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944 only runs on 2 cylinders!! help!!
hello, im new to this forum so i bought a Porsche 944 1985 (early) and it started fine when i bought it but it was only running on 2 cylinder.
here is what i have done to the engine so far... -replaced the dme/fuel pump relay -replace the cylinder head and all new gaskets (due to lost of compression) and the cylinder head was corroded and replace it (couldn't shave it  )-replace the ignition switch since it was cracked( i figure this would fix the no starting issue with no spark going to the wires) - i had replace the spark plug wires cause the old one one of them was bad. the only way the car start is if i insert starting fluid in the intake and crank it... and also all injector are firing but it only runs on the 1st and 4th cylinder!!! it would some times get spark to the 3rd cylinder but it only one spark and its gone. i took out and cleaned the both speed and reference sensors one of them might be bad since it had a circle in the middle like it was chipping...(pic below) ill replace that asap...(also i have to check the .8mm distance from the flywheel to the sensor i havent had time to do that yet but i will soon this week) but i would like your comments to see what else i can do to it. thanks this is a picture when everything is done  the bad cylinder head   Ignition switch replaced  one of the sensor im not sure which one  
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01-31-2010, 08:26 PM
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Location: Chicagoland
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looks like the sensor impacted on the flywheel or something.
have u verified spark on all 4 cylinders? verified compression on all 4/ |
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01-31-2010, 08:47 PM
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Join Date: Feb 2008
Posts: 18,795
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Quote:
I think that there might be something wrong at the cap and rotor. Are the wires on in the right order at the cap?
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dolor et pavor Copyright |
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01-31-2010, 09:25 PM
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well the cap and rotor are new and i check them and they both look fine to me(no cracks or corrosion). ill take pictures and posted them this week so you can see them.
the order is correct. but it only firing in one and four cylinder... it does fire in the third but it like only one spark and then it gone... but ill check the distance from the flywheel to the sensor and see where i go from there... ill replace either both or just that one bad sensor thanks guys |
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01-31-2010, 09:55 PM
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with the spark plug wires i had them in this order at first.. 1-2-3-4 for some reason idk why? but it still ran on 1st and 4th cylinder.... stupid me then i looked at the manual and the order i believe is 1-3-4-2 or something like that but i got it corrected and it still run on 1st and 4th cylinder...
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01-31-2010, 09:58 PM
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shiftdrfit944 is me as well i miss spell the first time i register so i made a new account
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01-31-2010, 10:37 PM
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Sounds more like a problem with the DME itself. I believe ignition output is handled by two transistors and paired up for the cylinders. I could be wrong and thinking of the fuel injection though... I have a schematic somewhere and I'll check later tonight.
That sensor is clearly hitting something, but as long as you can measure resistance across it then it should still be OK.
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-John '94 968 Iris Blue '85.5 944 White - Rally Cross and wrenching practice '84 944 Gemini Grey (gone, but missed...) |
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02-01-2010, 07:42 AM
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Join Date: Jan 2007
Posts: 2,444
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Yeah, it could be a broken solder joint in the DME at those driver transistors, but I can't remember either if that affects the fuel injectors or the ignition. The fuel injectors are driven in pairs, divided up between two transistors and all four are batch fired at once. Maybe it's a weak coil.
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1987 silver 924S made it to 225k mi! Sent to the big garage in the sky |
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02-01-2010, 05:26 PM
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well i order new reference sensor since one of them has no resistance when i checked it. so im replacing both of them.
HondadustR: yea i know the injector fire in pair but i have put in a new fuel pump in july and new dme/fuel pump relay. well it does start but i have to insert starting fluid in the intake then it start up but it run only on 1st and 4th cylinder and no spark to the others. i checked the resistance on the coil and its in spec |
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02-01-2010, 06:09 PM
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oh i got one question: could the oil pressure sensor prevent the car from starting? if it didn't notice any pressure it would tell the DME that there essentially no oil in the engine right?
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02-01-2010, 06:13 PM
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Redline Racer
Join Date: Jan 2007
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I'm pretty sure no. Sounds like it's a 90% chance that it's the crank sensor since it measured bad and it's only barely firing.
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1987 silver 924S made it to 225k mi! Sent to the big garage in the sky |
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02-01-2010, 06:21 PM
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shiftdrift944!If you are comfortable reading electronic cirquits go to Santos thread 944 non-turbo turns on and dies immediately.On page one you can find a drawing of the electronics. At the bottom of that side are the switching transis-tor...a Darlington one where the last of the two transistors switches the current to all four injectors at pin 14 & 15. Wires outside the injectors are paired cyl 1+2 & 3+4 and it may be possible that these wires are broken in some ways so that only cyl 1 & 4 will fire. I would definately check those cirquits with a multimeter (ohm). If it is a short here that Darlington transistor in DME will get damaged by the high short current so check wiring first. Good luck
 __________________________________ Lapponia 1984 944 NA |
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02-02-2010, 03:13 AM
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And, ohmic resistance in each injectors are 2,4 ohm, check that too with your multimeter.
So all four injectors parallelled is 0,6 ohm as I make out of it and that is a very low resistance here so a current limiting resistor is fitted in the line between Darlington transistor and pin 14&15. I believe that resistor is 10 ohm so total resistance makes 10,6 ohm and current will therefore make around 1,3 amps at 13,5 Volt over battery poles. __________________________ Lapponia |
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02-02-2010, 03:27 AM
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ok i got the sensor in today, and going to install them n check the distance with the old one with washer to the flywheel. and ill check the wiring to the injector and other thing
thanks Lapponia |
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02-08-2010, 09:44 AM
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ok new sensor installed and still it doesnt start? i check for fuel on the fuel rail and none!!! im going to jump the fuel pump to see if it just the dme/fuel relay. if so ill try to repair the old one or install the old one back on n see if it works
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02-09-2010, 09:57 AM
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did u properly install the sensors? they need to be gapped at 0.8mm from the flywheel....i think it was 0.8mm
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02-09-2010, 10:07 AM
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update as of today.... and running to rich..
yes i did gap them to right measurement .8mm i had to use to small washer but they added up to be .8mm
this are the two new sensor (bmw ones)...  but on the DG sensor (speed) i had to put a washer i made to be .8mm this was probably why the old speed sensor hit something...  this is a sheet of metal from a old radio shell... the bracket bolts were to tight and it was hard to get any leverage so i just adapt it to be a washer....  this is the speed sensor it to high up so the custom washer i made work fine!  so i had check the fuel rail for any fuel and it was empty i remove the nut... no fuel? so i use the relay jumper i made mines red but yea its the same as pictue below and it works...  then it started for the first time... but i turn it off and then there was no spark as i tried to start it again... then i remeber if the relay or jumper in this case is to hot it wont start up so i had my old fuel pump relay and hook it up and it started up fine... but now the car is running but its too rich... what could possibly cause the car to run rich? 02 sensor? |
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02-09-2010, 01:31 PM
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better pics of the old sensor i use to measure gap of .8 mm
 
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02-09-2010, 01:43 PM
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What ended up being the problem?
I have the exact same issue right now. No spark on cylinders 2 and 3. Car starts and runs but only on the two cylinders. Fuel injectors are spraying on all 4 New cap and rotor. Please help |
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03-10-2010, 10:11 AM
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Cochezz- well i got mine to run on all of them, well i can tell you what i did hope it helps
i check if the coil is good (coil resistance) turn out good i check the current going to the coil, injectors. oh i had a bad DME/computer that might be ur problem buddy you could try to replace that but idk? have you done a compression test on it?? you might have a bad head gasket, i replace mine but i still had the same problem after i think? idk but the new dme fixed everything till my bro was driving home from the shop it caught on fire! and i will also to check your fuel lines!!! and replace them if they havent been replaced |
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03-11-2010, 06:07 PM
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