My Turn.(Limp home mode? - rv)
11-05-2008, 12:12 PM
#46
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11-05-2008, 01:00 PM
#47
Rennlist Member
As noted it does NOT shut down one bank but 2 cylinders on each bank those which are on the same coil, same distributor cap. Also running on 4 cylinders is NOT LIMP HOME MODE !! Driving on 4 cylinders is said by Porsche to be very hard on the drive shaft inside the torque tube. Porsche felt the need to add that system in 1989 because the dual ignition cars ...(two coils ) were sometimes experiencing a failure in one circuit. The car would run poorly have little power BUT BIG BUT people would still try to "limp home" so with four cylinders not firing and pumping unburned fuel and air into the exhaust the catalytic convertor would glow red hot and the undercoating would catch on fire and the flames would burn up everything on top of the engine. So to avoid that stupidity Porsche added the protection circuit to shut of the injection to those 4 cylinders 2 on each side) which were not firing. However like any other device which can shut off it sometimes will fail and do it at the wrong time.....it is after all a RELAY getting information from temp sensors which passes through wires ! The real limp home is a stored program in the LH computer which under certain failures of the mass air sensor allows the engine to run at low engine speed without the information from a mass air sensor.....which is why most cars will run with a disconnected MAF just not rev up well . Just run well enough to pull off the freeway.
87-95 928s have a limp home mode (MAF related, but stored in LH computer)
87 & 88 928s do *not* have an intentional 4 cylinder mode
89-95 do have an intentional 4 cylinder mode
...and a good place to start looking for the 4 cylinder mode problem is first in the coils on all 87-95, then in the 4 cylinder relay on 89-95s?
11-05-2008, 01:09 PM
#48
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84 Euro , 85-88 32 valves have NO safety feature for ignition failure. Also several 89 > cars have had the relay BYPASSED rendered inoperative and they could have issues with cat fires if they have a cat 
and are driven with an ignition failure of one coil , one coil wire , one secondary stage.
and are driven with an ignition failure of one coil , one coil wire , one secondary stage.
11-05-2008, 04:30 PM
#49
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When examining the ignition system on my car, I traced the wires from each coil to each cylinder/spark plug, and it looked very much to me like the passenger-side coil fed all four passenger-side cylinders (1, 4, 6, 7), while the driver-side coil fed all four driver-side cylinders (2, 3, 5, 8). I did not see any spark plug wires crossing the engine, so I do not believe the above-quoted statement can be true - how can "two cylinders on each bank" be running off the same coil if the coil wires don't cross banks?
Or am I Just missing something?
11-05-2008, 04:39 PM
#50
Team Owner
your answer is in your own numbers each distributor cap holds the plug wires for 2 cylinders on each bank. The wires cross in front of the water pump
engine firing order
DS passenger side
5 1
6 2
7 3
8 4
What is getting shut down are the fuel injectors not the ignition systems
engine firing order
DS passenger side
5 1
6 2
7 3
8 4
What is getting shut down are the fuel injectors not the ignition systems
11-05-2008, 04:44 PM
#51
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One coil does feed Cyl 1,4,6,& 7 and the other does feed 2,3,5,& 8. That is clear But cyl are 1-4 front to back , passenger side (LHD) and cyl 5-8 are driver's side, front to back.
Suggest you trace the wires again.....
Suggest you trace the wires again.....
11-05-2008, 05:21 PM
#52
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I learn something new about these cars just about everyday even after like 16 YEARS of doing this as a full time job and playing with my own 928s as a hobby. Sometimes what I learn is that I was wrong Just not this time. But please do ..."I am questioning authority..." it helps keep everyone accurate.
Just not this time. But please do ..."I am questioning authority..." it helps keep everyone accurate.
11-05-2008, 05:26 PM
#53
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When examining the ignition system on my car, I traced the wires from each coil to each cylinder/spark plug, and it looked very much to me like the passenger-side coil fed all four passenger-side cylinders (1, 4, 6, 7), while the driver-side coil fed all four driver-side cylinders (2, 3, 5, 8). I did not see any spark plug wires crossing the engine, so I do not believe the above-quoted statement can be true - how can "two cylinders on each bank" be running off the same coil if the coil wires don't cross banks?
11-05-2008, 05:43 PM
#54
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My 1970 Maverick has a later 302 V-8. Ford uses two different firing orders for small block engines. The prior owner used the wrong one AND managed to cross two of those wires in the process. Needless to say it did NOT run well when I bought it ! Which is good because he sold it real cheap......although he wore out the starter motor trying to make it run and adjusted the crape out of a dirty plugged carb
11-05-2008, 06:34 PM
#56
Racer
Maybe this helps in getting clarity?
http://jenniskens.livedsl.nl/Technic...5/MyTip552.htm
Regards,
theo
http://jenniskens.livedsl.nl/Technic...5/MyTip552.htm
Regards,
theo
11-06-2008, 07:44 PM
#57
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Replaced MAF today....didn't fix the problem. I had a friend monitor the relay in the footwell while I tried to start . He said the Green LED was flickering on and off.
11-06-2008, 07:49 PM
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As for the coil wires...they're new. When timing belt/wp job was completed a few months ago, all new plugs, wires, and rotors. the only problem, one of the plugs wouldn't come out.