Coincidence??

[94 Cobra R]

So, little information: speedhut fuel pressure gauge started reading about 10lbs lower then normal and 10 below the Aeroforce gauge. This morning, it actually was reading around 5 total lbs of fuel pressure. Everything else still looked good, wideband reads good, idle is good, drivability is good, aeroforce reads normal.

This afternoon, I get a P0171 lean code. Coincidence? Car is just over 70k miles, so maybe the O2 is going? I’m going to order a new fuel pressure sending unit from speedhut in the mean time.


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[BlksvtCobra01]

So, little information: speedhut fuel pressure gauge started reading about 10lbs lower then normal and 10 below the Aeroforce gauge. This morning, it actually was reading around 5 total lbs of fuel pressure. Everything else still looked good, wideband reads good, idle is good, drivability is good, aeroforce reads normal.

This afternoon, I get a P0171 lean code. Coincidence? Car is just over 70k miles, so maybe the O2 is going? I’m going to order a new fuel pressure sending unit from speedhut in the mean time.


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Any vacuum leaks, sucking in unmetered air?


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[Huachipato]

I feel like I had a similar code in the past - can't remember which one it was. But you can set the Aeroforce to read the O2 voltage readings.

When I had the issue - I had a "Stuck" O2 sensor that was just not switching voltages nearly at the pace the other O2 sensor was. Since you have the gauge already - it might be something you can set to just see if that might be a similar issue you are having. In my case a new O2 did the trick.

 

[94 Cobra R]

I feel like I had a similar code in the past - can't remember which one it was. But you can set the Aeroforce to read the O2 voltage readings.

When I had the issue - I had a "Stuck" O2 sensor that was just not switching voltages nearly at the pace the other O2 sensor was. Since you have the gauge already - it might be something you can set to just see if that might be a similar issue you are having. In my case a new O2 did the trick.

Excellent idea! I will check that out and add those parameters!

Any vacuum leaks, sucking in unmetered air?

I’ll have to get a spray bottle and check. Not that I’m aware of, atleast, nothing giving me symptoms of it. BUT...I think I have an exhaust leak..

 

[94 Cobra R]

Curious, for those that have changed the O2 sensor, is it the upstream or downstream on the passenger side, since it really isn’t specifying?


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[BlksvtCobra01]

Upstream, while I haven’t on my 2004 all the rears are, are a catalyst monitor. I made the mistake on my 2001 Cobra way back when when I had a P0171 & P0174 of changing the front O2’s when it was intake gaskets sucking unmetered air.


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[94 Cobra R]

Upstream, while I haven’t on my 2004 all the rears are, are a catalyst monitor. I made the mistake on my 2001 Cobra way back when when I had a P0171 & P0174 of changing the front O2’s when it was intake gaskets sucking unmetered air.


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Ugh, that would suck. I’ll def wait and see if I have any vacuum or unmetered air issues going on. I’ll check it tomo after work. Car def still drives normal. Thanks for the reply!

 

[BlksvtCobra01]

Ugh, that would suck. I’ll def wait and see if I have any vacuum or unmetered air issues going on. I’ll check it tomo after work. Car def still drives normal. Thanks for the reply!

My 2001 drive fine it was just at the threshold of the pcm parameters. With it running take carb cleaner and spray around the intake and see if the idle fluctuates then.


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[cj428mach]

Logging fuel pressure with anything other than the frps is silly and over complicating things.

 

[94 Cobra R]

Logging fuel pressure with anything other than the frps is silly and over complicating things.

True. FP gauge was already in the car maybe I should pull it and put an oil pressure gauge in....

 

[94 Cobra R]

Update:

Monitored both banks O2 with the interceptor. At idle or a 1/10th load, they’re consistent with each other, but as soon as you give it gas, bank 1 drops under 100 (which I assume is lean) while bank 2 still stays above 500. Wide Band still shows perfect. Next will be the spray test on vacuum hoses.


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[94 Cobra R]

Also, just ordered a 2nd Interceptor gauge. Thinking about adding oil pressure to it. I like having a separate wideband to be able to look at, at all times.


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[hotcobra03]

Po171. Is front passenger o2.

This is a vacuum leak. The tinyest leak. Not a big one.

Most common area. Pcv line.

The hose going under blower.

This. Hose will harden.
It won’t pull off nipple underneath but it will spin. That’s a leak.
Ford didn’t use any clamps.

At pcv valve. That hose also will leak as also the rubber elbows on this line. They crumble. And a hole starts.

To me o2 isn’t bad. Its telling you you have a leak.

Po174 might get set in time if not found.

 

[94 Cobra R]

Po171. Is front passenger o2.

This is a vacuum leak. The tinyest leak. Not a big one.

Most common area. Pcv line.

The hose going under blower.

This. Hose will harden.
It won’t pull off nipple underneath but it will spin. That’s a leak.
Ford didn’t use any clamps.

At pcv valve. That hose also will leak as also the rubber elbows on this line. They crumble. And a hole starts.

To me o2 isn’t bad. Its telling you you have a leak.

Po174 might get set in time if not found.

Thanks for the info! I'll definitely be checking it this weekend!!!

 

[94 Cobra R]

Ok everyone, finally got the chance to check the vacuum lines. No leaks that I could tell. Sprayed every joint I could find (lord, can’t wait to perform a delete on this and get rid of so much stuff).

I guess the next step is the upper, passenger O2 sensor.


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[hotcobra03]

Ok everyone, finally got the chance to check the vacuum lines. No leaks that I could tell. Sprayed every joint I could find (lord, can’t wait to perform a delete on this and get rid of so much stuff).

I guess the next step is the upper, passenger O2 sensor.


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The very last vacuum connection This requires to remove lower intake.

Did you check that in hand?

 

[94 Cobra R]

The very last vacuum connection This requires to remove lower intake.

Did you check that in hand?

Ugh. No...if I need to pull the blower, then I’ll go ahead and get ready to do things I was planning, like valve covers, etc etc

 

[94 Cobra R]

Looks like good Info here:
https://www.svtperformance.com/threads/need-help-vacuum-leak-pcv-to-lower-intake.1158176/