New daily driver help needed.....not a mustang but mustang drivetrain.

Wayne Waldrep

Before I post a pic, do you have one of yours?
20+ Year Stangneter :roc</strong><span class=
Apr 14, 2003
Cuba, AL
So.....Stangnet has permanently ruined me. Other auto forums just suck. :) Even ones specifically for said vehicle. So I am going to post this here and the powers that be can decide if it's ok or not. I hope I'm not causing a problem doing this but I take full responsibility if so....just let me know.

I bought a Honda CRV several years back after being talked out of buying what I wanted. The Honda bit the dust a couple months ago. Total transmission failure. Luckily I knew a guy that wanted it to fix. I got $3k for it and counted this as fortunate. Drove it for 4 years without any trouble. Paid $3400 when i got it. No worries.

Now I have a 1998 Grand Marquis. A friend of mine passed away and his family knew I needed a vehicle so they called me and sold it to me at a very good price. The car needed some clean-up and basic maintenance items. Had to be jumped off from dead battery. Car sat for a few months but luckily had almost no fuel in it. So here is my post pasted from the other site. This is all the info at the moment.

Note these few things before reading:
-The car run perfectly smooth at IDLE.
-The car run perfectly smooth on the interstate until you turn the AC on.
-No check engine light at the moment.

Post 1
Car history:
-Purchased from the family of a friend that passed away. He bought it with 71k.
-current mileage 139k
-I've had it a month and a half
-car sat for 4 or 5 months and was filthy but cleaned up perfectly
-cloth interior that's almost perfect

Initial repairs-tune up....(car had a miss when I got it and didn't really want to go even 65mph on the interstate.)
-new coil packs, spark plugs, pcv valve and hose, air filter, fuel filter, cleaned MAF & IAT sensor.
-oil & filter
-battery & battery terminals
-hood lift struts
-sway bar end links (not installed yet)
The car has a miss. That's why I did the plugs and coils. Didn't fix it. Code shows cylinder 2 misfire. Like most, it's when going up a hill and in overdrive the most. It's still there at other times but under load it's a bad shake. You can feel that it's ignition. Leaving the driveway and easing around toward the interstate you can't feel the miss.
After getting the code, I took one of the old coils and put it on #2 to see. Seemed to smooth out and I thought I fixed it. But once on the interstate at 55 or 60 it came back. I'm beyond frustrated. The entire reason I got this car was as primary transportation and not a project car. I still have the 88 Mustang GT that I bought new. That's my project car if need be. Not this one. I need this car to be dependable like these cars are known to be. The whole reason I picked one of these was to get away from the expense I had with the Honda. It was great until the trans died then it was terminal.
I really want to keep this car. I know the history. My friend sold me his 2017 Mustang GT wheels and tires that he recently took off and that saved me from having to buy the tires that the car needed. They look great and were cheap. Unfortunately, I don't have money to keep throwing at it. It's either going to be fixed or sold. I've been looking at these cars for several years and wanted one instead of the Honda but I was talked out of it. Now that I have one, I've worked on it every single day since I got it. That was not the goal. I saw plenty of these cars for sale that needed zero work. Ready to roll. I'm not ready to give up yet but I'm close.
The Honda forums were useless. They weren't car guys. Their favorite advice was "stop trying to fix it and take it to the dealer like you should." That was between their rude responses. Not for me. I like Stangnet because we don't treat people like that. You get one warning then booted.

Many thanks!

Ps... If y'all can help me get this fixed we will figure out the front suspension next. But I'm not putting another dollar into other things until the miss is fixed.

Post 2
I've done some more troubleshooting. I decided to drive the car to the next town over and see if I could isolate some of the roughness I'm feeling. 25 miles one way. I left the house and went a couple miles to the interstate. No radio or AC and windows up so I could hear everything. Got on the interstate and set the cruise to 70. Zero issues so far. Car shifts good and maintains speed. No missing at all. So with about 5 miles left I was getting hot in the car with no AC on so I turned that on. Instant missing, bucking, stumbling...whatever you want to call it. So I turned it off. Back to totally smooth. On the way home I decided to do the same. Drove half way home with AC off and car was perfect. The second I turn the AC on it starts running rough again.
So I got a buddy of mine that made his living as a mechanic (then went into the Army and retired from there as a mechanic) to stop by. He focused on the AC. Said it was perfectly smooth at idle and the clutch engaged exactly as it should....which was my observation as well. No unusual noises around or near the compressor. Engine runs smooth at idle with or without AC on. That lead us both to think the idle air control valve was working as it should. If not, the idle would have shown it. Again, I'm having zero problems at idle.
He suggested to turn everything off and go take off aggressively (not to the floor though) and see 2 things: How the transmission shifts and if the fuel pump is weak under load. Reasonable acceleration should show this I think. He thought maybe the fuel pump was weak and was just not firing the injector and causing the stumbling. I don't think this is it because the acceleration test was perfect. Shifted great and no missing at all. Not sure what else to look at. Hoping you guys will help.

He has a set of noid lights I'm going to borrow later but I think I've eliminated that. The car runs perfect until I turn the AC on. Oh, and the AC itself works just fine.

The day I got it.....

After a month of work

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Personally I think those are great cruiser daily drivers...
You seem to think #2 is a a problem.. Have you compression tested it??
Can you take the belt off and turn on the AC? That would make me think you could eliminate the compressor???? Or the load the compressor puts on the engine when turned on?

I hate Honda's... But if it cost you $400 for 4 years of service it did you good.....
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Thanks man. #2 misfire was taken care of. Remember one of my main runs perfect until I turn AC on. I don't think a compression test would help considering that.....right? The only creepy part of these cars is the spark plug threads issue. I don't want to fool with them unless totally necessary. But I will if needed. The compressor turns totally quiet btw.
Thanks Noobz!! :doh:

Hope my normal homies find it in there!! I need all the help I can get as this seems to be a difficult one.

They will. I left a link in the original forum so, it still looks like it's over there.

Only difference is that it doesn't [bump] in the old forum. They'll all have found it by then.
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You're in luck!

It just so happens that I thought of that already.

Moved to "Other" Auto Tech :p
and raised his subscription rate.
now you will need to log in with your user name and two different passwords :doh:
Or give me a pic of the dog house or engine compartment for you youngsters.
Surprised that computer does not spit out some code for that.
Would Fourscan help? I'll look for it
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Wayne, the car looks great! Nice score!

A point to remember with these cars. Most, or at least many, of the Fords of this era had torque convertor shake that feels just like a mis-fire. Happens just like you described the mis-fire, on the road at light load and climb a slight incline. Do a search and you will uncover a plethora of posts about this problem. Keeping good, synthetic fluid in them seems to get the best results. I've owned a couple of Lincoln Mark VIII's and other full-sized Ford-based cars of this time period. All had the issues after a period of time.

That doesn't solve the issue that happens when the A/C comes on. I'd give all of the wiring and the ECU a close inspection. It seems like something is causing electrical interference somewhere. The ECU's on our Mustangs / F-150's need new caps, I'm sure that the Mercury is no different.

Good luck finding resolution.
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Since your mechanic buddy thinks its the fuel pump, then at least check the Fuel pressure with AC off and on.
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Okay this is crazy. Its 4:00 in the morning and I can't sleep because I'm worried about this stupid car. I'm mentally depleted and I'm sitting here at 4:00 a.m.... been up all night.... Now posting this. I don't want to get sidetracked on some maybe it could be the lug nuts falling off. Or some crazy mess. The car runs and drives perfectly fine until I turn the AC on. Then it feels like it's not even going to make it home. I've never felt anything like this in a vehicle before.

The guys over at crownvic site have gone down a rabbit hole and aren't even telling me what to test.

Can we please just start from scratch?
The car runs perfectly fine up and down the road as long as I don't turn the air conditioner on. It shifts fine. It doesn't overheat. The second I turn the air conditioner on it starts what feels like a miss, a stutter, or something.
What exactly am I supposed to be checking? And what exactly do y'all think the car is doing to cause this stutter? I've got to have some direction to go in.
I apologize for being so frustrated but I have ailing parents to take care of and I need this car to work properly. I bought this car on 5/7/2024. Today is 6/19/2024. I have worked on this thing every single day and it has worn me completely out. I do not have the money to take it to the Ford dealership locally and let them fix it. The only one within 150 miles of me has the worst reputation of any service department I've ever heard of. For my own peace of mind or mental health or whatever you want to say I either have to fix this car or sell it but I cannot continue to stay up all night worried about it.
Again, my apologies for my desperation. I need some kind of intervention So if all of you brilliant guys could jump on a bus or plane and show up here, we will work on it all day long and get it fixed and I can be done with this. Because I don't think I can take another night being up all night long.

Thank you all for all the help.

So can someone please answer a different question? I was told there is a way to simulate the AC compressor running. I'm trying to eliminate it. It's blowing cold and sounds perfect at idle. So every time i turn the switch on inside the car it starts the crazy acting. My buddy mentioned using a diode in the connector at the compressor. The idea is, when you turn it on, the computer gives certain commands (cooling fan on, idle air bump up, etc). I want these to still happen but eliminate the compressor. This is past my knowledge enough to where i can't even find a YouTube video on it.
Can someone give me some help please? Thanks

@General karthief @Mustang5L5
Never had one of these cars so, everything beyond this point is speculation:

You have a vacuum leak.
It is activated by turning on the A/C
You need a vacuum diagram for that car so you can see what the hell is going on when put the controls in A/C.
Maybe a blend door actuator in/around the evap coil? :shrug:

Look at all your vacuum lines under the dash and against the firewall.
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I did try something to check what you are saying. I unplugged the compressor coil connector and drove it to check for something like this. Turned the switch inside to Max and norm and no shaking or jolting. I figured the rest of the system wouldn't know if the actual compressor was spinning or not.

Thoughts on that?
Right now I'd like to know how to jump, bridge or whatever you call it to the AC coil plug. I want the car to think the compressor is running. That will be so helpful.
I agree, you have a vacuum leak, and the effect is magnified by it occurring at cruise speed. Try and rig up a vacuum gauge with a long hose, and hold it in your hand while you drive, cruising, and turn the AC on. If it drops significantly, you have a vacuum leak somewhere in the plenum controls or door drives. If not, then you should check for codes on the ECU. Just because the CEL is not on doesn’t mean there are no issues. Just my 2 cents.
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