Diagnose this problem

Get the codes and report back.

Good luck.

Did weld heat cook any of the wires under the drivers seat where the fp relay is

Did you disconnect the battery when welding? Check fuel pressure..see if the pressure is dropping off?? Just putting out some ideas
Code 41 is for lean condition...need to find the cause for that one..I would as above want to see fuel pressure while under throttle
91,96 also seem to indicate fuel issue..

Just think a fuel pressure gauge may show you pressure is falling off..they are inexpensive and may save you some time and headaches.

Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.
The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Code 96 – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits.

Look for a failing fuel pump relay, bad connections or broken wiring. The fuel pump relay is located under the Mass Air Meter on Fox bodied stangs built after 91. On earlier model cars is under the passenger seat. On Mass Air Conversions, the signal lead that tells the computer that the fuel pump has power may not have been wired correctly. See http://www.stangnet.com/tech/maf/massairconversion.html

To help troubleshoot the 96 code , follow this link for a wiring diagram for 87-90 models http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

For 91-93 models see http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif

Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. http://www.mustangworks.com/articles/electronics/eec-iv_codes.html for a description of the test connector. it. No voltage when jumpered, check the fuel pump relay and fuse links.

Using the diagram, check the red/black wire from the fuel pump relay: you should see 12 volts or so. If not, check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. No voltage there, check the Orange/Lt blue wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the Pink/black wire, swap the relay.

Andres2882 said:

Hey Joe, thanks for kicking in some info. I have a few basic questions for you though. My more mechanically inclined friend seems to think that it couldnt be a fuel pump issue seeing as how we were driving around, albeit crappily, it had to be getting power? Would a fuel issue coincide with a check engine light at a certain coolant temperature? He seems to think that something is tripping the coolant sensor to the ECU and that is causing wierd issues. Any truth to that thinking? I've already called up the shop that installed my SFCs and they said to bring it by in the morning and they will give it a once over, of course I'd rather not have to leave it there over the weekend. Any ideas?

Click to expand...

I don't think that the temp and a problem with the fuel pump are related unless it just takes that long for things elecrical to heat up and cause problems.

Check the FP wiring and the lines. If I remember correctly, the lines are very close to the SFC's are welded on. Maybe one of them got dinged.

As for the O2 sensors, use a voltmeter as referred to in my previous post to check the output. Check the wiring for damage when you get under the car. If the welder clamped the welder ground on the exhaust pipe, he could have zapped the O2 sensors. That would be hard to prove, but a voltage check will show if they are working at all.

yah neither could i, but my car runs lean in the early rpms and but RICH all the time...so there you go haha (still havent figured it out)