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eldorado '91
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25 Posts
Discussion Starter #1
I have a 91 eldorado with about 149900 miles on it and I'm having what I would assume is a bad misfire. The car starts right up and idles fine but once it is in drive or reverse it vibrates really bad and upon acceleration it has no power at all. Sounds like absolute crap. And doesn't even want to shift out of first until about 3000 rpm at a slow increase of speed then shifts really hard. I've never had problems with the tranny so I doubt that is the problem. I replaced the plugs and wires about a thousand miles ago and has been running great after. The catalytic converter started rattling so I replaced it with a magnaflow direct fit and it ran awesome for about three days and now there is no power. It backfires at mid rpms so I know its not burning the fuel it needs to burn. I check the spark plug wires and two had melted due to exhaust manifold heat so I replaced the plugs and the wires but still nothing. I have no trouble codes and the misfire is not noticeable at idle in park or neutral but in drive or reverse under load it runs absolutely terrible.

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The fuel economy is horrible. The problem started one morning when I was going to work. I pulled onto a main road and accelerated quickly and it pulled fine until it hit second then it lost all power. I have no clue what is causing it. Any ideas? Any help is appreciated and this is my daily driver to and from work. I have to figure it out soon because I have been looking for a new job and have several interviews coming up this week and I would hate to miss them just because the car wants to throw a bitch fit
 

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eldorado '91
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25 Posts
Discussion Starter #3
I replaced the hall effect switch and ignition control module in the distributor last summer when I had problems with a high idle last summer. I could try and replace the cap and rotor. I'm just tired of throwing parts at this problem

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To the parts store I suppose...

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Oh yea that's a no on replacing the cap and rotor
 

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2010 DTS
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That would be my next move then. Remember, there is a gap, just like a plug gap, between the rotor tip and each spark plug wire tower contact that the spark has to jump as the rotor turns.
Over time, the cap contacts get spark eroded and the gap widens. When the gap gets too wide, the spark can't make the jump and you get poor performance. That's why you should always do all four, plugs, wires, cap & rotor. It's worth a shot and cheap enough.
 

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eldorado '91
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Discussion Starter #5
Sounds like a solid lead to me Ranger. Thanks for the tips bud. I'll pick up a new cap and rotor tomorrow and install it after work. I'll get back to you to let you know if it worked for me
 

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eldorado '91
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Discussion Starter #6
Replaced the cap and rotor and still misfiring. The ignition coil looked to have a shorted wire cause I could see burn marks on one of them. I replaced the ignition coil and now it runs but still really rough. It at least moves without stalling now. I don't know what is causing the problem. Any more ideas?

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Is it possible all the plugs are fouled now dude to the bad ignition coil?
 

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eldorado '91
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Discussion Starter #8
Well I pulled the plugs and all out covered in black soot and carbon so they are in my book fouled. Not wet but dry carbon. They iridium NGK plugs so are they too "cold" of a plug? Do I need to stick with the original copper plugs
 

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eldorado '91
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Discussion Starter #9
Cleaned the plugs up and placed them back in the engine and now it runs worse than before. It has to be an internal compression issue on one or more cylinders
 

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eldorado '91
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Discussion Starter #11
But what is causing it run rich is the real question. Can't be the injectors. Maybe a intake leak
 

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2010 DTS
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An intake leak would make it run lean.

Why can't it be the injectors? A leaky injector or two could cause your problem as well as the poor fuel economy you complained about. Likewise a leaky FPR.
 

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eldorado '91
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Discussion Starter #15
Ranger is there a way to test for a leaky injector with the on board diagnostics? And what part are you referring to at the FPR? I'm still new to working with modern engines. And as for the egr valve I'll check it out and clean it up a bit.
 

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Cadillac 1993 Deville 4.9, 1991 Eldorado Touring Coupe
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The EGR valve cheap enough and easy to replace and a good idea considering your mileage on the car. Mine just crapped out at 68k ...sputtering, misfiring, and operating temperature went up. A field service manual will show you how to do a power balance test and cut power to each injector.I dont have my FSM nearby to copy and post here or i would for you.the FPR is Fuel Pressure regulator
 

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There is a balance test you can do with the onboard diagnostics. You basically disable each injector, one at a time and see if one does not make a difference.
You could also listen to each one with a stethoscope, but these two tests will only tell you if one is inoperative, not leaking.
The only way to test for a leaker is to pull the fuel rail with the injectors attached, leaving it connected to the supply line, and then turn the key on, but do not crank the engine. This will pressurize the fuel system and you will see a leaky injector.
 

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2011 Crown Vic LX, 2009 Chevy Malibu 2LT
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You can also do a balance test the old fashioned way by simply pulling plug wires one at a time. Does the same thing.

The only way to check for a leaking injector without pulling them out is by using a fuel pressure gauge to measure any pressure drop. Even then, you have to systematically eliminate other leak points (FPR, pump check valve) before you can assume an injector leak.

That said, searching for a leaking injector is a bit of a jump of the gun. I'd probably start by using the onboard diagnostics to look at the fuel trims - telling you if you have a rich/lean misfire. Generally, a lean misfire will point you to an ignition, vacuum, or fuel pressure problem. A rich misfire will usually point you towards a pressure leak or a control problem.

That will help point you to your next test. If you start off with a 'test this, test that, maybe this, replace that' mentality, you'll spend a lot of time and money before you correct your problem.
 

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eldorado '91
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Discussion Starter #19
Sorry for the late reply work has kept me busy. I still haven't found the problem. I was double checking the plug wires and their firing order yesterday and I discovered a broken sensor right above the cylinder 8 spark plug hole. The connector was broken due to the plastic becoming brittle. I'm not sure what this sensor is but if its broken and my car is hardly running there is a high possibility the sensor could be my problem. I know its not the IAT sensor so is it the coolant temp sensor?
 
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