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AC / Heat / Idle issues 1989 Mercury Grand Marquis


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finster
New User

Aug 25, 2016, 5:17 PM

Post #1 of 10 (869 views)
AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

OLD PROBLEM:
I had a suspected vacuum leak in my Grand Marquis as when I accelerate the AC would cut out. Idling is a little uneven and sometimes will accelerate faster than it should. I found a vacuum leak at the hose connecting the MAP sensor but patching it didn't completely solve the problem. I cant find other leaks but I think they might be there. I tried using carb cleaner and replacing as many vacuum lines as I can but no joy.

NEW PROBLEM:
I have since replaced my heater core as it previously had a leak and had been capped off. Now I have heat but no AC. I'm not sure if the heat is overpowering the AC but with the blower on it is blowing hot air even with the temp set to minimum. Also, when accelerating heat starts to flow through the vents even with the blower off.

Using an OBD 1 diagnostic code reader I get an error "EGR Valve not opening properly". Could this be the problem or could the error a symptom of a vacuum leak elsewhere? The EGR valve was replaced a couple of months ago.

Is it likely the same issue as before with the addition of heat into the equation or have I added a separate issue while replacing the heater core?

Any help would be greatly appreciated.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 25, 2016, 11:24 PM

Post #2 of 10 (852 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

It's still around so must be in decent shape in general, right?


IDK - finding vacuum leaks. #1 - almost all of these the small soup can on driver's side wheel well under hood will rust out where it's clamped at bottom. New not available but you can seal it up and paint it. Those are 9mm nuts from inside seen above wheel from outside over tire. They will break. Can use a long wire tie unseen thru existing holes if so.
Another is PCV grommet down back near firewall. NAPA can get next day still. Not maybe, if never done it's bad.


EGR - Try cleaning it. Carb cleaner with it off and pushing on pintle. New gasket needed if not covered in anti-seize or high temp silicone gasket maker can re-use those later.
What possible disasters happened doing a heater core? Did parts fit right and seal tight? They have to if you make or fix parts so they do. Heat will always overcome any A/C system if mixed in.


Other bull on these: Just checking trans fluid level you can bust up those plastic vacuum lines. Fix with rubber hose if broken. All those things matter.


Code readings: Take any with a grain of salt meaning they don't know much and will send you off in the wrong direction. Pretty much forget codes and find vacuum problems that will set off all kinds of misleading codes.


This is a tough, gutless wonder of an engine. Own just two now! One is an '89 some minor changes for production month August, 1988 - marked on door jam if original or rubber stamped under hood in yellow month/year made.


What condition is this car in, in general and your intent on keeping it or use it up till unfixable?


Tom



Discretesignals
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Aug 26, 2016, 4:41 AM

Post #3 of 10 (848 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

Honestly one of the best ways to find a vacuum leak in an HVAC system is by using a smoke machine. What is the EGR position sensor voltage with the EGR valve closed? If you manually open the valve with a vacuum pump, does the voltage change linearly?





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Hammer Time
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Aug 26, 2016, 11:02 AM

Post #4 of 10 (838 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



finster
New User

Aug 26, 2016, 11:21 AM

Post #5 of 10 (837 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

Hi, Thanks for the reply. Yes, the car is in very good shape for its age, no rust, comfortable, and drives very smoothly. Only 110,000 miles on it and it recently had quite a bit of work done on it replacing anything necessary.

Just took a close look at the 'soup can' and it looks good. No rust that I can see.

No disasters that I know of while changing the heater core. It was tough work getting it back into its position but got there in the end. Only thing I'd be worried about is if I pinched a vacuum line behind it but I don't know how I would check for that apart from taking it back out and that was a big job.

Transmission fluid is good.

It's a great car and I plan to have it for the foreseeable future. I don't think this is a major issue but I'd like to get to the bottom of it.

Thanks for your help.


finster
New User

Aug 26, 2016, 11:37 AM

Post #6 of 10 (835 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

Thanks, I think a smoke machine would be my best bet right now. I don't think I have any major leaks but likely a couple of minor ones. I've looked at some home made solutions but maybe I'm better off taking it to someone with a professional smoker. What's that likely to cost?

As for your EGR voltage question... I have no idea how to check that and I'm pretty sure I don't have the tools for the job. I got this car in April and this is my first time getting grease on my fingers.

Laugh


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 26, 2016, 11:50 AM

Post #7 of 10 (833 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

For just idle issues check for the bigger vacuum leaks. They'll alter idle and the way it runs. Small plastic hose will not allow heater controls to work properly nor if that "soup can" which is vacuum storage should hold tight. Just carefully unplug it and it should go 'whoosh' if not it's leaking. If not it will so be pro-active and see if it will come off to paint it up.


Heater a different game this just why doesn't it idle well? Vacuum leaking is the #1 reason IMO. Use what works - smoke machine, carb cleaner sprayed at suspect spots including the whole EGR and area.


With spray use caution for fire if on a hot spot risky so AYOR,


T


T



finster
New User

Aug 29, 2016, 8:19 AM

Post #8 of 10 (810 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

Great info guys. Thanks so much. I took the vacuum line off the 'soup can' and there is a good suction from the hose but you might be right about the can having a leak... I'm going to test it to be sure.

However, I did remove some of the vacuum hoses under the dash I I didn't get any vacuum suction on any of them. I think the main line(s) in must be disconnected/broken/pinched.


Hammer Time
Ultimate Carjunky / Moderator
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Aug 29, 2016, 8:30 AM

Post #9 of 10 (809 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

That plastic line can be broken anywhere along the route also. Check it at various points.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 29, 2016, 10:24 AM

Post #10 of 10 (801 views)
Re: AC / Heat / Idle issues 1989 Mercury Grand Marquis Sign In

Do you have a hand vacuum pump like a pistol type for testing vacuum things? Just use that on the can and see if it holds. Most don't!
Under side the bracket that holds it has bent crimps you find will be the first leak in those. Can be unbent and right paintable preferred goop would work then re-bend the bracken on a new spot and mount again.


The only thing that does is hold your heater (HVAC) diaphragms in position when your engine has no vacuum like long uphill driving, full throttle or even if engine if off duct would move once at least.


This wont cause engine to run poorly! Just annoying for the heater as hose to it isn't that large (shouldn't be) to mess up the whole show that much at all.
Said, 9mm nuts from inside driver's wheel well if you need to remove it. I do and did when these cars were just a few years old to paint them up real well.


It might not be a problem at all so just check it just because you should,


T







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