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Discussion Starter · #1 ·
We have a 1994 Mercury Marquis. Problem is when she starts and is cold, she has no power, backfires and is just a plain old slug. Give her about 2 miles of driving this way, or a 5min warm up session and she then runs great. I've given her new plugs, wires, air and gas filters, had her scanned (came back good) and a direct, high pressure injector cleaning with no luck. Mechanic that has had her has told me twice that she is fixed and should run good and I have had to take her back just as many times because she is not.

Any ideas or things to look for?
What about a cold oxygen sensor?
 

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Call up Harry & Sons and tell them to warm up the crusher. <_<
 

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QUOTE(PyrateJim @ Mar 5 2004, 09:01 AM)Any ideas or things to look for?
What about a cold oxygen sensor?
O2 sensors typically do not affect engine operation when cold or on startup. They provide feedback only after warm up. So that's probably not it.

possibly EGR, or maybe AIS (automatic Idle Speed) motor (aka stepper motor) The EGR would not set off a light. It also might be something as simple as a vacuum leak. That would confuse your computer as far as how much load you are putting on your engine. Does it backfire through the exhaust or the intake?
 

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The more I think about it the more I want to say vacuum leak or EGR. In both circumstances, after the O2 sensors start providing feedback, the engine would straighten it's self out.
 

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It's hard to say. It could also be a faulty coolant temp sensor which would cause the O2 sensor to richen or lean out the fuel mixture, causing the engine to stumble and back fire.
Good luck.
 

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How many miles are on it? Is there any fuel or fuel vapors in the oil? It could be wear. When the engine comes to temperature, it would cause the pistons/rings to expand and reduce the blow-by and restoring compression. This is probably unlikely, I would check the other suggestions first, but is a possibility.
 

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Ihad same problem with sunbird doing same thing after it being in the shop and them saying it’s fixed after replacing o2 sensor s 3 times map sensors. Then saying it was a switch in the transmission and having that replaced. And 2,500 latter it still wasn’t right. I took it to the dealership and traded it in on a new one. I made sure it was warm and running good for them to test drive, before I traded it in. I gave up on it figured who ever the dealer sold it to could come back on them to get it fixed that’s why I didn’t sell it my self. Good luck I know it can be frustrating,
 

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QUOTE(HazyMemory @ Mar 5 2004, 09:25 AM)possibly EGR, or maybe AIS (automatic Idle Speed) motor (aka stepper motor) The EGR would not set off a light. It also might be something as simple as a vacuum leak. That would confuse your computer as far as how much load you are putting on your engine. Does it backfire through the exhaust or the intake?
The check engine light does come on, but then will go off. Very sporatic. Can almost make it go on and off by accelerating or flooring it and then letting off the peddle.
Backfire seems to come fro the intake as I am getting nothing from the exhaust.
 

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QUOTE(PyrateJim @ Mar 5 2004, 02:18 PM)QUOTE(HazyMemory @ Mar 5 2004, 09:25 AM) possibly EGR, or maybe AIS (automatic Idle Speed) motor (aka stepper motor) The EGR would not set off a light. It also might be something as simple as a vacuum leak. That would confuse your computer as far as how much load you are putting on your engine. Does it backfire through the exhaust or the intake?
The check engine light does come on, but then will go off. Very sporatic. Can almost make it go on and off by accelerating or flooring it and then letting off the peddle.
Backfire seems to come fro the intake as I am getting nothing from the exhaust.
Ok, without looking at it, I would say that it seems to be running lean. See if you can find a loose vacuum line or maybe the gasket under the throttle body has a vacuum leak. Do you know how to check for a vacuum leak??
 

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Discussion Starter · #10 ·
QUOTE(HazyMemory @ Mar 5 2004, 01:46 PM)Do you know how to check for a vacuum leak??
I'll take some instruction here.
 

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If you are mechanically inclined at all, you should be ok. If not, give me a call.

Does the car seem to idle high at all?

With the car running at idle, can you hear a whistle or a sucking that is identifiable? If so, try to stop it with a finger or a pair of pliers.

With the car running at idle, take a water mister and spray around the intake manifold, throttle body and power brake booster area staying clear of the generator and the atmospheric side of the throttle body. Pay close attention to the engine speed as you are doing this. If it noticably slows, you have found your leak. Try to stop it with a finger or a pair of pliers.

If neither of those two work, try each of them again idling in drive with a helpers foot securely on the brake.

If this does not make sence or you do not know any of the parts that I have referred to -- don't do anything and call me or someone else.

I hope that helps.
 

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Discussion Starter · #12 ·
Hazy,
Yes it does make sense and I do know what you are talking about. I'll give it a try. The car does not seem to be idleing fast when first started up or even after she has warmed up.
 
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