91 Cadillac 4.9l

Too much overanalising going on by the tech...

Gimme the numbers (CO, HC, and CO2), but my bet is the O2 or the coolant sensor is just bad.

The system sounds like it is running rich (the smell, high CO and HC are indicative of this). Do you have a volt meter (capable of millivolts from 0-1 volt)? We can diagnose it with just the DVOM and a few minutes of your time...

Also, what state are you in? Is it just a single speed sniffer test or a loaded mode (dyno run) test?

On the 91 the computer will reset itself automatically (to no light) when the issue is resolved. It takes a dead short or open to set the hard light on any post 84 to pre 96 vehicle. To clear the code we simply disconnect the battery. Closed loop is not possible with the light on, and you are correct... the car will never pass in open loop . Typically, as long as the plugs aren't old as hell, just driving the car down the highway for a few minutes will clean the plugs up.

 

Code 85 is an idle throttle angle too high. Have him either adjust the idle (if the set plug has been knocked out of it, if not don't mess with it), or check the TPS voltage.

Do you need the procedure for resetting the computer for trouble codes?

Also, as far as open loop... the O2 needs to cycle for closed loop. If the car is running too rich, it will never get below 500Mv. BUT, anytime the light is on, the computer will add it's own preset values using the other sensors and mathmaticaly deducing what the vehicle needs to run correctly (called LIMP mode). When the computer has to substitue values, it is open loop

With the IM 240 I assume failure at idle correct? If not, simply adjusting the TPS will not be enough. I will address the other possible causes below:

Also, after corrections are made, the O2 needs to be checked. If the TP voltage is off (high as per the code), we CAN see the failure indicated (high CO, high HC, low NOX) at idle, of course it could be other things too . Off idle, under cruise or load, I expect the O2 sensor is the culprit rather than the TP. The code 85 is indicative of an idle failure only, and it will not affect the readings off idle. Code 70, 55, 21, or 22 are off idle failures of TPS that may affect the readings .

High HC is indicative of a missfire, high CO is a rich mixture (O2 is high as well I am sure, because if there is an incomplete burn there will be extra unburned O2 passing through the exhaust). With low NOX we know that feul is cooling the cylinder (Nox is created by high cylider temperatures), so we must assume a rich mixture is all that is causing the miss, and the failure.

The oil will be saturated with feul and changing it will be required as well. Failure to do this may result in high CO failure (all others normal) as PCV system takes in the raw fuel.

Good luck, and let me know if you need the reset procedure (through the Climate Controll system) or any other input.

 

The high idle to start with is typical, when you first let off the gas I mean, with the 4.1, 4.5, and 4.9 Caddys. They all use an idle stepper motor (to the front of the engine bay, a black cylinder with a plunger) and you will see it work... It is to prevent stalling when sudden deceleration occurs. Most cars use IAC motors, or basically a metered vaccum leak, but caddy went with the stepper (similar to an antideiseling valve on a carb). No issues there.

a couple points of note... KOEO is key on engine off, KOER is key on engine running. When I suggest checking the wire, leave it plugged in unless otherwise mentioned. Always backprobe the wire, do not pierce insulation. Use the paperclip, or a straightpin, or the best is a hatpin (shaped like a "T") and run it into the backside of the connector, through the rubber alongside the wire.

The TPS is a 3 wire sensor on the caddys I believe. In all cases with a sensor that is 3 wire, the outside 2 are power (Vref is 5 Volts) and ground. The center is signal return. Ground on DVOM to battery ground, and positive to both outside wires. We want to see 1 wire with roughly 5 volts (give or take about 250 Mv), the other with 0. Next we go to center. It should read (this is a typical voltage for GM, I will double check my "at idle" specs tomorrow to be sure, WOT is always the same) about .5 volts. Slowly sweeping the throttle to WOT you should see it slowly, evenly climb to 4.6 to 5 volts.

Also, I want you do check the O2. It is a single wire sensor and it should be a purple wire (provided it is a GM or AC Delco sensor) with a barrel connector at the back of the engine. KOER the voltage will fluctuate rapidly (on a DVOM at least once per second). It should range between roughly .2 and .8 volts. The vehicle must be warmed up to test this. If you notice a stagnant roughly .5 volt signal, it is the O2 causing all the issues. I'm willing to bet that is the problem. If it is high in the range (over .8 or .9 by the readings) the sensor is reading correctly and it is not the problem.

OK, I will tell you how to enter diagnostic mode on your car (as we have to enter it to clear the code) so you can do your own diagnosis next time. I have access to all codes at work (Monday through Friday) and have no problem helping out...

To enter, press the "off" and "warmer" button down (on the climate controll head) at the same time, and hold for a few seconds. The first pass of codes are history (soft), and the second pass are current (or hard) codes. (engine codes begin with "E" and body codes begin with "B"

To clear, After entering SD mode, you will press and hold "off" and "high" fan for ECM (engine controll) or the "off" and "low" fan buttons for BCM (body controll)

To exit, press "auto" on the CC head.

Good luck!!!

 

Does it crank at all? If not, test the Neutral safety/park-neutral switch and it's adjustment.