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1980 Eldorado Diesel 1995 Deville Base 4.9L
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9 Posts
Discussion Starter #1
Hey all. I did some searching around and nothing seems to make any sense to me. I bought this car 2 weeks ago and it ran okay but for hesitation when accelerating from a stop. At speed the acceleration was very strong.
The car has 105k miles on it presently.
Since the plugs were overdue I replaced the spark plugs, wires and rebuilt the distributor completely with new pickup coil, hall effect switch, module and cap and rotor and coil. All new parts for the ignition system.
The hesitation is gone completely but now it misfires horribly on cylinders 2 and 6.
I determined this by running the power balance check/fuel injector override PS04. Injectors 1,3,4,5,7,8 make the idle worse, 2 and 6 have no effect.

I replaced all 8 injectors and the regulator with new o rings everywhere. I mean new injectors. No remans or rebuilts. New injectors. The problem remains the same.
I have spark at 2 and 6 verified by my spark tester gapped at .060.
I used my computer safe test light and verified that the computer is pulsing the ground to the injectors like it should so I know the injectors are not shorted to ground.
Probing the harness all injectors ohm out at 12.1 ohms. Positive probe at one pink wire at a time and common probe at the grounds.
Spark plugs are Bosch double platinum plugs, cylinders 2 and 6 have been replaced with new NGK plugs with no change.
Spark plug wires are Denso.
I have no PCM codes set current or history except the battery power lost code when I disconnected the battery to take the fuel rails out.

I have to be missing something obvious. I have both factory manuals. If anyone has any suggestions I am all ears.
 

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Registered
1991 Cadillac Sedan deVille
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591 Posts
Probing the harness all injectors ohm out at 12.1 ohms. Positive probe at one pink wire at a time and common probe at the grounds.

I wouldn't use a common ground. Measure the injectors' resistance by moving both DVOM leads to the corresponding pairs of wires. Also, when did you measure the resistance - before or after engine warm up? Have you done both? Does the engine seem to act up after warming up or operating temperature doesn't seem to matter?

You mentioned, also, that you checked for pulsing, but have you listened with a stethoscope/screwdriver-to-your-ear to each of the injectors?
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,256 Posts
Hey all. I did some searching around and nothing seems to make any sense to me. I bought this car 2 weeks ago and it ran okay but for hesitation when accelerating from a stop. At speed the acceleration was very strong.
The car has 105k miles on it presently.
Since the plugs were overdue I replaced the spark plugs, wires and rebuilt the distributor completely with new pickup coil, hall effect switch, module and cap and rotor and coil. All new parts for the ignition system.
The hesitation is gone completely but now it misfires horribly on cylinders 2 and 6.
I determined this by running the power balance check/fuel injector override PS04. Injectors 1,3,4,5,7,8 make the idle worse, 2 and 6 have no effect.

I replaced all 8 injectors and the regulator with new o rings everywhere. I mean new injectors. No remans or rebuilts. New injectors. The problem remains the same.
I have spark at 2 and 6 verified by my spark tester gapped at .060.
I used my computer safe test light and verified that the computer is pulsing the ground to the injectors like it should so I know the injectors are not shorted to ground.
Probing the harness all injectors ohm out at 12.1 ohms. Positive probe at one pink wire at a time and common probe at the grounds.
Spark plugs are Bosch double platinum plugs, cylinders 2 and 6 have been replaced with new NGK plugs with no change.
Spark plug wires are Denso.
I have no PCM codes set current or history except the battery power lost code when I disconnected the battery to take the fuel rails out.

I have to be missing something obvious. I have both factory manuals. If anyone has any suggestions I am all ears.
------------------------------
try using a NOID light on the #2 and 6 injector plugs -
this will verify they are receiving the signal -
 

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Registered
1980 Eldorado Diesel 1995 Deville Base 4.9L
Joined
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9 Posts
Discussion Starter #4
Probing the harness all injectors ohm out at 12.1 ohms. Positive probe at one pink wire at a time and common probe at the grounds.

I wouldn't use a common ground. Measure the injectors' resistance by moving both DVOM leads to the corresponding pairs of wires. Also, when did you measure the resistance - before or after engine warm up? Have you done both? Does the engine seem to act up after warming up or operating temperature doesn't seem to matter?

You mentioned, also, that you checked for pulsing, but have you listened with a stethoscope/screwdriver-to-your-ear to each of the injectors?
I meant the COM or Negative probe lead on the multimeter, my mistake. Resistance was cold only. It misfires at all temperatures and all speeds. When it goes to closed loop, the RPM drops from bouncing around 825-900 RPM cold to 525-600 RPM hot. It switches to closed loop between 155 and 158F coolant temp. I will try the screwdriver trick next.

----------

Hmm. I will rent a NOID set and fuel pressure gauge tomorrow.
 

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Registered
1980 Eldorado Diesel 1995 Deville Base 4.9L
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9 Posts
Discussion Starter #5
Update. Passes NOID light test, light only lights up when it is supposed to and pulses normally on 2 and 6. One thing I did notice is that although my spark tester gets a blue spark, the plug itself strapped to the strut brace gives me an orange intermittent spark. I have a set of new Delco wires and plugs cap and rotor waiting on me at the parts store and I will swap those tomorrow along with triple checking the base timing.
 

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Registered
1991 Cadillac Sedan deVille
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591 Posts
Hm... the terminals for cylinders 4 and 6 on the distributor cap are right next to each other. Go out there and see if the cap is uniformly seated on the distributor base and all the screws are tightened well. It's been a couple of times I've had to chase problems from a cap not seated/bolted well. That might as well be your case. Also, while you're there, make sure the ignition coil also has all of the screws tight.
 

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Registered
1980 Eldorado Diesel 1995 Deville Base 4.9L
Joined
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9 Posts
Discussion Starter #7
Replaced cap and rotor along with Delco wires and plugs. Issue is mostly gone. Only #6 misfires now. I knew it had to be ignition related, ill reset the base timing and make sure I get a spark pulse on #6 with my inductive light. It runs a lot better on 7, but I want all 8 jugs online.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,256 Posts
Hm... the terminals for cylinders 4 and 6 on the distributor cap are right next to each other. Go out there and see if the cap is uniformly seated on the distributor base and all the screws are tightened well. It's been a couple of times I've had to chase problems from a cap not seated/bolted well. That might as well be your case. Also, while you're there, make sure the ignition coil also has all of the screws tight.
==========================
the terminals for cylinders 4 and 6 on the distributor cap
are right next to each other.

I don't think so -
the firing order of the 4.9 motor is 1-8-4-3-6-5-7-2-
 

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Registered
1991 Cadillac Sedan deVille
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591 Posts
==========================
the terminals for cylinders 4 and 6 on the distributor cap
are right next to each other.

I don't think so -
the firing order of the 4.9 motor is 1-8-4-3-6-5-7-2-
For some reason I thought it was 1-8-4-6-3-5-7-2 :bigroll:. Thanks for the correction!
 

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Registered
1980 Eldorado Diesel 1995 Deville Base 4.9L
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9 Posts
Discussion Starter #10
Welp I am embarrassed to say I found the problem after all. The number 6 injector connector was loose after I put the rails back in for the NOID light test. Unfortunately I have to pull the rails again to re-seat the connector and maybe angle it a touch to the left a bit to clear the valve cover this time eh? I only found this out after deciding to probe all injectors while the engine was hot and all showed 13 ohms except for 6 which was open. I knew it had to be something simple. Thanks for all the advice guys!
 

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1991 Cadillac Sedan deVille
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591 Posts
Good to know you found the cause :)

You can try to rotate the injector while it's seated with the fuel rail on the engine. The o-rings are lubricated so no worries there, but be gentle when you do it.
 
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