1993 LS 400 running on 4 cylinders
02-20-13, 08:50 AM
#1
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1993 LS 400 running on 4 cylinders
Rebuilt ECU, new coil packs, new crank sensor, timing belt OK. Car ran fine for 2 weeks the one morning started running on 4 cylinders. Check all of the above parts and they are OK. Tach needle jumping about. What signal drives the tach, and where is that device located? Is it from the coils, cam sensors or somewhere else? This is a great car but I do need all 8 cylinders.
02-22-13, 10:49 AM
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I just had to replace one of my coils this week. I had the same symptoms, just started running on 4 cylinders out of the blue.
Also, if the coils are cheap aftermarket ones, they might be bad even though they are new. I have also heard distributor caps and rotors can cause the same issue.
02-22-13, 06:40 PM
#4
I had an issue where after I replaced the wires the coil wire was getting pinched and it finally failed after a few weeks.
It was easy to miss when I put the covers back on and ran bad like 4 cylinders when it did fail.
It was easy to miss when I put the covers back on and ran bad like 4 cylinders when it did fail.
02-23-13, 02:18 AM
#5
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most likely: coil, coil wire, igniter, igniter wiring
a defective cam sensor would more likely to cause misfires than a complete loss of half the cylinders, but it is easy to tell if this is the problem: two scenarios:
A: if all of the cylinders not firing are on the same head (same side of engine) then it must be cam position sensor or cam position sensor wiring, but unlikely because ECU would turn on CE light and set code.
B: if the 4 cylinders not firing are all on the same distributor cap/coil, (cylinders not firing on both sides of engine) then it would be that coil, coil wire, igniter, igniter wiring, cap or rotor which correlate to that distributor cap & coil.
igniter, on the passenger side front fender
a defective cam sensor would more likely to cause misfires than a complete loss of half the cylinders, but it is easy to tell if this is the problem: two scenarios:
A: if all of the cylinders not firing are on the same head (same side of engine) then it must be cam position sensor or cam position sensor wiring, but unlikely because ECU would turn on CE light and set code.
B: if the 4 cylinders not firing are all on the same distributor cap/coil, (cylinders not firing on both sides of engine) then it would be that coil, coil wire, igniter, igniter wiring, cap or rotor which correlate to that distributor cap & coil.
What signal drives the tach, and where is that device located?
Last edited by LScowboyLS; 02-23-13 at 02:29 AM.
03-19-13, 06:16 AM
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Found Problem
It turned out to be the ignition coil wire on the drivers side. It was arcing when the covers were on. Installed new wiring and the problem is fixed! Thanks for the help.
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04-22-13, 04:46 AM
#8
07-01-15, 02:23 PM
#9
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Exact same problem - running on 4 - suddenly started one mile after removing and reinstalling instrument cluster. Will it hurt anything to disconnect one coil at a time and start the engine?
Never mind - not a coil. Not a position sensor. Think I killed the ECU when I pulled the instrument cluster without disconnecting the battery - then turned on the key to adjust the steering column. Almost wish Cowboy Bill from B'ham were still around to tell me what a dumbass I am - and to tell me how to diagnose a dead ECU.
Never mind - not a coil. Not a position sensor. Think I killed the ECU when I pulled the instrument cluster without disconnecting the battery - then turned on the key to adjust the steering column. Almost wish Cowboy Bill from B'ham were still around to tell me what a dumbass I am - and to tell me how to diagnose a dead ECU.
Last edited by TDIGREEN1; 07-03-15 at 10:02 AM.
07-03-15, 10:04 AM
#10
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Was a bad coil. Somehow I overlooked it on the first go round - not sure how but.... $60 and we're on the road again.
Last edited by TDIGREEN1; 07-04-15 at 07:43 PM. Reason: complete diagnosis
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