Ford Mustang Forum banner

Status
Not open for further replies.
1 - 11 of 11 Posts

·
Registered
Joined
·
274 Posts
Discussion Starter #1
Once again I need to draw on the knowledge of my 5 liter brethren to solve some (hopefully) simple problems with my car. BTW, I did look around a bit using the website search tool for the forums and couldn't find an answer to these problems.

I used my Equus code reader on my 1991 Mustang GT and here is what I came up with and here is what it said. I just have some quick questions before I start to tear into things.

Code 33C EGR valve not opening properly. Simply put, I think I need to replace the EGR valve. Is this easy? I have a Chilton's repair manual for all of these repairs but it is a bit vague.

Code 66C VAF/Mass air flow sensor fault, below minimum voltage. Does this mean that I need a new MAF? If so, should I go with a direct repalcement for what I have on there. The car is mildly modified but still has un un-tuned Ford MAF sensor on it.

Finally...

Code 51C ECT sensor out of range indicated / circuit open. What the heck does that mean? Is the ECT sensor a result of a bad MAF sensor? I will do some more research in my repair manual on this one to see what I can do to fix it but any advice would be gladly appreciated.

Thanks for your time!!
 

·
Registered
Joined
·
7 Posts
The EGR is up top the motor on backside of the throttle body. It's simple to take off few fasteners. often, carbon will get built up in them. Pull it off and remove the vaccum line. Make sure there's no big hunks of carbon jammin it up. If so, clean it out. Put a vacuum on the port and make sure it holds. If not it's abad EGR. Reason I say this first is EGR is much cheaper than mass air flow, more commonly is the prob, and will cause the other two codes to come up.
 

·
Registered
Joined
·
369 Posts
agreed, also u can usually clean ford egrs so just try and clean it first and more importantly check ur hoses to ur egr. look for dry rotting or sometimes they just crumble up or kink. there is a great article on cleaning ur mam on this site. again clean that thing either way just be careful when cleaning it.
 

·
Registered
Joined
·
274 Posts
Discussion Starter #4
Off to a good start.

Brad, I will try that first. Being that the care is almost 20 yrs old it might be time for a new EGR. Down at the auto parts store it'll cost me bout $35. Off to a good start!--Thanks!
 

·
Registered
Joined
·
5,170 Posts
That code doesn't always mean the EGR is bad. If the vacuum line to the EGR is not there. That code will show. If the EGR connector is unplugged, that code will show. I sugges you make sure that a vacuum source is actually reaching the EGR it self.

Code 51 usually means there is an open in one of the wires going to the ECT. If you put a volt meter across the two wires. It should read close to 5v. If not, you need to then remove the black lead of the meter and place it on a good body ground. If 5v then shows. Your issue is with the ECT ground circuit. If it doesn't show 5v, the issue is with the reference voltage circuit. Both could be due to a bad connection.
 

·
Registered
Joined
·
274 Posts
Discussion Starter #6
A few more answers.

89coupe, I think I will go ahead and will change both Engine Coolant Temperature sensors as I did a little more research and not only did I discover on this website with the ECT sensor actually is, but also how it works and some of the problems that not having a functional sensor can cause. Hey 89coupe, my car does have an Autometer temperature gauge installed in the A-pillar. I am guessing that this gauge is hooked up to some of the wiring to one of two ECT sensors. Do you think a bad spice job for that temp. gauge could be causing this code to come up? A possible short maybe? I think I will go ahead and will replace both sensors anyway, and will check the wiring like you recommened with a volt meter just to make sure I have all of my bases covered. Thank you for the great information.
 

·
Registered
Joined
·
6,328 Posts
Do you think a bad spice job for that temp. gauge could be causing this code to come up? A possible short maybe?
thats a good possibility if someone hacked into the wiring harness..
 

·
Registered
Joined
·
5,170 Posts
89coupe, I think I will go ahead and will change both Engine Coolant Temperature sensors as I did a little more research and not only did I discover on this website with the ECT sensor actually is, but also how it works and some of the problems that not having a functional sensor can cause. Hey 89coupe, my car does have an Autometer temperature gauge installed in the A-pillar. I am guessing that this gauge is hooked up to some of the wiring to one of two ECT sensors. Do you think a bad spice job for that temp. gauge could be causing this code to come up? A possible short maybe? I think I will go ahead and will replace both sensors anyway, and will check the wiring like you recommened with a volt meter just to make sure I have all of my bases covered. Thank you for the great information.
Only one is for the Computer. Thats the one on the passenger side of the intake in the black heater tube with 2 wires. The other is only for the gauge readings, and it has only one wire. It would have to be an electric gauge for them to wire it in to the sensor for the computer. If they did, then they screwed up.

Before I would buy a new ECT sensor. I would at least check the voltage going to it like I suggested. Its not cost effective to just replace it. If for some reason its a wiring issue, 12 new sensors wont fix that. Takes about 30 seconds to check the voltage at the 2 wire sensor for the computer. If you have a volt meter.
 

·
Registered
Joined
·
274 Posts
Discussion Starter #9
Question about the voltage.

89coupe, I have never used a volt meter to check auto wiring before, but I want to. Where do the wire(s) from the volt meter actually touch on the ECT sensor and it's wires? It would be easier to re-connect (and cheaper) or re fasten any break in the wires or hook something up that needs to be. Could you give me an order and color I need to follow? Also, do I need to set the volt meter for anything in particular? Should it be set for a certain resistance, miliamp, votage setting? I am kinda a newbie to this as you can tell.

I have a Chilton repair manual for my car with a ton of wiring schematics in it but unfortunately, for some odd reason, the ECT sensor doesn't have its' own repair section or even replacement part of the book that I can find.

Thanks again!
 

·
Registered
Joined
·
5,170 Posts
89coupe, I have never used a volt meter to check auto wiring before, but I want to. Where do the wire(s) from the volt meter actually touch on the ECT sensor and it's wires? It would be easier to re-connect (and cheaper) or re fasten any break in the wires or hook something up that needs to be. Could you give me an order and color I need to follow? Also, do I need to set the volt meter for anything in particular? Should it be set for a certain resistance, miliamp, votage setting? I am kinda a newbie to this as you can tell.

I have a Chilton repair manual for my car with a ton of wiring schematics in it but unfortunately, for some odd reason, the ECT sensor doesn't have its' own repair section or even replacement part of the book that I can find.

Thanks again!
You unplug the connector from the sensor. Put the volt meter on the DC voltage setting. Set it to the 20 setting, or auto depending on the meter used.

Red goes to the light green yellow wire. Black goes to the black/white wire on the connector, not the sensor itself. Turn the key on, and see what the voltage. If there is an open some where. you would fix that with a butt connector or some other type.
 

·
Registered
Joined
·
274 Posts
Discussion Starter #11
Thank you!

89coupe, I appreciate your step by step instructions. This should help me and other people out there with the same problem. Hopefully, it wont be anything more than a broken wire or something disconnected. I will wait to change the sensor until after check the votage. Thanks!!
 
1 - 11 of 11 Posts
Status
Not open for further replies.
Top