Hello everyone, I'm trying to get my bronco back on the road and need some help because I failed emissions very badly. Here is some background on my bronco.

In the past, my bronco used to pass emissions with flying colors. In 2008 I decided that I wanted more power power so I pulled the engine (195,000mi at this point) and had it rebuilt. Engine was bored .020, roller rockers 1.6 ratio, edlebrock heads and intake manifold (the truck version)and also the E303 cam. I did have my computer customer tuned in a shop to adjust to all the new changes, which the tune added something like 15 more HP.I also had the exhaust done with a new cat and 3 inch pipes from behind the Y-Pipe. Everything I put in the vehicle I payed close attention to make sure it said emissions legal.

In 2009 my emissions was due. I just barely passed with these results:

High Speed Reading Limit
HC 14 220
CO .02 1.20


Low Speed RPM Reading limit
HC 218 220
CO .63 1.20


As you can see the high speed rpm passed with flying colors and the low speed HC was only 2 points away from the limit.


Well I just had my new emissions due in Feb 2011, and here are the results.



High speed rpm Reading Limit
HC 46 220
CO .46 1.20

Low speed rpm Reading Limit
HC 1920 220
CO 1.26 1.20

As you can see, my high speed rpm is still well within the limits of passing but my low speed failed miserably.



Right before I took it to emissions this year I did a little bit of maintenance. I put new spark plugs, cap and rotor, found a failed vacuum sensor and replaced and checked the timing. When I first bought the vehicle I had the egr valve and 02 sensor replaced but that was 80-100k miles ago.


So heres my questions
1. What are some things that can cause my high speed to pass but my low speed rpm to fail on emissions
2. Do you think I should start by replacing my 02 sensor.
3. Any other suggestions for passing emissions?


Thanks in advance

 

Check for codes before anything to see if any sensor has failed, that should lead to bad values when the truck is at low rpm, i'm in fact suspecting of that O2 sensor of yours. Did you warm up the truck enough before taking the test? if the engine was cold that should affect negatively the emissions.

 

Yes the engine was warm. I drove it for about 20 minutes in stop and go traffic, being heavy on the pedal. As for the codes, I can complete the key on engine off without fault, but the key on engine on will not complete. The code reader gives a message that says, "cannot maintain engine rpm". Basically what happens is that when the code reader is testing the engine, it causes the rpms to go up to about 1800rpm and then it drops to idle. Sometimes when this happens the engine will shut off. Even without the code reader, if I step on the gas and let go really quicky (letting it get close to 2000 rpms) the engine will die. Its like the engine doesnt know how to keep it at idle when you step on it and let go

On another note, I bought this code reader about 3 years ago and it has never given me any codes on the several vehicles that i've tried it on. I might have got a dud. It was from checker auto parts. Maybe I should take the bronco to a shop and have them read the codes?

 

The "goose" test is a minimum 2000 rpm hold that the person administering the test must do DURING the course of the KOER test. The reader/computer cannot achieve this engine rpm without physical interaction from someone actually opening the throttle and maintaining a minimum 2000 rpm engine speed while that portion of the KOER is running. The computer uses the data from the goose test and compares it to the data from the idle test to determine the functional changes within certain components within the system. Without it, there is no data to compare so the computer aborts the test. The OD cancel switch must also be deactivated and reactivated, the brakes applied and released and the "goose" test performed to be certain of no false codes triggered during the KOER.

 

Thanks for that tip. That must be why the test says it could not maintain rpm. I do recall the scanner telling me to turn the steering wheel and turn on/off the OD but it never said for me to maintain the rpm. Guess thats what I get for getting a 200 el cheapo reader. I'll try the test tomorrow and hold the rpm at a min of 2000 and see what codes i may get.

Thanks again everyone for the help.

 

Finally got a chance to check the codes. Let engine warm up fully. Ran the code reader again, KOEO test passed, KOER test gave the following codes.( This time I held the RPM's just above 2000.

3 codes:

CYL:8
DTC:411 Cannot control rpm during the koer low rpm check
DTC:538 Insufficient rpm change during KOER dynamic response test. 2. (trucks only) invalid cylinder balance test due to throttle movement during test

I get these codes whether I hold the rpm at 2000 or not. When I dont hold at rpm and let it do its own thing (the manual doesnt specify to hold the rpm) the rpm fluctuates the rpm range from about 1200-1700 rpm.

Anyone have any ideas how to proceed?