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Discussion Starter #1
Ok so 2 Sundays ago I picked up my first fox. Always loved them, wife wanted a second car and she always loved stangs so here we are.

1990 5.0 LX Vert AOD

Everything is stock from what I can tell, she has been well maintained, for a 20 year old fox in SoCal there is no cracking/fading of the vinyl. But on to the problem at hand.

I went and had her smogged to register it, would have been in PA but its easier to get my title while I am stationed in Cali. Where she was registered she had to have the enhanced test done, aka 15 and 25 mph readings. Failed for NOx. Changed the registration to where I am which means just a basic test of idle and 2500 rpm. Here are the readings.

Speed/ RPM/ %cO2/ %O2/ HC max/ HC meas/ CO max/ CO meas/ NO max/ NO Meas

15mph/ 1237/ 11.2/ 5.0/ 85/ 62/ .54/ .01/ 613/ 741
25mph/ 982/ 11.1/ 5.1/ 67/ 55/ .45/ .02/ 664/ 380

So those are what my results showed. I next changed plugs, autolite 25 .052 gap, changed pcv and ccv screen, changed air filter, sprayed out the egr valve with carb cleaner, and adjusted the tps to .99v

Engine runs good and strong, everything shift fine and mixed driving I am pulling about 18 mpg with Military Exchange 87 gas.

So I did the KOEO and KOER tests:

I got KOEO :19
KOER: 91, 12 (adjusted the tps and it went away)
Cylinder test: 9

Me being new to mustangs what is the next step, you think the 91 would be fixed with a new O2 sensor?

As far as the 19 I am getting 11.9 volts on the red wire of the injectors.

About to go clean the MAF sensor as well.
 

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Code 91 is bank specific. It could be the 02 sensor. Quick test would be to unhook the 02s, take them out of the exhaust and swap them over. Driver side 02 in the Passenger side and vise versa. Rerun the codes and see if code 41 shows up. If it does, 02 sensor that was on the driver side that's now on the passenger side is bad. If 91 still shows, its a wiring issue, or an actual lean code that's concentrated on that side.
 

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Discussion Starter #3
I will check that out and give it a try, not a lot of time off with my schedule here, so I am looking for some ideas as to what else it could be so I can try to figure it out the next weekend I have off.


What would cause just a lean running problem on the one side?
 

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Upper to lower intake gasket leak, bad injector or clogged injector. Even a lower intake gasket leak.

And code 19 has nothing to do with injector power. The ECM doesn't supply the voltage to the injectors. They are just on the same circuit that powers the ECM up. Code 19 doesn't look good though. Its an internal error.
 

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Discussion Starter #5
Yeah saw that about code 19, gotta pull my comp out and look at the numbers for it to try to find a new one. Tested the voltage on the injectors since that is what I read to try to make sure it wasn't the relay.

I don't think I have any intake manifold leaks, I was using some carb cleaner earlier to spray all the vacuum lines looking for a leak and came up with nothing, no surge in idle, nadda. I know a lean running condition could cause the NOx levels to jump though. Oh and when I pulled the plugs and replaced them, they really didn't look that bad. One head's plugs looked just like the plugs on the other head :dunno:
 
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