Code 91 and limp mode

[broncobran68]

My 87 5.0 5 spd goes into limp mode sometimes once it warms up. If I turn it off and turn it right back on it runs fine. I scanned it and got a 91(oxygen sensor, fuel pressure out of specified range, or faulty injector). Is this causing the limp mode or is it something else the scanner is not picking up. It is the limp mode with dramatically reduced driveability.

 

[HISSIN50]

a lack of lambda input can cause it to go into open loop, as i recall. but i would think the car would still run strong.

my two cents - the masters will know!

 

[broncobran68]

Oh yeah I also have an Egr code because it is not plugged or supplied with vacuum. Should it have vacuum and should I have some sort of diodes on the wires?

 

[HISSIN50]

Oh yeah I also have an Egr code because it is not plugged or supplied with vacuum. Should it have vacuum and should I have some sort of diodes on the wires?

ah yeah, that would be a problem. running w/o EGR (and the puter thinking it is there) can lead to pinging and all sorts of bad stuff. the EGR gasses cool the chambers and since the spent gasses dilute the mixture, the puter dials in a ton of timing.

there is a solenoid (EVR, IIRC) that is puter controlled. when the puter tell it to, it supplies vacuum. dont just hook up manifold vac to the valve or anything.
i would fix it or burn a chip.

my two cents. good luck.

 

[broncobran68]

THe motor is actually a 289 so running egr is not an option. I need to figure out how to run it without it. I was under the impression that if I just unplug the electrical connector that it would run fine but set a code.

 

[broncobran68]

Anybody know what size resistors to use to trick the comp into thinking the egr is there or whatever? I remember seeing it in on fordfuelinjection.com but cant find it.

 

[IMPORTSMOKER]

well....the o2 sensors are most deffinatly needed to run closed loop...you need time, temperature, and 02 sensor = closed loop...therefor...check your 02 connections and clenliness...if you recently removed the sensors thay may be contaminated and need to be burned with propane to clean them...better than buying new ones....also...you need that egr hooked up.....i had similar problems with my car...turned out that th 02's were covered in carbon....burned em....runs good!

 

[broncobran68]

Well I wired some resistors into the harness to trick the comp into thinking egr was there. I believe I have a small exhaust leak before the 02 which would explain a lean mixture. I'll scan it again after I fix the leak. If that doesnt work I have a spare 02 Ill try out.