D_jet trouble shooting question - car is home, journey continues, June, update- no more problem-- the fix was simple.... |
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D_jet trouble shooting question - car is home, journey continues, June, update- no more problem-- the fix was simple.... |
DRPHIL914 |
Dec 15 2014, 12:39 PM
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#1
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Dr. Phil Group: Members Posts: 5,767 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
OK. car has been in shop for the past week, and today Bob spent several hours on it but what he found was when the MPS is disconnected from the vac hose it will idle and run, but when it gets connected it goes immediately lean and dies, and will not run with that hose on there- the MPS holds Vac no loss of pressure, but that doesnt mean that its not bad.
1- i thought that if an MPS went bad it defaulted rich? but when this is getting vac it goes lean right away and dies. but it will run and idle with out the vac , the AF meter then shows 9.8-10.2 or so which is of course rich but not flooding out. so the question is why is it going lean when hooked up? when this issue started about 2 weeks ago, it had been running just fine and all of a sudden it quit running. 2. could there be another issue we dont see that would be making it way to lean other than the MPS? might need to test another MPS, my 2nd one i just bought from someone here and it has never been opened but will not hold vac (slowly looses vac pressure) so it probably need to be opened and re-sealed. not a good candidate to trouble shoot with. ------ FYI- 1975 d-jet 2.0. newer wiring harness , CHT is newish(replaced 2 months before this issue started and was running perfect at that time) |
DRPHIL914 |
Dec 17 2014, 01:00 PM
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#2
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Dr. Phil Group: Members Posts: 5,767 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
D-Jet Trouble Shooting On the MPS check the ohms between: Terminal 7 & 15 = 90 ohms Termianl 8 & 10 = 350 ohms Check each terminal to the MPS case for ground short. Get the car home. you can do all the testing with an ohm meter, well most of it. Rich i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right? i also have 2 other s and one does not hold vac perfectly but the values were the same on it, 92 and 335. i think from here i can still test a known working MPS but i need to go thru the harness like Rich suggested since it seems like it may be something else making it super lean and taking the hose off the mps makes it default rich so it will run -? i kind of suspect either the new CHT went bad or that circuit did, either way this is what thact could cause. hm.... |
Spoke |
Dec 17 2014, 04:00 PM
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#3
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Jerry Group: Members Posts: 6,985 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right? I think what you've determined is there is no open in the electrical circuitry. The real key is the electrical inductance of the 2 sections. The purpose of the MPS is to sense the pressure and change the inductance accordingly. The inductances are used by the ECU in a monostable multivibrator to control the width of the injector pulses. Thus if the inductance is off, the engine will run lean or rich. When I got my 1.8L running with DJET the MPS was way off in its setting for the ECU as the engine was super lean. It wouldn't idle and ran like shit. I had to dig out the epoxy on the MPS and adjust it to richen up the mixture. By the engine running when the MPS disconnected from the intake vacuum, this is telling the MPS to apply maximum pulse width. So it sounds like your engine like mine is running really lean with the MPS. Initially I fooled the ECU by adding resistance in series with the CHT sender. This fooled the ECU into thinking the engine was cold and the ECU needed to widen the injector pulses making the engine run a bit richer. I solved this issue by adjusting the MPS. BTW, what resistance is the CHT sender reading when the engine is cold and hot? If the CHT is shorted or very low resistance, this could also cause the engine to run really lean. |
76-914 |
Dec 18 2014, 09:33 AM
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#4
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,505 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right? I think what you've determined is there is no open in the electrical circuitry. The real key is the electrical inductance of the 2 sections. The purpose of the MPS is to sense the pressure and change the inductance accordingly. The inductances are used by the ECU in a monostable multivibrator to control the width of the injector pulses. Thus if the inductance is off, the engine will run lean or rich. When I got my 1.8L running with DJET the MPS was way off in its setting for the ECU as the engine was super lean. It wouldn't idle and ran like shit. I had to dig out the epoxy on the MPS and adjust it to richen up the mixture. By the engine running when the MPS disconnected from the intake vacuum, this is telling the MPS to apply maximum pulse width. So it sounds like your engine like mine is running really lean with the MPS. Initially I fooled the ECU by adding resistance in series with the CHT sender. This fooled the ECU into thinking the engine was cold and the ECU needed to widen the injector pulses making the engine run a bit richer. I solved this issue by adjusting the MPS. BTW, what resistance is the CHT sender reading when the engine is cold and hot? If the CHT is shorted or very low resistance, this could also cause the engine to run really lean. I sent him a variable resistor so he could check that side of the puzzle, also. |
DRPHIL914 |
Dec 18 2014, 09:38 AM
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#5
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Dr. Phil Group: Members Posts: 5,767 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
going to re-test that CHT, and see wheere the values are before i us the variable resistor, then use that to see what's required to bring it into spec if its out- but on the advice of another member i went ahead and orederd another new CHT as well because i figured it could not hurt to have an extra one on hand
i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right? I think what you've determined is there is no open in the electrical circuitry. The real key is the electrical inductance of the 2 sections. The purpose of the MPS is to sense the pressure and change the inductance accordingly. The inductances are used by the ECU in a monostable multivibrator to control the width of the injector pulses. Thus if the inductance is off, the engine will run lean or rich. When I got my 1.8L running with DJET the MPS was way off in its setting for the ECU as the engine was super lean. It wouldn't idle and ran like shit. I had to dig out the epoxy on the MPS and adjust it to richen up the mixture. By the engine running when the MPS disconnected from the intake vacuum, this is telling the MPS to apply maximum pulse width. So it sounds like your engine like mine is running really lean with the MPS. Initially I fooled the ECU by adding resistance in series with the CHT sender. This fooled the ECU into thinking the engine was cold and the ECU needed to widen the injector pulses making the engine run a bit richer. I solved this issue by adjusting the MPS. BTW, what resistance is the CHT sender reading when the engine is cold and hot? If the CHT is shorted or very low resistance, this could also cause the engine to run really lean. I sent him a variable resistor so he could check that side of the puzzle, also. |
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