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1991 5.0 - fires up every time, idles perfectly, but once it’s warm it won’t idle for more than 15 seconds

14K views 213 replies 20 participants last post by  Enjoy_the_Ride 
The “only person actually trying to help me” hasn’t offered a shred of any explanation whatsoever aside from “the engine isn’t getting enough air”. All they’ve done is repeat what I already posted, and hurl insults my way. I really don’t understand why you guys just can’t talk about this like adults, and I don’t understand why you’re coming here to defend them when you have nothing further to add to the discussion.
Here's why...

When you've been on this forum for 20+ years trying to help people out, and the majority of them don't follow through with what you're telling them to do.. you might end up like indy.

Ok, maybe not like indy, but you can imagine how frustrating it can be when you're trying to teach someone how to properly diagnose an issue and not just throw parts at it.

Proper diagnosis is done in steps for a reason. You can't try 3 different things at once and expect to make any progress.

Indy is Indy. He means well and is very knowledgeable but shows some tough love when you don't listen to what he's saying. He does not hold back & comes off as a complete ***** to the new comers but like I said, it's tough love. He is not going to spoon feed anyone, period.. but I have seen him go pretty far for people that were willing to listen and show interest in what he had to offer. Think of him as that teacher/professor that wants to see their students do well but expects them to listen & put in the work.

I offer my help but when I see people that just want to throw parts or have zero interest in diagnosing the issue, I leave the thread. It can be very frustrating but you have to understand this.. I am not standing next to your car. I'm not able to listen to what it's doing or not doing, i'm not able to unplug sensors or backprobe pigtails to obtain voltage readings so i'm going to rely on you to perform these things properly and do it in the order i'm asking you to do them.
You can't get to step 4 by doing steps 1 & 3 but not 2.

Anyway, I'm not defending indy but to explain why some of the veterans here might be snippy after 20+ years of trying to help & teach - this is why.
 
Also it was mentioned a page or two back.. you have to ignore those that are here to troll or get Indy fired up.. some people get off on that.

Others are really investing their time and want to teach you, want to show you how to use a multimeter & how to read a wiring diagram so don't get all fired up & defensive.

How do you think we learned? We were all in your position at one time, not knowing how to use a DMM, not knowing how to look for 12VDC or continuity to ground but look at how many people are willing to teach you.

It's tough love here, you might get hazed a little bit.. that'll happen no matter where you go. At the end of the day when you figure out that the o2 is doing its job and telling you there's something else causing it to indicate lean & you figure out the problem, you'll be so damn happy that you didn't throw parts & you didn't pay someone hundreds of dollars to do something you were able to do on your own (with some corral help :) ).
 
One of the things that I dislike most about forums I put time into are threads like this that potentially have some really useful information and then go silent with no outcome.

Believe it or not people will show up in this thread with a similar problem that you're having, they will read through 10 pages of info & nonsense hoping to find the answer or some useful tips on where to look for their problem.. just to come to a deadend!

Why don't we continue on and solve your problem or at least hop back in here and tell us what you have found or fixed?
 
The oxygen sensor has 4 wires. Power, signal, signal return & ground. In basic explanation, there is a voltage source sent to the sensor, the sensor depending on if it's reading rich or lean will then send this rich or lean signal back to the EEC & there will be fuel trim adjustments made to reach the commanded AFR.

You can get this voltage reading on your DMM by probing the signal return wire & ground, which will indicate a voltage reading that translates to rich or lean. In a normal condition with the engine idling you would see the voltage constantly fluctuate up and down.
If the 91 code is true, the voltage would likely be pegged.

A narrow band o2 sensor is a 0v - 1v sensor, it does not indicate an air fuel ratio rather just lean or rich with the switching point between rich & lean close to the .48-.50v area. Lean would be <.50 and rich >.50, or somewhere close to that .50 number. With the engine idling at temperature or having someone steady the throttle to keep it running, read both oxygen sensors and compare their activity. The driver side should be indicating lean and the passenger side should be switching close to .1V to .9V.

You can also rev the engine to change rpm & watch what the o2's are doing. You can create a vacuum leak at idle and watch the o2's show lean followed by spraying carb cleaner into the vacuum leak to watch the o2's show a rich condition. This is a good way to look at what the o2's are doing as well as find a lazy o2 that might not respond quickly to the sudden changes.

Veryuseful has the o2 diagrams you need, give this a shot and report back!
 
No idea. I thought I noted a " cleaned up" tone from him recently, so I got the impression he'd been spoken to. He was a bit of a db, but (at least) he didn't troll. I know some will disagree, but I hope the ban is temporary.
Again, I agree. He has a lot to offer & has taught & helped a lot of members figure things out on their own.

Not sure what happened but i'm not surprised by the ban, hopefully not a permaban.
 
Hey Did you get this figured out? I had a similar problem. Have you checked you Map sensor? You can borrow one from a friend for a test.
Was hoping the OP would chime back in with his findings so there's not another open ended diagnostic thread [emoji2371]
 
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