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Greetings! I am experiencing a rich running engine in my 144. It goes something like this, engine starts up, runs fine and pulls hard. After about 10 minutes of driving the pedal becomes "mushy" and unresponsive, accompinied by a significant loss of power and high fuel consumption. What I have been able to deduce is that the engine runs great when cold and preformance drops as it warms up due to the constantly rich mixture.
I have checked the wires from the ECU to the #2 temp. sensor, and from the temp. sensor to ground. both wires seemed ok. And I replaced the #2 sensor just because, not that I expected it to help, and it didn't.
So I'm looking for other culprits. Could it be the vacuum sensor? Clogged air filter? Gremlins and bad mojo?
For your assistance, I thank you,
Jonathan.
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Should probably look at your plugs to see if the situation is on all cylinders
or not. Also check the wiring to the coolant temp sensor (smaller item screwed
into the side of the head at the front). If it always thinks it is too cold
the situation will get worse as the engine warms up.
--
George Downs, Bartlesville, Oklahoma, Central US
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posted by
someone claiming to be Rhys
on
Tue Jan 20 16:56 CST 2004 [ RELATED]
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First easiest thing to do is remove the vacuum hose from the manifold pressure sensor. Suck on it, and if you can draw any amount of air through it, the copper bellows are torn, and it will have to be replaced. Next is to check the fuel pressure - 28-31 psi is about right. Also look for any air leaks downstream of the throttle plate, which will cause rich running. Check the manifold vacuum to be sure.
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To the best of my knowledge, air leaks downstream of the throttle won't cause it to run rich, just idle fast. D-Jet doesn't ever directly measure the amount of air going into the engine, it just deduces it from the MAP sensor (and fine tunes that guess with the intake air temp sensor and an RPM map). Air leaks just slightly increase the air pressure in the manifold, and the computer will inject enough fuel in to match the resulting pressure. If you felt like it you could cut another hole in the plenum, and install another throttle valve (for whatwever reason) and it would cintinue to operate properly.
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I've never made sense of why, but I've seen air leaks between throttle and engine cause severe rich running with D-jet -- leaking manifold gasket.
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Possibly because a large vacuum leak (and the resulting rise in manifold pressure) would cause the MAP sensor to think the throttle plate had opened and it would call to the computer to extend the injection duration (enrichened mixture).
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True, but only enough to match the increased pressure - so an increased idle speed, but not rich running.
Of course, that is just based on conjecture on my part based on my understanding of how D-jet works. Perhaps the specially tuned idle mode (triggered by the closed throttle) is somehow fooled more easily by vacuum leaks? Or perhaps leaks down at the end of the intake runners create some sort of dynamic condition? I should mess around with my wideband O2 sensor and my 1800E sometime and see what I find out. You could simulate a badly leaking manifold gasket pretty easily just by loosening the collar on an injector and pulling it slightly out. Or unhooking the vacuum hose to the brake booster. And watch what the mixture does when that happens.
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posted by
someone claiming to be Rhys
on
Wed Jan 21 11:50 CST 2004 [ RELATED]
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John I have found that the D-jet will go very rich with the addition of false air. The copper bellows in the pressure sensor are very sensitive throughout the range. The pressure sensor determines load in these systems, not air flow. So anything that increases manifold pressure is interpreted as load, not mass air. That makes them overcompensate and run rich. Later mass meter systems that have false air will go lean, although within the range of it, the O2 sensor will compensate for that condition.
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Definitely a wealth of knowledge going on here, thanks!
For clarity the vacuum sensor =MAP sensor? .
I checked the vacuum sensor and found it airtight. And in doing some research I came across the idea that a partly clogged fuel return line could give similar symptoms. Hmmm. I added a bottle of Techtron to the gas and sucked on the vacuum sensor and the odd thing is the car ran pretty well, not great, but not miserable. I can't imagine that Tectron and testing the vacuum sensor cured my woes, well maybe the Tectron, but still that seems too easy. Especially for a bottle bought off the shelf at Pep Boys.
Although the leaking maifold gasket has merit due to having just replaced the exaust manifold with a header. If I were to check that by sraying WD-40 around the manifold and listening for a change in rpm's, would it work given that the engine is running rich due to an air leak, not lean?
Thank you all very much.
Jonathan
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posted by
someone claiming to be Rhys
on
Wed Jan 21 17:16 CST 2004 [ RELATED]
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The plot thickens Jonathan. So you installed a header exhaust and the problems began at that point? The large washers the B20 uses to bridge the separations between the intake and exhaust at four locations are critical to good clamping. If the flange thickness of the header is different from that of the aluminum manifold, you will have a problem with leaks. The WD-40 will show up a leak simply by changing the engine RPM. Whether it is rich or lean doesn't matter, as long as it confirms a leak.
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Indeed Rhys, I did install a new header, and ran it for a trouble free week and a half before experiencing any problems. The initial circumstances involved me running dangerously low on gas and the car dying while going up a steep hill. Total loss of power and then dead, wouldn't start. I get gas, the car starts after I goose the throtle a little, but still no power. After I get were I'm going, I look under the hood and find the wire for the #2 temp. sensor/ coolant sensor had worked lose. No big deal, plug it back in. Except the plastic plug had become brittle and desintergrated, so solder the female spade conectors back on. And that's were it stands.
I've checked the wiring, and replaced the temp. sensor. I've checked the MAP sensor and it's wiring (ohm reading of 91 and 340 for the wires and sensor). I've checked for a maifold leak and replaced the manifold nuts, while retaining the washers, and wrenched the nuts down (is there a torque setting I should be using?). I've pulled the gas return hose from the pressure regulator and have blown through it to check for a blockage. I've even adjusted my voltage regulator to lower the voltage, on the advice that too much voltage will cause the ECU to preform with the symptoms I have been experiencing.
Whew. What else is there? I understand some adjustment can had on the MAP sensor, I'll try that next. So, I'm not sure it's something simple, though I wouldn't be surprised.
I appreciate your advice and insight, thank you.
Jonathan
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posted by
someone claiming to be Rhys
on
Fri Jan 23 03:28 CST 2004 [ RELATED]
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You'll need to check the fuel pressure now Jonathan, given that it ran out of gas. Maybe a plugged filter. The MAP sensor adjustment should be left to last, and probably it doesn't need to be fiddled with at this point. I think the number 2 sensor is air temp, and compared to the coolant temp one it is no so important.
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