then it's fine. Whenever i suddenly floor it (hot or cold, althought it doesn't hesitate when hot) It always goes lean. I thought it should go RICH when floored. What gives here? I don't understand, as the reading off the ref point of the ECU is definately different to what i am getting!!! My bosch ECU LH 2.2 number ends in "544" i can't remember whether or not these modules have problems! Please help me!
Thanks !
Az

Don't have any experience with LH2.2. I've scoped the unheated sensors on my two LH2.0 cars; the ECU's mixture adjust test point faithfully follows the transitions across 500mV. Best rate (when well warmed) with the unheated sensor brand new is roughly 1.5 cycles per second. Much slower during warmup.

Mine always goes lean accelerating under load but I'm not absolutely confident there isn't some false air (vacuum leaks) and my injector performance is unknown, though the fuel pressure is well regulated.

I have a question for you regarding the mixture test point you connected the LED to: Are you getting any brightness from the LED? Can you see the transitions?

The Bentley manual describes the Volvo tool 5280 being connected (for both LH2.0 and LH2.2 240s) between battery and test point. My ECUs (503 and 510) provide this test point output directly from the 8039 processor through a 10K ohm resistor. This is hardly enough to directly drive an LED for practical viewing. Perhaps this is different in your ECU, but for mine to be useable I have to buffer the output driving the LED with a transistor.

Art Benstein

I'm not the expert but I decieded to go with a Exhaust Gas Temp meter after reading this article.
BTW there's lot of other good tech stuff at this site.

http://www.autospeed.com/A_0618/page1.html

I would NOT waste time looking at the 544 as a problem. Except for the stalling when cold with automatic transmission cars under load, the 544 is almost bullet proof. As long as all your wiring is connected and tight at the harnesses etc.
Actually, I tried a 554 substitution into my 86 245 (M46) and the car ran like crap. End of experimnent and back to the 544.

Az:

I would second steve's hypothesis and recommend you replace the pressure regulator. I was having all kinds of issues with my 1985 745t's fuel system, and am still operating with a slightly lean mixture at times. While i think my mixture is still a little lean, I can say with certainty that replacing the FPR worked wonders for the stability of the tach, idle, and fuel flow.

If the FPR is shot it will deliver inaccurate prssure to the injectors. Since they can only handle (or are "supposed" to handle) about 44psi in the turbo model, pressures as high as 100psi (which it CAN run up to) can work havoc on the injectors. You're basically trying to push a liquid at 100 psi through a hole the size of a pencil head. At a certain point the pressure will start to exceed the rate at which the fuel can exit the injector, and it will back up or retard the spray. Add to all this that you can get a new FPR online for about $35 and its a worthwhile upgrade (judging from the wrecks I see in my pulling yard, I don't think most owners EVER replace the FPR).

On a side note, I have now replaced my sender assembly, pre-pump, and FPR. I've run a few cycles of cleaner through, and the thing seems to be working beautifully. I'm "trying" to replace my fuel filter, but the damned thing is corroded onto itself and won't come off. I'd really like to know what genius at Volvo thought "hey, I know, let's put the main fuel elements UNDER the car! We'll leave them in an open container so they gets corroded and beaten by road conditions... that way the part will fail TWICE as quickly AND the owners won't be abl to fix it themselves without a headache!" Along with the blower positioning/shrouding/exposure, the fuel pump/filter placement/design was a definite design flaw.

Good luck,
Rick

Hi Az,

I am not a fuel system expert, but I do know the ECU you have has cold start problems (too lean) if the ambient temperature is about 45-80 deg. F.(7-26 C.) I have not heard of problems after the engine is warmed up. There is an article in the archives, http://www.brickboard.com/ARCHIVES/1998JAN/8303.shtml which addresses the condition. The normally aspirated engine with the 544 ECU will exhibit the problem unless the modification kit mentioned is installed. The 554 ECU incorporates the fix. The kit goes for about $80.00 U.S. I got the 554 ECU on e-bay for about $50.00.

I had messed with the idle speed, throttle plate adjustment, and mixture to try to overcome the stalling problem before I put in the ECU with the fix.

Good Luck,
Bruce Johnson

How old is your oxygen sensor? A lazy sensor can behave this way. Take a look as well at your fuel pressure regulator: if it misbehaves, it can cause a rich condition at various throttle positions.

Hey Steve,
I don't KNOW how old my oxygen sensor is, BUT, it has 2 white wires and a black wire on it, and it's white wires are still, well, white. Which leads me to believe it has to be more than 20,000k's old (when i bought the car) but not much older. My fuel regulator was a german made aftermarket one (by a reputable brand that i can't remember!). I don't know if the pressure is right, but, the car runs fine at WOT in any gear, all the way to 6000rpms with a perfect mixture, so i'd say it's fine. I am just finding it really unusual that my computer is reading off a different signal to what my meter is. My a/f meter uses a "PIC" (basically a programmable chip) and it basically just references the output of the sensor to a table and puts it on the display. It is supposedly designed for narrow-band sensors (volvo ones!) the bosch LSM-11. From the chart they look pretty much the same curves as mine. Ah well. Any help'd be good, thanks all,
Az