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#1 (permalink) Old 08-09-2011, 11:44 AM
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More D-Jet stuff

I have been having an intermittent Gremlin that has been driving me nuts, a "sputter" or "miss" under acceleration at 1500-2000 RPM's ever since I rebuilt the AAV and sealed the air leaks with new hoses, I am waiting on The PerTronix ignition, but...sometimes it seemed to run perfectly, even after warming up, then when I "hit it" hard I heard/felt it dramatically, and getting on the freeway taking it up to 70 i would feel it, but very subtle, driving around twon < 45MPH and driving it easy the problem doesn't "manifest"

I noticed it seemed to drive better when I had the air cleaner off and once I put the air filter on and forgot to hook up Temp Sensor 1, and the "improvement" seemed to carry over

Today I ran some tests, same temp, same route, "hit it HARD" on the same freeway onramp, and with Temp Sensor 1 connected, I got sputter, without it runs like a dream

Temperature Sensor I

Temperature Sensor I is an ambient air temperature sensor.As the ambient air temperature decreases,the density of the air increases.As a result,the ECU must inject more fuel on a cold day than on a warm day.

Temperature Sensor I is a temperature sensitive resistor known as negative temperature coefficient thermistor (NTC). This sensor has a resistance of between 400 and 500 ohms at 50 degrees F. At 100 degrees F.,the resistance is between 150 to 200 ohms.

Temperature Sensor I actually has little effect on the operation on most D Jetronic equipped vehicles.This is because most of these cars have tens of thousands of miles on the engine and are running very rich due to this wear.The troubleshooting consequence of this is that disconnecting the air temperature sensor during the diagnostic procedure may have little effect on the way the engine runs,and in some cases it may actually improve the way it runs.


I am interested in what this means, am I running too rich? too lean? lacking fuel pressure? I am lacking a CO2 meter and a Fuel Pressure sensor, I am going to have to knuckle under and start getting these and better tools, but off the top of their head, anyone have any ideas about why this should be so? it was probably 65F when I ran "the tests" I will also try at a -HOT- ambient temp day, but somewhere in this is the reason this car has never liked hot days

The ECU screw was/is adjusted about 2/3rds to the "rich" side, there are too many variables to try to set this right now, as in I don't...until I get the other parts functioning perfectly I will be unable to really test this with any real accuracy, when I set it right in the middle (towards "lean") I don't know if the sputter was caused by this or this gremlin

it's something pretty subtle, because under "these" conditions it runs like a dream, but under "those" conditions it loses power and "misses" from 1500-2000 Rpm's, subtly when cruising, dramatically when punching it, I just don't know exactly the difference between "these" and "those" conditions, the running great bit seems to be early, as in on the way to the parts store, on the way home, ie when it gets "hotter" it seems to get worse, I've driven at night, runs great, seems to run very well, better in cooler conditions regardless of the engine coolant temp

I just can't seem to make the mental leap to figure out if I am running rich or lean, probably rich but then why the change? does it get too rich? why does disconnecting the temp sensor make it run better? why does it seem to run worse on warmer days and after being driven harder, what is it about "hot" that changes the mixture that causes the sputtering

initially my suspects were the trigger points and the dist points, but as time passes I am not so sure, I will know more after I install pertronix I guess but I hate throwing parts at it when the truth is I have more important things to be doing with my money, like my disposable income has some pretty important old debts to pay from a bankruptcy a few years ago

Build a man a fire and he will be warm for a night, set a man on fire and he will be warm for the rest of his life


Last edited by The Proctologist; 08-09-2011 at 11:52 AM.
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#2 (permalink) Old 08-09-2011, 03:41 PM
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Drove it around 30 miles today in fairly "harsh" conditions, at speed, then stop and go, then speed, turned it off for 20 minutes and got a bite, all without temp sensor 1 attached and it ran perfectly all at above 90F ambient temp, stayed glued to 175 coolant temp

with temp sensor 1 attached the sputtering returned

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#3 (permalink) Old 08-09-2011, 05:55 PM
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The air sensor enrichens the mixture if the air temperature is below 70F. After that it does nothing.

Try this:

The colder it is, the more the fuel mixture is enrichened. Also the colder it is, the higher the resistance of the sensor. So, by pulling the plug you would have infinite (very high!) resistance and ECU would think it is VERY cold out. It would then enrichen the mixture.

This would say that your car is running lean.

Adjusting the ECU mixture knob does nothing to change the mixture, EXCEPT at idle when the throttle plate is closed. Once it moves more than 0.4mm off the stop, the MPS takes over and controls the mixture.

Could be you are on lean side. Maybe pull the plugs and post some pictures of them. Something to do in your spare time . You can adjust the MPS in very small increments, but without a meter, plugs may be only indication.

Regarding those tools - A CO meter is expensive. I installed a wideband AFR meter instead - cost about $300 by time I was finished. Local garage checked CO for me once for about $50.00 on their dyno!

A fuel pressure gauge can be a water pump gauge at under $10.00 at Ace Hardware! ( Make A Fuel Pressure Gauge - MiniMopar Resources )
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#4 (permalink) Old 08-09-2011, 06:52 PM
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Why not pull the sensor and measure the resistance cold and warm? I would check to make sure the sensor is functioning before over thinking the problem. Maybe do as MBgraham says and have someone check the CO, I once had a vacuum leak and plugged it, well the car was tuned to "mask" the vacuum leak so when the leak was plugged the car was running very rich and would stall out. I had my mechanic plug the vacuum line and set the mixture and all was good.

Good lucK!

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#5 (permalink) Old 08-10-2011, 01:02 AM
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Originally Posted by daryn View Post
Why not pull the sensor and measure the resistance cold and warm? I would check to make sure the sensor is functioning before over thinking the problem. Maybe do as MBgraham says and have someone check the CO, I once had a vacuum leak and plugged it, well the car was tuned to "mask" the vacuum leak so when the leak was plugged the car was running very rich and would stall out. I had my mechanic plug the vacuum line and set the mixture and all was good.

Good lucK!
Great stuff both of you, I think the car was tuned to cover the air leaks from both the fuel injection system -and- the faulty AAV, so when I fixed them, it let less air in and....oh god I'm confused again haha

I think it runs lean with the sensor as well, that's how it "feels"

last spark plug I pulled was pretty white, first time I pulled them they were fouled, I pulled one a week or so ago and it seemed abnormally white, not hot burned but...I will check it out

great idea on the fuel/water gauge, I will do that, and check the spark plugs

anyhow, the changes took place after I fixed the air leaks, fixed the aav and put new lines and it's been funny since, but that was coming off the whole "points" fiasco, so getting perTronix then chasing these down are -bound- to have positive effects, all in all, for how frustrating this has been, I can't remember having so much fun as bringing this absolutely beautiful car back from the dead with a limited budget, a 30 dollar socket set, 2 screwdrivers, a monkey wrench, a scrench, and a hammer and a vice haha

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#6 (permalink) Old 08-10-2011, 12:31 PM
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Originally Posted by The Proctologist View Post
all in all, for how frustrating this has been, I can't remember having so much fun as bringing this absolutely beautiful car back from the dead with a limited budget, a 30 dollar socket set, 2 screwdrivers, a monkey wrench, a scrench, and a hammer and a vice haha
This I can relate to! My car ran so badly at one time, but in chasing down the problems, I now have two of all major unobtainable parts and some neat dash gauges that tell me car is running great! Probably under $500 invested.

D-Jet was and still is a great system and is fun!
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#7 (permalink) Old 11-22-2011, 06:47 AM
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MPS??

Quote:
Originally Posted by MBGraham View Post
The air sensor enrichens the mixture if the air temperature is below 70F. After that it does nothing.

Try this:

The colder it is, the more the fuel mixture is enrichened. Also the colder it is, the higher the resistance of the sensor. So, by pulling the plug you would have infinite (very high!) resistance and ECU would think it is VERY cold out. It would then enrichen the mixture.

This would say that your car is running lean.

Adjusting the ECU mixture knob does nothing to change the mixture, EXCEPT at idle when the throttle plate is closed. Once it moves more than 0.4mm off the stop, the MPS takes over and controls the mixture.

Could be you are on lean side. Maybe pull the plugs and post some pictures of them. Something to do in your spare time . You can adjust the MPS in very small increments, but without a meter, plugs may be only indication.

Regarding those tools - A CO meter is expensive. I installed a wideband AFR meter instead - cost about $300 by time I was finished. Local garage checked CO for me once for about $50.00 on their dyno!

A fuel pressure gauge can be a water pump gauge at under $10.00 at Ace Hardware! ( Make A Fuel Pressure Gauge - MiniMopar Resources )
What and where is the MPS?

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#8 (permalink) Old 11-22-2011, 07:10 AM
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#9 (permalink) Old 11-22-2011, 07:48 AM
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Originally Posted by RDTS View Post
What and where is the MPS?

Manifold Pressure Sensor.
Usually bolted to the driver side fender, just under the front end of the master cylinder.

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#10 (permalink) Old 11-22-2011, 08:00 AM
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Your issue is a text-book (for non-Djet/Merc) symptom of a defective vacuum advance diagram. Just for giggles, I would take a Mighty-vac to the diaphragm to check it, and put a couple degrees more ignition advance in and take it out for a run. I too have an issue with my air temp sensor even though it ohms out correctly. As our cars get older and worn, we have to consider that what was correct when they were new, is now just a guideline.
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