Engine I am having trouble with the engine in my 1991 Mustang.

[sands9330014]

I am having trouble with the engine in my 1991 Mustang.　Idling is unstable.　　

I found the idol settings learning page and followed the steps, but the problem still persists.
・IAC replaced　　　・TPS replaced　・MAF sensor replaced
・Distributor replaced　・Ignition coil replaced　
・Injector replaced　　・I noticed that push rod number 7 was bent and replaced it, and also checked the movement of valves number 1 to 8.
・I also replaced two O2 sensors.

However, the symptoms remain the same.
Even though I'm just adjusting and checking the idling, I think the gas runs out very quickly. The black smoke from the exhaust is also terrible. I think there is often an after (back) fire inside the muffler.

At WOT, the throttle will rev up.
Is the amount of air low?
Is there a lot of fuel?
Fuel regulator pressure failure?
However, I don't have a device to measure fuel pressure.

Is the BAP sensor broken?

Even after disconnecting the BAP sensor connector, the condition does not go well.

Is the EGR broken?
The EGR vacuum hose did not feel any vacuum.

If you remove the brake booster vacuum hose with a tree, the rotation speed will increase. When I put in secondary air, the rotational speed increases, so I feel like I'm using a lot of gasoline. Please help me.

There are no error codes in the scan tool.
code11

Every time I check the spark plugs, they are all black.

 

[General karthief]

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

www.stangnet.com

Here is a checklist for resolving your issues but I suspect a bad fuel pressure regulator, it shows you how to check this.

 

[limp]

ECU Exchange needed?

 

[General karthief]

Codes will be of little help as bad as this is running although the vacuum looks good, you could see if it communicates with a reader, I imagine the 'check engine light ' is already on.
The 'rich' condition (black smoke, exhaust backfire) will foul the O2 sensors so they need to be cleaned or replace.

 

[Mustang5L5]

She's running rich.

Are you sure there are no codes? Should get three code 11's. Two with engine off, and one if you run the engine running codes. Oftentimes folks misunderstand that you need ot pull codes with engine off and with it running to get both sets. Since it's running pig rich, i would assume codes would show in the Engine Running config.

After that, vac leaks (smoke test) and fuel pressure are what I would look at.

I also wouldn't rule out failing capacitors in the ECU. At this point I assume any ECU that hasn't been recapped...should be.

 

[Noobz347]

ECU Exchange needed?

Unlikely with a Code 11 from the EEC scan.

 

[Mustang5L5]

Unlikely with a Code 11 from the EEC scan.

I wouldn't use that as a measure of ECU condition. It wouldn't rule it out in my mind.

 

[Noobz347]

I wouldn't use that as a measure of ECU condition. It wouldn't rule it out in my mind.

I have been actively searching for a scenario where the EEC is bad but passes a code 11 with no others, for little over a year.

If you find one before I do, definitely give me a shout.

 

[Mustang5L5]

I have been actively searching for a scenario where the EEC is bad but passes a code 11 with no others, for little over a year.

If you find one before I do, definitely give me a shout.

Well until the OP confirms he has three code 11's, we don't know that's the case. It's the engine running codes that will show the problems if the ECU is bad.

I can't imagine running bad enough to turn the plugs that black is not giving any codes

 

[sands9330014]

I replaced the fuel pressure solenoid and checked for vacuum leaks with a smoke check, but I couldn't find any vacuum leaks.
I'm also checking the TPS voltage and trying to learn idle, but it emits black smoke.
Please tell me how to fix the unstable idling.
I also removed the injector and checked. The return also heals the air and returns to the gas tank.

Help me

 

[Mustang5L5]

Can you confirm you pulled the codes in the engine off and engine running configuration and have three code 11s? Given how rich you are, there would have to be codes for the engine running config.

 

[sands9330014]

Only two check codes, 11, come back. I can't start the engine and check the codes. However, the engine was not running well and 87 and 96 came back once, but I cleared them and started the engine again. When I ran the scanner again with the idle not working well, only 11 came back. Is there a mechanical problem?

 

[AeroCoupe]

Those are both fuel pump related codes.

You should have the motor up to operating temp before pulling any codes. If you can get it started and bring it up to temp then run codes.

 

[sands9330014]

Those are both fuel pump related codes.

You should have the motor up to operating temp before pulling any codes. If you can get it started and bring it up to temp then run codes.

Yes. I keep the engine temperature high. When it goes into closed loop, it runs very badly and doesn't last, but I check it with a scanner afterwards. However, when the engine temperature is high, it is very hard to start even at WOT.

 

[Mustang5L5]

That’s because it’s overly rich. If you press the gas pedal to the firewall it will go into flood clear mode and disable the fuel injectors. The car should start up easier then.

Safe to say you likely will have codes in the engine running condition. It isn’t like OBD2 where you can pull all stored codes with the engine off. You need to pull these codes with the engine actually running due to the primitive nature of the ECU.

I’d be tempted to check the ECT sensor resistance.

Unplug it and check resistance with a multimeter. At around 70 degrees, you should have 36-37 K ohms of resistance.

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

 

[sands9330014]

I checked the smoke creek again. A very small amount of smoke leaks from the EGR. Is this important?　ECT and ACT are showing 41 ohms when cold.

View: https://youtube.com/shorts/r5o0g0J1jm0?si=2niNZgDZk9WJ_rEI

 

[sands9330014]

I ran the ECM scanner while starting the engine. The code was 40, so I stopped the engine while it was hot and checked the code again with the scanner. The code is 11.
I don't know how many times the engine temperature has changed, but when the idle becomes very unstable, I think it goes into a closed loop? So it's ECT20Ω.volt 1.195v　　ACT volt１.３５１

 

[sands9330014]

When the engine of my car gets warm, it starts idling very poorly and the engine stops.
It won't even restart. At that time, I measured the ECT voltage and Ω. 4.8kΩ for 1.2v.　　n the scanner tool, 40, 15, and 12 returned, but they disappear again.
I measured the compression again, checked the plug (black), and tried installing a different plug cord, but the symptoms are the same.

View: https://youtube.com/shorts/WeLeM2Z8VFg?feature=share

 

[General karthief]

Give us some background on this car, how long you have owned it, was it running good and developed the problem recently and any modifications.

 

[sands9330014]

Give us some background on this car, how long you have owned it, was it running good and developed the problem recently and any modifications.

The car is an original from 1991. It has 10,000 miles and hasn't been driven in a long time.