RENIX Failed emissions...questions

So, my '89 Limited failed emissions inspection yesterday, here are the readings:

15mph load test:

HC ppm - Limit 164 Reading 208 FAIL
CO% - Limit 1.38 Reading 4.45 FAIL
NO ppm - Limit 1110 Reading 120 PASS
RPM 1666 VALID
Dilution 16.8 VALID

25mph load test:

HC ppm - Limit 159 Reading 221 FAIL
CO% - Limit 1.78 Reading 4.26 FAIL
NO ppm - Limit 1015 Reading 116 PASS
RPM 1662 VALID
Dilution 16.7 Valid


Add to this information the fact that I am getting somewhere between 12-14 mpg, and it seems to me that I am running WAY rich. Now, on my old VWs, I could correct this by simply turning a screw to lean out the mixture, and adjust the idle speed accordingly(in much the same manner). Is there a way to do this with RENIX? And are there any other things I should be looking at to correct this problem?

Thanks in advance.

How many miles on your O2 sensor(s)? Sounds like you're running way rich and either your catalytic is not up to snuff (under a hundred for a new aftermarket unit) or your O2 sensors are flaking out. Check if you have a wiring issue and maybe replace the O2 sensors if they turn out to be bad or marginal.

Also, does your engine come up to temperature properly? I believe a Renix will not go into closed-loop mode until the coolant temp reaches either 170 or 180 degrees (anyone know for sure) so that can also affect it - if it never goes into closed loop, it doesn't matter if your O2 sensors are working or not because the ECU will simply ignore them till it thinks the engine is warmed up.

The truck does fine, temperature-wise. I upgraded to the open cooling system about 2 years back, and I haven't had a heating or cooling problem since.

One other thing about the drivability that may or may not be related - when the truck is warmed up, it hesitates slightly just off idle. It does not do this at all when it's still in it's cold-start cycle.

Check compression before spending a lot of time and money on other issues. What temperature do you run at?

Most likely is that the O2 is telling the computer to run rich. It could be doing this for a number of reasons, possibly including bad O2 sensor, exhaust leak, permanent open loop condition, and a few other things .

Check out the air charge sensor. It is quite a common failure but many don't even know it exists. You can check it with an ohmmeter.

O2 sensor seems the likely culprit. I spent a good while testing and replacing sensors in order to get it to idle properly, and that included replacement of the IAT sensor, MAP sensor, and coolant temp sensor in the block(along with the standard RENIX TPS adjustment and re-adjustment).

So am I to assume, then, that there is no way to make manual adjustments to the fuel mixture? Additionally, I have read that there are problems with the Bosch replacement O2 sensors, and that OEM should be used...any truth to that?

You can adjust the mixture via a MAP adjuster or dick with the air charge sensor resistance.

There's no "idle screw" on fuel injected engines. Heck there's not even a gas pedal, instead the driver only controls air flow and then the computer looks at all of the sensors to determine how much fuel needs to be added to match

Oh and the Bosch O2 sensor works well in my 91

I had the same problem with my Renix. Max HC was 220 and I was at 507. A bad O2 sensor was the culprit. Unplug the connector and put the ohmmeter test leads in terminals A&B. You should have between 5 and 7 ohms. Mine was open.

Renix will go closed loop with a cold engine, unlike HOs. It gets better fuel economy at higher operating temps, but will go closed loop at low temps.

kastein said:

How many miles on your O2 sensor(s)? Sounds like you're running way rich and either your catalytic is not up to snuff (under a hundred for a new aftermarket unit) or your O2 sensors are flaking out. Check if you have a wiring issue and maybe replace the O2 sensors if they turn out to be bad or marginal.

Also, does your engine come up to temperature properly? I believe a Renix will not go into closed-loop mode until the coolant temp reaches either 170 or 180 degrees (anyone know for sure) so that can also affect it - if it never goes into closed loop, it doesn't matter if your O2 sensors are working or not because the ECU will simply ignore them till it thinks the engine is warmed up.

Click to expand...

maalox said:

The truck does fine, temperature-wise. I upgraded to the open cooling system about 2 years back, and I haven't had a heating or cooling problem since.

One other thing about the drivability that may or may not be related - when the truck is warmed up, it hesitates slightly just off idle. It does not do this at all when it's still in it's cold-start cycle.

Click to expand...

The hesitation might be a bad (warn) spot (early warning) on the TPS. New TPS might also improve performance and MPGs a little.

old_man said:

Check out the air charge sensor. It is quite a common failure but many don't even know it exists. You can check it with an ohmmeter.

Click to expand...

More commonly called the MAT (Manifold Air Temp) sensor on Renix, sometimes called IAT Intake Air temp sensor. Good to know all three names when trying to buy one.

I agree the O2 sensor is the most likely suspect. There are several threads in this forum, where I have posted blow by blow instructions for testing the Renix O2 sensor (there IS ONLY ONE O2 sensor on a renix) live while the engine is running, and disconnected. It it is a series of ohm, voltage tests. Best done with an old style analog (gauge with a needle, not digital) volt meter.

When the O2 sensor goes, and the engine runs rich, it is not long before it overheats the Cat converter and burns out the platinum catalyst, so plan on replacing the Cat converter (only one on Renix) as well as the O2 sensor. If the O2 sensor tests OK, then you just need a new Cat converter. Your emissions data indicates to me that the Cat converter is dead, and that the O2 sensor is probably dead or on its last legs, or has a wire/relay/heater voltage problem (see my O2 sensor diagnostic threads). Also your low mileage points to a bad O2 sensor system (O2 sensor, wires, or relay)

I am using a Bosch O2 sensor. I have never heard of a bad new Bosch O2 sensor. I have heard many warnings about not using Bosch platinum spark plugs on Jeeps! Maybe that is what you heard? If anyone has had problems with Bosch brand Renix O2 sensors, I would like to hear more?????

The idle air flow and fuel flow rates are 100% computer controlled on Renix, they are not manually adjustable.

Cracked, or leaking manifolds (intake or exhaust) can cause issues as can mechanical engine issues, but I would follow the above for now, based on your data and symptoms, sounds like an O2 sensor system problem that needs fixing and then a new Cat to top it off to pass inspections.

I only paid about $60-70 ea for my O2 sensor and new CAT. Got the sensor at AZ, and Cat on Ebay (Magna Flow IIRC), and had the local muffler shop cut and weld the Cat in for another $30.

maalox said:

O2 sensor seems the likely culprit. I spent a good while testing and replacing sensors in order to get it to idle properly, and that included replacement of the IAT sensor, MAP sensor, and coolant temp sensor in the block(along with the standard RENIX TPS adjustment and re-adjustment).

So am I to assume, then, that there is no way to make manual adjustments to the fuel mixture? Additionally, I have read that there are problems with the Bosch replacement O2 sensors, and that OEM should be used...any truth to that?

Click to expand...

Motornoggin said:

I had the same problem with my Renix. Max HC was 220 and I was at 507. A bad O2 sensor was the culprit. Unplug the connector and put the ohmmeter test leads in terminals A&B. You should have between 5 and 7 ohms. Mine was open.

Click to expand...

That is one of several tests for the O2 sensor system. Yours had an open circuit heater inside the O2 sensor. Burned out heater element, that is there to keep the sensor hot at idle and start up, so the sensor can read O2 concentration accurately all the time.

Here is the testing FAQ I wrote recently:

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=Renix+oxygen+test