OBD-I jumper codes not working

Tiny
JOSHUA_R
  • MEMBER
  • 1995 FORD MUSTANG
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 88,000 MILES
Stepson recently just bought the car listed above (GT) for his first car. It wasn’t running. Checked the fuel system and it seemed good. Looked into the ignition system. Found that the pip signal to the ignition control module wasn’t working (removed wiring harness to ignition control module. Used a test light and on crank it should have been flashing. It didn’t.) I also used a meter on the coil and found the resistance read low. I replaced the distributor, ignition control module, coil, and plugs. Car started but ran really rough. Tried to pull signals using the OBD-I port under the hood. The service engine light just stayed on solid. I also tried using a test light on the port and it just stayed solid as well. I removed the battery cables and pulled the wiring harness to the PCM. Connected battery cables back and turned the key on engine off and the service light was off (so nothing should be grounded). Car is running rich (new plugs already have dry soot in the same day of changing them. Black smoke also coming out of the exhaust when giving it gas), OBD-I port isn’t working to get codes, and the ignition control module still isn’t getting the pip signal (test light flashing on crank) even after changing all the ignition components. Is this all related possibly? Possible bad PCM? Thank you in advance for any help!

To add, I found if I remove the big vacuum line that runs to the three nippled “valve” or connection right behind the throttle body. (Not sure what you call it) The car idles much better. You can give it throttle without shutting off. This valve has a vacuum line that connects to the EGR and two other things. I replaced the EGR, and this still happens. Not sure if this issue is related to the first topic. Thanks again!
Sunday, April 10th, 2022 AT 1:16 AM

4 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Hi,

By removing the vacuum hose, you are allowing more air to enter the combustion chamber. It sounds like it is getting too much fuel.

You indicated the fuel system seemed okay. Did you check fuel pressure? If you haven't, start there. If it is getting too much fuel, we need to determine if it is a regulator issue.

Here is a link that explains how to test pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Before jumping to the test, confirm the vacuum hose to the fuel pressure regulator is connected and has an engine vacuum when the engine is running. Additionally, when you disconnect the hose from the regulator, see if there is any evidence of fuel in the hose. I've seen the diaphragm fail in the regulator and then the engine sucks fuel straight through the vacuum hose.

I attached a pic below and highlighted the regulator.

Let me know the results or if you have other questions.

Take care,

Joe
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Sunday, April 10th, 2022 AT 8:35 PM
Tiny
JOSHUA_R
  • MEMBER
  • 3 POSTS
I checked the fuel pressure prior to finding issues with the ignition system. When you keyed on, I want to say it was at 40PSI and would stay about that while cranking. I can check this again tomorrow. I didn’t check fuel pressure while it was running.

So, today I purchased a Ford obd1 scanner tool since I couldn’t get the jumper test to work. This tool still wouldn’t pull the codes in the car. I removed the PCM and found corrosion and what looked to be burn marks on the board. I will attach photos. Do you believe this could be what is causing the obd1 port to not work with pulling codes? I just don’t want to be throwing parts at it and not be able to pull any codes. I also don’t want to purchase a new PCM if it isn’t really needed. Thank you for your help!
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Sunday, April 10th, 2022 AT 9:29 PM
Tiny
JOSHUA_R
  • MEMBER
  • 3 POSTS
So, I checked fuel pressure at idle. It runs on the range the service book says it should be. Remove vacuum and it only goes up 2-4PSI. Went ahead and just replaced the regulator and it still runs the same. When you remove the big line from the intake manifold that goes over to a vacuum block that then runs to the brake booster, fuel tank, etc, it starts to idle better. It also still has a lot of black smoke coming out of the exhaust when you rev it. Still running rich, it seems.
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Monday, April 11th, 2022 AT 3:59 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Hi,

The black smoke is likely the result of too much fuel. Since the fuel pressure is within spec, I want you to try something. Reconnect the vacuum hoses and disconnect the mass airflow sensor in the air inlet tube. See pic 1 below (number 5). See how it runs after that is disconnected. If there is no change, check to see if there is a change if you remove the air intake temp sensor (number 11).

If there is no change, we have two ways to go. First, check if we have injectors that have failed allowing too much fuel to the engine, or if the engine coolant temp sensor has failed and needs to be replaced. The ECT signals the computer of the coolant temperature. Based on that info, the computer determines the air/fuel mixture the engine needs to run its best.

If the sensor indicates -40F, the fuel mixture will be extremely rich. This won't set a code because as long as the computer is receiving a signal, it doesn't know if it is right or wrong.

Let me know your thoughts.

Joe
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Monday, April 11th, 2022 AT 8:08 PM

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