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engine misfiring at start up


WRS'99STS

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Hi all, It has been awhile. The old girl has been running smooth for many years with no problems. Until now.

I am having a misfire on cold start. It only lasts a minute or less, then smooths out. Doesnt happen again until the car has set for several hours. I have talked to several mechanics. There responses vary. One thinks it is the spark plug wires, or plugs. One says it is the egr valve. One thinks it is injectors. Any one else had this problem and would like to help me out?

It is a '99 STS with 82000 miles.

Thanks for any help.

Wayne

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I want to watch your thread, I am having the exact same problem. I have a strong fuel smell from the exhaust. I am going to lift my fuel rail and pressurize it this weekend, to see if any of my injectors leak on pressurization.

If you find a solution please post it

I changed my plugs, ignition wires and cleaned my EGR valve

You can review my long thread, search for the word SCARY...... and you will find the thread, SCARY is in the topic line

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I am having a misfire on cold start. It only lasts a minute or less, then smooths out.

That is one of the early head gasket symptoms. Are you using any coolant?

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I am having a misfire on cold start. It only lasts a minute or less, then smooths out.

That is one of the early head gasket symptoms. Are you using any coolant?

I am not using any coolant. I have noticed a wierd smell from the exhaust. I did add a can of Restore fuel system cleaner thinking that it might be injectors. I think that is the smell.

Wayne

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Well, if you are not using coolant, that is a good sign. The only other thing I can think of is fuel like BBF said. Have you checked the FPR for a leak?

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When you have the miss, smell your exhaust to see if you smell fuel.

I have vascillated between having a head gasket problem and not having a head gasket problem. I was about a half of a gallon of coolant low at the end of the winter....

My number 1 and 3 plugs had a white burned deposit on them

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I have the same issue, periodically. First start of the morning, the car fires up, and has a slightly 'off' idle. Once in gear, it really feels like a nasty misfire/bucking until I give it some throttle. After warming up for a few minutes (usually before I'm out of my driveway), all issues are gone.

I'm not using any coolant, overheating, or smelling anything odd out the exhaust. However, I did discover that my initial rough idle completely disappears when I turn off the A/C! If on my 'cold start' she starts to run rough, I'll punch off the a/c, and the motor goes to running totally smooth and even. Turn the a/c back on in a few seconds, and she runs fine. I haven't really had the time to play around, but I'm assuming the roughness is my A/C compressor adding some sort of bizarre load to the drivebelt or engine. Maybe this weekend I'll take a look.

Try turning off your A/C when the car is acting up, see if that affects it. I still haven't got to (or anywhere near) the root of it, but I'm assuming (in my case, and perhaps yours!) the problem is compressor-related.

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If it's backfiring through the intake manifold chances are it's the Fuel Pressure Regulator ("FPR") as Ranger suggested. Also, if you see white smoke coming from the intake manifold then this is the same symptom I experience with a defective FPR.

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Codes anyone?

:unsure:

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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I have a similar issue, minor but shouldn't be there.

P0171 - Fuel Trim System Lean Bank 1

I used my new scanner (more on it later) to track down the problem. At this point it appears to be the sensor failing. I am going to do more investigating to verify the cause.

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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Hi all, It has been awhile. The old girl has been running smooth for many years with no problems. Until now.

I am having a misfire on cold start. It only lasts a minute or less, then smooths out. Doesnt happen again until the car has set for several hours. I have talked to several mechanics. There responses vary. One thinks it is the spark plug wires, or plugs. One says it is the egr valve. One thinks it is injectors. Any one else had this problem and would like to help me out?

It is a '99 STS with 82000 miles.

Thanks for any help.

Wayne

Wayne,

A little educated guessing here, at 82,000 miles, your spark plugs could certainly be due for replacement. Yes, I know some may brag of spark plugs that last forever, but each car, driver, and driving conditions vary a lot. You are close to the recommended time for replacement so it is reasonable to expect them to be worn, or to have lost a platinum pad or two. (AC Delco 41-950 with .050" gap)

The spark plug wires are a bit more "iffy". With the engine running, take a look at the wires in a dark location; you are looking for arcing. Then spritz the wires with water from a spray bottle, to see if arcing appears. Arcing under either condition indicates the the wires are leaking and should be replaced. I would use AC Delco wires, not the on-sale sets commonly advertised as just as good. (online AC Delco's are priced at about $108 for a set)

Another thing to check, is the intake manifold. I was doing a little checking over on my DTS, tightening screw clamps, checking belts, etc. And I decided to check under the intake cover (just curious) and when I checked the intake manifold bolts, they were ALL loose. I gave them about a full turn + to get them secure. While the engine ran fine normally, I had noticed a little bit rougher idle in the morning. Almost all of that is now gone. The intake was leaking enough to upset the fuel mix at low engine speeds, but not a noticeable problem while cruising.

You could also clean the MAP Sensor. Carefully unplug and remove the sensor from the intake tube. Get an aerosol can of MAP Sensor Cleaner, and thoroughly spray the sensor grid clean. Do not touch the sensor grid with the spray straw, the grid is easily damaged. Also spray the electrical connection clean to be sure that it is making good contact. Allow to dry before putting back on the car.

Don't forget to replace the intake air filter if it is necessary.

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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UPDATE

Yesterday, I called the local Cadillac dealer to get it diagnosed. They said bring it in and leave it. When I got there, I was told that They needed me to leave it overnight to experience the misfire. However they are booked for several days. I asked abouth the head gasket issue and was told they have not had any in for that problem. They could put plugs, wires and add all kinds of parts until fixed. I was not happy, This dealership's service dept has a bad reputation for doing that. I then went to a recommended locally owned repair shop. There service writer was very familiar with the N*. He told me that he was 99% sure that it was the head gasket starting to fail. He said that when the car sits overnight, the cooling system hot, and under pressure forces vapor in the cylinders that are effected. When started cold, it takes time for the pistons to force the vapor out before the spark plugs can again spark the fuel. Does that make sense? He told me in this early stage to get some Bar's Leak Head Gasket fix and trade off the car.

There are no codes at all.

I am not sure what to do. I have been sure to flush the cooling system every 3 yrs and have always added the pellets.

I love the car, but don't have $4500.00 for new head gaskets, quoted by the dealer. I would not take the car to the local dealer to do the work, I don't trust them.

<_<

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"...He said that when the car sits overnight, the cooling system hot, and under pressure forces vapor in the cylinders that are effected. When started cold, it takes time for the pistons to force the vapor out before the spark plugs can again spark the fuel. Does that make sense?..."

Yes. But this is not necessarily your case. Coolant leaks can be detected by sampling the coolant for carbon byproducts. Some automotive stores carry these inexpensive kits.

Regarding the dealership, they have all of the tools to properly diagnose your car in a fairly straight forward manner. Throwing parts at the car, is expensive, and is NOT the way to fix it. The dealership should not be following you advice as to what needs to be done to fix the car. They should listen carefully to your description of the problem, test the vehicle, tell you what is wrong, and then get either your authorization to repair the car, or return it you.

For what it's worth; from my past experience, a friendly, and informed attitude can go a long way to getting the dealership to work with you. If you come across as a know it all, or adversarial, they can be a real pain. If they are not helpful, just do not let them have your business.

As for the spark plugs, wires, etc., I was assuming that you would be doing those items. Please try the items that I have suggested. They are free or very low cost, and see if they improve the condition.

I would not advise flushing the coolant system on these engines. Just drain what you can, and replace with the proper coolant mixed at 50%. Flushing can exacerbate existing conditions.

The Bars Leak Gold is a good coolant system leak preventive, but it will not stop a cylinder pressure leak into the cooling system. It stops coolant from leaking out the radiator, hoses, heater core, etc. Once a leak (small channel) is going from the cylinder to the cooling system, the only way to fix it is by replacing the head gasket; as the metal is gone.

If you decide to sell the car, I would not tamper with the existing conditions, you could make it worse. Now is a good time to use it as a trade-in for a later, or new model vehicle.

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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[i Please try the items that I have suggested. They are free or very low cost, and see if they improve the condition.

Thanks for the info George. I just finished the map sensor cleaning, throttle body cleaning The spark plugs and wires look to be ok. The intake manifold bolts were also loose. It is running much better. Time will tell if the problem is solved.

Thanks again. I will report results later.

Wayne

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Yes, as Growe3 said, that is the scenario for early HG failure, BUT that does not automatically condemn them. Get the block test kit from Napa to confirm or rule it out. Then make your decisions from there.

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UPDATE

He said that when the car sits overnight, the cooling system hot, and under pressure forces vapor in the cylinders that are effected. When started cold, it takes time for the pistons to force the vapor out before the spark plugs can again spark the fuel. Does that make sense? He told me in this early stage to get some Bar's Leak Head Gasket fix and trade off the car.

<_<

In a couple of hours the coolant will cool down and the pressure will drop. So, whatever happens happens in a couple of hours. Why leave it overnight? You can try to relieve the pressure when engine cools down (carefully) and see if it misfires right after that or in the morning.

Trading off a car with KNOWN and intentionally hidden very costly problem. Nice recomendation. :rolleyes:

The saddest thing in life is wasted talent

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You have to love people's poor ethics these days

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Trading off a car with KNOWN and intentionally hidden very costly problem. Nice recomendation.

Just for the record, I felt the same way and thought, do I want this guy messing around with my car?

If the problem does turn out to be the HG, I will come up with a way to get it fixed, or donate the car to a highschool or college auto mechanics program. I could not live with myself If I sold or traded it knowing that it had a blown HG.

It started up fine this morning, no misfire and ran great for a nice Sunday drive.

Thanks everbody for your help and suggestions.

I will let you know what happens.

Good Day All

Wayne :)

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