Questions on 89' 2.7L DME/FI specs
01-19-2005, 09:33 PM
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Questions on 89' 2.7L DME/FI specs
I'm posting from the 944/944s group hoping to get a response.
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For starters, I'm a new member and find this site detailed and very useful. I currently own two 944s and a 924. I'm the original owner of one of the 944s and the 2nd owner of the other two cars. I've been driving and working on Porsches for over 20 yrs so I may be able to help out with info from time to time.
I'm looking for three injection system specs for the 2.7L engine that I have installed in my 85 944 and hope someone in this forum can help.
First, what is the DME output voltage spec for pin 9 (supply or ref voltage to the Air Flow sensor)
Second, what is the resistance spec for the NTC I (pins 1 and 4 or the outer flat pins) of the Air Flow sensor.
Third, what is the specified voltage range for the airflow sensor output (pin 2 of air flow sensor) from full close to full open.
Background. I have an 89' 2.7 L engine. The DME unit is Porsche 944.618.121.06. My Porsche shop manual addresses the 2.7L eng but I think there are some DME specs that didn't get updated.
Specifically, there is a 15 point ignition check that covers several components. I find that the DME reference our output voltage to the Air Flow sensor (coming from pin 9 of the DME unit) is 5.0 volts. The spec according to my manual is > 8.0 volts with no mention of a difference btwn the 2.7 L DME unit and the other units. So I picked up a used 89' 2.7 L DME unit from a salvage yard and it too put out about 5 volts at pin 9. I checked my 84' unit and the output was 10.2 volts, right in spec.
Symptom. The 2.7L will start but die in a second or two. I can keep the engine running by manually operating the air flow sensor flap. In a bold move I put the 84 DME unit on the car and the engine started and ran pretty good (Idle a little slow and rough when cold but expected as the 84 unit does not support idle control valve ops). Once warm the eng ran relatively good, a little flat off idle and running a tad lean but that is expected.
Additional info. These are the specs in my Porsche shop manual (but it does not specify DME application or year).
DME Pin 9 voltage Spec (which goes to pin 3 on Air Flow sensor): >8.0 volts
Air Flow NTC I(air temp sensor) resistance 15-30 deg C as measured at pins 1 and 4 of air flow sensor (plug disconnected): 1.45 - 3.3 k ohms.
Air Flow sensor control signal output range (pin 2 of air flow sensor, plug connected, ign on): 150 mVolts with air flow sensor plate full shut to > 8.0 Volts when manually actuating the air flow sensor to full open.
These are the areas I've identified as potential problems. If I missed something or you have suggestions on what to check please let me know.
FYI I have the proper injectors and pressure regulators. I have verified fuel delivery rate and fuel manifold pressure. I do not have a "coding plug" (straight wire loop) or "variance plug" (impedence loop) installed. I don't think they are required or would cause the problem I am having but I'm not sure.
Thanks for any info you can provide.
a.r.r.
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For starters, I'm a new member and find this site detailed and very useful. I currently own two 944s and a 924. I'm the original owner of one of the 944s and the 2nd owner of the other two cars. I've been driving and working on Porsches for over 20 yrs so I may be able to help out with info from time to time.
I'm looking for three injection system specs for the 2.7L engine that I have installed in my 85 944 and hope someone in this forum can help.
First, what is the DME output voltage spec for pin 9 (supply or ref voltage to the Air Flow sensor)
Second, what is the resistance spec for the NTC I (pins 1 and 4 or the outer flat pins) of the Air Flow sensor.
Third, what is the specified voltage range for the airflow sensor output (pin 2 of air flow sensor) from full close to full open.
Background. I have an 89' 2.7 L engine. The DME unit is Porsche 944.618.121.06. My Porsche shop manual addresses the 2.7L eng but I think there are some DME specs that didn't get updated.
Specifically, there is a 15 point ignition check that covers several components. I find that the DME reference our output voltage to the Air Flow sensor (coming from pin 9 of the DME unit) is 5.0 volts. The spec according to my manual is > 8.0 volts with no mention of a difference btwn the 2.7 L DME unit and the other units. So I picked up a used 89' 2.7 L DME unit from a salvage yard and it too put out about 5 volts at pin 9. I checked my 84' unit and the output was 10.2 volts, right in spec.
Symptom. The 2.7L will start but die in a second or two. I can keep the engine running by manually operating the air flow sensor flap. In a bold move I put the 84 DME unit on the car and the engine started and ran pretty good (Idle a little slow and rough when cold but expected as the 84 unit does not support idle control valve ops). Once warm the eng ran relatively good, a little flat off idle and running a tad lean but that is expected.
Additional info. These are the specs in my Porsche shop manual (but it does not specify DME application or year).
DME Pin 9 voltage Spec (which goes to pin 3 on Air Flow sensor): >8.0 volts
Air Flow NTC I(air temp sensor) resistance 15-30 deg C as measured at pins 1 and 4 of air flow sensor (plug disconnected): 1.45 - 3.3 k ohms.
Air Flow sensor control signal output range (pin 2 of air flow sensor, plug connected, ign on): 150 mVolts with air flow sensor plate full shut to > 8.0 Volts when manually actuating the air flow sensor to full open.
These are the areas I've identified as potential problems. If I missed something or you have suggestions on what to check please let me know.
FYI I have the proper injectors and pressure regulators. I have verified fuel delivery rate and fuel manifold pressure. I do not have a "coding plug" (straight wire loop) or "variance plug" (impedence loop) installed. I don't think they are required or would cause the problem I am having but I'm not sure.
Thanks for any info you can provide.
a.r.r.
01-20-2005, 04:29 AM
#3
Race Director
Your AFM is mis-calibrated. This typically happens with a monkey messes with the spring-preload on the flapper-door in a misguided and mistaken attempt at getting more power by fooling the computer into thinking more air is flowing than actual. Adding more fuel DOES NOT make more power, so best to adjust everything back to stock.
"First, what is the DME output voltage spec for pin 9 (supply or ref voltage to the Air Flow sensor)
It's about 8v for the early cars prior to '85.5. For the later cars, it's 5v.
"Second, what is the resistance spec for the NTC I (pins 1 and 4 or the outer flat pins) of the Air Flow sensor."
Looks OK to me. The air-temp sensor tells the DME how much fuel to add on cold-start enrichment. It also makes minor adjustments based upon air-density, very, very minor.
"Third, what is the specified voltage range for the airflow sensor output (pin 2 of air flow sensor) from full close to full open."
Measure this signal at pin-7 near the DME (small green/red-stripe wire) to make sure that the signal is making it into the DME properly. Fully-closed flapper door should be putting out about 0.25v. Then have someone smoothly open the door and voltage should increase smoothly with no jumps or drop-outs. With door fully open, voltage reading should be 4.6v.
Make sure you have the proper '85.5+ AFM that works with the 5.0v reference voltage coming from the DME. The voltage-calibration curve (volts vs. flapper-door angle) is completely different between the early 0-8v AFM vs. the later 0-5v AFMs.
"First, what is the DME output voltage spec for pin 9 (supply or ref voltage to the Air Flow sensor)
It's about 8v for the early cars prior to '85.5. For the later cars, it's 5v.
"Second, what is the resistance spec for the NTC I (pins 1 and 4 or the outer flat pins) of the Air Flow sensor."
Looks OK to me. The air-temp sensor tells the DME how much fuel to add on cold-start enrichment. It also makes minor adjustments based upon air-density, very, very minor.
"Third, what is the specified voltage range for the airflow sensor output (pin 2 of air flow sensor) from full close to full open."
Measure this signal at pin-7 near the DME (small green/red-stripe wire) to make sure that the signal is making it into the DME properly. Fully-closed flapper door should be putting out about 0.25v. Then have someone smoothly open the door and voltage should increase smoothly with no jumps or drop-outs. With door fully open, voltage reading should be 4.6v.
Make sure you have the proper '85.5+ AFM that works with the 5.0v reference voltage coming from the DME. The voltage-calibration curve (volts vs. flapper-door angle) is completely different between the early 0-8v AFM vs. the later 0-5v AFMs.
01-24-2005, 04:45 PM
#4
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SUCCESS!!! Turned out to be the AFS. With the specs Danno provided I was able to nail it down. Whatever the cause, the low end (full shut) impedence was too high causing too low of a signal (voltage) back to the DME (measure btwn the middle two pins of the AFS with the terminal connected and ign on). Replaced the AFS and good to go. I can provide more details concerning the before and after voltages if anyone is interested.
For bsbiker, you need to know it's not a simple swap. I had to modify my 85 DME harness with the an 89 harness from a salvage yard using the schematics from 85 and 89. The 89 DME has more pins populated for some additional functionality and some pins are just different.
For example you need to add the pins for the idle control and the input for your A/C compressor (no longer have or need the aux air valve and A/C bypass air valve with the 89 engine with the 89 DME). Note some say you can use the old DME but the 89 injectors have different resistance and the 2.7 DME is different part number from the 2.5 DME if I'm not mistaken (don't have my manual in front of me) so injector dwell times, timing etc might be different so I felt more comfortable with the 89 DME. Other examples of deltas btwn 85 and 89 include: In the 89 DME, pin 11 is vestigial but it still provides the correct signal to drive your pre 85.5 tachometer and economy ckts. Also need to look at the pin for altitude sensor input. This is just a binary switch (ground, no ground) but the 89 uses a different pin. You need to add the lead to the crankcase ventilator valve htr. I used the 12v power lead that originally went to the aux air valve for this.
I made a list of all the pins, differences, then mapped out all the changes to the harness, including the instrumentation plugs before I started the harness project. I don't have the list in front of me but I highlited the major deltas here to give you a feel for what needs to be done. For me it was not a big deal as the engines and I had the two harnesses. I elected to use the 85 harness as the base as it had the right grommets and connectors then dissassmebled and pulled the appropriate pins from the 89.
Bottom line it works great and everything works.
Hope this helps... and good luck. And thanks for the help and info from the forum. My shop manual had the wrong spec (missing a change) and I found the critical spec that allowed me to isolate the problem on the first attempt and avoid the "easter egging" approach. Thanks.
For bsbiker, you need to know it's not a simple swap. I had to modify my 85 DME harness with the an 89 harness from a salvage yard using the schematics from 85 and 89. The 89 DME has more pins populated for some additional functionality and some pins are just different.
For example you need to add the pins for the idle control and the input for your A/C compressor (no longer have or need the aux air valve and A/C bypass air valve with the 89 engine with the 89 DME). Note some say you can use the old DME but the 89 injectors have different resistance and the 2.7 DME is different part number from the 2.5 DME if I'm not mistaken (don't have my manual in front of me) so injector dwell times, timing etc might be different so I felt more comfortable with the 89 DME. Other examples of deltas btwn 85 and 89 include: In the 89 DME, pin 11 is vestigial but it still provides the correct signal to drive your pre 85.5 tachometer and economy ckts. Also need to look at the pin for altitude sensor input. This is just a binary switch (ground, no ground) but the 89 uses a different pin. You need to add the lead to the crankcase ventilator valve htr. I used the 12v power lead that originally went to the aux air valve for this.
I made a list of all the pins, differences, then mapped out all the changes to the harness, including the instrumentation plugs before I started the harness project. I don't have the list in front of me but I highlited the major deltas here to give you a feel for what needs to be done. For me it was not a big deal as the engines and I had the two harnesses. I elected to use the 85 harness as the base as it had the right grommets and connectors then dissassmebled and pulled the appropriate pins from the 89.
Bottom line it works great and everything works.
Hope this helps... and good luck. And thanks for the help and info from the forum. My shop manual had the wrong spec (missing a change) and I found the critical spec that allowed me to isolate the problem on the first attempt and avoid the "easter egging" approach. Thanks.
01-27-2005, 01:07 AM
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I went a different route. I had such a bad mix of parts on the engine that I bought that I converted everything back to the 83 stuff. I don't know if I should have done that but I really didn't have a choice. I do have mine running now, well sort of. I know I need one injector so after I get that I will try again.
