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Discussion Starter · #1 ·
I have been through all the posts on the board and can't find a solution to my problem. The car has been in the shop for 1 week and the mechanic phoned yesterday and said to come pick it up as they could not find the problem.

1996 Mercury Sable U-3.0L 160,000km

Symptoms: Initially misfiring on 2-3 cylinders in idle, park and neutral with SES. Now frequently misfiring throughout all gears with a constant flashing SES. I don't know which cylinders are misfiring but the problem is getting worse.

Work Done: Replaced camshaft sensor, crankshaft sensor and Egr backpressure sensor (the car had recently failed aircare with high NOx emmissions). These all showed as error codes and I don't know what is showing now. The speed sensor was replaced a couple of weeks ago.

Engine compression is normal, sparks & plugs are normal, no obvious loose electrical connections. The car idles at 600-700rpm and hesitates on acceleration.

My only other option here seems to be Ford and they can't even look at the car for another week. I do have a GM mechanic who said he would spend an hour on the car and let me know if he was even interested in going further into it and he can't look at it till next week.

Any advice you can offer me will be greatly appreciated.
 

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The first action I'd take is to pull the spark plugs. Are they worn out? But most importantly, HOW DO THEY LOOK? If you could post a picture, that would really help - especially if one or two plugs look different from the rest.

Trying to troubleshoot a misfire problem via a Bulletin Board can be a challenge, to put it nicely. :p But we've got to find the problem before it can be fixed.
 

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Alberto from American Motorsport might be able to give you some insight into what the PCM might be doing if it is related to the misfire problem. He's got a pretty strong technical background. You can usually find him hanging out in the EEC Tuning section of the performance forum.

-Dan
 

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To me it sounds like a mass air flow sensor problem... check that its connected for one and not loose. Make sure there isn't any crud on the sensor wire, maybe you could pick up some sensor cleaner. But being that I don't know what the codes are or anything.... its hard to come up with a solution. But I'm leaning towards MAF....
 

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Discussion Starter · #6 ·
Thanks for all your replies.

The spark plugs and leads are fine according to our mechanic.
I will try to hunt down Alberto.
The MAF is spotless and securely plugged in. I will get a volt meter and test it.

I will find out what codes the car is showing after the GM mechanic has a look at it and hopefully they will be of some help.

I have been in contact with another member on the board that had the same problem with a 96 Taurus in June and their's is still not resolved. Yikes!
 

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Which codes did you get, telling you it's misfire? Might make a difference. I, too, have a '96 Taurus, but it runs fine. For now. So, I have a vested interest in this problem too, just in case!

Did some searching, came up with the possibilities of a vaccum leak or PCV failure.
 
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Codes will definitely help us solve your problem. Get the numbers (Autozone even does this for free), and post them up here. We'll get it solved, there's a lot of knowledgable people on here to help you out!

For now, here's some common misfire problems I've had with Vulcans (the code U engine in your car):

Plugs- If they're not Motorcraft, that could be it. I had a hell of a time with Bosch plugs, and since they were new, I never thought they were the problem.

Wires- Make sure they test them for resistance. A good rule of thumb is 5k ohms/foot.

Vacuum leaks- this will usually cause a misfire, and also codes for both banks running lean.

Some recommendations:

Check all the plugs, as mentioned. Pay particular attention to the number one plug (rear bank, passenger's side from the front of the car). Most of the Vulcans I've worked on with blown head gaskets have failed on the #1 cylinder, causing problems like you've mentioned. In most cases, compression was fine also, the gasket was just starting to go, depositing coolant on the plug causing it to foul out.

When the cam sensor was replaced, make sure they only did the sensor, and not the body. If they did the body, it needs to be timed. Moving the body changes the injector timing, and will cause misfires.
 

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Discussion Starter · #9 ·
Thanks again.

I do have some reservations about the cam sensor. The complete unit was replaced as they had to chisel the old one out. They also asked me to drop off the Haynes manual to show them how to adjust it. The engine was misfiring when we took it in so if the sensor was bad then is still might not be working properly.

The engine has now started intermitently misfiring through all gears and the SES is flashing constantly. The problem is getting worse.

I will ask this new mechanic to check the cam sensor and I will find out what codes are showing now and post them.

Thanks again for everyone's help.
 

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Discussion Starter · #10 ·
I still don't know what codes the engine is throwing, but the latest mechanic to look at the car thinks the timing belt has slipped, causing the engine to misfire. He is doing this work in his off time so it will be a couple of days before we know for sure.
 
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There's no timing belt on this car, it's a chain and sprockets. It's also pretty uncommon for it to slip, but it's not a bad idea to check it anyway.

Since the first guy that called to ask you how to set the cam position sensor seemed to not know what he was doing, I'd guess it's a problem with that.
 

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Discussion Starter · #12 ·
Thanks again everyone.

The timing chain and sprockets are fine. I asked the mechanic about the codes and be said they were meaningless because there is low or no engine compression after ignition. The compression is fine during startup.

He said the cam sensor appeared to be adjusted properly and the previous mechanic said the injector spray pattern was normal.

I have no way to check the cam sensor myself and it looks like the next stop is the Ford dealer. I am hoping this additional information may help pinpoint the problem. I really appreciate everyone taking the time to answer my posts. I wish I was more knowledgeable about the newer cars. My automotive experience is restricted to helping my son work on his 1983 Chevette. Not quite the same league.
 

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Originally posted by Brian@Jul 16 2004, 01:35 PM
I asked the mechanic about the codes and he said they were meaningless because there is low or no engine compression after ignition. The compression is fine during startup.
This confused me.

I know of no way to test the compression of an engine once it's started. Was he looking at a vaccum gauge, maybe?
 

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[I asked the mechanic about the codes and be said they were meaningless because there is low or no engine compression after ignition. The compression is fine during startup.]


Being a mechanic at a Ford dealer myself, i must say that your mechanic sounds like an idiot. Codes are never meaningless - they are set for a reason, and a flashing SES (opposed to one that is on steady) means that the problem is serious and could damage the cat converters. I recommend not drivng the car at all, or very little if you have to, and get it to the ford dealer ASAP. Obviously, the other guys you've taken it to don't have a clue. The most important thing to do to start, especially when the SES light is on, is to get the codes - they will point you in the right direction to start properly diagnosing the cause of the problem. Also - the cam sensor won't cause a misfire - it's only used to time the fuel injection, not the spark. Spark timing is taken only off the crank sensor - so you probably changed that cam sensore for nothing. Have they checked the coil pack? You said the plugs and wires are fine, but what about that? Is doesn't sound like a vacuum leak, since the car would likely idle higher, and maybe have a fluctuating idle as well. And like the other guy said, you can't check engine compression with it running, only with the plugs out, and cranking. You can do a relative compression check with the engine running and using the proper scan tool - i've done this many times. But all that test does it tell you how the compression of each cylinder is in comparison with all the others, expressed as a percentage. It doesn't tell you what the actual compression pressure is.

Anyway, if you wanna try to tackle this yourself, first find out what the codes are, and post them all, in the order they appeared on the code reader, and we'll try to help you from there. If you are going to take it to a shop, please go to a ford dealer, and stop using these other guys, who seem to have gotten their licenses from a Cracker Jack box. From what you say they are telling you, they aren't fit to work on lawnmowers, let alone cars. Sorry to sound like a jerk, but it's dumba** mechanics like those guys who make the rest of us look bad.
 
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